Mybatis使用示例

下面是一个简单的Mybatis使用DEMO

　　整体结构

POM依赖

需要引用两个jar包，一个是mybatis，另一个是mysql-connector-java，如果是maven工程的话，pom里如下添加依赖就可以了。

<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>

数据准备

在MySQL中造点数据进行测试用：

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‘);

配置文件

需要两类配置文件，一类是MyBatis的配置文件mybatis-config.xml，示例中是一个很简单配置，详细的配置网上有很多说明。

<?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>

另一类是数据访问接口映射文件：示例中是UserMapper.xml。这个文件一般放在src/main/resource下面或子目录下mybatis就可以找到了，在mybatis-config.xml中由mappers/mapper节点的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">
    <!-- 这里namespace必须是UserMapper接口的路径” -->
    <insert id="insertUser" parameterType="User">
        insert into user(name,age) values(#{name},#{age})
        <!-- 这里sql结尾不能加分号，否则报“ORA-00911”的错误 -->
    </insert>

    <!-- 这里的id必须和UserMapper接口中的接口方法名相同 -->
    <select id="getUser" resultType="User" parameterType="java.lang.String">
        select * from user where name=#{name}
    </select>
</mapper>

对应这个映射文件就是test.mybatis这个命名空间下的UserMapper这个接口，只是定义了访问数据表的接口：

package test.mybatis;

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

    public User getUser(String name);
}

需要一个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();
    }
}

测试

通过MyBatis操作数据库用到的是一个叫SqlSession的类，这个类是通过SqlSessionFactory产生的，一般建议在全局维护一个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;
    }
}

测试代码如下：

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();// 这里一定要提交，不然数据进不去数据库中
        } 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();
        }
    }
}

注意事项：

1、mybatis会用log4j记录日志，但是开启debug模式貌似对性能影响非常厉害。

2、mybatis的查询缓存对性能的影响非常大，启用和不启用差距非常大

注意：mapper文件中一定要加上cache这一行，否则不生效。