MapStruct - Using expression

MapStruct allows to call a conversion method for customized logic. We can use expression to achieve the same where we can pass any java object and call its method to do the conversion.

Syntax

@Mapping(target = "target-property", 
   expression = "java(target-method())")

Here

• target-property − the property for which we are doing the mapping.

• expression − mapper will call the java method written in the expression.

• target-method − target-method is the method to be called. In case method is present in different class, use new class-name.target-method()

Example - Using expression

Open project mapping as updated in Mapping Using dateFormat chapter in Eclipse.

Update CarEntity.java with following code −

CarEntity.java

package com.tutorialspoint.entity;
import java.util.GregorianCalendar;

public class CarEntity {
   private int id;
   private double price;
   private GregorianCalendar manufacturingDate;
   public int getId() {
      return id;
   }
   public void setId(int id) {
      this.id = id;
   }
   public double getPrice() {
      return price;
   }
   public void setPrice(double price) {
      this.price = price;
   }
   public GregorianCalendar getManufacturingDate() {
      return manufacturingDate;
   }
   public void setManufacturingDate(GregorianCalendar manufacturingDate) {
      this.manufacturingDate = manufacturingDate;
   }
}

Update Car.java with following code −

Car.java

package com.tutorialspoint.model;

public class Car {
   private int id;
   private String price;
   private String manufacturingDate;
   public int getId() {
      return id;
   }
   public void setId(int id) {
      this.id = id;
   }
   public String getPrice() {
      return price;
   }
   public void setPrice(String price) {
      this.price = price;
   }
   public String getManufacturingDate() {
      return manufacturingDate;
   }
   public void setManufacturingDate(String manufacturingDate) {
      this.manufacturingDate = manufacturingDate;
   }
}

Update CarMapper.java with following code −

CarMapper.java

package com.tutorialspoint.mapper;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.GregorianCalendar;
import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import com.tutorialspoint.entity.CarEntity;
import com.tutorialspoint.model.Car;

@Mapper
public interface CarMapper {
   @Mapping(source = "price", target = "price", numberFormat = "$#.00")
   @Mapping(target = "manufacturingDate", 
      expression = "java(getManufacturingDate(carEntity.getManufacturingDate()))")
   Car getModelFromEntity(CarEntity carEntity);

   default String getManufacturingDate(GregorianCalendar manufacturingDate) {
      Date d = manufacturingDate.getTime();
      SimpleDateFormat sdf = new SimpleDateFormat( "dd.MM.yyyy" );
      return sdf.format( d );
   }
}

Update CarMapperTest.java with following code −

CarMapperTest.java

package com.tutorialspoint.test;

import static org.junit.jupiter.api.Assertions.assertEquals;
import java.util.GregorianCalendar;
import org.junit.jupiter.api.Test;
import org.mapstruct.factory.Mappers;
import com.tutorialspoint.entity.CarEntity;
import com.tutorialspoint.mapper.CarMapper;
import com.tutorialspoint.model.Car;

public class CarMapperTest {
   private CarMapper carMapper = Mappers.getMapper(CarMapper.class);

   @Test
   public void testEntityToModel() {
      CarEntity entity = new CarEntity();
      entity.setPrice(345000);
      entity.setId(1);
      entity.setManufacturingDate(new GregorianCalendar(2015, 3, 5));
      Car model = carMapper.getModelFromEntity(entity);
      assertEquals(model.getPrice(), "$345000.00");
      assertEquals(entity.getId(), model.getId());
      assertEquals("05.04.2015", model.getManufacturingDate());
   }
}

Run the following command to test the mappings.

mvn clean test

Output

Once command is successful. Verify the output.

mvn clean test
[INFO] Scanning for projects...
...
[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running com.tutorialspoint.test.[1mCarMapperTest[m
[INFO] [1;32mTests run: [0;1;32m1[m, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.037 s -- in com.tutorialspoint.test.[1mCarMapperTest[m
[INFO] Running com.tutorialspoint.test.[1mDeliveryAddressMapperTest[m
[INFO] [1;32mTests run: [0;1;32m1[m, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.006 s -- in com.tutorialspoint.test.[1mDeliveryAddressMapperTest[m
[INFO] Running com.tutorialspoint.test.[1mStudentMapperTest[m
[INFO] [1;32mTests run: [0;1;32m2[m, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.004 s -- in com.tutorialspoint.test.[1mStudentMapperTest[m
[INFO] 
[INFO] Results:
[INFO] 
[INFO] [1;32mTests run: 4, Failures: 0, Errors: 0, Skipped: 0[m
[INFO] 
[INFO] [1m------------------------------------------------------------------------[m
[INFO] [1;32mBUILD SUCCESS[m
[INFO] [1m------------------------------------------------------------------------[m
[INFO] Total time:  3.886 s
[INFO] Finished at: 2025-09-14T12:05:42+05:30
[INFO] [1m------------------------------------------------------------------------[m