当前位置:网站首页>【详细】快速实现对象映射的几种方式
【详细】快速实现对象映射的几种方式
2022-07-06 01:19:00 【菜鸟是大神】
项目开发过程中,经常需要编写model之间的转换,最常见的有:
- 实体转DTO
- DTO转实体
- …
举个例子:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | // 实体:User @Data @Builder @NoArgsConstructor @AllArgsConstructor public class User { private Integer id; private String email; private String username; private String password; private Integer gender; private Date birthday; } // DTO:UserRegisterReq @Data public class UserRegisterReq { private String username; private String password; private String confirmPassword; private String email; } |
其中:
- UserRegisterReq是用户注册时,Controller层的请求入参
- User是用户实体
在执行注册时,我们需要将UserRegisterReq转换成User对象,再存储到数据库。此时,我们往往会编写类似如下的代码:
1 2 3 4 5 6 7 8 9 | @PostMapping("/users/reg") public void reg(@RequestBody UserRegisterReq userRegisterReq) { // 省略password 与 confirmPassword等值判断 User user = new User(); user.setEmail(userRegisterReq.getEmail()); user.setPassword(userRegisterReq.getPassword()); user.setUsername(userRegisterReq.getUsername()); // 保存user... } |
如上的代码虽然可行,但是如果类里面的field非常多,那么就会比较麻烦——我们写了一堆代码,只不过是为了实现对象的转换而已。
方法一、IDEA插件快速转换
IDEA提供GenerateAllSetter插件,可帮助我们快速生成上述代码。
- 插件主页:GenerateAllSetter - IntelliJ IDEs Plugin | Marketplace
- GitHub:GitHub - gejun123456/intellij-generateAllSetMethod: Intellij plugin to generate call to setter method value for class
演示如下图:
只需安装插件,然后按Alt + Enter(macOS则是Option + Enter),即可自动生成对象转换代码。
方法二、借助对象映射框架实现对象转换
方法一虽然很方便,但如果对象的字段非常多,那么还是会导致代码非常啰嗦,不够简洁。
事实上,Java生态有很多对象映射框架,专门帮助我们实现对象间的转换。这里笔者列出了业界相对常用的选项:
产品 | Dozer | Orika | MapStruct | CGLib BeanCopier | Spring BeanUtils | Apache BeanUtils |
---|---|---|---|---|---|---|
GitHub | dozer 1.9K stars | orika 1.2K stars | mapstruct 5K stars | cglib 4.3K stars | - | commons-beanutils 0.2K stars |
工作原理 | 大量反射,主要基于Field.set(obj, obj)为field赋值 | 基于javassist生成对象映射字节码,并加载生成的字节码文件 | 基于JSR269,在在编译期生成对象映射代码 | 基于ASM的MethodVisitor为field赋值 | 基于Spring反射工具类 | 基于反射 |
性能排名 | 5 | 2 | 1 | 4 | 3 | 6 |
虽然选项很多,但笔者目前只建议大家使用MapStruct。
MapStruct优势:
- 编译器生成Getter/Setter,无运行期性能损耗,性能强劲
- 基于JSR269,配置灵活
- 基于Getter/Setter,和自己手写Getter/Setter没有区别,搜索字段引用等较方便
缺点:
- 由于配置灵活,所以上手成本比其他组件稍微高一点点
MapStruct上手
配置IDE
参考 IDE Support – MapStruct ,配置你的IDE
整合
在项目中添加如下内容:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
<!-- ref: https://mapstruct.org/documentation/installation/ --> <properties> <org.mapstruct.version>1.4.2.Final</org.mapstruct.version> </properties> ... <dependencies> <dependency> <groupId>org.mapstruct</groupId> <artifactId>mapstruct</artifactId> <version>${org.mapstruct.version}</version> </dependency> </dependencies> ... <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>3.8.1</version> <configuration> <source>1.8</source> <!-- depending on your project --> <target>1.8</target> <!-- depending on your project --> <annotationProcessorPaths> <path> <groupId>org.mapstruct</groupId> <artifactId>mapstruct-processor</artifactId> <version>${org.mapstruct.version}</version> </path> <!-- other annotation processors --> </annotationProcessorPaths> </configuration> </plugin> </plugins> </build>
如果你的项目使用了Lombok,或使用了spring-boot-configuration-processor,则使用类似如下的配置:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
