[detailed] several ways to quickly realize object mapping

Project development process , Often need to write model Conversion between , The most common ones are ：

• Entity transfer DTO
• DTO Transfer to entity
• …

for instance ：

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// Entity ：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; }

among ：

• UserRegisterReq When the user registers ,Controller Request input of layer
• User Is a user entity

When performing registration , We need to UserRegisterReq convert to User object , Then store it in the database . here , We often write code similar to the following ：

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@PostMapping("/users/reg") public void reg(@RequestBody UserRegisterReq userRegisterReq) { // Omit password And confirmPassword Equivalent judgment User user = new User(); user.setEmail(userRegisterReq.getEmail()); user.setPassword(userRegisterReq.getPassword()); user.setUsername(userRegisterReq.getUsername()); // preservation user... }

Although the above code is feasible , But if the class field A lot , Then it will be more troublesome —— We wrote a lot of code , It's just to realize the conversion of objects .

Method 1 、IDEA Plug in fast conversion

IDEA Provide GenerateAllSetter plug-in unit , It can help us generate the above code quickly .

• Plug in home page ：GenerateAllSetter - IntelliJ IDEs Plugin | Marketplace
• GitHub：GitHub - gejun123456/intellij-generateAllSetMethod: Intellij plugin to generate call to setter method value for class

The demonstration is shown in the following figure ：

Just install the plug-in , Then press Alt + Enter（macOS It is Option + Enter）, Object conversion code can be generated automatically .

Method 2 、 Realize object transformation with the help of object mapping framework

Method one is very convenient , But if the object has many fields , Then the code will still be very verbose , It's not simple enough .

in fact ,Java Ecology has many object mapping frameworks , It specially helps us realize the conversion between objects . Here the author lists the options commonly used in the industry ：

product	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
working principle	A lot of reflection , Based mainly on Field.set(obj, obj) by field assignment	be based on javassist Generate object mapping bytecode , And load the generated bytecode file	be based on JSR269, Generate object mapping code at compile time	be based on ASM Of MethodVisitor by field assignment	be based on Spring Reflection tools	Based on reflection
Performance ranking	5	2	1	4	3	6

Although there are many options , But the author only suggests that you use MapStruct.

MapStruct advantage ：

• Compiler generation Getter/Setter, No performance loss during operation , Strong performance
• be based on JSR269, Flexible configuration
• be based on Getter/Setter, And write by yourself Getter/Setter There is no difference between , It is more convenient to search for field references

shortcoming ：

• Due to the flexible configuration , So the starting cost is a little higher than other components

MapStruct Get started

To configure IDE

Reference resources  IDE Support – MapStruct , Configure your IDE

Integrate

• Add the following to the project ：

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  <!-- 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>

• If your project uses Lombok, Or use spring-boot-configuration-processor, Then use a configuration similar to the following ：

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  <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>

Use

• Defining interfaces , The code is similar to ：

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  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 { /** * Fixed writing ：Mappers.getMapper( The interface name .class); */ UserConverter INSTANCE = Mappers.getMapper(UserConverter.class); User toUser(UserRegisterReq req); }

• Use ：

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  @PostMapping("/users/reg") public void reg2(@RequestBody UserRegisterReq userRegisterReq) { // Omit password And confirmPassword Equivalent judgment User user = UserConverter.INSTANCE.toUser(userRegisterReq); // preservation user... }

  From the code , Just use the following code , Can be UserRegisterReq transformation User.

  1	User user = UserConverter.INSTANCE.toUser(userRegisterReq);

principle

Compile code , And in front UserConverter On the interface , Press shortcut key  Command + Option + B （ Or click on  Navigate - Implementation(s) ） , lookup UserConverter Implementation class of , You can jump to the following code ：

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@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(); } }

From the code ,MapStruct During compilation , Generated UserConverterImpl, And realize the conversion between objects .

and Spring Integrate

MapStruct Support and Spring Integrate , Just follow the steps below ：

• To write Mapper Interface , And add  (componentModel = "spring")  attribute ：

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  @Mapper(componentModel = "spring") public interface UserSpringConverter { User toUser(UserRegisterReq req); }

• When used , Just inject  UserSpringConverter  that will do ：

  1 2	@Autowired UserSpringConverter userSpringConverter;

  This is because , Use  (componentModel = "spring")  after , The generated implementation class will be automatically added  @Component  annotation

expand

This article only introduces a relatively simple example , in fact ,MapStruct Support very flexible configuration , for example ：

• Enumeration mapping

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  @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); }

• Custom expression mapping ：

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  @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); }