别再写满屏的 get-set 了，太 Low！MapStruct 高级玩法，这篇栈长带你上正道！

1、自定义映射

当我们映射 DTO 的时候，如果某些参数的值 MapStruct 的映射配置不能满足要求，可以使用自定义方法。

新增两个 DTO 类：

UserCustomDTO 类里面包含了 UserExtDTO 对象。

/*** 微信公众号：Java技术栈* @author 栈长*/
@Data
public class UserCustomDTO {private String name;private int sex;private boolean married;private String birthday;private String regDate;private UserExtDTO userExtDTO;private String memo;}

/*** 微信公众号：Java技术栈* @author 栈长*/
@Data
public class UserExtDTO {private String regSource;private String favorite;private String school;private int kids;private String memo;}

自定义映射：

如果 UserExtDTO 对象不想使用默认的映射，可以添加一个该参数的自定义映射方法。

/*** 微信公众号：Java技术栈* @author 栈长*/
@Mapper(componentModel = "spring")
public interface UserCustomStruct {@Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd")@Mapping(target = "regDate", expression = "java(org.apache.commons.lang3.time.DateFormatUtils.format(userDO.getRegDate(),\"yyyy-MM-dd HH:mm:ss\"))")@Mapping(source = "userExtDO", target = "userExtDTO")@Mapping(target = "memo", ignore = true)UserCustomDTO toUserCustomDTO(UserDO userDO);default UserExtDTO toUserExtDTO(UserExtDO userExtDO) {UserExtDTO userExtDTO = new UserExtDTO();userExtDTO.setKids(userExtDO.getKids());userExtDTO.setFavorite(userExtDO.getFavorite());// 覆盖这两个值userExtDTO.setRegSource("默认来源");userExtDTO.setSchool("默认学校");return userExtDTO;}}

当映射 UserExtDTO 对象的时候，会自动调用该接口中的自定义 toUserExtDTO 方法，完成自定义映射。

来看下生成的实现类源码：

@Component
public class UserCustomStructImpl implements UserCustomStruct {public UserCustomStructImpl() {}public UserCustomDTO toUserCustomDTO(UserDO userDO) {if (userDO == null) {return null;} else {UserCustomDTO userCustomDTO = new UserCustomDTO();if (userDO.getBirthday() != null) {userCustomDTO.setBirthday((new SimpleDateFormat("yyyy-MM-dd")).format(userDO.getBirthday()));}userCustomDTO.setUserExtDTO(this.toUserExtDTO(userDO.getUserExtDO()));userCustomDTO.setName(userDO.getName());userCustomDTO.setSex(userDO.getSex());userCustomDTO.setMarried(userDO.isMarried());userCustomDTO.setRegDate(DateFormatUtils.format(userDO.getRegDate(), "yyyy-MM-dd HH:mm:ss"));return userCustomDTO;}}
}

没错，setUserExtDTO 方法调用了 this.toUserExtDTO 自定义方法映射。

Spring Boot 基础这篇就不介绍了，系列基础教程和示例源码可以看这里：https://github.com/javastacks/spring-boot-best-practice

测试一下：

/*** 微信公众号：Java技术栈* @author 栈长*/
@RunWith(SpringRunner.class)
@SpringBootTest
public class UserCustomStructTest {@Autowiredprivate UserCustomStruct userCustomStruct;@Testpublic void test1() {UserExtDO userExtDO = new UserExtDO();userExtDO.setRegSource("公众号：Java技术栈");userExtDO.setFavorite("写代码");userExtDO.setSchool("社会大学");userExtDO.setKids(1);UserDO userDO = new UserDO();userDO.setName("栈长自定义方法");userDO.setSex(1);userDO.setAge(18);userDO.setBirthday(new Date());userDO.setPhone("18888888888");userDO.setMarried(true);userDO.setRegDate(new Date());userDO.setMemo("666");userDO.setUserExtDO(userExtDO);UserCustomDTO userCustomDTO = userCustomStruct.toUserCustomDTO(userDO);System.out.println("=====自定义方法=====");System.out.println(userCustomDTO);}
}

