• mybatis 中也提供了注解式开发⽅式，采⽤注解可以减少 Sql 映射⽂件的配置。
• 使⽤注解式开发的话，sql语句是写在java程序中的，这种⽅式也会给sql语句的维护带来成本。
  • 官⽅是这么说的：使⽤注解来映射简单语句会使代码显得更加简洁，但对于稍微复杂⼀点的语句，Java 注解不仅⼒不从⼼，还会让你本就复杂的 SQL 语句更加混乱不堪。 因此，如果你需要做⼀些很复杂的操作，最好⽤ XML 来映射语句。
• 总结：一般对单表的 CRUD 可以采用注解的方式开发。

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一、准备开发环境

1.添加依赖

<?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>coml.gdb</groupId><artifactId>mybatis-annotation</artifactId><version>1.0-SNAPSHOT</version><properties><maven.compiler.source>17</maven.compiler.source><maven.compiler.target>17</maven.compiler.target><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><dependencies><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.14</version></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.33</version></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.13.2</version><scope>test</scope></dependency></dependencies>
</project>

2.jdbc.properties

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/自己的数据库名字
jdbc.username=用户名
jdbc.password=密码

3.mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration><properties resource="jdbc.properties"></properties><settings><setting name="logImpl" value="STDOUT_LOGGING"/></settings><environments default="development"><environment id="development"><transactionManager type="JDBC"/><dataSource type="POOLED"><property name="driver" value="${jdbc.driver}"/><property name="url" value="${jdbc.url}"/><property name="username" value="${jdbc.username}"/><property name="password" value="${jdbc.password}"/></dataSource></environment></environments><mappers><!--sql映射⽂件创建好之后，需要将该⽂件路径配置到这⾥--><!-- 注意：这里不是使用的mapper配置项，而是使用的package --><package name="com.gdb.annotation.mapper"/></mappers></configuration>

4.Article实体类

package com.gdb.annotation.pojo;import java.time.LocalDateTime;public class Article {private Integer id;private Integer userId;private String summary;private String title;private Integer readCount;private LocalDateTime createTime;private LocalDateTime updateTime;@Overridepublic String toString() {return "Article{" +"id=" + id +", userId=" + userId +", summary='" + summary + '\'' +", title='" + title + '\'' +", readCount=" + readCount +", createTime=" + createTime +", updateTime=" + updateTime +'}';}public Article() {}public Article(Integer id, Integer userId, String summary, String title, Integer readCount, LocalDateTime createTime, LocalDateTime updateTime) {this.id = id;this.userId = userId;this.summary = summary;this.title = title;this.readCount = readCount;this.createTime = createTime;this.updateTime = updateTime;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public Integer getUserId() {return userId;}public void setUserId(Integer userId) {this.userId = userId;}public String getSummary() {return summary;}public void setSummary(String summary) {this.summary = summary;}public String getTitle() {return title;}public void setTitle(String title) {this.title = title;}public Integer getReadCount() {return readCount;}public void setReadCount(Integer readCount) {this.readCount = readCount;}public LocalDateTime getCreateTime() {return createTime;}public void setCreateTime(LocalDateTime createTime) {this.createTime = createTime;}public LocalDateTime getUpdateTime() {return updateTime;}public void setUpdateTime(LocalDateTime updateTime) {this.updateTime = updateTime;}
}

5.SqlSessionUtil工具类

package com.gdb.annotation.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;public class SqlSessionUtil {private static SqlSessionFactory sqlSessionFactory;/*** 类加载时初始化sqlSessionFactory对象*/static {try {SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();sqlSessionFactory = sqlSessionFactoryBuilder.build(Resources.getResourceAsStream("mybatis-config.xml"));} catch (Exception e) {e.printStackTrace();}}/*** 每调⽤⼀次openSession()可获取⼀个新的会话*/public static SqlSession openSession() {return sqlSessionFactory.openSession();}
}

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二、Insert

• ArticleMapper 接口

package com.gdb.annotation.mapper;import com.gdb.annotation.pojo.Article;
import org.apache.ibatis.annotations.Insert;public interface ArticleMapper {@Insert("insert into article values (null, #{userId}, #{title}, #{summary}, #{readCount}, #{createTime}, #{updateTime})")int insert(Article article);}

• Annotation.InsertAnnotationtest

package com.gdb.annotationTest;import com.gdb.annotation.mapper.ArticleMapper;
import com.gdb.annotation.pojo.Article;
import com.gdb.annotation.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;import java.time.LocalDateTime;public class Annotation {@Testpublic void insertAnnotationTest(){SqlSession sqlSession = MybatisUtils.openSession();ArticleMapper mapper = sqlSession.getMapper(ArticleMapper.class);Article article = new Article(null, 12346, "springboot 配置文件", "外部化配置文件", 12346, LocalDateTime.now(), LocalDateTime.now());int count = mapper.insert(article);System.out.println("插入的记录条数 ===> " + count);sqlSession.commit();sqlSession.close();}
}

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三、Delete

• ArticleMapper 接口

@Delete("delete from article where id = #{id}")
int delete(int id);

• Annotation.deleteAnnotationTest

@Test
public void deleteAnnotationTest(){SqlSession sqlSession = MybatisUtils.openSession();ArticleMapper mapper = sqlSession.getMapper(ArticleMapper.class);int count = mapper.delete(13);System.out.println("删除的记录条数 ===> " + count);sqlSession.commit();sqlSession.close();}

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四、Update

• ArticleMapper 接口

@Update("update article set user_id=#{userId}, title=#{title} where id=#{id}")
int update(Article article);

• Annotation.updateAnnotationTest

@Test
public void updateAnnotationTest(){SqlSession sqlSession = MybatisUtils.openSession();ArticleMapper mapper = sqlSession.getMapper(ArticleMapper.class);Article article = new Article(19, 12346, "springboot 配置文件", "外部化配置文件", 12346, LocalDateTime.now(), LocalDateTime.now());int count = mapper.update(article);System.out.println("插入的记录条数 ===> " + count);sqlSession.commit();sqlSession.close();
}

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五、Select

• ArticleMapper 接口

@Select("select * from Article where id = #{id}")
@Results({@Result(property = "userId", column = "user_id"),@Result(property = "readCount", column = "read_count"),@Result(property = "createTime", column = "create_time"),@Result(property = "updateTime", column = "update_time")
})
Article selectById(int id);

• Annotation.seleteAnnotationTest

@Test
public void selectAnnotationTest(){SqlSession sqlSession = MybatisUtils.openSession();ArticleMapper mapper = sqlSession.getMapper(ArticleMapper.class);Article article = mapper.selectById(1);System.out.println(article);sqlSession.commit();sqlSession.close();
}

• 注意：如果不想使用 @Results 注解的话可以在mybatis-config.xml 配置文件中添加如下配置。

    <settings><setting name="mapUnderscoreToCamelCase" value="true"/></settings>

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