MyBatis系列：基于MyBatisUtils工具类完成CRUD操作

Posted 2020-08-11

Emp.java

package com.rk.entity;

public class Emp {
    private Integer id;
    private String name;
    private Double sal;
    public Emp(){}
    
    public Emp(Integer id, String name, Double sal) {
        this.id = id;
        this.name = name;
        this.sal = sal;
    }

    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Double getSal() {
        return sal;
    }
    public void setSal(Double sal) {
        this.sal = sal;
    }
    
}

EmpMapper.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">
<!-- namespace属性是名称空间，必须唯一 -->
<mapper namespace="mynamespace">
    <insert id="add" parameterType="com.rk.entity.Emp">
        insert into emp(id,name,sal) values(#{id},#{name},#{sal})
    </insert>
    <update id="update" parameterType="com.rk.entity.Emp">
        update emp set name=#{name},sal=#{sal} where id=#{id}
    </update>
    <select id="findById" resultType="com.rk.entity.Emp">
        select id,name,sal from emp where id=#{anything123}
    </select>
    <select id="findAll" resultType="com.rk.entity.Emp">
        select id,name,sal from emp
    </select>
    <delete id="delete" parameterType="com.rk.entity.Emp">
        delete from emp where id=#{id}
    </delete>
</mapper>

findById也可以这样写

	<!-- 根据ID查询
		 如果参数不是一个实体的话，只是一个普通变量，例如:int,double,String
		 这里的#{中间的变量名可以随便写}，不过提倡就用方法的形参
	 -->
	<select id="findById" parameterType="int" resultType="com.rk.entity.Emp">
		select id,name,sal from students where id = #{id}
	</select>

mybatis.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>
    <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/testdb"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/rk/entity/EmpMapper.xml"/>
    </mappers>
</configuration>

MyBatisUtils.java

package com.rk.utils;

import java.io.IOException;
import java.io.Reader;
import java.sql.Connection;

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

public class MyBatisUtils {
    private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
    private static SqlSessionFactory sqlSessionFactory;
    static{
        try {
            Reader reader = Resources.getResourceAsReader("mybatis.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
    private MyBatisUtils() {}
    public static SqlSession getSqlSession(){
        SqlSession sqlSession = threadLocal.get();
        if(sqlSession == null){
            sqlSession = sqlSessionFactory.openSession();
            threadLocal.set(sqlSession);
        }
        return sqlSession;
    }
    
    public static void closeSqlSession(){
        SqlSession sqlSession = threadLocal.get();
        if(sqlSession != null){
            sqlSession.close();
            threadLocal.remove();
        }
    }
    
    public static void main(String[] args) {
        Connection conn = MyBatisUtils.getSqlSession().getConnection();
        System.out.println(conn!=null ? "连接成功" : "连接失败");
    }
}

EmpDao.java

package com.rk.dao;

import java.util.List;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import com.rk.entity.Emp;
import com.rk.utils.MyBatisUtils;

public class EmpDao {
    @Test
    public void add(){
        Emp emp = new Emp(3, "小刚", 300D);
        SqlSession sqlSession = null;
        try {
            sqlSession = MyBatisUtils.getSqlSession();
            int i = sqlSession.insert("mynamespace.add", emp);
            System.out.println("本次操作影响"+i+"行数据");
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
        }
        finally{
            MyBatisUtils.closeSqlSession();
        }
    }
    
    @Test
    public void update(){
        Emp emp = new Emp(3, "Tomcat", 400D);
        SqlSession sqlSession = null;
        try {
            sqlSession = MyBatisUtils.getSqlSession();
            int i = sqlSession.update("mynamespace.update", emp);
            System.out.println("本次操作影响"+i+"行数据");
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
        }
        finally{
            MyBatisUtils.closeSqlSession();
        }        
    }
    
    @Test
    public void findById(){
        SqlSession sqlSession = null;
        try {
            sqlSession = MyBatisUtils.getSqlSession();
            Emp emp = sqlSession.selectOne("mynamespace.findById", 3);
            System.out.println( emp.getName() + ":"+emp.getSal());
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
        }
        finally{
            MyBatisUtils.closeSqlSession();
        }        
    }
    
    @Test
    public void findAll(){
        SqlSession sqlSession = null;
        try {
            sqlSession = MyBatisUtils.getSqlSession();
            List<Emp> list = sqlSession.selectList("mynamespace.findAll");
            if(list != null && list.size()>0){
                for(Emp emp : list){
                    System.out.println( emp.getName() + ":"+emp.getSal());
                }
            }
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
        }
        finally{
            MyBatisUtils.closeSqlSession();
        }        
    }
    
    @Test
    public void delete(){
        SqlSession sqlSession = null;
        try {
            sqlSession = MyBatisUtils.getSqlSession();
            Emp emp = new Emp(3, "", 0D);
            sqlSession.delete("mynamespace.delete", emp);
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
        }
        finally{
            MyBatisUtils.closeSqlSession();
        }        
    }
}