Mybatis的使用詳解

Mybatis所需要的jar包：
需要引用兩個jar包，一個是mybatis，另一個是mysql-connector-java，如果是maven工程的話，pom裡如下新增依賴就可以了。

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.2.3</version>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.26</version>
</dependency>

資料準備：
在MySQL中造點資料進行測試用：

CREATE DATABASE mybatis_test;

CREATE TABLE user
(
    age INTEGER NOT NULL,
    name VARCHAR(64) NOT NULL DEFAULT ''

);

insert user values(18,'zhanjindong');
insert user values(20,'zhangsan');

配置檔案：
需要兩類配置檔案，一類是MyBatis的配置檔案mybatis-config.xml，示例中是一個很簡單配置，詳細的配置網上有很多說明。

<?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>   
    <settings>   
        <!-- changes from the defaults for testing -->   
        <setting name="cacheEnabled" value="false" />   
        <setting name="useGeneratedKeys" value="true" />   
        <setting name="defaultExecutorType" value="REUSE" />   
    </settings>   
    <typeAliases>   
       <typeAlias alias="User" type="test.mybatis.User"/>   
    </typeAliases>   
    <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://192.168.71.38:3306/mybatis_test"/>   
              <property name="username" value="root"/>   
              <property name="password" value="123456"/>   
           </dataSource>   
       </environment>   
    </environments>   
    <mappers>   
        <mapper resource="mappers/UserMapper.xml" />   
    </mappers>   
</configuration>

另一類是資料訪問介面對映檔案：示例中是UserMapper.xml。這個檔案一般放在src/main/resource下面或子目錄下mybatis就可以找到了，在mybatis-config.xml中由mappers/mapper節點的resource指定。

<?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="test.mybatis.UserMapper">
    <!-- 這裡namespace必須是UserMapper介面的路徑” -->
    <insert id="insertUser" parameterType="User">
        insert into user(name,age) values(#{name},#{age})
        <!-- 這裡sql結尾不能加分號，否則報“ORA-00911”的錯誤 -->
    </insert>

    <!-- 這裡的id必須和UserMapper介面中的介面方法名相同 -->
    <select id="getUser" resultType="User" parameterType="java.lang.String">
        select * from user where name=#{name}
    </select>
</mapper>

對應這個對映檔案就是test.mybatis這個名稱空間下的UserMapper這個介面，只是定義了訪問資料表的介面：

package test.mybatis;

public interface UserMapper {
    public void insertUser(User user);

    public User getUser(String name);
}

需要一個POJO:User.java

package test.mybatis;

public class User {
    private String name;
    private Integer age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public User(String name, Integer age) {
        super();
        this.name = name;
        this.age = age;
    }

    public User() {
        super();
    }
}

測試：
通過MyBatis運算元據庫用到的是一個叫SqlSession的類，這個類是通過SqlSessionFactory產生的，一般建議在全域性維護一個SqlSessionFactory就可以了。

TestMyBatis.java

package test.mybatis;

import java.io.IOException;
import java.io.Reader;

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

public class MyBatisUtil {
    private final static SqlSessionFactory sqlSessionFactory;
    static {
        String resource = "mybatis-config.xml";
        Reader reader = null;
        try {
            reader = Resources.getResourceAsReader(resource);
        } catch (IOException e) {
            System.out.println(e.getMessage());

        }
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
    }

    public static SqlSessionFactory getSqlSessionFactory() {
        return sqlSessionFactory;
    }
}

測試程式碼如下：

TestMyBatis.java

package test.mybatis;

import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;

public class TestMyBatis {
    static SqlSessionFactory sqlSessionFactory = null;
    static {
        sqlSessionFactory = MyBatisUtil.getSqlSessionFactory();
    }

    public static void main(String[] args) {
        testAdd();
        getUser();
    }

    public static void testAdd() {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            User user = new User("lisi", new Integer(25));
            userMapper.insertUser(user);
            sqlSession.commit();// 這裡一定要提交，不然資料進不去資料庫中
        } finally {
            sqlSession.close();
        }
    }

    public static void getUser() {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            User user = userMapper.getUser("zhangsan");
            System.out.println("name: " + user.getName() + "|age: "
                    + user.getAge());
        } finally {
            sqlSession.close();
        }
    }
}

1、mybatis會用log4j記錄日誌，但是開啟debug模式貌似對效能影響非常厲害。

2、mybatis的查詢快取對效能的影響非常大，啟用和不啟用差距非常大