幾百行程式碼寫個Mybatis,原理搞的透透的!

小傅哥發表於2021-08-02


作者:小傅哥
部落格:https://bugstack.cn

沉澱、分享、成長,讓自己和他人都能有所收穫!?

一、前言

Mybatis 最核心的原理也是它最便於使用的體現,為什麼這說?

因為我們在使用 Mybatis 的時候,只需要定義一個不需要寫實現類的介面,就能通過註解或者配置SQL語句的方式,對資料庫進行 CRUD 操作。

那麼這是怎麼做到的呢,其中有一點非常重要,就是在 Spring 中可以把你的代理物件交給 Spring 容器,這個代理物件就是可以當做是 DAO 介面的具體實現類,而這個被代理的實現類就可以完成對資料庫的一個操作,也就是這個封裝過程被稱為 ORM 框架。

說了基本的流程,我們來做點測試,讓大家可以動手操作起來!學知識,一定是上手,才能得到!你可以通過以下原始碼倉庫進行練習

原始碼https://github.com/fuzhengwei/CodeGuide/wiki


二、把Bean塞到Spring容器,分幾步

Bean註冊

  • 關於Bean註冊的技術場景,在我們日常用到的技術框架中,MyBatis 是最為常見的。通過在使用 MyBatis 時都只是定義一個介面不需要寫實現類,但是這個介面卻可以和配置的 SQL 語句關聯,執行相應的資料庫操作時可以返回對應的結果。那麼這個介面與資料庫的操作就用到的 Bean 的代理和註冊。
  • 我們都知道類的呼叫是不能直接呼叫沒有實現的介面的,所以需要通過代理的方式給介面生成對應的實現類。接下來再通過把代理類放到 Spring 的 FactoryBean 的實現中,最後再把這個 FactoryBean 實現類註冊到 Spring 容器。那麼現在你的代理類就已經被註冊到 Spring 容器了,接下來就可以通過註解的方式注入到屬性中。

按照這個實現方式,我們來操作一下,看看一個 Bean 的註冊過程在程式碼中是如何實現的。

1. 定義介面

public interface IUserDao {

    String queryUserInfo();

}
  • 先定義一個類似 DAO 的介面,基本這樣的介面在使用 MyBatis 時還是非常常見的。後面我們會對這個介面做代理和註冊。

2. 類代理實現

ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
Class<?>[] classes = {IUserDao.class};    

InvocationHandler handler = (proxy, method, args) -> "你被代理了 " + method.getName();
IUserDao userDao = (IUserDao) Proxy.newProxyInstance(classLoader, classes, handler); 

String res = userDao.queryUserInfo();
logger.info("測試結果:{}", res);
  • Java 本身的代理方式使用起來還是比較簡單的,用法也很固定。
  • InvocationHandler 是個介面類,它對應的實現內容就是代理物件的具體實現。
  • 最後就是把代理交給 Proxy 建立代理物件,Proxy.newProxyInstance

3. 實現Bean工廠

public class ProxyBeanFactory implements FactoryBean {

    @Override
    public Object getObject() throws Exception {

        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
        Class[] classes = {IUserDao.class};
        InvocationHandler handler = (proxy, method, args) -> "你被代理了 " + method.getName();

        return Proxy.newProxyInstance(classLoader, classes, handler);
    }

    @Override
    public Class<?> getObjectType() {
        return IUserDao.class;
    } 

}
  • FactoryBean 在 spring 起到著二當家的地位,它將近有70多個小弟(實現它的介面定義),那麼它有三個方法;
    • T getObject() throws Exception; 返回bean例項物件
    • Class<?> getObjectType(); 返回例項類型別
    • boolean isSingleton(); 判斷是否單例,單例會放到Spring容器中單例項快取池中
  • 在這裡我們把上面使用Java代理的物件放到了 getObject() 方法中,那麼現在再從 Spring 中獲取到的物件,就是我們的代理物件了。

4. Bean 註冊

public class RegisterBeanFactory implements BeanDefinitionRegistryPostProcessor {

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {

        GenericBeanDefinition beanDefinition = new GenericBeanDefinition();
        beanDefinition.setBeanClass(ProxyBeanFactory.class);

        BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(beanDefinition, "userDao");
        BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, registry);
    }

}

在 Spring 的 Bean 管理中,所有的 Bean 最終都會被註冊到類 DefaultListableBeanFactory 中,以上這部分程式碼主要的內容包括:

  • 實現 BeanDefinitionRegistryPostProcessor.postProcessBeanDefinitionRegistry方法,獲取 Bean 註冊物件。
  • 定義 Bean,GenericBeanDefinition,這裡主要設定了我們的代理類工廠。
  • 建立 Bean 定義處理類,BeanDefinitionHolder,這裡需要的主要引數;定義 Bean 和名稱 setBeanClass(ProxyBeanFactory.class)
  • 最後將我們自己的bean註冊到spring容器中去,registry.registerBeanDefinition()

5. 測試驗證

在上面我們已經把自定義代理的 Bean 註冊到了 Spring 容器中,接下來我們來測試下這個代理的 Bean 被如何呼叫。

1. 定義 spring-config.xml

<bean id="userDao" class="org.itstack.interview.bean.RegisterBeanFactory"/>
  • 這裡我們把 RegisterBeanFactory 配置到 spring 的 xml 配置中,便於啟動時載入。

2. 單元測試

@Test
public void test_IUserDao() {
    BeanFactory beanFactory = new ClassPathXmlApplicationContext("spring-config.xml");
    IUserDao userDao = beanFactory.getBean("userDao", IUserDao.class);
    String res = userDao.queryUserInfo();
    logger.info("測試結果:{}", res);
}

測試結果

22:53:14.759 [main] DEBUG o.s.c.e.PropertySourcesPropertyResolver - Could not find key 'spring.liveBeansView.mbeanDomain' in any property source
22:53:14.760 [main] DEBUG o.s.b.f.s.DefaultListableBeanFactory - Returning cached instance of singleton bean 'userDao'
22:53:14.796 [main] INFO  org.itstack.interview.test.ApiTest - 測試結果:你被代理了 queryUserInfo

Process finished with exit code 0
  • 從測試結果可以看到,我們已經可以通過注入到Spring的代理Bean物件,實現我們的預期結果。
  • 其實這個過程也是很多框架中用到的方式,尤其是在一些中介軟體開發,類似的 ORM 框架都需要使用到。

三、手寫個Mybatis

擴充套件上一篇原始碼分析工程;itstack-demo-mybatis,增加 like 包,模仿 Mybatis 工程。完整規程下載 https://github.com/fuzhengwei/CodeGuide/wiki

itstack-demo-mybatis
└── src
    ├── main
    │   ├── java
    │   │   └── org.itstack.demo
    │   │       ├── dao
    │   │       │	├── ISchool.java		
    │   │       │	└── IUserDao.java	
    │   │       ├── like
    │   │       │	├── Configuration.java
    │   │       │	├── DefaultSqlSession.java
    │   │       │	├── DefaultSqlSessionFactory.java
    │   │       │	├── Resources.java
    │   │       │	├── SqlSession.java
    │   │       │	├── SqlSessionFactory.java
    │   │       │	├── SqlSessionFactoryBuilder.java	
    │   │       │	└── SqlSessionFactoryBuilder.java	
    │   │       └── interfaces     
    │   │         	├── School.java	
    │   │        	└── User.java
    │   ├── resources	
    │   │   ├── mapper
    │   │   │   ├── School_Mapper.xml
    │   │   │   └── User_Mapper.xml
    │   │   ├── props	
    │   │   │   └── jdbc.properties
    │   │   ├── spring
    │   │   │   ├── mybatis-config-datasource.xml
    │   │   │   └── spring-config-datasource.xml
    │   │   ├── logback.xml
    │   │   ├── mybatis-config.xml
    │   │   └── spring-config.xml
    │   └── webapp
    │       └── WEB-INF
    └── test
         └── java
             └── org.itstack.demo.test
                 ├── ApiLikeTest.java
                 ├── MybatisApiTest.java
                 └── SpringApiTest.java

關於整個 Demo 版本,並不是把所有 Mybatis 全部實現一遍,而是撥絲抽繭將最核心的內容展示給你,從使用上你會感受一模一樣,但是實現類已經全部被替換,核心類包括;

  • Configuration
  • DefaultSqlSession
  • DefaultSqlSessionFactory
  • Resources
  • SqlSession
  • SqlSessionFactory
  • SqlSessionFactoryBuilder
  • XNode

1. 先測試下整個DemoJdbc框架

ApiLikeTest.test_queryUserInfoById()

@Test
public void test_queryUserInfoById() {
    String resource = "spring/mybatis-config-datasource.xml";
    Reader reader;
    try {
        reader = Resources.getResourceAsReader(resource);
        SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader);
        SqlSession session = sqlMapper.openSession();
		
        try {
            User user = session.selectOne("org.itstack.demo.dao.IUserDao.queryUserInfoById", 1L);
            System.out.println(JSON.toJSONString(user));
        } finally {
            session.close();
            reader.close();
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

一切順利結果如下(新人往往會遇到各種問題);

{"age":18,"createTime":1576944000000,"id":1,"name":"水水","updateTime":1576944000000}

