Mybatis的使用详解

Mybatis所需要的jar包：
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();        }    }}

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