mybatis 的配置与应用

1，创建一个maven项目

2，在pom文件中引入依赖

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
    </dependency>
    
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.8</version>
    </dependency>
    
    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.2.5</version>
    </dependency>
  </dependencies>

3，打开本地数据库，新建一张表，插入数据

4，新建与表对应的实体类

package model;

import java.util.Date;

/**
 * user
 *
 */
public class User {
    private int id;
    private String loginName;
    private String userName;
    private String password;
    private int createUser;
    private Date createDate;
    
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getLoginName() {
		return loginName;
	}
	public void setLoginName(String loginName) {
		this.loginName = loginName;
	}
	public String getUserName() {
		return userName;
	}
	public void setUserName(String userName) {
		this.userName = userName;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
	public int getCreateUser() {
		return createUser;
	}
	public void setCreateUser(int createUser) {
		this.createUser = createUser;
	}
	public Date getCreateDate() {
		return createDate;
	}
	public void setCreateDate(Date createDate) {
		this.createDate = createDate;
	}
    
}

5，在resource下，新建一database.properties

# ========================================================
# mysql database setting
# ========================================================
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/users
username=root
password=123456

6，在resource下，建一个mybatis-config.xml，引入database.properties中的数据库配置

<?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="database.properties"></properties>
   <environments default="dev">
      <environment id="dev">
          <transactionManager type="jdbc"></transactionManager>
          <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="UserMapper.xml"/>
   </mappers>
</configuration>

7，建一个UserMapper.xml，并在上面的config的mapper中引入，namespace是下面 UserMapper.java的全路径，resultMap的id可以随意取，type是实体类的全路径，里面表的列名和实体类一一对应

<?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="mapper.UserMapper">

	<resultMap id="BaseResultMap" type="model.User">
		<id column="id" property="id" jdbcType="BIGINT" />
		<result column="user_name" property="userName" jdbcType="BIGINT" />
		<result column="login_name" property="loginName" jdbcType="VARCHAR" />
		<result column="password" property="password" jdbcType="INTEGER" />
		<result column="create_date" property="createDate" jdbcType="VARCHAR" />
		<result column="create_user" property="createUser" jdbcType="VARCHAR" />
	</resultMap>

	<!-- 根据pk查询 -->
	<select id="selectById" resultMap="BaseResultMap">
		 select * from saut_m_user where id = 1
	</select>
</mapper>

8，写一个接口UserMapper.java，里面写上查询方法，方法名和 UserMapper.xml中的select的id一致

package mapper;

import model.User;

public interface UserMapper {

	User selectById();
}

9，创建一个SqlSessionFactory.java，用来获取SQLSession

package dao;

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

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class SqlSessionFactory {

	public static SqlSession getSqlSession(){
	    String resource = "mybatis-config.xml";
  	    InputStream in;
  	    SqlSession ss = null;
		try {
			in = Resources.getResourceAsStream(resource);
			org.apache.ibatis.session.SqlSessionFactory build = new SqlSessionFactoryBuilder().build(in);
		  	ss = build.openSession();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return ss; 
	}
}

10，建一个UserService.java，获取sqlSession，并调用查询方法，返回结果

package service;
import org.apache.ibatis.session.SqlSession;

import dao.SqlSessionFactory;
import mapper.UserMapper;
import model.User;

public class UserService {
	 
	public User selectById(){
		SqlSession sqlSession = SqlSessionFactory.getSqlSession();
		UserMapper mapper = sqlSession.getMapper(UserMapper.class);
		User user = mapper.selectById();
		return user;
	}
}

11，写一个JunitTest

package mybatis.demo;

import java.io.IOException;

import org.junit.Test;

import dao.UserDao;
import model.User;
import service.UserService;

/**
 * Unit test for simple App.
 */
public class AppTest{
	
	UserDao userDao = new UserDao();
	UserService service = new UserService();
	
	@Test
    public void test1() throws IOException{
    	User user = userDao.selectById();
    	System.err.println(user.getLoginName());
    }
	@Test
	public void test2() throws IOException{
		User user = service.selectById();
		System.err.println(user.getLoginName());
	}
	
}

12，调用方法，打印结果

到这里一个简单的调用就算完成了，当然我们也可以不创建接口UserMapper.java，直接用sqlSession调用，用namespace + '.' + select的id值即可，结果是一样的

package dao;

import java.io.IOException;
import org.apache.ibatis.session.SqlSession;
import dao.SqlSessionFactory;
import model.User;

public class UserDao {
       public User selectById() throws IOException{
    	   SqlSession sqlSession = SqlSessionFactory.getSqlSession();
    	   User user = sqlSession.selectOne("mapper.UserMapper.selectById");
    	   return user;
       }
}

扩展：一、mybatis 的缓存

mybatis 有一级缓存和二级缓存

一级缓存是session级的，就是同一个session调用同一个查询语句并且参数相同，就会触发一级缓存，默认开启状态，并且无法关闭；

二级缓存是名称空间（namespace）级的，就是在一个名称空间下，不同的session调用同一个查询语句并且参数相同，就会触发，默认开启，可以关闭

<setting name="cacheEnabled" value="false" />

二、mybatis的分页查询

导入依赖

		<!-- mybatis分页组件 -->
		<dependency>
			<groupId>com.github.pagehelper</groupId>
			<artifactId>pagehelper</artifactId>
			<version>${pagehelper.version}</version>
		</dependency>

在配置文件中配置

	<plugins>
		<!-- 分页查询插件 -->
		<plugin interceptor="com.github.pagehelper.PageHelper">
			<property name="dialect" value="mysql" />
			<property name="reasonable" value="true" />
			<property name="pageSizeZero" value="true"/>
		</plugin>
	</plugins>

在查询中的应用

	/**
	 * ====================================================================
	 *功 能： 分页查询
	----------------------------------------------------------------------
	 *修改记录 ：
	 *日 期  版本 修改人 修改内容
	 *2018年04月19日 v0.0.1 codeGenerator 创建
	====================================================================
	 */
	@Override
	public Pager selectByPage(Context<OrgVo> context) {
		Pager pager = null;
		try {
			PageHelper.startPage(context.getPageNum(), context.getPageSize(), true);
			if (!StringUtils.isEmpty(context.getOrderBy())) {
				// 处理排序规则
				PageHelper.orderBy(context.getOrderBy());
			}
			List<OrgVo> list = orgExtendMapper.selectByVo(context.getObject());
			PageInfo<OrgVo> pageInfo = new PageInfo<OrgVo>(list);
			pager = new Pager(
					pageInfo.getPageSize(), pageInfo.getPageNum(), pageInfo.getPages(),
					pageInfo.getTotal(), pageInfo.getList());
		} catch (Exception e) {
			// 记录底层异常信息情况
			logger.error("查询失败：{}", e);
			// 转化异常信息并将异常信息抛至上层
			Exceptions.throwBusinessException("查询失败！");
		}
		return pager;
	}

项目总览

mybatis 的配置与应用

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