Java: How to update some of POJO fields according to a given map of values?

Question

I need to update several POJO fields according to a map which holds only the changes.

For example (loosely coded) :

Class MyClass{

   public MyClass(a,b,c);

   private int a;
   private int b;
   private int c;
}

int main(){
  Map<String, String> keyValueMap = new HashMap<>();

  MyClass obj = new MyClass(1,2,3);
  keyValueMap.put("c", 6);
  keyValueMap.put("b", 4);

  //Update only b and c values of obj:
  updateObj(obj, keyValueMap);

  keyValueMap.put("a", 5);
  keyValueMap.put("b", 7);

  //Update only a and b values of obj:
  updateObj(obj, keyValueMap);
}

void updateObj(MyClass obj, Map<String, String> keyValueMap){

 for (Map.Entry<String,String> entry : keyValueMap.entrySet())  
      if(entry.getKey().equals("a")
        obj.setA(entry.getValue();
      if(entry.getKey().equals("b")
        obj.setB(entry.getValue();
      if(entry.getKey().equals("c")
        obj.setC(entry.getValue();
  }
}

Is there a better method to implement updateObj() apart of a complete if's chain?

Thank you all.

Maybe reflection API will help You with this? https://stackoverflow.com/questions/24094871/set-field-value-with-reflection — PastorPL, May 05 '20 at 06:58
Reflection is what you need. May you find this article usefull : https://crunchify.com/create-simple-pojo-and-multiple-java-reflection-examples/ , as I did. — Marcellin Wabo, May 05 '20 at 07:05

score 1 · Answer 1 · answered May 05 '20 at 07:15

Example code (update method):

static void updateObj(MyClass obj, Map<String, Integer> keyValueMap) {
        try {
            Field declaredField =  null;
            for(String key:keyValueMap.keySet()) {
                declaredField = MyClass.class.getDeclaredField(key);
                boolean accessible = declaredField.isAccessible();
                declaredField.setAccessible(true);
                declaredField.set(obj, keyValueMap.get(key));
                declaredField.setAccessible(accessible);
            }
        } catch (NoSuchFieldException | IllegalAccessException e) {
            e.printStackTrace();
        }

    }

Itamar Kerbel · Accepted Answer · 2020-05-05T07:37:00.063

1

You can use Java reflection to do what you want to do:

static void updateObj(Main obj, Map<String, Integer> keyValueMap){
    try {
        for (Map.Entry<String,Integer> entry : keyValueMap.entrySet()) {
            Field field = Main.class.getField(entry.getKey());
            field.setAccessible(true)
            field.set(obj,entry.getValue());
        }
    } catch(Exception e) {}
}

edited May 05 '20 at 07:37

answered May 05 '20 at 07:18

Itamar Kerbel

2,508
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Toda Itamar. I used getDeclaredField() instead of getField() to fully use your solution. – dushkin May 05 '20 at 08:12

score 0 · Answer 3 · answered May 05 '20 at 07:19

You can simply use Reflection API. Here is an example based on your code:

public class Main1 {
    public static void main(String[] args) {
        Map<String, String> keyValueMap = new HashMap<>();

        MyClass obj = new MyClass(1,2,3);
        keyValueMap.put("c", "6");
        keyValueMap.put("b", "4");

        System.out.println(obj);

        //Update only b and c values of obj:
        updateObj(obj, keyValueMap);

        System.out.println(obj);

        keyValueMap.put("a", "5");
        keyValueMap.put("b", "7");

        //Update only a and b values of obj:
        updateObj(obj, keyValueMap);

        System.out.println(obj);
    }

    private static void updateObj(MyClass myClass, Map<String, String> map) {
        Class<MyClass> clazz = MyClass.class;
        for (String fieldName: map.keySet()) {
            try {
                Field field = clazz.getDeclaredField(fieldName);
                field.setAccessible(true);
                field.set(myClass, Integer.parseInt(map.get(fieldName)));
            } catch (NoSuchFieldException ex) {
                System.out.println("No Such Field Found!!!");
            } catch (IllegalAccessException ex) {
                System.out.println(ex);
            }
        }
    }
}

class MyClass {
    private int a;
    private int b;
    private int c;

    public MyClass(int a, int b, int c) {
        this.a = a;
        this.b = b;
        this.c = c;
    }

    @Override
    public String toString() {
        return "MyClass{" + "a=" + a + ", b=" + b + ", c=" + c + '}';
    }
}

Note: Do not forget to use field.setAccessible(true); for private members; Otherwise you will get an IllegalAccessException.

Java: How to update some of POJO fields according to a given map of values?

3 Answers3