resultmapMybatis开发要点:resultType和resultMap的区别

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Mybatis返回Xml返回值有resultType和resultMap，我们一般都该如何选择呢？

一、resultType

1.1 resultType介绍

当使用resultType做SQL语句返回结果类型处理时，对于SQL语句查询出的字段在相应的POJO中必须有和它相同的字段对应，而resultType中的内容就是pojo在本项目中的位置。

1.2 映射规则

基本类型：resultType=基本类型 List类型： resultType=List中元素的类型Map类型单条记录：resultType =map 多条记录：resultType =Map中value的类型

1.3 自动映射注意事项

前提：Sql列名和JavaBean的属性是一致的；使用resultType，如用简写需要配置typeAliases （别名）；如果列名和JavaBean不一致，但列名符合单词下划线分割，Java是驼峰命名法，则mapUnderscoreToCamelCase可设置为true；

1.4 代码演示

（1）t_user_test.sql准备

CREATE TABLE `t_user_test` ( `id` int(20) NOT NULL AUTO_INCREMENT, `user_name` varchar(60) DEFAULT NULL COMMENT '用户名称', `real_name` varchar(60) DEFAULT NULL COMMENT '真实名称', `sex` tinyint(3) DEFAULT NULL COMMENT '姓名', `mobile` varchar(20) DEFAULT NULL COMMENT ' ', `email` varchar(60) DEFAULT NULL COMMENT '邮箱', `note` varchar(200) DEFAULT NULL COMMENT '备注', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=142 DEFAULT CHARSET=utf8;

（2）实体类

package com.enjoylearning.mybatis.entity; import Java.io.Serializable; import java.util.List; import org.apache.ibatis.annotations.Param; import com.mysql.jdbc.Blob; public class TUser implements Serializable{ private Integer id; private String userName; private String realName; private Byte sex; private String mobile; private String email; private String note; private TPosition position; private List<TJobHistory> jobs ; private List<HealthReport> healthReports; private List<TRole> roles; @Override public String toString() { String positionId= (position == null ? "" : String.valueOf(position.getId())); return "TUser [id=" + id + ", userName=" + userName + ", realName=" + realName + ", sex=" + sex + ", mobile=" + mobile + ", email=" + email + ", note=" + note + ", positionId=" + positionId + "]"; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName; } public String getRealName() { return realName; } public void setRealName(String realName) { this.realName = realName; } public Byte getSex() { return sex; } public void setSex(Byte sex) { this.sex = sex; } public String getMobile() { return mobile; } public void setMobile(String mobile) { this.mobile = mobile; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public String getNote() { return note; } public void setNote(String note) { this.note = note; } public TPosition getPosition() { return position; } public void setPosition(TPosition position) { this.position = position; } public List<TJobHistory> getJobs() { return jobs; } public void setJobs(List<TJobHistory> jobs) { this.jobs = jobs; } public List<HealthReport> getHealthReports() { return healthReports; } public void setHealthReports(List<HealthReport> healthReports) { this.healthReports = healthReports; } public List<TRole> getRoles() { return roles; } public void setRoles(List<TRole> roles) { this.roles = roles; } }

（3）Mapper接口类

public interface TUserTestMapper { TUser selectByPrimaryKey(Integer id); List<TUser> selectAll(); }

（4）Mapper xml

<?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.mybatis.mapper.TUserTestMapper"> <select id="selectByPrimaryKey" resultType="TUser"> select id, user_name, real_name, sex, mobile, email, note from t_user_test where id = #{id,jdbcType=INTEGER} </select> <select id="selectAll" resultType="TUser"> select id, user_name, real_name, sex, mobile, email, note from t_user_test </select> </mapper>

（5）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> <properties resource="db.properties"/> <settings>  <setting name="mapUnderscoreToCamelCase" value="true" />   <setting name="aggressiveLazyLoading" value="false" /> </settings>  <typeAliases> <package name="com.enjoylearning.mybatis.entity" /> </typeAliases> <plugins> <plugin interceptor="com.enjoylearning.mybatis.Interceptors.ThresholdInterceptor"> <property name="threshold" value="10"/> </plugin> <plugin interceptor="com.github.pagehelper.PageInterceptor"> <property name="pageSizeZero" value="true" /> </plugin> </plugins>  <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://ip：port/test?useUnicode=true" /> <property name="username" value="root" /> <property name="password" value="123456" /> </dataSource> </environment> </environments>  <mappers>  <mapper resource="sqlmapper/TUserTestMapper.xml" /> </mappers> </configuration>

