MyBatis入门--创建第一个MyBatis程序

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创建一个数据库来操作

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CREATE DATABASE `mybatis`;
USE `mybatis`;
CREATE TABLE `user`(
`id` INT(20) NOT NULL COMMENT '用户ID' PRIMARY KEY,
`name` VARCHAR(20) NOT NULL COMMENT '用户姓名' ,
`pwd` VARCHAR(50) NOT NULL COMMENT '用户密码'
)ENGINE
= INNODB
DEFAULT CHARSET = utf8
INSERT INTO `user` (`id`,`name`,`pwd`)
VALUES(1,'小红','123456'),(2,'小蓝','123465'),(3,'小黑','22222')

导入mybatis所需要的依赖----junit 数据库驱动 mybatis

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<!--mybatis需要导入的依赖-数据库驱动、mybatis、junit-->
<dependencies>
<!--junit-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
<!--mybatis-->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.2</version>
</dependency>
<!--数据库驱动-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.41</version>
</dependency>
</dependencies>

创建一个模块,编写mybatis核心配置mybatis-config.xml

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<?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">
<!-- 配置文件的根元素 -->
<configuration>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="${localhost}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
</configuration>

编写SqlSessionFactory工具类

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package com.study.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();
}
}

编写对应的实体类对象

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package com.study.pojo;
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;
}
}

编写对应的接口UserDao/UserMapper

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

编写接口实现类

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<?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绑定一个对应的接口-->
<mapper namespace="com.study.dao.UserDao">
<select id="getUserList">
select * from mybatis.user
</select>
</mapper>

编写测试类

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public class UserDaoTest {
@Test
public void test(){
//第一步：获取SqlSessionFactory对象
SqlSession sqlSession = MybatisUtils.getSqlSession();
//第二步：getMapper
UserDao mapper = sqlSession.getMapper(UserDao.class);
//通过获得的接口调用对应的getUserList()方法
List<User> userList = mapper.getUserList();
for (User user : userList) {
System.out.println(user);
}
//关闭SqlSession
sqlSession.close();
}
}

编写完毕之后，点击进行测试，发现运行不成功：Type interface com.study.dao.UserDao is not known to the MapperRegistry. 错误信息为UserDao为注册

解决：在mybatis-config.xml中进行注册：

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<mappers>
<mapper resource="com/study/dao/UserMapper.xml"/>
</mappers>

再次点击测试，发生错误：java.lang.ExceptionInInitializerError，查看traget目录下未生成*.xml文件

解决:在pom.xml中添加一下配置，或者把xml文件放到resources文件目录下

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

然后再次点击测试。运行成功。

CRUD

namespace:

namespace 中的包名要与接口的包名保持一致~！

select

选择，查询语句

id:为对应的namespace下的方法名

resultType:返回值类型

insert、delete、update

使用增删改的时候，需要事务，对事务进行提交，否则操作无效，数据库中并不会成功。

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//提交事务
sqlSession.commit();

使用Map进行CRUD

dao/mapper层

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int addUser2(Map<String,Object> map);

mapper.xml

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 <insert id="addUser2" parameterType="Map">
insert into
mybatis.user(id, name, pwd) VALUES (#{userId},#{userName},#{password})
</insert>

Test：

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 @Test
public void addUser2(){
//第一步：获取SqlSessionFactory对象
SqlSession sqlSession = MybatisUtils.getSqlSession();
//第二步：getMapper
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
Map<String,Object> map = new HashMap();
// xml文件中的values中的值#{userId},#{userName},#{password}
map.put("userId",5);//map中key的值可以随意填写，只要与xml文件中的字段保持一致就可以
map.put("userName","王五");
map.put("password","123456");
mapper.addUser2(map);
//关闭SqlSession
sqlSession.commit();
sqlSession.close();
}