mybatis3 简单入门

官网文档：http://mybatis.github.io/mybatis-3/zh/index.html

源码：https://github.com/mybatis/mybatis-3

maven依赖：

<dependency>            <groupId>org.mybatis</groupId>            <artifactId>mybatis</artifactId>            <version>3.2.6</version></dependency>

不管使用哪种持久层框架都先得有POJO和DAO

package me.poplaris.mybatis.bean;/** * User: poplar * Date: 14-7-4 下午5:56 */public class User {  private int id;  private String name;  public int getId() {    return id;  }  public void setId(int id) {    this.id = id;  }  public String getName() {    return name;  }  public void setName(String name) {    this.name = name;  }}

package me.poplaris.mybatis.dao;import me.poplaris.mybatis.bean.User;/** * User: poplar * Date: 14-7-4 下午5:59 */public interface UserDao {  public User getUserId(int id);}

建立好POJO和DAO后我们开始使用MyBatis

每 一 个 MyBatis 的 应 用 程 序 都 以 一 个 SqlSessionFactory 对 象 的 实 例 为 核 心 。 SqlSessionFactory 对 象 的 实 例 可 以 通 过 SqlSessionFactoryBuilder 对 象 来 获 得，我们先介绍使用XML来构建

  @Test  public void buildUseXml() throws IOException {//    String resource = "org/mybatis/example/mybatis-config.xml";    String resource = "mybatis-config.xml";    //从 XML 中构建 SqlSessionFactory    Reader reader = Resources.getResourceAsReader(resource);    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);    //从 SqlSessionFactory 中获取 SqlSession    SqlSession session = sqlSessionFactory.openSession();    try {      User user = session.selectOne("me.poplaris.mybatis.dao.UserDao.getUserId",1);    } finally {      session.close();    }  }

一个简单的XML配置文件最主要的是配置数据源和事务管理器：

<?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/test?autoReconnect=true"/>                <property name="username" value="root"/>                <property name="password" value="123456"/>            </dataSource>        </environment>    </environments></configuration>

有时候你可能想从properties来读取数据源配置，而不是写死在XML中。在mybatis-config中添加properties配置

<properties resource="config.properties"></properties>

config.properties文件如下：

driver=com.mysql.jdbc.Driverurl=jdbc:mysql://127.0.0.1:3306/test?autoReconnect=trueusername=rootpassword=root

修改过后的mybatis-config：

<?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>    <properties resource="config.properties"></properties>    <environments default="development">        <environment id="development">            <transactionManager type="JDBC"/>            <dataSource type="POOLED">                <property name="driver" value="${driver}"/>                <property name="url" value="${url}"/>                <property name="username" value="${username}"/>                <property name="password" value="${password}"/>            </dataSource>        </environment>    </environments></configuration>

执行buildUseXml测试，出现异常

java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for me.poplaris.mybatis.dao.UserDao.getUserId

这是因为Mapped中没有实现UserDao，在mybatis-config.xml中添加POJO别名和mappers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>    <properties resource="config.properties"></properties>    <typeAliases>        <typeAlias alias="User" type="me.poplaris.mybatis.bean.User"/>    </typeAliases>    <environments default="development">        <environment id="development">            <transactionManager type="JDBC"/>            <dataSource type="POOLED">                <property name="driver" value="${driver}"/>                <property name="url" value="${url}"/>                <property name="username" value="${username}"/>                <property name="password" value="${password}"/>            </dataSource>        </environment>    </environments>    <mappers>        <mapper resource="mybatis/User.xml"/>    </mappers></configuration>

并实现UserDao，新增XML配置文件User.xml

<?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="me.poplaris.mybatis.dao.UserDao">    <select id="getUserId" parameterType="int" resultType="User">        select            *        from            `user`        where            id = #{id}    </select></mapper>

User.xml中mapper的namespace对应我们定义的DAO接口类UserDao，id为getUserId的select操作对应UserDao里的getUserId(int id)方法

再次执行buildUseXml测试，打印出了正常数据，一个简单的使用XML配置来读取数据成功实现。

在buildUseXml中

session.selectOne("me.poplaris.mybatis.dao.UserDao.getUserId",1);

因为我们在mapper中已经配置了这个namespace，所以这行代码有更简单安全的方式来代替

UserDao userDao = session.getMapper(UserDao.class);User user = userDao.getUserId(1);

所以整个buildUseXml测试变成了这样：

  @Test  public void buildUseXml() throws IOException {//    String resource = "org/mybatis/example/mybatis-config.xml";    String resource = "mybatis-config.xml";    //从 XML 中构建 SqlSessionFactory    Reader reader = Resources.getResourceAsReader(resource);    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);    //从 SqlSessionFactory 中获取 SqlSession    SqlSession session = sqlSessionFactory.openSession();    try {//      User user = session.selectOne("me.poplaris.mybatis.dao.UserDao.getUserId",1);      UserDao userDao = session.getMapper(UserDao.class);      User user = userDao.getUserId(1);      System.out.println(user);    } finally {      session.close();    }  }

使用XML配置实现mybatis操作已经简单的介绍完毕，更多详细的XML配置，动态SQL等可以参看官方文档

下面介绍不依赖XML配置来实现mybatis操作，下面的测试方法是使用JAVA程序来创建一个简单的配置实例

  @Test  public void buildUseAnno(){    String url = "jdbc:mysql://127.0.0.1:3306/test?autoReconnect=true";    String userName = "root";    String password = "root";    //数据源    DataSource dataSource = new MyDefaultDataSource(url,userName,password);    //事务工厂    TransactionFactory transactionFactory = new JdbcTransactionFactory();    Environment environment = new Environment("development", transactionFactory, dataSource);    Configuration configuration = new Configuration(environment);    //绑定DAO mapper    configuration.addMapper(UserDaoWithAnno.class);    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);    SqlSession session = sqlSessionFactory.openSession();    try {      UserDaoWithAnno userDao = session.getMapper(UserDaoWithAnno.class);      User user = userDao.getUserId(1);      System.out.println(user);      List<User> userList = userDao.getUsers();      System.out.println(userList);    } finally {      session.close();    }  }

首先需要自己实现DataSource，MyDefaultDataSource核心的代码片段如下：

  @Override  public Connection getConnection(String username, String password) throws SQLException {    return DriverManager.getConnection(url,username,password);  }

运行buildUseAnno测试，出现异常

org.apache.ibatis.binding.BindingException: Invalid bound statement (not found): me.poplaris.mybatis.dao.UserDaoWithAnno.getUserId

这是因为mapper绑定未完成，我们需要对具体的SQL操作做绑定

使用这种方式配置主要是添加映射类。

configuration.addMapper(UserDaoWithAnno.class);

映射类是 Java 类,这些类包含 SQL 映射语句的注解从而避免了XML文件的依赖

package me.poplaris.mybatis.dao;import me.poplaris.mybatis.bean.User;import org.apache.ibatis.annotations.Select;import java.util.List;/** * User: poplar * Date: 14-7-4 下午5:59 */public interface UserDaoWithAnno {  @Select("select * from user where id= #{id}")  public User getUserId(int id);  @Select("select * from user")  public List<User> getUsers();}

使用Select注解完成注册mapper，再次执行buildUseAnno测试，成功。

OK，简单的使用注解方式来完成mybatis操作也已经介绍完毕，更多的注解方案请参看官方文档，实例代码请点击这里