Process finished with exit code 0

可能乍一看這測試類完全和 MybatisApiTest.java 測試的程式碼一模一樣呀,也看不出區別。其實他們的引入的包是不一樣;

MybatisApiTest.java 裡面引入的包

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

ApiLikeTest.java 裡面引入的包

import org.itstack.demo.like.Resources;
import org.itstack.demo.like.SqlSession;
import org.itstack.demo.like.SqlSessionFactory;
import org.itstack.demo.like.SqlSessionFactoryBuilder;

好!接下來我們開始分析這部分核心程式碼。

2. 載入XML配置檔案

這裡我們採用 mybatis 的配置檔案結構進行解析,在不破壞原有結構的情況下,最大可能的貼近原始碼。mybatis 單獨使用的使用的時候使用了兩個配置檔案;資料來源配置、Mapper 對映配置,如下;

mybatis-config-datasource.xml & 資料來源配置

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">

<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://127.0.0.1:3306/itstack?useUnicode=true"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="mapper/User_Mapper.xml"/>
        <mapper resource="mapper/School_Mapper.xml"/>
    </mappers>

</configuration>

User_Mapper.xml & Mapper 對映配置

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.itstack.demo.dao.IUserDao">

    <select id="queryUserInfoById" parameterType="java.lang.Long" resultType="org.itstack.demo.po.User">
        SELECT id, name, age, createTime, updateTime
        FROM user
        where id = #{id}
    </select>

    <select id="queryUserList" parameterType="org.itstack.demo.po.User" resultType="org.itstack.demo.po.User">
        SELECT id, name, age, createTime, updateTime
        FROM user
        where age = #{age}
    </select>

</mapper>

這裡的載入過程與 mybaits 不同,我們採用 dom4j 方式。在案例中會看到最開始獲取資源,如下;

ApiLikeTest.test_queryUserInfoById() & 部分擷取

String resource = "spring/mybatis-config-datasource.xml";
	Reader reader;
	try {
		reader = Resources.getResourceAsReader(resource);
	...

從上可以看到這是通過配置檔案地址獲取到了讀取流的過程,從而為後面解析做基礎。首先我們先看 Resources 類,整個是我們的資源類。

Resources.java & 資源類

/**
 * 博 客 | https://bugstack.cn
 * Create by 小傅哥 @2020
 */
public class Resources {

    public static Reader getResourceAsReader(String resource) throws IOException {
        return new InputStreamReader(getResourceAsStream(resource));
    }

    private static InputStream getResourceAsStream(String resource) throws IOException {
        ClassLoader[] classLoaders = getClassLoaders();
        for (ClassLoader classLoader : classLoaders) {
            InputStream inputStream = classLoader.getResourceAsStream(resource);
            if (null != inputStream) {
                return inputStream;
            }
        }
        throw new IOException("Could not find resource " + resource);
    }

    private static ClassLoader[] getClassLoaders() {
        return new ClassLoader[]{
                ClassLoader.getSystemClassLoader(),
                Thread.currentThread().getContextClassLoader()};
    }

}

這段程式碼方法的入口是getResourceAsReader,直到往下以此做了;

  1. 獲取 ClassLoader 集合,最大限度搜尋配置檔案
  2. 通過 classLoader.getResourceAsStream 讀取配置資源,找到後立即返回,否則丟擲異常

3. 解析XML配置檔案

配置檔案載入後開始進行解析操作,這裡我們也仿照 mybatis 但進行簡化,如下;

SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader);

SqlSessionFactoryBuilder.build() & 入口構建類

public DefaultSqlSessionFactory build(Reader reader) {
    SAXReader saxReader = new SAXReader();
    try {
        Document document = saxReader.read(new InputSource(reader));
        Configuration configuration = parseConfiguration(document.getRootElement());
        return new DefaultSqlSessionFactory(configuration);
    } catch (DocumentException e) {
        e.printStackTrace();
    }
    return null;
}
  • 通過讀取流建立 xml 解析的 Document 類
  • parseConfiguration 進行解析 xml 檔案,並將結果設定到配置類中,包括;連線池、資料來源、mapper關係

SqlSessionFactoryBuilder.parseConfiguration() & 解析過程

private Configuration parseConfiguration(Element root) {
    Configuration configuration = new Configuration();
    configuration.setDataSource(dataSource(root.selectNodes("//dataSource")));
    configuration.setConnection(connection(configuration.dataSource));
    configuration.setMapperElement(mapperElement(root.selectNodes("mappers")));
    return configuration;
}
  • 在前面的 xml 內容中可以看到,我們需要解析出資料庫連線池資訊 datasource,還有資料庫語句對映關係 mappers

SqlSessionFactoryBuilder.dataSource() & 解析出資料來源

private Map<String, String> dataSource(List<Element> list) {
    Map<String, String> dataSource = new HashMap<>(4);
    Element element = list.get(0);
    List content = element.content();
    for (Object o : content) {
        Element e = (Element) o;
        String name = e.attributeValue("name");
        String value = e.attributeValue("value");
        dataSource.put(name, value);
    }
    return dataSource;
}
  • 這個過程比較簡單,只需要將資料來源資訊獲取即可

SqlSessionFactoryBuilder.connection() & 獲取資料庫連線

private Connection connection(Map<String, String> dataSource) {
    try {
        Class.forName(dataSource.get("driver"));
        return DriverManager.getConnection(dataSource.get("url"), dataSource.get("username"), dataSource.get("password"));
    } catch (ClassNotFoundException | SQLException e) {
        e.printStackTrace();
    }
    return null;
}
  • 這個就是jdbc最原始的程式碼,獲取了資料庫連線池

SqlSessionFactoryBuilder.mapperElement() & 解析SQL語句

private Map<String, XNode> mapperElement(List<Element> list) {
    Map<String, XNode> map = new HashMap<>();
    Element element = list.get(0);
    List content = element.content();
    for (Object o : content) {
        Element e = (Element) o;
        String resource = e.attributeValue("resource");
        try {
            Reader reader = Resources.getResourceAsReader(resource);
            SAXReader saxReader = new SAXReader();
            Document document = saxReader.read(new InputSource(reader));
            Element root = document.getRootElement();
            //名稱空間
            String namespace = root.attributeValue("namespace");
            // SELECT
            List<Element> selectNodes = root.selectNodes("select");
            for (Element node : selectNodes) {
                String id = node.attributeValue("id");
                String parameterType = node.attributeValue("parameterType");
                String resultType = node.attributeValue("resultType");
                String sql = node.getText();
                // ? 匹配
                Map<Integer, String> parameter = new HashMap<>();
                Pattern pattern = Pattern.compile("(#\\{(.*?)})");
                Matcher matcher = pattern.matcher(sql);
                for (int i = 1; matcher.find(); i++) {
                    String g1 = matcher.group(1);
                    String g2 = matcher.group(2);
                    parameter.put(i, g2);
                    sql = sql.replace(g1, "?");
                }
                XNode xNode = new XNode();
                xNode.setNamespace(namespace);
                xNode.setId(id);
                xNode.setParameterType(parameterType);
                xNode.setResultType(resultType);
                xNode.setSql(sql);
                xNode.setParameter(parameter);
                
                map.put(namespace + "." + id, xNode);
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    return map;
}
  • 這個過程首先包括是解析所有的sql語句,目前為了測試只解析 select 相關
  • 所有的 sql 語句為了確認唯一,都是使用;namespace + select中的id進行拼接,作為 key,之後與sql一起存放到 map 中。
  • 在 mybaits 的 sql 語句配置中,都有佔位符,用於傳參。where id = #{id} 所以我們需要將佔位符設定為問號,另外需要將佔位符的順序資訊與名稱存放到 map 結構,方便後續設定查詢時候的入參。

4. 建立DefaultSqlSessionFactory

最後將初始化後的配置類 Configuration,作為引數進行建立 DefaultSqlSessionFactory,如下;

public DefaultSqlSessionFactory build(Reader reader) {
    SAXReader saxReader = new SAXReader();
    try {
        Document document = saxReader.read(new InputSource(reader));
        Configuration configuration = parseConfiguration(document.getRootElement());
        return new DefaultSqlSessionFactory(configuration);
    } catch (DocumentException e) {
        e.printStackTrace();
    }
    return null;
}

DefaultSqlSessionFactory.java & SqlSessionFactory的實現類

public class DefaultSqlSessionFactory implements SqlSessionFactory {
    
	private final Configuration configuration;
    
	public DefaultSqlSessionFactory(Configuration configuration) {
        this.configuration = configuration;
    }
	
    @Override
    public SqlSession openSession() {
        return new DefaultSqlSession(configuration.connection, configuration.mapperElement);
    }
	
}
  • 這個過程比較簡單,建構函式只提供了配置類入參
  • 實現 SqlSessionFactory 的 openSession(),用於建立 DefaultSqlSession,也就可以執行 sql 操作

5. 開啟SqlSession

SqlSession session = sqlMapper.openSession();

上面這一步就是建立了DefaultSqlSession,比較簡單。如下;

@Override
public SqlSession openSession() {
    return new DefaultSqlSession(configuration.connection, configuration.mapperElement);
}

