编写一个Mybatis程序

CREATE DATABASE `mybatis`

USE `mybatis`

CREATE TABLE `user`(
	`id` INT(20) NOT NULL PRIMARY KEY,
	`name` VARCHAr(30) DEFAULT NULL,
	`pwd` VARCHAr(30) DEFAULT NULL
)ENGINE=INNODB DEFAULT CHARSET=utf8;

INSERT INTO `user`(`id`,`name`,`pwd`) VALUES
(1,'马西莫','123456'),
(2,'张三','123456'),
(3,'李四','123890')

    4.0.0


    com.massimo
    Mybatis
    1.0-SNAPSHOT


    
        
        
            mysql
            mysql-connector-java
            5.1.47
        
        
        
            org.mybatis
            mybatis
            3.5.2
        
        
        
            junit
            junit
            4.11
        
    

在新建模块下的src/main/resource下新建一个mybatis-config.xml文件，如下：

package com.massimo.utils;

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

//sqlSessionFactory  -->  sqlSession
public class MybatisUtils {

    private static SqlSessionFactory sqlSessionFactory;

    static {
        try {
            //使用Mybatis第一步：获取sqlSessionFactory对象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }

}

package com.massimo.pojo;

//实体类
public class User {
    private int id;
    private String name;
    private String pwd;

    public User() {
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    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 getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + ''' +
                ", pwd='" + pwd + ''' +
                '}';
    }
}

package com.massimo.dao;

import com.massimo.pojo.User;

import java.util.List;

public interface UserDao {
    List getUserList();
}

    
    
        select * from mybatis.user
    

注意点一：org-apache.ibatis. binding. BindingException: Type interface com.kuang.dao.UserDao is not known to the MapperRegistry.

大概意思是这个UserDao接口，MapperRegistry不知道。

MapperRegistry是什么?
核心配置文件中注册mappers

每一个Mapper.xml都需要在Mybatis核心配置文件中注册！注册如下：

注意点二：

原因：maven由于他的约定大于配置，所以可以能遇到写的配置文件,无法被导出或者生效的问题。

解决方案:在pom.xml配置文件中添加如下：

    
        
            
                src/main/resources
                
                    ***.xml
                
                true
            
            
                src/main/java
                
                    ***.xml
                
                true
            
        
    

测试代码：

package com.massimo.dao;

import com.massimo.pojo.User;
import com.massimo.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserDaoTest {
    @Test
    public void test(){
        //第一步：获得sqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserDao userDao= sqlSession.getMapper(UserDao.class);
        List userList = userDao.getUserList();

        for (User user : userList) {
            System.out.println(user);
        }
        //关闭sqlSession
        sqlSession.close();
    }
}

效果：

PS：根据以上操作，如果还出现错误，那么就将xml中的注释都删除掉，试一下。