输出结果：

可以看到自定义方法覆盖的两个值，结果验证成功。

2、多参数映射

之前介绍的映射方法中只有一个参数，如果有多个参数映射成一个 DTO，该怎么弄呢？

比如：有两具单独的 DO，UserDO、UserAddressDO 映射成 UserMultiDTO。

直接上代码：

/*** 微信公众号：Java技术栈* @author 栈长*/
@Mapper(componentModel = "spring")
public interface UserMultiStruct {@Mapping(source = "userDO.birthday", target = "birthday", dateFormat = "yyyy-MM-dd")@Mapping(target = "userDO.regDate", expression = "java(org.apache.commons.lang3.time.DateFormatUtils.format(user.getRegDate(),\"yyyy-MM-dd HH:mm:ss\"))")@Mapping(source = "userAddressDO.postcode", target = "postcode")@Mapping(source = "userAddressDO.address", target = "address")@Mapping(target = "memo", ignore = true)UserMultiDTO toUserMultiDTO(UserDO userDO, UserAddressDO userAddressDO);}

直接使用指定的 对象名.属性名 形式映射即可。

来看下生成的实现类源码：

@Component
public class UserMultiStructImpl implements UserMultiStruct {public UserMultiStructImpl() {}public UserMultiDTO toUserMultiDTO(UserDO userDO, UserAddressDO userAddressDO) {if (userDO == null && userAddressDO == null) {return null;} else {UserMultiDTO userMultiDTO = new UserMultiDTO();if (userDO != null) {if (userDO.getBirthday() != null) {userMultiDTO.setBirthday((new SimpleDateFormat("yyyy-MM-dd")).format(userDO.getBirthday()));}userMultiDTO.setName(userDO.getName());userMultiDTO.setSex(userDO.getSex());userMultiDTO.setMarried(userDO.isMarried());if (userDO.getRegDate() != null) {userMultiDTO.setRegDate((new SimpleDateFormat()).format(userDO.getRegDate()));}}if (userAddressDO != null) {userMultiDTO.setPostcode(userAddressDO.getPostcode());userMultiDTO.setAddress(userAddressDO.getAddress());}return userMultiDTO;}}
}

测试一下：

/*** 微信公众号：Java技术栈* @author 栈长*/
@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMultiStructTest {@Autowiredprivate UserMultiStruct userMultiStruct;@Testpublic void test1() {UserDO userDO = new UserDO();userDO.setName("多参数映射");userDO.setSex(1);userDO.setAge(18);userDO.setBirthday(new Date());userDO.setPhone("18888888888");userDO.setMarried(true);userDO.setRegDate(new Date());userDO.setMemo("666");UserAddressDO userAddressDO = new UserAddressDO();userAddressDO.setProvince("广东省");userAddressDO.setCity("深圳市");userAddressDO.setPostcode("666666");userAddressDO.setAddress("001号大街Java技术栈公众号");userAddressDO.setMemo("地址信息");UserMultiDTO userMultiDTO = userMultiStruct.toUserMultiDTO(userDO, userAddressDO);System.out.println("=====多参数映射=====");System.out.println(userMultiDTO);}
}

输出结果：

个人信息和地址信息都输出来了，结果验证成功。

本文实战源代码完整版已经上传：

https://github.com/javastacks/spring-boot-best-practice

3、嵌套映射

如果一个 DTO 中的值都是从一个对象中的多个嵌套对象映射时，如果不想一个个写映射，目标可以用 . 表示。

直接上代码：

/*** 微信公众号：Java技术栈* @author 栈长*/
@Mapper(componentModel = "spring")
public interface UserNestedStruct {@Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd")@Mapping(target = "regDate", expression = "java(org.apache.commons.lang3.time.DateFormatUtils.format(userNestedDO.getRegDate(),\"yyyy-MM-dd HH:mm:ss\"))")@Mapping(source = "userAddressDO", target = ".")@Mapping(source = "userExtDO", target = ".")@Mapping(source = "userExtDO.memo", target = "memo")UserNestedDTO toUserNestedDTO(UserNestedDO userNestedDO);}