6. 執行SQL語句

User user = session.selectOne("org.itstack.demo.dao.IUserDao.queryUserInfoById", 1L);

在 DefaultSqlSession 中通過實現 SqlSession,提供資料庫語句查詢和關閉連線池,如下;

SqlSession.java & 定義

public interface SqlSession {

    <T> T selectOne(String statement);

    <T> T selectOne(String statement, Object parameter);

    <T> List<T> selectList(String statement);

    <T> List<T> selectList(String statement, Object parameter);

    void close();
}

接下來看具體的執行過程,session.selectOne

DefaultSqlSession.selectOne() & 執行查詢

public <T> T selectOne(String statement, Object parameter) {
    XNode xNode = mapperElement.get(statement);
    Map<Integer, String> parameterMap = xNode.getParameter();
    try {
        PreparedStatement preparedStatement = connection.prepareStatement(xNode.getSql());
        buildParameter(preparedStatement, parameter, parameterMap);
        ResultSet resultSet = preparedStatement.executeQuery();
        List<T> objects = resultSet2Obj(resultSet, Class.forName(xNode.getResultType()));
        return objects.get(0);
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}
  • selectOne 就objects.get(0);,selectList 就全部返回

  • 通過 statement 獲取最初解析 xml 時候的儲存的 select 標籤資訊;

    <select id="queryUserInfoById" parameterType="java.lang.Long" resultType="org.itstack.demo.po.User">
    	SELECT id, name, age, createTime, updateTime
    	FROM user
    	where id = #{id}
    </select>
    
  • 獲取 sql 語句後交給 jdbc 的 PreparedStatement 類進行執行

  • 這裡還需要設定入參,我們將入參設定進行抽取,如下;

    private void buildParameter(PreparedStatement preparedStatement, Object parameter, Map<Integer, String> parameterMap) throws SQLException, IllegalAccessException {
    
          int size = parameterMap.size();
          // 單個引數
          if (parameter instanceof Long) {
              for (int i = 1; i <= size; i++) {
                  preparedStatement.setLong(i, Long.parseLong(parameter.toString()));
              }
              return;
          }
    
          if (parameter instanceof Integer) {
              for (int i = 1; i <= size; i++) {
                  preparedStatement.setInt(i, Integer.parseInt(parameter.toString()));
              }
              return;
          }
    
          if (parameter instanceof String) {
              for (int i = 1; i <= size; i++) {
                  preparedStatement.setString(i, parameter.toString());
              }
              return;
          }
    
          Map<String, Object> fieldMap = new HashMap<>();
          // 物件引數
          Field[] declaredFields = parameter.getClass().getDeclaredFields();
          for (Field field : declaredFields) {
              String name = field.getName();
              field.setAccessible(true);
              Object obj = field.get(parameter);
              field.setAccessible(false);
              fieldMap.put(name, obj);
          }
    
          for (int i = 1; i <= size; i++) {
              String parameterDefine = parameterMap.get(i);
              Object obj = fieldMap.get(parameterDefine);
    
              if (obj instanceof Short) {
                  preparedStatement.setShort(i, Short.parseShort(obj.toString()));
                  continue;
              }
    
              if (obj instanceof Integer) {
                  preparedStatement.setInt(i, Integer.parseInt(obj.toString()));
                  continue;
              }
    
              if (obj instanceof Long) {
                  preparedStatement.setLong(i, Long.parseLong(obj.toString()));
                  continue;
              }
    
              if (obj instanceof String) {
                  preparedStatement.setString(i, obj.toString());
                  continue;
              }
    
              if (obj instanceof Date) {
                  preparedStatement.setDate(i, (java.sql.Date) obj);
              }
    
          }
    
      }
    
    • 單個引數比較簡單直接設定值即可,Long、Integer、String ...
    • 如果是一個類物件,需要通過獲取 Field 屬性,與引數 Map 進行匹配設定
  • 設定引數後執行查詢 preparedStatement.executeQuery()

  • 接下來需要將查詢結果轉換為我們的類(主要是反射類的操作),resultSet2Obj(resultSet, Class.forName(xNode.getResultType()));

    private <T> List<T> resultSet2Obj(ResultSet resultSet, Class<?> clazz) {
    	List<T> list = new ArrayList<>();
    	try {
    		ResultSetMetaData metaData = resultSet.getMetaData();
    		int columnCount = metaData.getColumnCount();
    		// 每次遍歷行值
    		while (resultSet.next()) {
    			T obj = (T) clazz.newInstance();
    			for (int i = 1; i <= columnCount; i++) {
    				Object value = resultSet.getObject(i);
    				String columnName = metaData.getColumnName(i);
    				String setMethod = "set" + columnName.substring(0, 1).toUpperCase() + columnName.substring(1);
    				Method method;
    				if (value instanceof Timestamp) {
    					method = clazz.getMethod(setMethod, Date.class);
    				} else {
    					method = clazz.getMethod(setMethod, value.getClass());
    				}
    				method.invoke(obj, value);
    			}
    			list.add(obj);
    		}
    	} catch (Exception e) {
    		e.printStackTrace();
    	}
    	return list;
    }
    
    • 主要通過反射生成我們的類物件,這個類的型別定義在 sql 標籤上
    • 時間型別需要判斷後處理,Timestamp,與 java 不是一個型別

7. Sql查詢補充說明

sql 查詢有入參、有不需要入參、有查詢一個、有查詢集合,只需要合理包裝即可,例如下面的查詢集合,入參是物件型別;

ApiLikeTest.test_queryUserList()

@Test
public void test_queryUserList() {
    String resource = "spring/mybatis-config-datasource.xml";
    Reader reader;
    try {
        reader = Resources.getResourceAsReader(resource);
        SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader);
        SqlSession session = sqlMapper.openSession();
        
		try {
            User req = new User();
            req.setAge(18);
            List<User> userList = session.selectList("org.itstack.demo.dao.IUserDao.queryUserList", req);
            System.out.println(JSON.toJSONString(userList));
        } finally {
            session.close();
            reader.close();
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
	
}

**測試結果:

[{"age":18,"createTime":1576944000000,"id":1,"name":"水水","updateTime":1576944000000},{"age":18,"createTime":1576944000000,"id":2,"name":"豆豆","updateTime":1576944000000}]

Process finished with exit code 0

四、原始碼分析(mybatis)

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.4.6</version>
</dependency>

Mybatis的整個原始碼還是很大的,以下主要將部分核心內容進行整理分析,以便於後續分析Mybatis與Spring整合的原始碼部分。簡要包括;容器初始化、配置檔案解析、Mapper載入與動態代理。

1. 從一個簡單的案例開始

要學習Mybatis原始碼,最好的方式一定是從一個簡單的點進入,而不是從Spring整合開始分析。SqlSessionFactory是整個Mybatis的核心例項物件,SqlSessionFactory物件的例項又通過SqlSessionFactoryBuilder物件來獲得。SqlSessionFactoryBuilder物件可以從XML配置檔案載入配置資訊,然後建立SqlSessionFactory。如下例子:

MybatisApiTest.java

public class MybatisApiTest {

    @Test
    public void test_queryUserInfoById() {
        String resource = "spring/mybatis-config-datasource.xml";
        Reader reader;
        try {
            reader = Resources.getResourceAsReader(resource);
            SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader);

            SqlSession session = sqlMapper.openSession();
            try {
                User user = session.selectOne("org.itstack.demo.dao.IUserDao.queryUserInfoById", 1L);
                System.out.println(JSON.toJSONString(user));
            } finally {
                session.close();
                reader.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

dao/IUserDao.java

public interface IUserDao {

     User queryUserInfoById(Long id);

}

spring/mybatis-config-datasource.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">

<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://127.0.0.1:3306/itstack?useUnicode=true"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="mapper/User_Mapper.xml"/>
    </mappers>

</configuration>

如果一切順利,那麼會有如下結果:

{"age":18,"createTime":1571376957000,"id":1,"name":"花花","updateTime":1571376957000}

從上面的程式碼塊可以看到,核心程式碼;SqlSessionFactoryBuilder().build(reader),負責Mybatis配置檔案的載入、解析、構建等職責,直到最終可以通過SqlSession來執行並返回結果。

2. 容器初始化

從上面程式碼可以看到,SqlSessionFactory是通過SqlSessionFactoryBuilder工廠類建立的,而不是直接使用構造器。容器的配置檔案載入和初始化流程如下:

微信公眾號:bugstack蟲洞棧 & 初始化流程

  • 流程核心類
    • SqlSessionFactoryBuilder
    • XMLConfigBuilder
    • XPathParser
    • Configuration

SqlSessionFactoryBuilder.java

public class SqlSessionFactoryBuilder {

  public SqlSessionFactory build(Reader reader) {
    return build(reader, null, null);
  }

  public SqlSessionFactory build(Reader reader, String environment) {
    return build(reader, environment, null);
  }

  public SqlSessionFactory build(Reader reader, Properties properties) {
    return build(reader, null, properties);
  }

  public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        reader.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }

  public SqlSessionFactory build(InputStream inputStream) {
    return build(inputStream, null, null);
  }

  public SqlSessionFactory build(InputStream inputStream, String environment) {
    return build(inputStream, environment, null);
  }

  public SqlSessionFactory build(InputStream inputStream, Properties properties) {
    return build(inputStream, null, properties);
  }

  public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        inputStream.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }
    
  public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
  }

}

從上面的原始碼可以看到,SqlSessionFactory提供三種方式build構建物件;

