java注解处理器之MapStruct
介绍
MapStruct是一个可以生成类型安全的，高性能的且无依赖的 JavaBean 映射代码的注解处理器，可以在编译期生成对应的mapping，既没有BeanUtils等工具使用反射的性能问题，又免去了自己写映射代码的繁琐。
使用
简单转换
maven依赖
<dependency>
<groupId>org.mapstruct</groupId>
<artifactId>mapstruct-jdk8</artifactId>
<version>1.3.0.Final</version>
</dependency>
<dependency>
<groupId>org.mapstruct</groupId>
<artifactId>mapstruct-processor</artifactId>
<version>1.3.0.Final</version>
</dependency>
先定义两个entity
@Data
public class Source {
private String id;
private Integer num;
private Integer count;
}
@Data
public class Target {
private String id;
private Integer num;
private Integer count;
}
Source 为转换类，Target 为待转换类，接下来定义转换器
@Mapper
public interface SourceMapper {
SourceMapper INSTANCE = Mappers.getMapper(SourceMapper.class);
Target source2target(Source source);
}
定义一个 INSTANCE 是为了方便调用，方法名没有限制，mapstruct会帮我们生成一个接口的实现类，
@Generated(
value = "org.mapstruct.ap.MappingProcessor",
date = "2020-08-01T19:56:53+0800",
comments = "version: 1.3.0.Final, compiler: javac, environment: Java 1.8.0_181 (Oracle Corporation)"
)
public class SourceMapperImpl implements SourceMapper {
@Override
public Target source2target(Source source) {
if ( source == null ) {
return null;
}
Target target = new Target();
target.setId( source.getId() );
target.setNum( source.getNum() );
target.setCount( source.getCount() );
return target;
}
}
调用转换器
public class Client {
public static void main(String[] args) {
Source source = new Source();
source.setId("1");
source.setNum(2);
source.setCount(3);
Target target = SourceMapper.INSTANCE.source2target(source);
System.out.println(source);
System.out.println(target);
}
}
输出结果为
Source(id=1, num=2, count=3)
Target(id=1, num=2, count=3)
属性名不同的转换
如果属性名不同的话，可以通过 Mapping 注解来转换
@Data
public class Source {
private String sourceId;
private Integer sourceNum;
private Integer sourceCount;
}
@Data
public class Target {
private String targetId;
private Integer targetNum;
private Integer targetCount;
}
@Mapper
public interface SourceMapper {
SourceMapper INSTANCE = Mappers.getMapper(SourceMapper.class);
@Mapping(source = "sourceId", target = "targetId")
@Mapping(source = "sourceNum", target = "targetNum")
@Mapping(source = "sourceCount", target = "targetCount")
Target source2target(Source source);
}
Mapping 注解是一个可重复注解，通过 Mapping 注解指定源属性名和目标属性名就可以了。
public class Client {
public static void main(String[] args) {
Source source = new Source();
source.setSourceId("1");
source.setSourceNum(2);
source.setSourceCount(3);
Target target = SourceMapper.INSTANCE.source2target(source);
System.out.println(source);
System.out.println(target);
}
}
结果符合预期。
自定义转换
有时候，某些类型的转换不能通过 mapstruct 来实现，我们可以定义自己的转换逻辑。
@Data
public class Source {
private String sourceId;
private Integer sourceNum;
private Integer sourceCount;
private SubSource subSource;
}
@Data
public class SubSource {
private String deleted;
}
@Data
public class Target {
private String targetId;
private Integer targetNum;
private Integer targetCount;
private SubTarget subTarget;
}
@Data
public class SubTarget {
private Boolean deleted;
}
定义 SubSource 转换器
@Mapper
public class SubSourceMapper {
SubTarget subSource2subTarget(SubSource subSource) {
if (subSource == null) {
return null;
}
SubTarget subTarget = new SubTarget();
// 特殊的转换逻辑
subTarget.setDeleted(subSource.getDeleted().equals("T"));
return subTarget;
}
}
让 SourceMapper 使用自定义的转换器
@Mapper(uses = SubSourceMapper.class)
public interface SourceMapper {
SourceMapper INSTANCE = Mappers.getMapper(SourceMapper.class);
@Mapping(source = "sourceCount", target = "targetCount")
@Mapping(source = "sourceNum", target = "targetNum")
@Mapping(source = "sourceId", target = "targetId")
@Mapping(source = "subSource", target = "subTarget")
Target source2target(Source source);
}
Mapper注解的uses属性表示使用的其他转换器，既可以是我们自定义的，也可以是
mapstruct 生成的。java8之后我们也可以通过默认方法的方式来实现自定义转换。
@Mapper
public interface SourceMapper {
SourceMapper INSTANCE = Mappers.getMapper(SourceMapper.class);
