1. What is it MapStruct?
1.1 MapStruct
MapStructis a code generator that greatly simplifies the implementation of mappings between Java bean types based on a convention-over-configuration approach. The generated mapping code uses simple method calls and is therefore fast, type-safe and easy to understand.
When decorating a house, some cables should be routed as far as possible 内线, paying attention to make the room look more tidy and beautiful. MapStructSimplify the conversion of Java Beans like a code decoration expert.
1.2 Add dependencies
<dependency>
<groupId>org.mapstruct</groupId>
<artifactId>mapstruct</artifactId>
<version>1.3.1.Final</version>
</dependency>
2. Application scenarios
2.1 Equal conversion of field names
2.1.1 Single object conversion
conversion mapper
import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
...
@Mapper(componentModel = "spring")
public interface StudentMapper {
/**
* 转 responseDto
* @param s
* @return
*/
StudentResponseDTO entityToResponseDTO(Student s);
}
StudentEntity class before conversion
{
"age": 24,
"className": "一年级五班",
"entranceTime": "2022-10-18",
"height": 180.0,
"name": "我玩亚索我会C",
"weight": 140.0
}
after conversionStudentResponseDTO
{
"className": "一年级五班",
"name": "我玩亚索我会C"
}
2.1.2 Collection conversion
Conversion Mapper
import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
@Mapper(componentModel = "spring")
public interface StudentMapper {
/**
* 转 responseDto list
* @return
*/
List<StudentResponseDTO> listEntityToResponseListDto(List<Student> studentes);
}
StudentList collection before conversion
[
{
"age": 24,
"className": "一年级五班",
"height": 180.0,
"name": "我玩亚索我会C",
"weight": 140.0
},
{
"age": 25,
"className": "铃兰五班",
"height": 184.0,
"name": "泷谷源治",
"weight": 130.0
},
{
"age": 26,
"className": "铃兰一班",
"height": 178.0,
"name": "芹泽多摩雄",
"weight": 160.0
},
{
"age": 24,
"className": "铃兰火箭班",
"height": 175.0,
"name": "辰川时生",
"weight": 120.0
}
]
converted StudentResponseDTOcollection
[
{
"className": "一年级五班",
"name": "我玩亚索我会C"
},
{
"className": "铃兰五班",
"name": "泷谷源治"
},
{
"className": "铃兰一班",
"name": "芹泽多摩雄"
},
{
"className": "铃兰火箭班",
"name": "辰川时生"
}
]
2.2 Field unequal conversion
2.2.1 Single object conversion
When the attribute name in the converted object is not equal to the attribute name in the converted object, use the annotation @Mapping to manually map, indicating the
targettarget,sourceindicating the source, and manual mapping is tosourcemap the attributes in totargetthe attributes in.
Conversion Mapper
import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
...
@Mapper(componentModel = "spring")
public interface StudentMapper {
/**
* 转实体
* @param dto
* @return
*/
@Mapping(target = "name",source = "studentName")
@Mapping(target = "className",source = "studentClassName")
Student requestDTOToEntity(StudentRequestDTO dto);
}
before conversionStudentRequestDTO
{
"studentClassName": "E班",
"studentName": "林田惠"
}
after conversionStudent
{
"className": "E班",
"name": "林田惠"
}
2.2.2 Collection conversion
When the field unequal sets are converted to each other, two Mappers need to be defined, one is the conversion of a single object, and the other is the conversion of a collection object.