  • 位元組流:java.io.InputStream
  • 字元流:java.io.Reader
  • 配置類:org.apache.ibatis.session.Configuration

那麼,位元組流、字元流都會建立配置檔案解析類:XMLConfigBuilder,並通過parser.parse()生成Configuration,最後呼叫配置類構建方法生成SqlSessionFactory。

XMLConfigBuilder.java

public class XMLConfigBuilder extends BaseBuilder {

  private boolean parsed;
  private final XPathParser parser;
  private String environment;
  private final ReflectorFactory localReflectorFactory = new DefaultReflectorFactory();

  ...
  public XMLConfigBuilder(Reader reader, String environment, Properties props) {
    this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props);
  }
  ...
}  
  1. XMLConfigBuilder對於XML檔案的載入和解析都委託於XPathParser,最終使用JDK自帶的javax.xml進行XML解析(XPath)
  2. XPathParser(Reader reader, boolean validation, Properties variables, EntityResolver entityResolver)
    1. reader:使用字元流建立新的輸入源,用於對XML檔案的讀取
    2. validation:是否進行DTD校驗
    3. variables:屬性配置資訊
    4. entityResolver:Mybatis硬編碼了new XMLMapperEntityResolver()提供XML預設解析器

XMLMapperEntityResolver.java

public class XMLMapperEntityResolver implements EntityResolver {

  private static final String IBATIS_CONFIG_SYSTEM = "ibatis-3-config.dtd";
  private static final String IBATIS_MAPPER_SYSTEM = "ibatis-3-mapper.dtd";
  private static final String MYBATIS_CONFIG_SYSTEM = "mybatis-3-config.dtd";
  private static final String MYBATIS_MAPPER_SYSTEM = "mybatis-3-mapper.dtd";

  private static final String MYBATIS_CONFIG_DTD = "org/apache/ibatis/builder/xml/mybatis-3-config.dtd";
  private static final String MYBATIS_MAPPER_DTD = "org/apache/ibatis/builder/xml/mybatis-3-mapper.dtd";

  /*
   * Converts a public DTD into a local one
   * 
   * @param publicId The public id that is what comes after "PUBLIC"
   * @param systemId The system id that is what comes after the public id.
   * @return The InputSource for the DTD
   * 
   * @throws org.xml.sax.SAXException If anything goes wrong
   */
  @Override
  public InputSource resolveEntity(String publicId, String systemId) throws SAXException {
    try {
      if (systemId != null) {
        String lowerCaseSystemId = systemId.toLowerCase(Locale.ENGLISH);
        if (lowerCaseSystemId.contains(MYBATIS_CONFIG_SYSTEM) || lowerCaseSystemId.contains(IBATIS_CONFIG_SYSTEM)) {
          return getInputSource(MYBATIS_CONFIG_DTD, publicId, systemId);
        } else if (lowerCaseSystemId.contains(MYBATIS_MAPPER_SYSTEM) || lowerCaseSystemId.contains(IBATIS_MAPPER_SYSTEM)) {
          return getInputSource(MYBATIS_MAPPER_DTD, publicId, systemId);
        }
      }
      return null;
    } catch (Exception e) {
      throw new SAXException(e.toString());
    }
  }

  private InputSource getInputSource(String path, String publicId, String systemId) {
    InputSource source = null;
    if (path != null) {
      try {
        InputStream in = Resources.getResourceAsStream(path);
        source = new InputSource(in);
        source.setPublicId(publicId);
        source.setSystemId(systemId);        
      } catch (IOException e) {
        // ignore, null is ok
      }
    }
    return source;
  }

}
  1. Mybatis依賴於dtd檔案進行進行解析,其中的ibatis-3-config.dtd主要是用於相容用途
  2. getInputSource(String path, String publicId, String systemId)的呼叫裡面有兩個引數publicId(公共識別符號)和systemId(系統標示符)

XPathParser.java

public XPathParser(Reader reader, boolean validation, Properties variables, EntityResolver entityResolver) {
  commonConstructor(validation, variables, entityResolver);
  this.document = createDocument(new InputSource(reader));
}

private void commonConstructor(boolean validation, Properties variables, EntityResolver entityResolver) {
  this.validation = validation;
  this.entityResolver = entityResolver;
  this.variables = variables;
  XPathFactory factory = XPathFactory.newInstance();
  this.xpath = factory.newXPath();
}

private Document createDocument(InputSource inputSource) {
  // important: this must only be called AFTER common constructor
  try {
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    factory.setValidating(validation);
    factory.setNamespaceAware(false);
    factory.setIgnoringComments(true);
    factory.setIgnoringElementContentWhitespace(false);
    factory.setCoalescing(false);
    factory.setExpandEntityReferences(true);
    DocumentBuilder builder = factory.newDocumentBuilder();
    builder.setEntityResolver(entityResolver);
    builder.setErrorHandler(new ErrorHandler() {
      @Override
      public void error(SAXParseException exception) throws SAXException {
        throw exception;
      }
      @Override
      public void fatalError(SAXParseException exception) throws SAXException {
        throw exception;
      }
      @Override
      public void warning(SAXParseException exception) throws SAXException {
      }
    });
    return builder.parse(inputSource);
  } catch (Exception e) {
    throw new BuilderException("Error creating document instance.  Cause: " + e, e);
  }
  
}    
  1. 從上到下可以看到主要是為了建立一個Mybatis的文件解析器,最後根據builder.parse(inputSource)返回Document

  2. 得到XPathParser例項後,接下來在呼叫方法:this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props);

     XMLConfigBuilder.this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props);
    
     private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
       super(new Configuration());
       ErrorContext.instance().resource("SQL Mapper Configuration");
       this.configuration.setVariables(props);
       this.parsed = false;
       this.environment = environment;
       this.parser = parser;
     }
    
  3. 其中呼叫了父類的建構函式

    public abstract class BaseBuilder {
      protected final Configuration configuration;
      protected final TypeAliasRegistry typeAliasRegistry;
      protected final TypeHandlerRegistry typeHandlerRegistry;
    
      public BaseBuilder(Configuration configuration) {
        this.configuration = configuration;
        this.typeAliasRegistry = this.configuration.getTypeAliasRegistry();
        this.typeHandlerRegistry = this.configuration.getTypeHandlerRegistry();
      }
    }
    
  4. XMLConfigBuilder建立完成後,sqlSessionFactoryBuild呼叫parser.parse()建立Configuration

    public class XMLConfigBuilder extends BaseBuilder {    
         public Configuration parse() {
           if (parsed) {
             throw new BuilderException("Each XMLConfigBuilder can only be used once.");
           }
           parsed = true;
           parseConfiguration(parser.evalNode("/configuration"));
           return configuration;
         }
    }
    

3. 配置檔案解析

這一部分是整個XML檔案解析和裝載的核心內容,其中包括;

  1. 屬性解析propertiesElement
  2. 載入settings節點settingsAsProperties
  3. 載自定義VFS loadCustomVfs
  4. 解析型別別名typeAliasesElement
  5. 載入外掛pluginElement
  6. 載入物件工廠objectFactoryElement
  7. 建立物件包裝器工廠objectWrapperFactoryElement
  8. 載入反射工廠reflectorFactoryElement
  9. 元素設定settingsElement
  10. 載入環境配置environmentsElement
  11. 資料庫廠商標識載入databaseIdProviderElement
  12. 載入型別處理器typeHandlerElement
  13. (核心)載入mapper檔案mapperElement
parseConfiguration(parser.evalNode("/configuration"));

private void parseConfiguration(XNode root) {
    try {
      //issue #117 read properties first
      //屬性解析propertiesElement
      propertiesElement(root.evalNode("properties"));
      //載入settings節點settingsAsProperties
      Properties settings = settingsAsProperties(root.evalNode("settings"));
      //載入自定義VFS loadCustomVfs
      loadCustomVfs(settings);
      //解析型別別名typeAliasesElement
      typeAliasesElement(root.evalNode("typeAliases"));
      //載入外掛pluginElement
      pluginElement(root.evalNode("plugins"));
      //載入物件工廠objectFactoryElement
      objectFactoryElement(root.evalNode("objectFactory"));
      //建立物件包裝器工廠objectWrapperFactoryElement
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      //載入反射工廠reflectorFactoryElement
      reflectorFactoryElement(root.evalNode("reflectorFactory"));
      //元素設定
      settingsElement(settings);
      // read it after objectFactory and objectWrapperFactory issue #631
      //載入環境配置environmentsElement
      environmentsElement(root.evalNode("environments"));
      //資料庫廠商標識載入databaseIdProviderElement
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
      //載入型別處理器typeHandlerElement
      typeHandlerElement(root.evalNode("typeHandlers"));
      //載入mapper檔案mapperElement
      mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
} 

