copy object content to other object of other type

Question

I have one class with name OldClass and one class with name NewClass. Both classes have exact the same fields. Can I copy the values from OldClass to NewClass without calling getters and setters manually for about 100 fields per class (200 such class pairs).

Answer 1

Yes you can. I suggest you take a look at MapStruct. It should be a perfect fit for your requirements.

Just define a mapper interface for your class and let MapStruct create the implementation.

Take a look at http://mapstruct.org/

Answer 2

Just serialize the object A and deserialize to ObjectB.

ObjectMapper mapper = new ObjectMapper();
String jsonResult = mapper.writerWithDefaultPrettyPrinter()
  .writeValueAsString(objectA);

TypeReference<ObjectB> typeRef 
  = new TypeReference<ObjectB>() {};
ObjectB objectB = mapper.readValue(jsonInput, typeRef);

Answer 3

I'd suggest to use Commons BeanUtils for this task:

BeanUtils.copyProperties(destObj, srcObj);

For this to work both objects must be Java Beans, which boils down to having getters and setters that follow the bean naming convention and a no-args constructor.

Basic example:

import org.apache.commons.beanutils.BeanUtils;

public class BeanUtilsTest {

    public static final class Bean1 {
        private String name;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }
    }

    public static final class Bean2 {
        private String name;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }
    }

    public static void main(String[] args) throws Exception {
        final Bean1 bean1 = new Bean1();
        final Bean2 bean2 = new Bean2();

        bean1.setName("");
        BeanUtils.copyProperties(bean2, bean1);
        System.out.println("'" + bean2.getName() + "'"); // prints ''

        bean1.setName(null);
        BeanUtils.copyProperties(bean2, bean1);
        System.out.println("'" + bean2.getName() + "'"); // prints 'null'
    }
}

Answer 4

Pure Java SDK Solution:

You can use Java Reflection.

Compiling Example (assumes that field names and types are equal).

import java.lang.reflect.Field;

public class Test {

    public static void main(String[] args) throws Exception {
        final OldClass oldClass = new OldClass();
        oldClass.setA("foo");
        oldClass.setB("bar");

        final NewClass newClass = new NewClass();
        copyAllFields(oldClass, newClass);

        System.out.println(newClass); // Prints: NewClass [a=foo, b=bar]
    }

    private static void copyAllFields(OldClass pOldClass, NewClass pNewClass) throws Exception {
        final Field[] fields = pOldClass.getClass().getDeclaredFields();

        for (Field fieldOldClass : fields) {
            fieldOldClass.setAccessible(true);
            final Object fieldValue = fieldOldClass.get(pOldClass);

            final Field fieldNewClass = pNewClass.getClass().getDeclaredField(fieldOldClass.getName());
            fieldNewClass.setAccessible(true);
            fieldNewClass.set(pNewClass, fieldValue);
        }

    }
}

NewClass.java

public class NewClass {
    private String a;
    private String b;

    @Override
    public String toString() {
        return "NewClass [a=" + a + ", b=" + b + "]";
    }
}

OldClass.java

public class OldClass {
    private String a;
    private String b;

    @Override
    public String toString() {
        return "OldClass [a=" + a + ", b=" + b + "]";
    }

    public void setA(String pA) {
        a = pA;
    }

    public void setB(String pB) {
        b = pB;
    }
}