如果嵌套对象中出现重名的映射冲突，可以手动指定来源哪个嵌套对象。

来看下生成的实现类源码：

@Component
public class UserNestedStructImpl implements UserNestedStruct {public UserNestedStructImpl() {}public UserNestedDTO toUserNestedDTO(UserNestedDO userNestedDO) {if (userNestedDO == null) {return null;} else {UserNestedDTO userNestedDTO = new UserNestedDTO();if (userNestedDO.getBirthday() != null) {userNestedDTO.setBirthday((new SimpleDateFormat("yyyy-MM-dd")).format(userNestedDO.getBirthday()));}userNestedDTO.setMemo(this.userNestedDOUserExtDOMemo(userNestedDO));userNestedDTO.setCity(this.userNestedDOUserAddressDOCity(userNestedDO));userNestedDTO.setAddress(this.userNestedDOUserAddressDOAddress(userNestedDO));userNestedDTO.setRegSource(this.userNestedDOUserExtDORegSource(userNestedDO));userNestedDTO.setFavorite(this.userNestedDOUserExtDOFavorite(userNestedDO));userNestedDTO.setSchool(this.userNestedDOUserExtDOSchool(userNestedDO));userNestedDTO.setName(userNestedDO.getName());userNestedDTO.setSex(userNestedDO.getSex());userNestedDTO.setMarried(userNestedDO.isMarried());userNestedDTO.setRegDate(DateFormatUtils.format(userNestedDO.getRegDate(), "yyyy-MM-dd HH:mm:ss"));return userNestedDTO;}}private String userNestedDOUserExtDOMemo(UserNestedDO userNestedDO) {if (userNestedDO == null) {return null;} else {UserExtDO userExtDO = userNestedDO.getUserExtDO();if (userExtDO == null) {return null;} else {String memo = userExtDO.getMemo();return memo == null ? null : memo;}}}private String userNestedDOUserAddressDOCity(UserNestedDO userNestedDO) {if (userNestedDO == null) {return null;} else {UserAddressDO userAddressDO = userNestedDO.getUserAddressDO();if (userAddressDO == null) {return null;} else {String city = userAddressDO.getCity();return city == null ? null : city;}}}private String userNestedDOUserAddressDOAddress(UserNestedDO userNestedDO) {if (userNestedDO == null) {return null;} else {UserAddressDO userAddressDO = userNestedDO.getUserAddressDO();if (userAddressDO == null) {return null;} else {String address = userAddressDO.getAddress();return address == null ? null : address;}}}private String userNestedDOUserExtDORegSource(UserNestedDO userNestedDO) {if (userNestedDO == null) {return null;} else {UserExtDO userExtDO = userNestedDO.getUserExtDO();if (userExtDO == null) {return null;} else {String regSource = userExtDO.getRegSource();return regSource == null ? null : regSource;}}}private String userNestedDOUserExtDOFavorite(UserNestedDO userNestedDO) {if (userNestedDO == null) {return null;} else {UserExtDO userExtDO = userNestedDO.getUserExtDO();if (userExtDO == null) {return null;} else {String favorite = userExtDO.getFavorite();return favorite == null ? null : favorite;}}}private String userNestedDOUserExtDOSchool(UserNestedDO userNestedDO) {if (userNestedDO == null) {return null;} else {UserExtDO userExtDO = userNestedDO.getUserExtDO();if (userExtDO == null) {return null;} else {String school = userExtDO.getSchool();return school == null ? null : school;}}}
}

从源码可以看到，从嵌套对象来的值都会新增一个方法判断一下，以避免出现空指定。

测试一下：

/*** 微信公众号：Java技术栈* @author 栈长*/
@RunWith(SpringRunner.class)
@SpringBootTest
public class UserNestedStructTest {@Autowiredprivate UserNestedStruct userNestedStruct;@Testpublic void test1() {UserExtDO userExtDO = new UserExtDO();userExtDO.setRegSource("公众号：Java技术栈");userExtDO.setFavorite("写代码");userExtDO.setSchool("社会大学");userExtDO.setKids(1);userExtDO.setMemo("扩展信息");UserAddressDO userAddressDO = new UserAddressDO();userAddressDO.setProvince("广东省");userAddressDO.setCity("深圳市");userAddressDO.setPostcode("666666");userAddressDO.setAddress("001号大街Java技术栈公众号");userAddressDO.setMemo("地址信息");UserNestedDO userNestedDO = new UserNestedDO();userNestedDO.setName("栈长嵌套映射");userNestedDO.setSex(1);userNestedDO.setAge(18);userNestedDO.setBirthday(new Date());userNestedDO.setPhone("18888888888");userNestedDO.setMarried(true);userNestedDO.setRegDate(new Date());userNestedDO.setMemo("666");userNestedDO.setUserExtDO(userExtDO);userNestedDO.setUserAddressDO(userAddressDO);UserNestedDTO userNestedDTO = userNestedStruct.toUserNestedDTO(userNestedDO);System.out.println("=====嵌套映射=====");System.out.println(userNestedDTO);}
}