所有的root.evalNode()底層都是呼叫XML DOM方法:Object evaluate(String expression, Object item, QName returnType),表示式引數expression,通過XObject resultObject = eval( expression, item )返回最終節點內容,可以參考http://mybatis.org/dtd/mybatis-3-config.dtd,如下;

<!ELEMENT configuration (properties?, settings?, typeAliases?, typeHandlers?, objectFactory?, objectWrapperFactory?, reflectorFactory?, plugins?, environments?, databaseIdProvider?, mappers?)>
 
<!ELEMENT databaseIdProvider (property*)>
<!ATTLIST databaseIdProvider
type CDATA #REQUIRED
>
 
<!ELEMENT properties (property*)>
<!ATTLIST properties
resource CDATA #IMPLIED
url CDATA #IMPLIED
>
 
<!ELEMENT property EMPTY>
<!ATTLIST property
name CDATA #REQUIRED
value CDATA #REQUIRED
>
 
<!ELEMENT settings (setting+)>
 
<!ELEMENT setting EMPTY>
<!ATTLIST setting
name CDATA #REQUIRED
value CDATA #REQUIRED
>
 
<!ELEMENT typeAliases (typeAlias*,package*)>
 
<!ELEMENT typeAlias EMPTY>
<!ATTLIST typeAlias
type CDATA #REQUIRED
alias CDATA #IMPLIED
>
 
<!ELEMENT typeHandlers (typeHandler*,package*)>
 
<!ELEMENT typeHandler EMPTY>
<!ATTLIST typeHandler
javaType CDATA #IMPLIED
jdbcType CDATA #IMPLIED
handler CDATA #REQUIRED
>
 
<!ELEMENT objectFactory (property*)>
<!ATTLIST objectFactory
type CDATA #REQUIRED
>
 
<!ELEMENT objectWrapperFactory EMPTY>
<!ATTLIST objectWrapperFactory
type CDATA #REQUIRED
>
 
<!ELEMENT reflectorFactory EMPTY>
<!ATTLIST reflectorFactory
type CDATA #REQUIRED
>
 
<!ELEMENT plugins (plugin+)>
 
<!ELEMENT plugin (property*)>
<!ATTLIST plugin
interceptor CDATA #REQUIRED
>
 
<!ELEMENT environments (environment+)>
<!ATTLIST environments
default CDATA #REQUIRED
>
 
<!ELEMENT environment (transactionManager,dataSource)>
<!ATTLIST environment
id CDATA #REQUIRED
>
 
<!ELEMENT transactionManager (property*)>
<!ATTLIST transactionManager
type CDATA #REQUIRED
>
 
<!ELEMENT dataSource (property*)>
<!ATTLIST dataSource
type CDATA #REQUIRED
>
 
<!ELEMENT mappers (mapper*,package*)>
 
<!ELEMENT mapper EMPTY>
<!ATTLIST mapper
resource CDATA #IMPLIED
url CDATA #IMPLIED
class CDATA #IMPLIED
>
 
<!ELEMENT package EMPTY>
<!ATTLIST package
name CDATA #REQUIRED
>

mybatis-3-config.dtd 定義檔案中有11個配置檔案,如下;

  1. properties?,
  2. settings?,
  3. typeAliases?,
  4. typeHandlers?,
  5. objectFactory?,
  6. objectWrapperFactory?,
  7. reflectorFactory?,
  8. plugins?,
  9. environments?,
  10. databaseIdProvider?,
  11. mappers?

以上每個配置都是可選。最終配置內容會儲存到org.apache.ibatis.session.Configuration,如下;

public class Configuration {

  protected Environment environment;
  // 允許在巢狀語句中使用分頁(RowBounds)。如果允許使用則設定為false。預設為false
  protected boolean safeRowBoundsEnabled;
  // 允許在巢狀語句中使用分頁(ResultHandler)。如果允許使用則設定為false。
  protected boolean safeResultHandlerEnabled = true;
  // 是否開啟自動駝峰命名規則(camel case)對映,即從經典資料庫列名 A_COLUMN 到經典 Java 屬性名 aColumn 的類似對映。預設false
  protected boolean mapUnderscoreToCamelCase;
  // 當開啟時,任何方法的呼叫都會載入該物件的所有屬性。否則,每個屬性會按需載入。預設值false (true in ≤3.4.1)
  protected boolean aggressiveLazyLoading;
  // 是否允許單一語句返回多結果集(需要相容驅動)。
  protected boolean multipleResultSetsEnabled = true;
  // 允許 JDBC 支援自動生成主鍵,需要驅動相容。這就是insert時獲取mysql自增主鍵/oracle sequence的開關。注:一般來說,這是希望的結果,應該預設值為true比較合適。
  protected boolean useGeneratedKeys;
  // 使用列標籤代替列名,一般來說,這是希望的結果
  protected boolean useColumnLabel = true;
  // 是否啟用快取 {預設是開啟的,可能這也是你的面試題}
  protected boolean cacheEnabled = true;
  // 指定當結果集中值為 null 的時候是否呼叫對映物件的 setter(map 物件時為 put)方法,這對於有 Map.keySet() 依賴或 null 值初始化的時候是有用的。
  protected boolean callSettersOnNulls;
  // 允許使用方法簽名中的名稱作為語句引數名稱。 為了使用該特性,你的工程必須採用Java 8編譯,並且加上-parameters選項。(從3.4.1開始)
  protected boolean useActualParamName = true;
  //當返回行的所有列都是空時,MyBatis預設返回null。 當開啟這個設定時,MyBatis會返回一個空例項。 請注意,它也適用於巢狀的結果集 (i.e. collectioin and association)。(從3.4.2開始) 注:這裡應該拆分為兩個引數比較合適, 一個用於結果集,一個用於單記錄。通常來說,我們會希望結果集不是null,單記錄仍然是null
  protected boolean returnInstanceForEmptyRow;
  // 指定 MyBatis 增加到日誌名稱的字首。
  protected String logPrefix;
  // 指定 MyBatis 所用日誌的具體實現,未指定時將自動查詢。一般建議指定為slf4j或log4j
  protected Class <? extends Log> logImpl;
   // 指定VFS的實現, VFS是mybatis提供的用於訪問AS內資源的一個簡便介面
  protected Class <? extends VFS> vfsImpl;
  // MyBatis 利用本地快取機制(Local Cache)防止迴圈引用(circular references)和加速重複巢狀查詢。 預設值為 SESSION,這種情況下會快取一個會話中執行的所有查詢。 若設定值為 STATEMENT,本地會話僅用在語句執行上,對相同 SqlSession 的不同呼叫將不會共享資料。
  protected LocalCacheScope localCacheScope = LocalCacheScope.SESSION;
  // 當沒有為引數提供特定的 JDBC 型別時,為空值指定 JDBC 型別。 某些驅動需要指定列的 JDBC 型別,多數情況直接用一般型別即可,比如 NULL、VARCHAR 或 OTHER。
  protected JdbcType jdbcTypeForNull = JdbcType.OTHER;
  // 指定物件的哪個方法觸發一次延遲載入。
  protected Set<String> lazyLoadTriggerMethods = new HashSet<String>(Arrays.asList(new String[] { "equals", "clone", "hashCode", "toString" }));
  // 設定超時時間,它決定驅動等待資料庫響應的秒數。預設不超時
  protected Integer defaultStatementTimeout;
  // 為驅動的結果集設定預設獲取數量。
  protected Integer defaultFetchSize;
  // SIMPLE 就是普通的執行器;REUSE 執行器會重用預處理語句(prepared statements); BATCH 執行器將重用語句並執行批量更新。
  protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE;
  // 指定 MyBatis 應如何自動對映列到欄位或屬性。 NONE 表示取消自動對映;PARTIAL 只會自動對映沒有定義巢狀結果集對映的結果集。 FULL 會自動對映任意複雜的結果集(無論是否巢狀)。
  protected AutoMappingBehavior autoMappingBehavior = AutoMappingBehavior.PARTIAL;
  // 指定發現自動對映目標未知列(或者未知屬性型別)的行為。這個值應該設定為WARNING比較合適
  protected AutoMappingUnknownColumnBehavior autoMappingUnknownColumnBehavior = AutoMappingUnknownColumnBehavior.NONE;
  // settings下的properties屬性
  protected Properties variables = new Properties();
  // 預設的反射器工廠,用於操作屬性、構造器方便
  protected ReflectorFactory reflectorFactory = new DefaultReflectorFactory();
  // 物件工廠, 所有的類resultMap類都需要依賴於物件工廠來例項化
  protected ObjectFactory objectFactory = new DefaultObjectFactory();
  // 物件包裝器工廠,主要用來在建立非原生物件,比如增加了某些監控或者特殊屬性的代理類
  protected ObjectWrapperFactory objectWrapperFactory = new DefaultObjectWrapperFactory();
  // 延遲載入的全域性開關。當開啟時,所有關聯物件都會延遲載入。特定關聯關係中可通過設定fetchType屬性來覆蓋該項的開關狀態。
  protected boolean lazyLoadingEnabled = false;
  // 指定 Mybatis 建立具有延遲載入能力的物件所用到的代理工具。MyBatis 3.3+使用JAVASSIST
  protected ProxyFactory proxyFactory = new JavassistProxyFactory(); // #224 Using internal Javassist instead of OGNL
  // MyBatis 可以根據不同的資料庫廠商執行不同的語句,這種多廠商的支援是基於對映語句中的 databaseId 屬性。
  protected String databaseId;
  ...
}

