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mybatis 持久层crud

java厂长 人气:0

1、MyBatis第一个程序

思路流程:搭建环境–>导入Mybatis—>编写代码—>测试

1.1、代码演示

​ 1.搭建实验数据库

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 DEFAULT CHARSET=utf8;
insert into `user`(`id`,`name`,`pwd`) values (1,'hhh','123456'),(2,'张
三','abcdef'),(3,'李四','987654');

​ 2.导入MyBatis相关 jar 包

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.2</version>
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.49</version>
</dependency>

编写MyBatis核心配置文件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核心环境-->
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
<!--                数据库8.0以上useSSL=false-->
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&amp;useUnicode=true&amp;characterEncoding=utf8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/sxau/dao/UserMapper.xml"/>
    </mappers>
</configuration>

编写MyBatis工具类MybatisUtils.java

package com.sxau.utils;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.io.Resources;
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();
        }
    }
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

创建实体类

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

编写Mapper接口类

package com.sxau.dao;
import com.sxau.pojo.User;
import java.util.List;
import java.util.Map;
public interface UserMapper {
    List<User> getUserList();
}

编写Mapper.xml配置文件

namespace 十分重要,不能写错!

<?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.sxau.dao.UserMapper">
    <select id="getUserList" resultType="com.sxau.pojo.User">
        select * from mybatis.user
    </select>
</mapper>

编写测试类Junit 包测试

public class MyTest {
    @Test
    public void  test(){
        //第一步: 获得sqlSession
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //方式一:执行SQL语句 getmapper
        //        UserDao mapper = sqlSession.getMapper(UserDao.class);
        //        List<User> userList = mapper.getUserList();
        //方式二:
        List<User> userList = sqlSession.selectList("com.sxau.dao.UserMapper.getUserList");
        for (User user : userList) {
            System.out.println(user);
        }
        sqlSession.close();
    }
}

运行测试

image-20220213103037883

1.2、问题说明

可能出现问题说明:Maven静态资源过滤问题

在pom.xml中加入以下代码块

<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>

2、CRUD操作

2.1、namespace

结论

配置文件中namespace中的名称为对应Mapper接口或者Dao接口的完整包名,必须一致!

2.2、select

需求:根据id查询用户

在UserMapper中添加对应方法

package com.sxau.dao;
import com.sxau.pojo.User;
import java.util.List;
import java.util.Map;
public interface UserMapper {
    //查询全部用户
    List<User> getUserList();
    //根据id查询用户
    User getUserById(int id);
}

在UserMapper.xml中添加Select语句

<select id="getUserById" parameterType="int" resultType="com.sxau.pojo.User">
    select * from mybatis.user where id = #{id}
</select>

测试类中进行测试

Test
public void getUserById(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    User user = mapper.getUserById(1);
    System.out.println(user);
    sqlSession.close();
}

小练习:根据 密码用户名 查询用户信息

思路一:直接在方法中传递参数

//通过密码和名字查询用户
User selectUserByNameAndPwd(@Param("username") String username,@Param("pwd") String pwd);

/*
<select id="selectUserByNameAndPwd" resultType="com.sxau.pojo.User">
	select * from user where name = #{username} and pwd = #{pwd}
</select>
*/

思路二:使用万能的Map

​ 1. 在接口方法中,参数直接传递Map;

User selectUserByNP2(Map<String,Object> map);

编写sql语句的时候,需要传递参数类型,参数类型为map

<select id="selectUserByNP2" parameterType="map"
    resultType="com.sxau.pojo.User">
    select * from user where name = #{username} and pwd = #{pwd}
</select>

在使用方法的时候,Map的 key 为 sql中取的值即可,没有顺序要求!

@Test
public void selectUserByNP2(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    Map<String, Object> map = new HashMap<String, Object>();
    map.put("username","hhh");
    map.put("pwd","123456");
    User user = mapper.selectUserByNP2(map);
    //提交事务
    sqlSession.commit();
    sqlSession.close();
}

image-20220213110008457

如果参数过多,我们可以考虑直接使用Map来实现参数传递,如果参数比较少,直接传递参数即可

2.3、insert

我们一般使用insert标签进行插入操作,它的配置和select标签差不多!

需求:给数据库增加一个用户

在UserMapper接口中添加对应的方法

//添加用户
int addUser(User user);

在UserMapper.xml中添加insert语句

<!--对象中的属性,可以直接取出来-->
<insert id="addUser" parameterType="com.sxau.pojo.User">
    insert into mybatis.user(id, name, pwd) VALUES (#{id},#{name},#{pwd});
</insert>

​ 3.在测试类中进行测试

//增删改 需要提交事务
@Test
public void addUser(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    mapper.addUser(new User(4,"hahah","123123"));
    //提交事务
    sqlSession.commit();
    sqlSession.close();
}

image-20220213105940258

注意点:增、删、改操作需要提交事务!

2.4、update

我们一般使用update标签进行更新操作,它的配置和select标签差不多!

需求:修改用户的信息

在UserMapper接口中添加对应的方法

//修改用户
int updateUser(User user);

在UserMapper.xml中添加update语句

<update id="updateUser" parameterType="com.sxau.pojo.User">
    update mybatis.user
    set  name=#{name},pwd=#{pwd}
    where id=#{id};
</update>

​ 3.在测试类中进行测试

@Test
public void updateUser(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    mapper.updateUser(new User(4,"qqq","123123"));
    sqlSession.commit();
    sqlSession.close();
}

image-20220213115738870

2.5、delete

我们一般使用delete标签进行删除操作,它的配置和select标签差不多!

需求:根据id删除一个用户

在UserMapper接口中添加对应的方法

根据id删除用户
int deleteUser(int id);

在UserMapper.xml中添加delete语句

<delete id="deleteUser" parameterType="int">
    delete from mybatis.user where id=#{id}
</delete>

​ 3.在测试类中进行测试

@Test
public void deleteUser(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    int i = mapper.deleteUser(4);
    sqlSession.commit();
    sqlSession.close();
}

image-20220213120024393

小结

2.6、拓展思维

在MyBatis中模糊查询like语句该怎么写?

第1种:在Java代码中添加sql通配符。

//like模糊查询
List<User> getUserLike(String value);

<select id="getUserLike" resultType="com.sxau.pojo.User">
    select * from mybatis.user where name like #{value}
</select>
    
@Test
public void getUserLike(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);

    List<User> userLike = mapper.getUserLike("%李%");
    for (User user : userLike) {
        System.out.println(user);
    }
}

第2种:在sql语句中拼接通配符,会引起sql注入

//like模糊查询
List<User> getUserLike(String value);
<select id=”getUserLike”>
	select * from foo where bar like "%"#{value}"%"
</select>
    
@Test
public void getUserLike(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    List<User> userLike = mapper.getUserLike("李");
    for (User user : userLike) {
        System.out.println(user);
    }
}

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