02-第一个Mybatis程序

第一个Mybatis程序

搭建环境

搭建数据库

新建项目

1.新建Maven项目 检查maven配置看是不是自己的maven

2.删除src目录，当作父工程

3.导入maven依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.tian</groupId>
    <artifactId>mybatis</artifactId>
    <version>1.0-SNAPSHOT</version>

<dependencies>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.19</version>
    </dependency>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.2</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
        <scope>test</scope>
    </dependency>
</dependencies>

</project>

创建一个模块

编写mybatis-config.xml（固定的）

<?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">
<!--核心配置环境-->
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8&amp;serverTimezone=GMT%2B8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>


</configuration>

编写mybatis工具类（固定的）

package com.tian.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;

public class MybatisUtils {
    private static  SqlSessionFactory sqlSessionFactory;
    static {
        try{
            //使用mybatis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();
        }

    }
    //既然有了 SqlSessionFactory.顺名思义，我们就可以从中获得 SqlSession 的实例了
    // sqlSession完全包含面向数据库执行sql命令所需的所有方法。
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

编写代码

• dao接口

public interface UserDao {
    List<User> getUserList();
}

• 接口实现类(由原来的UserDaoImpl转变成一个Mapper配置文件)

<?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 绑定一个对应的dao/mapper文件-->
<mapper namespace="com.tian.dao.UserDao">

<!--
		select 		查询语句
		id   		对应方法名
		resultType  返回值类型
-->
        <select id="getUserList" resultType="com.tian.pojo.User" >
    select * from mybatis.user
    </select>


</mapper>

测试

• junit测试

import com.tian.dao.UserDao;
import com.tian.pojo.User;
import com.tian.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class UserDaoTest {
    @Test
    public void test(){
        //获得sqlsession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //方式一：getMapper（推荐的）  执行sql
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List<User> userList = userDao.getUserList();

  /*      //方式二 （了解就行）
        List<User> userList = sqlSession.selectList("com.tian.dao.UserDao.getUserList");*/
        for (User user : userList) {
            System.out.println(user);
        }

        //关闭sqlsession
        sqlSession.close();
    }
}

注意点

报错一：

org.apache.ibatis.binding.BindingException: Type interface com.tian.dao.UserDao is not known to the MapperRegistry.

原因:mybatis-config.xml中mappers没注册

<!--在mybatis-config.xml中加入以下代码-->
<!--每一个Mapper.xml都需要在mybatis核心配置文件中注册！-->
<mappers>
    <mapper resource="com/tian/dao/UserMapper.xml"/>
</mappers>

报错二:

The error may exist in com/tian/dao/UserMapper.xml

原因:约定大于配置

<!--在pom.xml中加入以下代码-->
<build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

报错三:

• (我是mysql8的，mysql8的错误应该是，之前mysql5.7就没有):

Caused by: org.apache.ibatis.exceptions.PersistenceException: 
### Error building SqlSession.
### Cause: org.apache.ibatis.builder.BuilderException: Error creating document instance.  
Cause: com.sun.org.apache.xerces.internal.impl.io.MalformedByteSequenceException: 1 字节的 UTF-8 序列的字节 1 无效。

原因：

配置文件中引入了<?xml version="1.0" encoding="UTF-8"?>,
在配置文件可能包含有中文注释，
导致在编译后中文注释在配置文件乱码抛异常。
在项目依赖配置文件pom.xml上加入构建项目编码属性：

解决方案一:

<!--在pom.xml中加入以下代码-->   
<properties>        
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>    
</properties>

解决方案二：把UserMapper.xml里面的中文注释删掉，再运行即可