以上可以看到,Mybatis把所有的配置;resultMap、Sql語句、外掛、快取等都維護在Configuration中。這裡還有一個小技巧,在Configuration還有一個StrictMap內部類,它繼承於HashMap完善了put時防重、get時取不到值的異常處理,如下;

protected static class StrictMap<V> extends HashMap<String, V> {

    private static final long serialVersionUID = -4950446264854982944L;
    private final String name;

    public StrictMap(String name, int initialCapacity, float loadFactor) {
      super(initialCapacity, loadFactor);
      this.name = name;
    }

    public StrictMap(String name, int initialCapacity) {
      super(initialCapacity);
      this.name = name;
    }

    public StrictMap(String name) {
      super();
      this.name = name;
    }

    public StrictMap(String name, Map<String, ? extends V> m) {
      super(m);
      this.name = name;
    }
}    

(核心)載入mapper檔案mapperElement

Mapper檔案處理是Mybatis框架的核心服務,所有的SQL語句都編寫在Mapper中,這塊也是我們分析的重點,其他模組可以後續講解。

XMLConfigBuilder.parseConfiguration()->mapperElement(root.evalNode("mappers"));

private void mapperElement(XNode parent) throws Exception {
   if (parent != null) {
     for (XNode child : parent.getChildren()) {
       // 如果要同時使用package自動掃描和通過mapper明確指定要載入的mapper,一定要確保package自動掃描的範圍不包含明確指定的mapper,否則在通過package掃描的interface的時候,嘗試載入對應xml檔案的loadXmlResource()的邏輯中出現判重出錯,報org.apache.ibatis.binding.BindingException異常,即使xml檔案中包含的內容和mapper介面中包含的語句不重複也會出錯,包括載入mapper介面時自動載入的xml mapper也一樣會出錯。
       if ("package".equals(child.getName())) {
         String mapperPackage = child.getStringAttribute("name");
         configuration.addMappers(mapperPackage);
       } else {
         String resource = child.getStringAttribute("resource");
         String url = child.getStringAttribute("url");
         String mapperClass = child.getStringAttribute("class");
         if (resource != null && url == null && mapperClass == null) {
           ErrorContext.instance().resource(resource);
           InputStream inputStream = Resources.getResourceAsStream(resource);
           XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
           mapperParser.parse();
         } else if (resource == null && url != null && mapperClass == null) {
           ErrorContext.instance().resource(url);
           InputStream inputStream = Resources.getUrlAsStream(url);
           XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
           mapperParser.parse();
         } else if (resource == null && url == null && mapperClass != null) {
           Class<?> mapperInterface = Resources.classForName(mapperClass);
           configuration.addMapper(mapperInterface);
         } else {
           throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
         }
       }
     }
   }
}
  • Mybatis提供了兩類配置Mapper的方法,第一類是使用package自動搜尋的模式,這樣指定package下所有介面都會被註冊為mapper,也是在Spring中比較常用的方式,例如:

    <mappers>
      <package name="org.itstack.demo"/>
    </mappers>
    
  • 另外一類是明確指定Mapper,這又可以通過resource、url或者class進行細分,例如;

    <mappers>
        <mapper resource="mapper/User_Mapper.xml"/>
        <mapper class=""/>
        <mapper url=""/>
    </mappers>
    

4. Mapper載入與動態代理

通過package方式自動搜尋載入,生成對應的mapper代理類,程式碼塊和流程,如下;

private void mapperElement(XNode parent) throws Exception {
  if (parent != null) {
    for (XNode child : parent.getChildren()) {
      if ("package".equals(child.getName())) {
        String mapperPackage = child.getStringAttribute("name");
        configuration.addMappers(mapperPackage);
      } else {
        ...
      }
    }
  }
}

微信公眾號:bugstack蟲洞棧 & 動態代理過程

Mapper載入到生成代理物件的流程中,主要的核心類包括;

  1. XMLConfigBuilder
  2. Configuration
  3. MapperRegistry
  4. MapperAnnotationBuilder
  5. MapperProxyFactory

MapperRegistry.java

解析載入Mapper

public void addMappers(String packageName, Class<?> superType) {
  // mybatis框架提供的搜尋classpath下指定package以及子package中符合條件(註解或者繼承於某個類/介面)的類,預設使用Thread.currentThread().getContextClassLoader()返回的載入器,和spring的工具類殊途同歸。
  ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();   
  // 無條件的載入所有的類,因為呼叫方傳遞了Object.class作為父類,這也給以後的指定mapper介面預留了餘地
  resolverUtil.find(new ResolverUtil.IsA(superType), packageName); 
 // 所有匹配的calss都被儲存在ResolverUtil.matches欄位中
  Set<Class<? extends Class<?>>> mapperSet = resolverUtil.getClasses();
  for (Class<?> mapperClass : mapperSet) {   
    //呼叫addMapper方法進行具體的mapper類/介面解析
    addMapper(mapperClass);
  }
}

生成代理類:MapperProxyFactory

public <T> void addMapper(Class<T> type) {    
  // 對於mybatis mapper介面檔案,必須是interface,不能是class
  if (type.isInterface()) {
    if (hasMapper(type)) {
      throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
    }
    boolean loadCompleted = false;
    try {      
      // 為mapper介面建立一個MapperProxyFactory代理
      knownMappers.put(type, new MapperProxyFactory<T>(type));
      // It's important that the type is added before the parser is run
      // otherwise the binding may automatically be attempted by the
      // mapper parser. If the type is already known, it won't try.
      MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
      parser.parse();
      loadCompleted = true;
    } finally {
      if (!loadCompleted) {
        knownMappers.remove(type);
      }
    }
  }
}

在MapperRegistry中維護了介面類與代理工程的對映關係,knownMappers;

private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<Class<?>, MapperProxyFactory<?>>();

MapperProxyFactory.java

public class MapperProxyFactory<T> {
  private final Class<T> mapperInterface;
  private final Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<Method, MapperMethod>();
  public MapperProxyFactory(Class<T> mapperInterface) {
    this.mapperInterface = mapperInterface;
  }
  public Class<T> getMapperInterface() {
    return mapperInterface;
  }
  public Map<Method, MapperMethod> getMethodCache() {
    return methodCache;
  }
  @SuppressWarnings("unchecked")
  protected T newInstance(MapperProxy<T> mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }
  public T newInstance(SqlSession sqlSession) {
    final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }
}

如上是Mapper的代理類工程,建構函式中的mapperInterface就是對應的介面類,當例項化時候會獲得具體的MapperProxy代理,裡面主要包含了SqlSession。

五、原始碼分析(mybatis-spring)

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis-spring</artifactId>
    <version>1.3.2</version>
</dependency>

作為一款好用的ORM框架,一定是蘿莉臉(單純)、御姐心(強大),鋪的了床(遮蔽與JDBC直接打交道)、暖的了房(速度效能好)!鑑於這些優點幾乎在國內網際網路大部分開發框架都會使用到Mybatis,尤其在一些需要高效能的場景下需要優化sql那麼一定需要手寫sql在xml中。那麼,準備好了嗎!開始分析分析它的原始碼;

1. 從一個簡單的案例開始

與分析mybatis原始碼一樣,先做一個簡單的案例;定義dao、編寫配置檔案、junit單元測試;

SpringApiTest.java

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("classpath:spring-config.xml")
public class SpringApiTest {

    private Logger logger = LoggerFactory.getLogger(SpringApiTest.class);

    @Resource
    private ISchoolDao schoolDao;
    @Resource
    private IUserDao userDao;

    @Test
    public void test_queryRuleTreeByTreeId(){
        School ruleTree = schoolDao.querySchoolInfoById(1L);
        logger.info(JSON.toJSONString(ruleTree));

        User user = userDao.queryUserInfoById(1L);
        logger.info(JSON.toJSONString(user));
    }

}

spring-config-datasource.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">

    <!-- 1.資料庫連線池: DriverManagerDataSource 也可以使用DBCP2-->
    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="${db.jdbc.driverClassName}"/>
        <property name="url" value="${db.jdbc.url}"/>
        <property name="username" value="${db.jdbc.username}"/>
        <property name="password" value="${db.jdbc.password}"/>
    </bean>

    <!-- 2.配置SqlSessionFactory物件 -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <!-- 注入資料庫連線池 -->
        <property name="dataSource" ref="dataSource"/>
        <!-- 配置MyBaties全域性配置檔案:mybatis-config.xml -->
        <property name="configLocation" value="classpath:mybatis-config.xml"/>
        <!-- 掃描entity包 使用別名 -->
        <property name="typeAliasesPackage" value="org.itstack.demo.po"/>
        <!-- 掃描sql配置檔案:mapper需要的xml檔案 -->
        <property name="mapperLocations" value="classpath:mapper/*.xml"/>
    </bean>