输出结果：

可以看到嵌套对象值，并且 memo 也是从指定的嵌套对象来的，结果验证成功。

4、映射现有实例

以上介绍的都是映射并生成一个新的 DTO 实例，如果是已有的现有 DTO 实例呢，该怎么映射呢？

直接上代码：

/*** 微信公众号：Java技术栈* @author 栈长*/
@Mapper(componentModel = "spring")
public interface UserExistStruct {@Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd")@Mapping(target = "regDate", expression = "java(org.apache.commons.lang3.time.DateFormatUtils.format(userDO.getRegDate(),\"yyyy-MM-dd HH:mm:ss\"))")@Mapping(source = "userExtDO.regSource", target = "registerSource")@Mapping(source = "userExtDO.favorite", target = "favorite")@Mapping(target = "name", ignore = true)@Mapping(target = "memo", ignore = true)void toUserShowDTO(@MappingTarget UserShowDTO userShowDTO, UserDO userDO);}

在方法上新增 DTO 对象参数并使用 @MappingTarget 对象修饰，参数位置可以调换。

来看下生成的实现类源码：

@Component
public class UserExistStructImpl implements UserExistStruct {public UserExistStructImpl() {}public void toUserShowDTO(UserShowDTO userShowDTO, UserDO userDO) {if (userDO != null) {if (userDO.getBirthday() != null) {userShowDTO.setBirthday((new SimpleDateFormat("yyyy-MM-dd")).format(userDO.getBirthday()));} else {userShowDTO.setBirthday((String)null);}userShowDTO.setRegisterSource(this.userDOUserExtDORegSource(userDO));userShowDTO.setFavorite(this.userDOUserExtDOFavorite(userDO));userShowDTO.setSex(userDO.getSex());userShowDTO.setMarried(userDO.isMarried());userShowDTO.setRegDate(DateFormatUtils.format(userDO.getRegDate(), "yyyy-MM-dd HH:mm:ss"));}}private String userDOUserExtDORegSource(UserDO userDO) {if (userDO == null) {return null;} else {UserExtDO userExtDO = userDO.getUserExtDO();if (userExtDO == null) {return null;} else {String regSource = userExtDO.getRegSource();return regSource == null ? null : regSource;}}}private String userDOUserExtDOFavorite(UserDO userDO) {if (userDO == null) {return null;} else {UserExtDO userExtDO = userDO.getUserExtDO();if (userExtDO == null) {return null;} else {String favorite = userExtDO.getFavorite();return favorite == null ? null : favorite;}}}
}

userShowDTO 是作为方法参数传入的，而不是新创建的。

测试一下：

/*** 微信公众号：Java技术栈* @author 栈长*/
@RunWith(SpringRunner.class)
@SpringBootTest
public class UserExistStructTest {@Autowiredprivate UserExistStruct userExistStruct;@Testpublic void test1() {UserExtDO userExtDO = new UserExtDO();userExtDO.setRegSource("公众号：Java技术栈");userExtDO.setFavorite("写代码");userExtDO.setSchool("社会大学");UserDO userDO = new UserDO();userDO.setName("栈长");userDO.setSex(1);userDO.setAge(18);userDO.setBirthday(new Date());userDO.setPhone("18888888888");userDO.setMarried(true);userDO.setRegDate(new Date());userDO.setMemo("666");userDO.setUserExtDO(userExtDO);System.out.println("=====映射现有实例前=====");UserShowDTO userShowDTO = new UserShowDTO();userShowDTO.setName("栈长NAME");userShowDTO.setMemo("栈长MEMO");System.out.println(userShowDTO);System.out.println("=====映射现有实例后=====");userExistStruct.toUserShowDTO(userShowDTO, userDO);System.out.println(userShowDTO);}
}

输出结果：

可以看到已有 DTO 对象的值及新映射的值，结果验证成功。

注意：默认是以覆盖原有值的方式映射的，如果要保留原有 XX 的值，使用 ignore 忽略即可

总结

本文栈长介绍了 MapStruct 的 4 个高级玩法，足以应对各种 Bean 类映射了，其实还有很多复杂的、个性化用法，一篇难以写完，栈长后面有时间会整理出来，陆续给大家分享。

感兴趣的也可以参考官方文档：

https://mapstruct.org/documentation/reference-guide/

另外，栈长一直介绍的是 DO --> DTO 的映射，其实反过来 DTO --> DO、BO 也是一样的，只是对象名称不一样，映射的用法是一样的，这样在服务 A 接收到服务 B 过来的 DTO 数据时，可以再进行一次反射映射供业务使用。

本文实战源代码完整版已经上传：

https://github.com/javastacks/spring-boot-best-practice

欢迎 Star 学习，后面 Spring Boot 示例都会在这上面提供！