<properties> <org.mapstruct.version>1.4.2.Final</org.mapstruct.version> </properties> ... <dependencies> <dependency> <groupId>org.mapstruct</groupId> <artifactId>mapstruct</artifactId> <version>${org.mapstruct.version}</version> </dependency> </dependencies> ... <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>3.8.1</version> <configuration> <source>8</source> <target>8</target> <encoding>UTF-8</encoding> <!-- https://mapstruct.org/documentation/installation/ --> <!-- https://mapstruct.org/documentation/stable/reference/html/#lombok --> <annotationProcessorPaths> <path> <groupId>org.mapstruct</groupId> <artifactId>mapstruct-processor</artifactId> <version>${org.mapstruct.version}</version> </path> <path> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.18.16</version> </path> <path> <groupId>org.projectlombok</groupId> <artifactId>lombok-mapstruct-binding</artifactId> <version>0.1.0</version> </path> <path> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-configuration-processor</artifactId> <version>2.4.1</version> </path> </annotationProcessorPaths> </configuration> </plugin> </plugins> </build>
使用
定义接口,代码类似如下:
1 2 3 4 5 6 7 8 9 10 11 12 13 14
import com.itmuch.gogolive1.domain.User; import com.itmuch.gogolive1.domain.UserRegisterReq; import org.mapstruct.Mapper; import org.mapstruct.factory.Mappers; @Mapper public interface UserConverter { /** * 固定写法:Mappers.getMapper(接口名.class); */ UserConverter INSTANCE = Mappers.getMapper(UserConverter.class); User toUser(UserRegisterReq req); }
使用:
1 2 3 4 5 6
@PostMapping("/users/reg") public void reg2(@RequestBody UserRegisterReq userRegisterReq) { // 省略password 与 confirmPassword等值判断 User user = UserConverter.INSTANCE.toUser(userRegisterReq); // 保存user... }
由代码可知,只需如下代码,即可将UserRegisterReq转换User。
1
User user = UserConverter.INSTANCE.toUser(userRegisterReq);
原理
编译代码,并在前面的UserConverter接口上,按快捷键 Command + Option + B
(或点击 Navigate - Implementation(s)
) ,查找UserConverter的实现类,可跳转到类似如下代码:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | @Generated( value = "org.mapstruct.ap.MappingProcessor", date = "2022-03-22T00:29:49+0800", comments = "version: 1.4.2.Final, compiler: javac, environment: Java 11.0.9.1 (Azul Systems, Inc.)" ) public class UserConverterImpl implements UserConverter { @Override public User toUser(UserRegisterReq req) { if ( req == null ) { return null; } UserBuilder user = User.builder(); user.email( req.getEmail() ); user.username( req.getUsername() ); user.password( req.getPassword() ); return user.build(); } } |
由代码可知,MapStruct在编译期间,生成了UserConverterImpl,并在其中实现了对象之间的转换。
和Spring整合
MapStruct支持与Spring整合,只需按如下步骤操作即可:
编写Mapper接口,并在其中添加
(componentModel = "spring")
属性:1 2 3 4
@Mapper(componentModel = "spring") public interface UserSpringConverter { User toUser(UserRegisterReq req); }
当使用时,只需注入
UserSpringConverter
即可:1 2
@Autowired UserSpringConverter userSpringConverter;
这是因为,使用
(componentModel = "spring")
后,生成的实现类会自动添加@Component
注解
拓展
本文只是介绍了较为简单的例子,事实上,MapStruct支持非常灵活的配置,例如:
枚举映射
1 2 3 4 5 6 7 8 9 10 11 12
@Mapper public interface OrderMapper { OrderMapper INSTANCE = Mappers.getMapper( OrderMapper.class ); @ValueMappings({ @ValueMapping(target = "SPECIAL", source = "EXTRA"), @ValueMapping(target = "DEFAULT", source = "STANDARD"), @ValueMapping(target = "DEFAULT", source = "NORMAL") }) ExternalOrderType orderTypeToExternalOrderType(OrderType orderType); }
自定义表达式映射:
1 2 3 4 5 6 7 8
@Mapper public interface SourceTargetMapper { SourceTargetMapper INSTANCE = Mappers.getMapper( SourceTargetMapper.class ); @Mapping(target = "timeAndFormat", expression = "java( new org.sample.TimeAndFormat( s.getTime(), s.getFormat() ) )") Target sourceToTarget(Source s); }
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