Using Mapstruct we can create mapping of map objects using @MapMapping annotation. Other rules of mapping are same as we”ve seen so far.

Syntax

@Mapper
public interface UtilityMapper {
   @MapMapping(valueDateFormat = "dd.MM.yyyy")
   Map<String, String> getMap(Map<Long, GregorianCalendar> source);
}

Following example demonstrates the same.

Example

Open project mapping as updated in Mapping List chapter in Eclipse.

Create UtilityMapper.java with following code −

UtilityMapper.java

package com.tutorialspoint.mapper;

import java.util.GregorianCalendar;
import java.util.Map;
import org.mapstruct.MapMapping;
import org.mapstruct.Mapper;

@Mapper
public interface UtilityMapper {
   @MapMapping(valueDateFormat = "dd.MM.yyyy")
   Map<String, String> getMap(Map<Long, GregorianCalendar> source);
}

Create UtilityMapperTest.java with following code −

UtilityMapperTest.java

package com.tutorialspoint.mapping;

import static org.junit.jupiter.api.Assertions.assertEquals;
import java.util.GregorianCalendar;
import java.util.HashMap;
import java.util.Map;
import org.junit.jupiter.api.Test;
import org.mapstruct.factory.Mappers;
import com.tutorialspoint.mapper.UtilityMapper;

public class UtilityMapperTest {
   private UtilityMapper utilityMapper = Mappers.getMapper(UtilityMapper.class);

   @Test
   public void testMapMapping() {
      Map<Long, GregorianCalendar> source = new HashMap<>();
      source.put(1L, new GregorianCalendar(2015, 3, 5));

      Map<String, String> target = utilityMapper.getMap(source);
      assertEquals("05.04.2015", target.get("1"));		
   }
}

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] --- maven-surefire-plugin:2.12.4:test (default-test) @ mapping ---
[INFO] Surefire report directory: mvnmappingtargetsurefire-reports

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running com.tutorialspoint.mapping.CarMapperTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.327 sec
Running com.tutorialspoint.mapping.DeliveryAddressMapperTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.001 sec
Running com.tutorialspoint.mapping.StudentMapperTest
Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.001 sec
Running com.tutorialspoint.mapping.UtilityMapperTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.001 sec

Results :

Tests run: 5, Failures: 0, Errors: 0, Skipped: 0
...