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
- 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;
- 獲取 ClassLoader 集合,最大限度搜尋配置檔案
- 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:
- 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);
}
...
}
- 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)
- XPathParser(Reader reader, boolean validation, Properties variables, EntityResolver entityResolver)
- reader:使用字元流建立新的輸入源,用於對XML檔案的讀取
- validation:是否進行DTD校驗
- variables:屬性配置資訊
- 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;
}
}
- 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
- 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);
}
}
-
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
-
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; }
-
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(); } }
-
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;
- 屬性解析propertiesElement
- 載入settings節點settingsAsProperties
- 載自定義VFS loadCustomVfs
- 解析型別別名typeAliasesElement
- 載入外掛pluginElement
- 載入物件工廠objectFactoryElement
- 建立物件包裝器工廠objectWrapperFactoryElement
- 載入反射工廠reflectorFactoryElement
- 元素設定settingsElement
- 載入環境配置environmentsElement
- 資料庫廠商標識載入databaseIdProviderElement
- 載入型別處理器typeHandlerElement
- (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;
- properties?,
- settings?,
- typeAliases?,
- typeHandlers?,
- objectFactory?,
- objectWrapperFactory?,
- reflectorFactory?,
- plugins?,
- environments?,
- databaseIdProvider?,
- 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 {
...
}
}
}
}
Mapper載入到生成代理物件的流程中,主要的核心類包括;
- XMLConfigBuilder
- Configuration
- MapperRegistry
- MapperAnnotationBuilder
- 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;
執行流程如下;
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;
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
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;