    <!-- 3.配置掃描Dao介面包,動態實現Dao介面,注入到spring容器中 -->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <!-- 注入sqlSessionFactory -->
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
        <!-- 給出需要掃描Dao介面包,多個逗號隔開 -->
        <property name="basePackage" value="org.itstack.demo.dao"/>
    </bean>
              
</beans>

如果一切順利,那麼會有如下結果:

{"address":"北京市海淀區頤和園路5號","createTime":1571376957000,"id":1,"name":"北京大學","updateTime":1571376957000}
{"age":18,"createTime":1571376957000,"id":1,"name":"花花","updateTime":1571376957000}

從上面單元測試的程式碼可以看到,兩個沒有方法體的註解就這麼神奇的執行了我們的xml中的配置語句並輸出了結果。其實主要得益於以下兩個類;

  • org.mybatis.spring.SqlSessionFactoryBean
  • org.mybatis.spring.mapper.MapperScannerConfigurer

2. 掃描裝配註冊(MapperScannerConfigurer)

MapperScannerConfigurer為整個Dao介面層生成動態代理類註冊,啟動到了核心作用。這個類實現瞭如下介面,用來對掃描的Mapper進行處理:

  • BeanDefinitionRegistryPostProcessor
  • InitializingBean
  • ApplicationContextAware
  • BeanNameAware

整體類圖如下;

微信公眾號:bugstack蟲洞棧 & MapperScannerConfigurer類圖

執行流程如下;

微信公眾號:bugstack蟲洞棧 & 執行流程圖

上面的類圖+流程圖,其實已經很清楚的描述了MapperScannerConfigurer初始化過程,但對於頭一次看的新人來說依舊是我太難了,好繼續!

MapperScannerConfigurer.java & 部分擷取

@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
  if (this.processPropertyPlaceHolders) {
    processPropertyPlaceHolders();
  }
  ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
  scanner.setAddToConfig(this.addToConfig);
  scanner.setAnnotationClass(this.annotationClass);
  scanner.setMarkerInterface(this.markerInterface);
  scanner.setSqlSessionFactory(this.sqlSessionFactory);
  scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
  scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
  scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
  scanner.setResourceLoader(this.applicationContext);
  scanner.setBeanNameGenerator(this.nameGenerator);
  scanner.registerFilters();
  scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
}
  • 實現了BeanDefinitionRegistryPostProcessor.postProcessBeanDefinitionRegistry用於註冊Bean到Spring容器中
  • 306行:new ClassPathMapperScanner(registry); 硬編碼類路徑掃描器,用於解析Mybatis的Mapper檔案
  • 317行:scanner.scan 對Mapper進行掃描。這裡包含了一個繼承類實現關係的呼叫,也就是本文開頭的測試題。

ClassPathMapperScanner.java & 部分擷取

@Override
public Set<BeanDefinitionHolder> doScan(String... basePackages) {
  Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);
  if (beanDefinitions.isEmpty()) {
    logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.");
  } else {
    processBeanDefinitions(beanDefinitions);
  }
  return beanDefinitions;
}
  • 優先呼叫父類的super.doScan(basePackages);進行註冊Bean資訊

ClassPathBeanDefinitionScanner.java & 部分擷取

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
	Assert.notEmpty(basePackages, "At least one base package must be specified");
	Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>();
	for (String basePackage : basePackages) {
		Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
		for (BeanDefinition candidate : candidates) {
			ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
			candidate.setScope(scopeMetadata.getScopeName());
			String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
			if (candidate instanceof AbstractBeanDefinition) {
				postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
			}
			if (candidate instanceof AnnotatedBeanDefinition) {
				AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate)
			}
			if (checkCandidate(beanName, candidate)) {
				BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
				definitionHolder =
						AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.regi
				beanDefinitions.add(definitionHolder);
				registerBeanDefinition(definitionHolder, this.registry);
			}
		}
	}
	return beanDefinitions;
}
  • 優先呼叫了父類的doScan方法,用於Mapper掃描和Bean的定義以及註冊到DefaultListableBeanFactory。{DefaultListableBeanFactory是Spring中IOC容器的始祖,所有需要例項化的類都需要註冊進來,之後在初始化}
  • 272行:findCandidateComponents(basePackage),掃描package包路徑,對於註解類的有另外的方式,大同小異
  • 288行:registerBeanDefinition(definitionHolder, this.registry);註冊Bean資訊的過程,最終會呼叫到:org.springframework.beans.factory.support.DefaultListableBeanFactory

ClassPathMapperScanner.java & 部分擷取

**processBeanDefinitions(beanDefinitions);**

private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
  GenericBeanDefinition definition;
  for (BeanDefinitionHolder holder : beanDefinitions) {
    definition = (GenericBeanDefinition) holder.getBeanDefinition();
    if (logger.isDebugEnabled()) {
      logger.debug("Creating MapperFactoryBean with name '" + holder.getBeanName() 
        + "' and '" + definition.getBeanClassName() + "' mapperInterface");
    }
    // the mapper interface is the original class of the bean
    // but, the actual class of the bean is MapperFactoryBean
    definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59
    definition.setBeanClass(this.mapperFactoryBean.getClass());
    definition.getPropertyValues().add("addToConfig", this.addToConfig);
    boolean explicitFactoryUsed = false;
    if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
      definition.getPropertyValues().add("sqlSessionFactory", new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
      explicitFactoryUsed = true;
    } else if (this.sqlSessionFactory != null) {
      definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
      explicitFactoryUsed = true;
    }
    if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
      if (explicitFactoryUsed) {
        logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
      }
      definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
      explicitFactoryUsed = true;
    } else if (this.sqlSessionTemplate != null) {
      if (explicitFactoryUsed) {
        logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
      }
      definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
      explicitFactoryUsed = true;
    }
    if (!explicitFactoryUsed) {
      if (logger.isDebugEnabled()) {
        logger.debug("Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
      }
      definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
    }
  }
}
  • 163行:super.doScan(basePackages);,呼叫完父類方法後開始執行內部方法:processBeanDefinitions(beanDefinitions)
  • 186行:definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); 設定BeanName引數,也就是我們的:ISchoolDao、IUserDao
  • 187行:definition.setBeanClass(this.mapperFactoryBean.getClass());,設定BeanClass,介面本身是沒有類的,那麼這裡將MapperFactoryBean類設定進來,最終所有的dao層介面類都是這個MapperFactoryBean

MapperFactoryBean.java & 部分擷取

這個類有繼承也有介面實現,最好先了解下整體類圖,如下;

微信公眾號:bugstack蟲洞棧 & MapperFactoryBean類圖

這個類就非常重要了,最終所有的sql資訊執行都會通過這個類獲取getObject(),也就是SqlSession獲取mapper的代理類:MapperProxyFactory->MapperProxy

public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> {

  private Class<T> mapperInterface;

  private boolean addToConfig = true;

  public MapperFactoryBean() {
    //intentionally empty 
  }
  
  public MapperFactoryBean(Class<T> mapperInterface) {
    this.mapperInterface = mapperInterface;
  }

  /**  
   * 當SpringBean容器初始化時候會呼叫到checkDaoConfig(),他是繼承類中的抽象方法
   * {@inheritDoc}
   */
  @Override
  protected void checkDaoConfig() {
    super.checkDaoConfig();

    notNull(this.mapperInterface, "Property 'mapperInterface' is required");

    Configuration configuration = getSqlSession().getConfiguration();
    if (this.addToConfig && !configuration.hasMapper(this.mapperInterface)) {
      try {
        configuration.addMapper(this.mapperInterface);
      } catch (Exception e) {
        logger.error("Error while adding the mapper '" + this.mapperInterface + "' to configuration.", e);
        throw new IllegalArgumentException(e);
      } finally {
        ErrorContext.instance().reset();
      }
    }
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public T getObject() throws Exception {
    return getSqlSession().getMapper(this.mapperInterface);
  }

  ...
}
  • 72行:checkDaoConfig(),當SpringBean容器初始化時候會呼叫到checkDaoConfig(),他是繼承類中的抽象方法

  • 95行:getSqlSession().getMapper(this.mapperInterface);,通過介面獲取Mapper(代理類),呼叫過程如下;

    • DefaultSqlSession.getMapper(Class type),獲取Mapper

    • Configuration.getMapper(Class type, SqlSession sqlSession),從配置中獲取

    • MapperRegistry.getMapper(Class type, SqlSession sqlSession),從註冊中心獲取到例項化生成

      public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
        final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
        if (mapperProxyFactory == null) {
          throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
        }
        try {
          return mapperProxyFactory.newInstance(sqlSession);
        } catch (Exception e) {
          throw new BindingException("Error getting mapper instance. Cause: " + e, e);
        }
      }
      
      
    • mapperProxyFactory.newInstance(sqlSession);,通過反射工程生成MapperProxy

      @SuppressWarnings("unchecked")
      protected T newInstance(MapperProxy<T> mapperProxy) {
        return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
      }
      public T newInstance(SqlSession sqlSession) {
        final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
        return newInstance(mapperProxy);
      }
      

