Java+MyBatis+MySQL开发环境搭建流程详解

主要搭建过程

1. pom.xml文件中加入mybatis和数据库依赖，这里使用mysql：

<properties>
 <mybatis.version>3.2.3</mybatis.version>
 <mysql.version>5.1.26</mysql.version>
 <slf4j.api.version>1.7.5</slf4j.api.version>
 <testng.version>6.8.7</testng.version>
</properties> 

<dependencies>
 <dependency>
  <groupId>org.mybatis</groupId>
  <artifactId>mybatis</artifactId>
  <version>${mybatis.version}</version>
 </dependency>
 <!-- Database driver -->
 <dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
  <version>${mysql.version}</version>
 </dependency>
 <!-- mybatis启动要加载log4j -->
 <dependency>
  <groupId>org.slf4j</groupId>
  <artifactId>slf4j-log4j12</artifactId>
  <version>${slf4j.api.version}</version>
 </dependency>
 <!-- Test -->
 <dependency>
  <groupId>org.testng</groupId>
  <artifactId>testng</artifactId>
  <version>${testng.version}</version>
 </dependency>
</dependencies>

2. 在类路径下创建mybatis的配置文件Configuration.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>
  <typeAliases><!-- 别名 -->
    <typeAlias alias="User" type="com.john.hbatis.model.User" />
  </typeAliases> 

  <environments default="development">
   <environment id="development">
    <transactionManager type="JDBC"/>
    <dataSource type="POOLED"><!-- 数据源 -->
      <property name="driver" value="com.mysql.jdbc.Driver" />
      <property name="url" value="jdbc:mysql://localhost:3306/hbatis" />
      <property name="username" value="root" />
      <property name="password" value="123456" />
    </dataSource>
   </environment>
  </environments> 

  <mappers><!-- ORM映射文件 -->
    <mapper resource="com/john/hbatis/model/User.xml" />
  </mappers>
 </configuration>

3. 执行创建数据库和表的sql：

-- Create the database named 'hbatis'.
-- It's OK to use `, not OK to use ' or " surrounding the database name to prevent it from being interpreted as a keyword if possible.
CREATE DATABASE IF NOT EXISTS `hbatis`
DEFAULT CHARACTER SET = `UTF8`; 

-- Create a table named 'User'
CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(50) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  `address` varchar(200) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8; 

-- Insert a test record
Insert INTO `user` VALUES ('1', 'john', '120', 'hangzhou,westlake');

4. com.john.hbatis.model.User类：

public class User {
  private int id;
  private String name;
  private String age;
  private String address;
  // Getters and setters are omitted 

  // 如果有带参数的构造器，编译器不会自动生成无参构造器。当查询需要返回对象时，ORM框架用反射来调用对象的无参构造函数，导致异常：java.lang.NoSuchMethodException: com.john.hbatis.model.User.<init>()
  // 这时需要明确写出：
  public User() {
  } 

  public User(int id, String address) {
    this.id = id;
    this.address = address;
  } 

  public User(String name, int age, String address) {
    this.name = name;
    this.age = age;
    this.address = address;
  }
}

com/john/hbatis/model路径下的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="com.john.hbatis.model.UserMapper">
  <select id="getUserById" parameterType="int" resultType="User">
    select * from `user` where id = #{id}
  </select>
</mapper>

5. 测试类：

public class MyBatisBasicTest {
  private static final Logger log = LoggerFactory.getLogger(MyBatisBasicTest.class);
  private static SqlSessionFactory sqlSessionFactory; 

  private static Reader reader; 

  @BeforeClass
  public static void initial() {
    try {
      reader = Resources.getResourceAsReader("Configuration.xml");
      sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
    } catch (IOException e) {
      log.error("Error thrown while reading the configuration: {}", e);
    } finally {
      if (reader != null) {
        try {
          reader.close();
        } catch (IOException e) {
          log.error("Error thrown while closing the reader: {}", e);
        }
      }
    }
  } 

  @Test
  public void queryTest() {
    SqlSession session = sqlSessionFactory.openSession();
    User user = (User)session.selectOne("com.john.hbatis.model.UserMapper.getUserById", 1);
    log.info("{}: {}", user.getName(), user.getAddress());
  }
}

以接口方式交互数据
上面的环境搭建是采用SqlSession的通用方法并强制转换的方式，存在着转换安全的问题：

User user = (User)session.selectOne("com.john.hbatis.model.UserMapper.getUserById", 1);

可以采用接口加sql语句的方式来解决，sql语句理解为是接口的实现：

1. 新建接口类：

package com.john.hbatis.mapper; 

import com.john.hbatis.model.User; 

public interface IUserMapper {
  User getUserById(int id);
}

2. 修改User.xml文件，确保namespace属性值和接口的全限定名相同，且id属性值和接口方法名相同：

<mapper namespace="com.john.hbatis.mapper.IUserMapper">
  <select id="getUserById"

3. 在MyBatisBasicTest类中添加测试方法：

@Test
public void queryInInterfaceWayTest() {
  SqlSession session = sqlSessionFactory.openSession();
  IUserMapper mapper = session.getMapper(IUserMapper.class); // 如果namespace和接口全限定名不一致，报org.apache.ibatis.binding.BindingException: Type interface com..IUserMapper is not known to the MapperRegistry异常。
  User user = mapper.getUserById(1);
  log.info("{}: {}", user.getName(), user.getAddress());
}

附：
上面的实现是把sql语句放在XML文件中，并通过一定的约束来保证接口能够在XML中找到对应的SQL语句；
还有一种方式是通过接口+注解SQL方式来交互数据：

1. 新建接口类：

package com.john.hbatis.mapper; 

import org.apache.ibatis.annotations.Select; 

import com.john.hbatis.model.User; 

public interface IUserMapper2 {
  @Select({ "select * from `user` where id = #{id}" })
  User getUserById(int id);
}

2. 在Configuration.xml文件中加入：

<mappers>
  <mapper class="com.john.hbatis.mapper.IUserMapper2" />
</mappers>

或在初始化语句中加入：

sqlSessionFactory.getConfiguration().addMapper(IUserMapper2.class);

3. 相应修改上面的测试方法：

IUserMapper2 mapper = session.getMapper(IUserMapper2.class);