Conversion Mapper
import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
...
import java.util.List;
@Mapper(componentModel = "spring")
public interface StudentMapper {
/**
* 转 responseDto 字段不同
* @param student
* @return
*/
@Mapping(target = "studentName",source = "name")
@Mapping(target = "studentClassName",source = "className")
StudentInfoResponseDTO entityToResponseList(Student student);
/**
* 转 responseDto list 字段不同
* @return
*/
List<StudentInfoResponseDTO> listEntityToResponseLists(List<Student> students);
}
Studentcollection before conversion
[
{
"age": 24,
"className": "一年级五班",
"height": 180.0,
"name": "我玩亚索我会C",
"weight": 140.0
},
{
"age": 25,
"className": "铃兰五班",
"height": 184.0,
"name": "泷谷源治",
"weight": 130.0
},
{
"age": 26,
"className": "铃兰一班",
"height": 178.0,
"name": "芹泽多摩雄",
"weight": 160.0
},
{
"age": 24,
"className": "铃兰火箭班",
"height": 175.0,
"name": "辰川时生",
"weight": 120.0
}
]
converted StudentInfoResponseDTOcollection
[
{
"studentClassName": "一年级五班",
"studentName": "我玩亚索我会C"
},
{
"studentClassName": "铃兰五班",
"studentName": "泷谷源治"
},
{
"studentClassName": "铃兰一班",
"studentName": "芹泽多摩雄"
},
{
"studentClassName": "铃兰火箭班",
"studentName": "辰川时生"
}
]
2.3 Multiple sources
Some fields are not attributes in the object, but if you want to assign a value to the converted object, you can pass the attribute as a parameter.
Conversion Mapper
import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
...
import java.util.List;
@Mapper(componentModel = "spring")
public interface StudentMapper {
/**
* 额外参数 转 实体类
* @param dto
* @param entranceTime 额外参数 入学时间
* @return
*/
@Mapping(target = "name",source = "dto.studentName")
@Mapping(target = "className",source = "dto.studentClassName")
@Mapping(target = "entranceTime",source = "entranceTime")
Student extraParamsToEntity(StudentRequestDTO dto,String entranceTime);
}
before conversionStudentRequestDTO
{
"studentClassName": "E班",
"studentName": "林田惠"
}
after conversionStudent
{
"className": "E班",
"entranceTime": "2022-10-18",
"name": "林田惠"
}
Note: When there are multiple parameters of the mapper method, an alias needs to be specified when manually mapping, such as:@Mapping(target = "name",source = "dto.studentName")
2.4 Default values
To set default values for properties in an object use
defaultValue
import javax.xml.crypto.Data;
import java.time.LocalDateTime;
@Mapper(componentModel = "spring")
public interface StudentMapper {
/**
* 默认参数 转 实体类
* @param dto
* @return
*/
@Mapping(target = "className",defaultValue = "五班")
Student defaultToEntity(StudentRequestDTO dto);
}
2.5 Data type mapping
2.5.1 Date type
Specifies the date format.
import javax.xml.crypto.Data;
import java.time.LocalDateTime;
@Mapper(componentModel = "spring")
public interface StudentMapper {
/**
* 日期类型映射 转 实体类
* @param dto
* @param entranceTime 入学时间
* @return
*/
@Mapping(target = "entranceTime",dateFormat = "yyyy-MM-dd",source = "entranceTime")
Student dateTypeToEntity(StudentRequestDTO dto,String entranceTime);
}
2.5.2 Numeric types
Round to two decimal places.
import javax.xml.crypto.Data;
import java.time.LocalDateTime;
@Mapper(componentModel = "spring")
public interface StudentMapper {
/**
* 数字类型映射 转 实体类
* @param dto
* @param entranceTime 入学时间
* @return
*/
@Mapping(target = "tuition",numberFormat = "$#.00",source = "tuitionFee")
Student dateTypeToEntity(StudentRequestDTO dto,String entranceTime);
}
2.6 Expressions
entranceTimeset to the current time
studentNoset to a random number
@Mapper(componentModel = "spring",imports = {
LocalDateTime.class, UUID.class})
public interface StudentMapper {
/**
* 表达式 转 实体类
* @param dto
* @return
*/
@Mapping(target = "entranceTime",expression = "java(LocalDateTime.now())")
@Mapping(target = "studentNo",expression = "java(UUID.randomUUID().toString())")
List<Student> expressionToEntities(List<StudentRequestDTO> dto);
}
3. Precautions
When using MapStruct, if there is a change in the mapped field, be sure to clearclear the compiled file and recompile install.