3入门实例

1.在mybatis中XML有两类，

• 一类是基础配置文件mybatis-config.xml,主要是配置基本的上下文参数和运行环境，如数据库环境和加载映射文件等
• 另一类是和Mapper文件对应xml文件，主要配置映射规则

2.使用xml构建SqlSessionFactroy,让它生产SqlSession

• 先配置基础配置文件mybatis-conifg.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><!-- 类的别名-->
      <typeAlias alias="role" type="com.learn.ssm.chapter3.pojo.Role"/>
  </typeAliases>
  <!-- 数据库环境 -->
  <environments default="development">
    <environment id="development">
        <!--使用jdbc的事务管理-->
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/chapter3"/>
        <property name="username" value="root"/>
        <property name="password" value="123456"/>
      </dataSource>
    </environment>
  </environments>
  <!-- 加载进来映射文件用来基本运行 -->
  <mappers>
    <mapper resource="com/learn/ssm/chapter3/mapper/RoleMapper.xml"/>
    <mapper class="com.learn.ssm.chapter3.mapper.RoleMapper2"/> 
  </mappers>
</configuration>

• 将生产SQLSession的过程封装在一个文件SqlSessionFactoryUtils.java中以便以后用

package com.learn.ssm.chapter3.utils;

import java.io.IOException;
import java.io.InputStream;

import org.apache.ibatis.datasource.pooled.PooledDataSource;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.mapping.Environment;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.apache.ibatis.transaction.TransactionFactory;
import org.apache.ibatis.transaction.jdbc.JdbcTransactionFactory;

import com.learn.ssm.chapter3.mapper.RoleMapper;
import com.learn.ssm.chapter3.mapper.RoleMapper2;
import com.learn.ssm.chapter3.pojo.Role;

public class SqlSessionFactoryUtils {

	private final static Class<SqlSessionFactoryUtils> LOCK = SqlSessionFactoryUtils.class;

	private static SqlSessionFactory sqlSessionFactory = null;

	private SqlSessionFactoryUtils() {
	}

	public static SqlSessionFactory getSqlSessionFactory() {
		synchronized (LOCK) {
			if (sqlSessionFactory != null) {
				return sqlSessionFactory;
			}
			String resource = "mybatis-config.xml";
			InputStream inputStream;
			try {
				inputStream = Resources.getResourceAsStream(resource);
				sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
			} catch (IOException e) {
				e.printStackTrace();
				return null;
			}
			return sqlSessionFactory;
		}
	}

	public static SqlSession openSqlSession() {
		if (sqlSessionFactory == null) {
			getSqlSessionFactory();
		}
		return sqlSessionFactory.openSession();
	}
}

• 以后就可以这样生成Sqlsession对象，它有3个作用：
  
  1.获取Mapper接口
  2.发送SQl语句给数据库
  3.控制数据库事务

SqlSession sqlSession = SqlSessionFactoryUtils.openSqlSession();

3.配置Mapper，由接口和对应的映射xml文件组成,将它们两放在同一个包里。它可以配置以下内容：

• 提供sql语句，并可以附带配置sql的参数类型，返回类型，缓存刷新等
• 配置缓存

3.1

• 先写个普通的pojo，如Role.java

package com.learn.ssm.chapter3.pojo;

public class Role {

	private Long id;
	private String roleName;
	private String note;

	/** setter and getter **/
	public Long getId() {
		return id;
	}

	public void setId(Long id) {
		this.id = id;
	}

	public String getRoleName() {
		return roleName;
	}

	public void setRoleName(String roleName) {
		this.roleName = roleName;
	}

	public String getNote() {
		return note;
	}

	public void setNote(String note) {
		this.note = note;
	}

}

• 再写pojo对应的接口和其要访问数据库的方法，如RoleMapper.java

package com.learn.ssm.chapter3.mapper;
import java.util.List;
import com.learn.ssm.chapter3.pojo.Role;
public interface RoleMapper {
	public int insertRole(Role role);
	public int deleteRole(Long id);
	public int updateRole(Role role);
	public Role getRole(Long id);
	public List<Role> findRoles(String roleName);
}

• 然后写接口对应的映射规则文件，如RoleMapper.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">
  <!--通过这个可以找到对应的接口-->
<mapper namespace="com.learn.ssm.chapter3.mapper.RoleMapper">
    <!--id对应接口里的方法，parameter对应方法的参数 ,#{}代表传进来的值-->
	<insert id="insertRole" parameterType="role">
		insert into t_role(role_name, note) values(#{roleName}, #{note})
	</insert>

	<delete id="deleteRole" parameterType="long">
		delete from t_role where id= #{id}
	</delete>

	<update id="updateRole" parameterType="role">
		update t_role set role_name = #{roleName}, note = #{note} where id= #{id}
	</update>
    
    <!--resultType的值类的别名，表示结果类型-->
	<select id="getRole" parameterType="long" resultType="role">
		select id,
		role_name as roleName, note from t_role where id = #{id}
	</select>

	<select id="findRoles" parameterType="string" resultType="role">
		select id, role_name as roleName, note from t_role
		where role_name like concat('%', #{roleName}, '%')
	</select>
</mapper>

4.测试

        Logger log = Logger.getLogger(Chapter3Main.class);
		SqlSession sqlSession = null;
		try {
			sqlSession = SqlSessionFactoryUtils.openSqlSession();
			RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
			Role role = roleMapper.getRole(1L);
			log.info(role.getRoleName());
		} finally {
			if (sqlSession != null) {
				sqlSession.close();
			}
		}