MyBatis入门（select查）

前言：

打开MySQL，创建数据库创建一个学生表

导入如下jar包（mybatis所需jar包，连接MySQL所需jar包，单元测试类所需jar包）

1.创建pojo实体层Student学生类

package com.mybatis.pojo;

public class Student {
    private Integer id;
    private String username;
    private String password;
    private Integer role;

  /*  public Student(Integer id, String username, String password, Integer role) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.role = role;
    }*/

    @Override
    public String toString() {
        return
                "{id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", role=" + role+ "}";
    }
}

2.创建dao数据层StudentMapper学生映射类

要拿什么数据做什么

package com.mybatis.dao;

import com.mybatis.pojo.Student;

public interface StudentMapper {
    public Student queryStudent(int role);
}

3.创建test包、resources包，在项目根目录下创建并且配置好路径（这样就方便了写文件的路径）

4.在resources文件夹下创建MybatisConfig.xml配置文件

• 一定要有文件头
• 连接MySQL数据库
• 映射dao

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://localhost:3306/yeujuan?useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            dataSource>
        environment>
    environments>

    <mappers> 
            <mapper resource="StudentMapper.xml"/> 
    mappers>
configuration>

5.在resources文件夹下创建StudentMapper.xml文件（文件名要和dao层类名一致）

DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">



<mapper namespace="com.mybatis.dao.StudentMapper"> 
		
        <select id="queryStudent" resultType="com.mybatis.pojo.Student"> 
            SELECT `id`, `username`, `password`,`role` FROM `user` WHERE `role` = #{role}
        select>
mapper>

6.测试，在test文件夹中创建StudentTest测试类

import com.mybatis.dao.StudentMapper;
import com.mybatis.pojo.Student;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;

public class StudentTest {
    @Test
    public void studentTest(){
        SqlSession sqlSession=getSqlSession();   //SQLSession是线程不安全的，要及时关闭
        try {
            // 1.这个写法不推荐, 因为没有使用映射接口, 只是用了映射的配置文件
            List<Student> student=sqlSession.selectList("com.mybatis.dao.StudentMapper.queryStudent",2);

            // 2.推荐这种写法, 也是使用mybatis 绝大部分写得最多的语句
            StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
            Student student1 = mapper.queryStudent(2);

            System.out.println(student1);
        }finally {
            sqlSession.close();
        }
    }
    public SqlSession getSqlSession(){
        //拿到SqlSessionFactory 工厂对象
        //1. 拿到全局配置文件的路径跟文件名
        String mybatisConfigFile = "MybatisConfig.xml";

        try {
            //2. 把1. 用Resources getResourceAsStream 方法取得一个输入流的对象
            InputStream inputStream = Resources.getResourceAsStream(mybatisConfigFile);

            //3. 把2. 用来实例化SqlSessionFactory 对象
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            return sqlSessionFactory.openSession();

        }catch (IOException e){
            e.printStackTrace();
        }

        return null;

    }
}

import com.mybatis.pojo.Student;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class StudentTest {
    @Test
    public void studentTest(){
        SqlSession sqlSession=getSqlSession();
        //由于根据role查询返回的记录数可能超过1，这里我们采用list集合装进来
        List<Student> student=sqlSession.selectList("com.mybatis.dao.StudentMapper.queryStudent",2);//参1：dao层映射类的方法全路径；参2：传入的参数值
        System.out.println(student);
    }

	//封装获取SqlSeesion对象方法
    public SqlSession getSqlSession(){
        //拿到SqlSessionFactory 工厂对象
        //1. 拿到全局配置文件的路径跟文件名
        String mybatisConfigFile = "MybatisConfig.xml";

        try {
            //2. 用Resources getResourceAsStream 方法取得一个输入流的对象
            InputStream inputStream = Resources.getResourceAsStream(mybatisConfigFile);

            //3. 用来实例化SqlSessionFactory 对象
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            return sqlSessionFactory.openSession();
        }catch (IOException e){
            e.printStackTrace();
        }
        return null;
    }
}

结果：

另外，我们可以配置好日志的文件，在resources文件夹下创建log4j.xml文件

DOCTYPE log4j:configuration SYSTEM "http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/xml/doc-files/log4j.dtd">

<log4j:configuration debug="true">

    <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
        <param name="Encoding" value="UTF-8" />
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m  (%F:%L) \n" />
        layout>
    appender>
    <logger name="java.sql">
        <level value="debug" />
    logger>
    <logger name="org.apache.ibatis">
        <level value="info" />
    logger>
    <root>
        <level value="debug" />
        <appender-ref ref="STDOUT" />
    root>
log4j:configuration>

就可以得到结果图里面的日志了

全局配置文件补充

DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">



<configuration> 

    
    <properties resource="dbconfig.properties">properties>

    
    <settings>
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    settings>

    
    <typeAliases>


                <package name="com.mybatis.pojo"/>

    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> 




    <package name="com.mybatis.dao"/>
    mappers>
configuration>

dbconfigproperties

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/yeujuan?useSSL=false
username=root
password=root