@Mapping(source = "sourceCount", target = "targetCount")
@Mapping(source = "sourceNum", target = "targetNum")
@Mapping(source = "sourceId", target = "targetId")
@Mapping(source = "subSource", target = "subTarget")
Target source2target(Source source);
default SubTarget subSource2subTarget(SubSource subSource) {
if (subSource == null) {
return null;
}
SubTarget subTarget = new SubTarget();
subTarget.setDeleted(subSource.getDeleted().equals("T"));
return subTarget;
}
}
多对一转换
将多个对象转换成一个
@Data
public class Person {
private String firstName;
private String lastName;
private int height;
private String description;
}
@Data
public class Address {
private String street;
private int zipCode;
private int houseNo;
private String description;
}
@Data
public class DeliveryAddress {
private String firstName;
private String lastName;
private int height;
private String street;
private int zipCode;
private int houseNumber;
private String description;
}
@Mapper
public interface AddressMapper {
AddressMapper INSTANCE = Mappers.getMapper(AddressMapper.class);
@Mapping(source = "person.description", target = "description")
@Mapping(source = "address.houseNo", target = "houseNumber")
DeliveryAddress personAndAddress2DeliveryAddress(Person person, Address address);
}
两个输入源都有description，必须指定一个输入源。
装饰器
装饰器可以让我们在转换前后添加一些额外的逻辑，以上一个程序为例，重新设置DeliveryAddress的description。
public abstract class AddressMapperDecorate implements AddressMapper {
private final AddressMapper delegate;
protected AddressMapperDecorate(AddressMapper addressMapper) {
this.delegate = addressMapper;
}
// 装饰器逻辑 重新设置description
@Override
public DeliveryAddress personAndAddress2DeliveryAddress(Person person, Address address) {
DeliveryAddress deliveryAddress = delegate.personAndAddress2DeliveryAddress(person, address);
deliveryAddress.setDescription(person.getDescription() + ":" + address.getDescription());
return deliveryAddress;
}
}
定义一个装饰器，必须实现转换接口并添加一个接口的构造器，定义为抽象类可以让我们只装饰指定的方法。
使用DecoratedWith注解来表明所使用的装饰器
@Mapper
@DecoratedWith(AddressMapperDecorate.class)
public interface AddressMapper {
AddressMapper INSTANCE = Mappers.getMapper(AddressMapper.class);
@Mapping(source = "person.description", target = "description")
@Mapping(source = "address.houseNo", target = "houseNumber")
DeliveryAddress personAndAddress2DeliveryAddress(Person person, Address address);
}
前置后置处理器
我们可以在转换方法调用前后做一些操作
@Mapper
public interface AddressMapper {
AddressMapper INSTANCE = Mappers.getMapper(AddressMapper.class);
@Mapping(source = "person.description", target = "description")
@Mapping(source = "address.houseNo", target = "houseNumber")
DeliveryAddress personAndAddress2DeliveryAddress(Person person,
Address address,
@Context Locale locale);
@BeforeMapping
default void beforeMapping(Person person,
Address address,
@MappingTarget DeliveryAddress deliveryAddress,
@TargetType Class<DeliveryAddress> deliveryAddressClass,
@Context Locale locale) {
System.out.println("before mapping start...");
System.out.println(person);
System.out.println(address);
System.out.println(deliveryAddress);
System.out.println(deliveryAddressClass);
System.out.println(locale);
System.out.println("before mapping end...");
}
@AfterMapping
default void afterMapping(Person person,
Address address,
@MappingTarget DeliveryAddress deliveryAddress) {
deliveryAddress.setDescription(person.getDescription() + "," + address.getDescription());
}
}
BeforeMapping 注解表示前置处理器，AfterMapping 注解表示后置处理器，MappingTarget 注解表示此参数为target实例，TargetType 注解表示参数为target类型，Context 注解表示参数为上下文参数，对应转换方法中的上下文，其余的参数为source。
依赖注入
我们也可以将转换器定义为spring的bean
@Mapper(componentModel = "spring")
public interface AddressMapper {
AddressMapper INSTANCE = Mappers.getMapper(AddressMapper.class);
@Mapping(source = "person.description", target = "description")
@Mapping(source = "address.houseNo", target = "houseNumber")
DeliveryAddress personAndAddress2DeliveryAddress(Person person, Address address);
}
接口实现类上会加上 Component 注解。
