mybatis的第一个程序

Posted 2020-10-16

1，用eclipse创建一个web项目

2，导入jar包，名字就是红框标记的

3，数据库架构

简单的一张mysql表

4，创建dao service entity

总览

UserMapper.java

package cn.abc.dao;

import cn.abc.entity.User;

public interface UserMapper {
    /**
     * 通过id查找User
     * 
     * @return
     */
    public User getUserById(int id);
}

UserMapper.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="cn.abc.dao.UserMapper">
    <select id="getUserById" parameterType="Integer" resultType="User">
        select * from t_user where id = #{id};
    </select>
</mapper>

User.java

package cn.abc.entity;

public class User {
    private int id;
    private String name;
    private String password;
    public User() {
        super();
    }
    public User(String name, String password) {
        super();
        this.name = name;
        this.password = password;
    }
    public User(int id, String name, String password) {
        super();
        this.id = id;
        this.name = name;
        this.password = password;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + ", password=" + password
                + "]";
    }
    
    
}

UserService.java

package cn.abc.service;

import cn.abc.entity.User;

public interface UserService {
    /**
     * 通过id查找User
     * 
     * @return
     */
    public User getUserById(int id);
}

UserServiceImpl.java

package cn.abc.service.impl;

import cn.abc.dao.UserMapper;
import cn.abc.entity.User;
import cn.abc.service.UserService;

public class UserServiceImpl implements UserService{
    //定义接口对象
    private UserMapper userMapper;
    @Override
    public User getUserById(int id) {
        // TODO Auto-generated method stub
        return userMapper.getUserById(id);
    }

}

5,在src上创建source文件夹resources，并放入以下文件

跟src是平级的  不是普通的文件夹，

jdbc.properties

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/db_ssm?useUnicode=true&characterEncoding=utf-8
user=root
password=myw123456

log4j.properties

log4j.rootLogger=DEBUG,CONSOLE
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.Target=System.out
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=[%p] %d %c - %m%n

    

 

mybatis-config.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>
    <properties resource="jdbc.properties"/>
    
     <typeAliases>
        <!-- <typeAlias alias="Student" type="com.abc.entity.Student"/> -->
        <package name="cn.abc.entity"/>
    </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="${user}" />
                <property name="password" value="${password}" />
            </dataSource>
        </environment>
        
    </environments>
    <mappers>
    <!--     <mapper resource="com/abc/mappers/StudentMapper.xml" /> -->
        <package name="cn.abc.dao"/>
    </mappers>
</configuration>

6，mybatis工具类 MybatisUtil

代码

package cn.abc.util;

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.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class MybatisUtil {
    private static  SqlSessionFactory sqlSessionFactory;
    
    public static SqlSessionFactory getSqlSessionFactory() {
        try {
            InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            System.out.println("加载文件出错");
            e.printStackTrace();
        }
        return sqlSessionFactory;
        
    }
    
    public static SqlSession openSession() {
        return getSqlSessionFactory().openSession();
    }
}

7，测试类 创建junit测试类  Test001.java   注意，此处要导入junitjar包，不再贴图，因为eclipse创建junit时会自己导包的

 

 代码

package cn.abc.test;

import static org.junit.Assert.*;

import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import cn.abc.dao.UserMapper;
import cn.abc.entity.User;
import cn.abc.util.MybatisUtil;

public class Test001 {
    private static Logger logger = Logger.getLogger(Test001.class);
    private SqlSession sqlSession =  null;
    private UserMapper userMapper = null;

    @Before
    public void setUp() throws Exception {
        sqlSession =  MybatisUtil.openSession();
        userMapper = sqlSession.getMapper(UserMapper.class);
    }

    @After
    public void tearDown() throws Exception {
    
        sqlSession.close();
    }

    @Test
    public void test() {
        User user = userMapper.getUserById(1);
        System.out.println(user.toString());
    }

}

 

 运行结果

name怎么是null呢。经查找是数据库名称与类的名称不匹配所致。

8，解决错误

修改数据库中的属性

修改前

修改后

注意，修改了name 

重新运行test001.java测试

ok，成功了。出现错误的原因是实体类与数据库不匹配所致，以后要多加注意。