Finding field exist or not through reflection

Question

My class structure is as follows

   ClassA{}
   ClassB extends ClassA{}
   ClassC extends ClassB{}

these classes contains a field say name, I did not know in which class this field is present, i have a string name and object of ClassC. I am using reflection to get the field my code is

  private static Field getType(Object obj,String fieldName){

            Field type = null;
            try
            {
                    type = obj.getClass().getDeclaredField(fieldName);
            } 
            catch (NoSuchFieldException e) {
                    try
                    {
                            type = obj.getClass().getSuperclass().getDeclaredField(fieldName);
                    }
                    catch (NoSuchFieldException e1) {
                            e.printStackTrace();
                    }
            } catch (SecurityException e) {
                    e.printStackTrace();
            }
            return type;
    }

But it will check for field only in the current class and its super class, if i want to check the field till top level class, I need to keep write try catch blocks. i think it is not the correct way. Is there any alternate solution for this? Thanks in advance

See it in http://stackoverflow.com/questions/7324991/see-if-field-exists-in-class — Venkat, Apr 17 '17 at 11:55

score 5 · Accepted Answer · answered Dec 05 '13 at 11:36

I think that you are trying to do something like:

   Class cls = obj.getClass();        
    for (Class acls = cls; acls != null; acls = acls.getSuperclass()) {
      try {
        Field field = acls.getDeclaredField(fieldName);
        // if not found exception thrown
        // else return field
        return field;
      } catch (NoSuchFieldException ex) {
        // ignore
      }
    }

score 2 · Answer 2 · answered Dec 05 '13 at 11:29

2

Use getField instead of getDeclaredField. It will look for the field in interfaces and parent classes recursively if it's not found immediately in the given class.

answered Dec 05 '13 at 11:29

Joni

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Thanks for reply, but all my fields are private so i can not get the fields using getfields i guess, please correct me if i am wrong – Siva Dec 05 '13 at 11:30
If your fields are private, then the subclass would not have inherited them anyway. – NickJ Dec 05 '13 at 11:32
Correct: `getField` only gets public fields. – Joni Dec 05 '13 at 11:32
@NickJ: you are write, So if i use getField, it is throwing nosuchfield exception, though my class has the field name(private) – Siva Dec 05 '13 at 11:35

score 2 · Answer 3 · answered Dec 05 '13 at 11:36

What about wrapping try block into the loop:

Field type = null;  
Class clz = object.getClass();
while(clz != null || clz != Object.class) {
    try
    {
        type = clz.getDeclaredField(fieldName);
        break;
    } catch (NoSuchFieldException e) {
        clz = object.getSuperclass();
    } 
}
return type;

score 0 · Answer 4 · answered Dec 05 '13 at 11:50

You can use a while (or any other similar) loop to keep scanning down until you find a match.

private static Field getType(Object obj,String fieldName){

Field type = null;
Class clazz = obj.getClass();
while (type==null && clazz!=null) {
   try {
       type = obj.getClass().getDeclaredField(fieldName);
   } catch (NoSuchFieldException e) {
       clazz = clazz.getSuperClass();
   } catch (SecurityException e) {
       e.printStackTrace();
       return null;
   }
   return type;
}

It would be better to check if the field exists rather than using the exception to control flow but this will work.

score 0 · Answer 5 · answered Aug 17 '17 at 14:53

Try this it will take care of superclass and nested properties.

public static boolean isFieldExist(Class<?> clazz, String property) {
String[] fields = property.split("\\.");

    try {
        Field file = clazz.getDeclaredField(fields[0]);

        if (fields.length > 1) {
            return isFieldExist(file.getType(), property.substring(property.indexOf('.') + 1, property.length()));
        }

        return true;
    } catch (NoSuchFieldException | SecurityException e) {
        if (clazz.getSuperclass() != null) {
            return isFieldExist(clazz.getSuperclass(), property);
        }

        return false;
    }
}

Finding field exist or not through reflection

5 Answers5