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一、第一个Mybatis程序

（一）分析思路

思路流程：搭建环境-->导入Mybatis--->编写代码--->测试

（二）创建一个数据库并建一张表

CREATE DATABASE `Mybatis`;
use `Mybatis`;
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user`  (
  `id` int(20) NOT NULL,
  `name` varchar(30) DEFAULT NULL,
  `pwd` varchar(30) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE = InnoDB CHARACTER SET = utf8;
INSERT INTO `user` VALUES (1, '赵惟', 'zhaowei');
INSERT INTO `user` VALUES (2, '彭浩', 'penghao');
INSERT INTO `user` VALUES (3, '郝文虎', 'haowenhu');

（三）创建一个普通Maven项目并删除src目录

注意更改Maven版本为3.6.1，不要使用IDEA自带的版本在这里插入图片描述

（四）导入相关依赖

mybatis、mysql、junit

<dependencies>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.2</version>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.47</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
</dependencies>

（五）创建一个模块（子工程）

在这里插入图片描述

（六）编写Mybatis核心配置文件

<?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://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=utf8"/>
                <property name="username" value="root"/>
                <property name="password" value="1234"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="org/mybatis/example/BlogMapper.xml"/> <!--这里千万注意是“/”号-->
    </mappers>
</configuration>

（七）IDEA与mysql数据库连接

在这里插入图片描述

（八）编写Mybatis工具类

package com.bby.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 {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //获取SqlSession
    public static SqlSession getSession() {
        return sqlSessionFactory.openSession();
    }
}

（九）编写实体类

package com.bby.pojo;

public class User {
    private int id;
    private String name;
    private String 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;
    }
}

（十）编写Mapper接口类

package com.bby.Dao;

import com.bby.pojo.User;

import java.util.List;

public interface UserMapper {
    List<User> selectUser();
}

（十一）编写UserMapper.xml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">
<mapper namespace="com.bby.Dao.UserMapper">
    <select id="selectUser" resultType="com.bby.pojo.User">
        select * from User
    </select>
</mapper>

（十二）添加核心配置文件mybatis-config中的mapper

<mappers>
    <mapper resource="com/bby/Dao/UserMapper.xml"/>
</mappers>

（十三）使用JUnit测试

package com.bby.Dao;

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

import java.util.List;

public class UserMapperTest {
    @Test
    public void test() {
        SqlSession sqlSession = MybatisUtils.getSession();
        //方式一（推荐）
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> users = mapper.selectUser();
        //方式二
        List<User> users1 = sqlSession.selectList("com.bby.Dao.UserMapper.selectUser");

        for(User user : users) {
            System.out.println(user);
        }
    }
}

（十四）常见问题

1.配置文件加载不出来

（1）情况一：resource里面的路径错误

mybatis核心配置文件的mapper 中的资源路径必须使用 " / "

在这里插入图片描述

（2）情况二：Maven资源没有导出问题

Maven没有在build中配置resource，导致资源读取不到，因为正常情况下，xml配置文件应该放在resources目录下，而Maven约定大于配置，所以可能读取不到

java.lang.ExceptionInInitializerError
	at com.bby.Dao.UserMapperTest.test(UserMapperTest.java:13)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:221)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
Caused by: org.apache.ibatis.exceptions.PersistenceException: 
### Error building SqlSession.
### The error may exist in com/bby/Dao/UserMapper.xml
### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource com/bby/Dao/UserMapper.xml
	at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
	at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:80)
	at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:64)
	at com.bby.utils.MybatisUtils.<clinit>(MybatisUtils.java:22)
	... 23 more
Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource com/bby/Dao/UserMapper.xml
	at org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:121)
	at org.apache.ibatis.builder.xml.XMLConfigBuilder.parse(XMLConfigBuilder.java:98)
	at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:78)
	... 25 more
Caused by: java.io.IOException: Could not find resource com/bby/Dao/UserMapper.xml
	at org.apache.ibatis.io.Resources.getResourceAsStream(Resources.java:114)
	at org.apache.ibatis.io.Resources.getResourceAsStream(Resources.java:100)
	at org.apache.ibatis.builder.xml.XMLConfigBuilder.mapperElement(XMLConfigBuilder.java:372)
	at org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:119)
	... 27 more


进程已结束，退出代码为 -1

解决方式：

在父工程和子工程中都配置一下pom.xml文件：

<build>
    <resources>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>true</filtering>
        </resource>
        <resource>
            <directory>src/main/resources</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>true</filtering>
        </resource>
    </resources>
</build>

2.空指针异常

java.lang.NullPointerException

在这里插入图片描述

3.标签错误

insert、update、select、delete标签不要乱用，应该一一对应

4.namespace

在这里插入图片描述

5.输出的xml文件中存在中文乱码问题

在这里插入图片描述

Mybatis | 第一个Mybatis程序

一、第一个Mybatis程序

（一）分析思路

（二）创建一个数据库并建一张表

（三）创建一个普通Maven项目并删除src目录

（四）导入相关依赖

（五）创建一个模块（子工程）

（六）编写Mybatis核心配置文件

（七）IDEA与mysql数据库连接

（八）编写Mybatis工具类

（九）编写实体类

（十）编写Mapper接口类

（十一）编写UserMapper.xml配置文件

（十二）添加核心配置文件mybatis-config中的mapper

（十三）使用JUnit测试

（十四）常见问题

1.配置文件加载不出来

（1）情况一：resource里面的路径错误

（2）情况二：Maven资源没有导出问题

2.空指针异常

3.标签错误

4.namespace

5.输出的xml文件中存在中文乱码问题