MapperProxy.java & 部分擷取

public class MapperProxy<T> implements InvocationHandler, Serializable {

  private static final long serialVersionUID = -6424540398559729838L;
  private final SqlSession sqlSession;
  private final Class<T> mapperInterface;
  private final Map<Method, MapperMethod> methodCache;

  public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
    this.sqlSession = sqlSession;
    this.mapperInterface = mapperInterface;
    this.methodCache = methodCache;
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      if (Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
      } else if (isDefaultMethod(method)) {
        return invokeDefaultMethod(proxy, method, args);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    return mapperMethod.execute(sqlSession, args);
  }

  private MapperMethod cachedMapperMethod(Method method) {
    MapperMethod mapperMethod = methodCache.get(method);
    if (mapperMethod == null) {
      mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
      methodCache.put(method, mapperMethod);
    }
    return mapperMethod;
  }

  @UsesJava7
  private Object invokeDefaultMethod(Object proxy, Method method, Object[] args)
      throws Throwable {
    final Constructor<MethodHandles.Lookup> constructor = MethodHandles.Lookup.class
        .getDeclaredConstructor(Class.class, int.class);
    if (!constructor.isAccessible()) {
      constructor.setAccessible(true);
    }
    final Class<?> declaringClass = method.getDeclaringClass();
    return constructor
        .newInstance(declaringClass,
            MethodHandles.Lookup.PRIVATE | MethodHandles.Lookup.PROTECTED
                | MethodHandles.Lookup.PACKAGE | MethodHandles.Lookup.PUBLIC)
        .unreflectSpecial(method, declaringClass).bindTo(proxy).invokeWithArguments(args);
  }

  ...
}
  • 58行:final MapperMethod mapperMethod = cachedMapperMethod(method);,從快取中獲取MapperMethod

  • 59行:mapperMethod.execute(sqlSession, args);,執行SQL語句,並返回結果(到這關於查詢獲取結果就到骨頭(幹)層了);INSERT、UPDATE、DELETE、SELECT

    public Object execute(SqlSession sqlSession, Object[] args) {
      Object result;
      switch (command.getType()) {
        case INSERT: {
        Object param = method.convertArgsToSqlCommandParam(args);
          result = rowCountResult(sqlSession.insert(command.getName(), param));
          break;
        }
        case UPDATE: {
          Object param = method.convertArgsToSqlCommandParam(args);
          result = rowCountResult(sqlSession.update(command.getName(), param));
          break;
        }
        case DELETE: {
          Object param = method.convertArgsToSqlCommandParam(args);
          result = rowCountResult(sqlSession.delete(command.getName(), param));
          break;
        }
        case SELECT:
          if (method.returnsVoid() && method.hasResultHandler()) {
            executeWithResultHandler(sqlSession, args);
            result = null;
          } else if (method.returnsMany()) {
            result = executeForMany(sqlSession, args);
          } else if (method.returnsMap()) {
            result = executeForMap(sqlSession, args);
          } else if (method.returnsCursor()) {
            result = executeForCursor(sqlSession, args);
          } else {
            Object param = method.convertArgsToSqlCommandParam(args);
            result = sqlSession.selectOne(command.getName(), param);
          }
          break;
        case FLUSH:
          result = sqlSession.flushStatements();
          break;
        default:
          throw new BindingException("Unknown execution method for: " + command.getName());
      }
      if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
        throw new BindingException("Mapper method '" + command.getName() 
            + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
      }
      return result;
    }
    

以上對於MapperScannerConfigurer這一層就分析完了,從掃描定義注入到為Spring容器準備Bean的資訊,代理、反射、SQL執行,基本就包括全部核心內容了,接下來在分析下SqlSessionFactoryBean

3. SqlSession容器工廠初始化(SqlSessionFactoryBean)

SqlSessionFactoryBean初始化過程中需要對一些自身內容進行處理,因此也需要實現如下介面;

  • FactoryBean
  • InitializingBean -> void afterPropertiesSet() throws Exception
  • ApplicationListener

微信公眾號:bugstack蟲洞棧 & SqlSessionFactoryBean初始化流程

以上的流程其實已經很清晰的描述整個核心流程,但同樣對於新手上路會有障礙,那麼!好,繼續!

SqlSessionFactoryBean.java & 部分擷取

public void afterPropertiesSet() throws Exception {
  notNull(dataSource, "Property 'dataSource' is required");
  notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
  state((configuration == null && configLocation == null) || !(configuration != null && configLocation != null),
            "Property 'configuration' and 'configLocation' can not specified with together");
  this.sqlSessionFactory = buildSqlSessionFactory();
}
  • afterPropertiesSet(),InitializingBean介面為bean提供了初始化方法的方式,它只包括afterPropertiesSet方法,凡是繼承該介面的類,在初始化bean的時候都會執行該方法。
  • 380行:buildSqlSessionFactory();內部方法構建,核心功能繼續往下看。

SqlSessionFactoryBean.java & 部分擷取

protected SqlSessionFactory buildSqlSessionFactory() throws IOException {
  Configuration configuration;
  XMLConfigBuilder xmlConfigBuilder = null;
  
  ...

  if (!isEmpty(this.mapperLocations)) {
    for (Resource mapperLocation : this.mapperLocations) {
      if (mapperLocation == null) {
        continue;
      }
      try {
        XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
            configuration, mapperLocation.toString(), configuration.getSqlFragments());
        xmlMapperBuilder.parse();
      } catch (Exception e) {
        throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
      } finally {
        ErrorContext.instance().reset();
      }
      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Parsed mapper file: '" + mapperLocation + "'");
      }
    }
  } else {
    if (LOGGER.isDebugEnabled()) {
      LOGGER.debug("Property 'mapperLocations' was not specified or no matching resources found");
    }
  }
  return this.sqlSessionFactoryBuilder.build(configuration);
}

  • 513行:for (Resource mapperLocation : this.mapperLocations) 迴圈解析Mapper內容
  • 519行:XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(...) 解析XMLMapperBuilder
  • 521行:xmlMapperBuilder.parse() 執行解析,具體如下;

XMLMapperBuilder.java & 部分擷取

public class XMLMapperBuilder extends BaseBuilder {
   private final XPathParser parser;
   private final MapperBuilderAssistant builderAssistant;
   private final Map<String, XNode> sqlFragments;
   private final String resource;

   private void bindMapperForNamespace() {
     String namespace = builderAssistant.getCurrentNamespace();
     if (namespace != null) {
       Class<?> boundType = null;
       try {
         boundType = Resources.classForName(namespace);
       } catch (ClassNotFoundException e) {
         //ignore, bound type is not required
       }
       if (boundType != null) {
         if (!configuration.hasMapper(boundType)) {
           // Spring may not know the real resource name so we set a flag
           // to prevent loading again this resource from the mapper interface
           // look at MapperAnnotationBuilder#loadXmlResource
           configuration.addLoadedResource("namespace:" + namespace);
           configuration.addMapper(boundType);
         }
       }
     }
   }
}
  • 這裡413行非常重要,configuration.addMapper(boundType);,真正到了新增Mapper到配置中心

MapperRegistry.java & 部分擷取

public class MapperRegistry {

  public <T> void addMapper(Class<T> type) {
    if (type.isInterface()) {
      if (hasMapper(type)) {
        throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
      }
      boolean loadCompleted = false;
      try {
        knownMappers.put(type, new MapperProxyFactory<T>(type));
        // It's important that the type is added before the parser is run
        // otherwise the binding may automatically be attempted by the
        // mapper parser. If the type is already known, it won't try.
        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
        parser.parse();
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }
  
}
  • 67行:建立代理工程knownMappers.put(type, new MapperProxyFactory(type));

截至到這,MapperScannerConfigurer、SqlSessionFactoryBean,兩個類乾的事情就相融合了;

  • 第一個用於掃描Dao介面設定代理類註冊到IOC中,用於後續生成Bean實體類,MapperFactoryBean,並可以通過mapperInterface從Configuration獲取Mapper

  • 另一個用於生成SqlSession工廠初始化,解析Mapper裡的XML配置進行動態代理MapperProxyFactory->MapperProxy注入到Configuration的Mapper

  • 最終在註解類的幫助下進行方法注入,等執行操作時候即可獲得動態代理物件,從而執行相應的CRUD操作

    @Resource
    private ISchoolDao schoolDao;
    
    schoolDao.querySchoolInfoById(1L);
    

六、綜上總結

  • 分析過程較長篇幅也很大,不一定一天就能看懂整個流程,但當耐下心來一點點研究,還是可以獲得很多的收穫的。以後在遇到這類的異常就可以迎刃而解了,同時也有助於面試、招聘!
  • 之所以分析Mybatis最開始是想在Dao上加自定義註解,發現切面攔截不到。想到這是被動態代理的類,之後層層往往下扒直到MapperProxy.invoke!當然,Mybatis提供了自定義外掛開發。
  • 以上的原始碼分析只是對部分核心內容進行分析,如果希望瞭解全部可以參考資料;MyBatis 3原始碼深度解析,並除錯程式碼。IDEA中還是很方便看原始碼的,包括可以檢視類圖、呼叫順序等。
  • mybatis、mybatis-spring中其實最重要的是將Mapper配置檔案解析與介面類組裝成代理類進行對映,以此來方便對資料庫的CRUD操作。從原始碼分析後,可以獲得更多的程式設計經驗(套路)。
  • Mybatis相關連結;

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