java——mybatis——Mybatis的CRUD——查询单个数据操作

比眉伴天荒 2023-09-28 23:42 12阅读 0赞

在第一个xml示例项目的基础上，进行操作：

mybatis-config.xml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/mysql8?characterEncoding=utf8" />
                    <property name="username" value="root" />
                    <property name="password" value="123456" />
                </dataSource>
            </environment>
        </environments>
        
        <mappers>
            <mapper resource="com/sunxl/dao/UserDao.xml"/>
        </mappers>
    </configuration>

![ce419e30ca3dd0ab0210fd113a024b21.png][]

POJO类保持不变：

package com.sunxl.pojo;
    
    public class User {
    
        Integer id;
        String name;
        Integer age;
    
        public Integer getId() {
            return id;
        }
    
        public void setId(Integer id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Integer getAge() {
            return age;
        }
    
        public void setAge(Integer age) {
            this.age = age;
        }
    
        @Override
        public String toString() {
            return "Users{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    
    }

![ac090084e38e85e4374e39b1bd2841c7.png][]

增加一个DAO接口，

package com.sunxl.dao;
    
    import com.sunxl.pojo.User;
    import org.apache.ibatis.annotations.Select;
    
    import java.util.List;
    
    public interface UserDao {
    
        List<User> findAll();
    
        int saveUser(User user);
    
    
        int updateUser(User user);
    
    
        int deleteUser(Integer id);
    
    
        User findById(Integer id);
    
    }

![306b26349d3292dceb9416878138340c.png][]

修改mapper映射文件：

<?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.sunxl.dao.UserDao">
        
        <select id="findAll" resultType="com.sunxl.pojo.User">
            select * from USERs
        </select>
    
        <insert id="saveUser" parameterType="com.sunxl.pojo.User">
                insert into users(id,name,age) values(#{id},#{name},#{age})
        </insert>
    
        <update id="updateUser" parameterType="com.sunxl.pojo.User">
                update users set name = #{name},age = #{age} where id = #{id}
        </update>
    
        <delete id="deleteUser" parameterType="java.lang.Integer">
                delete from users where id = #{id}
        </delete>
    
        <select id="findById" parameterType="java.lang.Integer" resultType="com.sunxl.pojo.User">
            select * from USERs where id = #{id}
        </select>
    
    </mapper>

![ba86f391309462424700f6bafcc13747.png][]

执行操作：

import com.sunxl.dao.UserDao;
    import com.sunxl.pojo.User;
    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;
    import java.util.List;
    
    public class MybatisTest {
    
        public static void main(String[] args) throws IOException {
    
    //        InputStream config = Resources.getResourceAsStream("mybatis-config.xml");
    //
    //        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
    //
    //        SqlSessionFactory factory = builder.build(config);
    //
    //        SqlSession ss = factory.openSession();
    //
    //        UserDao userdao = ss.getMapper(UserDao.class);
    //
    //        List<User> users = userdao.findAll();
    //
    //        for (User user: users){
    //            System.out.println(user);
    //        }
    //
    //        ss.commit();
    //
    //        //4. 释放资源
    //        ss.close();
    //
    //        config.close();
    
            InputStream config = Resources.getResourceAsStream("mybatis-config.xml");
    
            SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
    
            SqlSessionFactory factory = builder.build(config);
    
            SqlSession ss = factory.openSession();
    
    
            User user = new User();
            user.setId(1001);
            user.setName("mybatis_1001");
            user.setAge(1002);
    
    
            UserDao userdao = ss.getMapper(UserDao.class);
    
            User a = userdao.findById(1000);
    
            System.out.println(a.getId());
            System.out.println(a.getName());
            System.out.println(a.getAge());
    
            ss.commit();
    
            //4. 释放资源
            ss.close();
    
            config.close();
    
        }
    }

![70c4bb40faca2e90497ddba740c710df.png][]

执行结果：

![335336207d9f5c8659f0e4e6414c871d.png][]

[ce419e30ca3dd0ab0210fd113a024b21.png]: https://img-blog.csdnimg.cn/img_convert/ce419e30ca3dd0ab0210fd113a024b21.png
[ac090084e38e85e4374e39b1bd2841c7.png]: https://img-blog.csdnimg.cn/img_convert/ac090084e38e85e4374e39b1bd2841c7.png
[306b26349d3292dceb9416878138340c.png]: https://img-blog.csdnimg.cn/img_convert/306b26349d3292dceb9416878138340c.png
[ba86f391309462424700f6bafcc13747.png]: https://img-blog.csdnimg.cn/img_convert/ba86f391309462424700f6bafcc13747.png
[70c4bb40faca2e90497ddba740c710df.png]: https://img-blog.csdnimg.cn/img_convert/70c4bb40faca2e90497ddba740c710df.png
[335336207d9f5c8659f0e4e6414c871d.png]: https://img-blog.csdnimg.cn/img_convert/335336207d9f5c8659f0e4e6414c871d.png