（6）启动测试类

public class mybatisDemo2 { private SqlSessionFactory sqlSessionFactory; @Before public void init() throws IOException { //--------------------之一阶段--------------------------- // 1.读取mybatis配置文件创SqlSessionFactory String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); // 1.读取mybatis配置文件创SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); inputStream.close(); } @Test //知识点：resultType public void testAutoMapping() throws IOException { // 2.获取sqlSession SqlSession sqlSession = sqlSessionFactory.openSession(); // 3.获取对应mapper TUserTestMapper mapper = sqlSession.getMapper(TUserTestMapper.class); // 4.执行查询语句并返回多条数据 List<TUser> users = mapper.selectAll(); for (TUser tUser : users) { System.out.println(tUser); } } }

（7）执行结果

sql语句：“com.mysql.jdbc.JDBC4PreparedStatement@654f0d9c: select id, user_name, real_name, sex, mobile, email, note from t_user_test”执行时间为：35毫秒，已经超过阈值！ TUser [id=1, userName=zhangsan, realName=张三, sex=1, mobile=186995587411, email=zhangsan@qq.com, note=zhangsan的备注, positionId=] TUser [id=2, userName=lisi, realName=李四, sex=1, mobile=18677885200, email=lisi@qq.com, note=lisi的备注, positionId=] TUser [id=3, userName=wangwu, realName=王五, sex=2, mobile=18695988747, email=xxoo@163.com, note=wangwu's note, positionId=]

resultType当返基本类型的时候建议选择，当返回POJO类的时候由于需要完全和数据库字段进行对应，存在不灵活、问题排查难等问题。

二、resultMap

2.1 resultMap 介绍

resultMap 元素是 MyBatis 中最重要最强大的元素。它可以让你从 90% 的 JDBC ResultSets 数据提取代码中解放出来,在对复杂语句进行联合映射的时候，它很可能可以代替数千行的同等功能的代码。ResultMap 的设计思想是，简单的语句不需要明确的结果映射，而复杂一点的语句只需要描述它们的关系就行了。

2.2 resultMap属性

2.3 使用场景

字段有自定义的转化规则复杂的多表查询

2.4 resultMap子元素属性

id –一个 ID 结果;标记出作为 ID 的结果可以帮助提高整体性能,一对多的查询中用于结果***并；result – 注入到字段或 JavaBean 属性的普通结果association – 一个复杂类型的关联;许多结果将包装成这种类型。关联可以指定为一个 resultMap 元素，或者引用一个collection – 一个复杂类型的***

2.5 代码演示

实体类，配置文件同上

（1）mapper接口

public interface TUserMapper { List<TUser> selectTestResultMap(); }

（2）Mapper.xml

<?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.mybatis.mapper.TUserMapper"> <resultMap id="UserResultMap" type="TUser" autoMapping="true"> <id column="id" property="id" /> <result column="userName" property="userName"/> <result column="realName" property="realName" /> <result column="sex" property="sex" /> <result column="mobile" property="mobile" /> <result column="email" property="email" /> <result column="note" property="note" /> <association property="position" javaType="TPosition" columnPrefix="post_"> <id column="id" property="id"/> <result column="name" property="postName"/> <result column="note" property="note"/> </association> </resultMap> <select id="selectTestResultMap" resultMap="UserResultMap" > select a.id, userName, realName, sex, mobile, email, a.note, b.id post_id, b.post_name, b.note post_note from t_user a, t_position b where a.position_id = b.id </select> </mapper>

（3）启动测试

public class MybatisDemo2 { private SqlSessionFactory sqlSessionFactory; @Before public void init() throws IOException { //--------------------之一阶段--------------------------- // 1.读取mybatis配置文件创SqlSessionFactory String resource = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); // 1.读取mybatis配置文件创SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); inputStream.close(); } @Test public void testResultMap() throws IOException { //--------------------第二阶段--------------------------- // 2.获取sqlSession SqlSession sqlSession = sqlSessionFactory.openSession(); // 3.获取对应mapper TUserMapper mapper = sqlSession.getMapper(TUserMapper.class); //--------------------第三阶段--------------------------- // 4.执行查询语句并返回单条数据 List<TUser> users = mapper.selectTestResultMap(); for (TUser tUser : users) { System.out.println(tUser.getUserName()); System.out.println(tUser.getPosition().getPostName()); } } }

（4）执行结果

sql语句：“com.mysql.jdbc.JDBC4PreparedStatement@19bb07ed: select a.id, userName, realName, sex, mobile, email, a.note, b.id post_id, b.post_name, b.note post_note from t_user a, t_position b where a.position_id = b.id”执行时间为：52毫秒，已经超过阈值！ zhangsan 总经理 lisi 零时工 wangwu 总经理

三、结论

当返回对象为基础类型时建议走resultType，当返回对象为POJO时，强制走resultMap。同时可以参考阿里巴巴JAVA开发手册中的5.4.3节，返回要解耦，不讷讷更直接使用resultClass。

原文链接：https://blog.csdn.net/b379685397/article/details/114265301

正文

resultmapMybatis开发要点:resultType和resultMap的区别

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