Java - get a class attribute name when get Method is called

Question

Can anyone please clarify me, if it is possible to get a class attribute name when I call get/set method of the class in java.
I saw something on online that it is possible to get class attribute name using Reflection concept.

My situation:
Trying to write a method that checks the value of the attribute for null/empty and return the attribute name in case the attribute value is null/empty.

example:

Class:

public class MyClass {
  private appName;

  public void setAppName(String appName) {
  this.appName = appName;
  }

  public String getAppName() {
  return this.appName;
  }
}

Validation Method:

public String validateForNull(MyClass myclass) {
   String name = myclass.getAppName();
   if(name == null || name.isEmpty()) {
   return //here I want to return attributeName which will be "appName"
   }
}

I realized returning the constant string that represent attribute name will be lot easier and neat way for the approach. But I was wondering if I can do it as a generic way where validate method takes the class object and check all/specified attributes for null/empty and return attribute name in case null/empty value.

Thanks

It's not particularly clear to me what exactly you want, but if I understand anything, then this sounds like some sort of Bean Validation case. If I'm right, you can either directly use the bean validation API or look for ideas in one of its implementations. — M. Prokhorov
– M. Prokhorov, Commented Dec 21, 2017 at 15:51

Guillaume Barré · Accepted Answer · 2017-12-21 15:47:18Z

You can not get the name of the attribute calling a getter or setter.

By the way you have no guarantee that the method you invoke just set or return a simple attribute.

But you are right, you can, by reflection, get the values of the attributes for a given object.

   public String validateForNull(MyClass myclass) throws IllegalArgumentException, IllegalAccessException {
        // Get the attributes of the class
        Field[] fs = myclass.getClass().getFields();
        for(Field f : fs) {
            // make the attribute accessible if it's a private one
            f.setAccessible(true);

            // Get the value of the attibute of the instance received as parameter  
            Object value = f.get(myclass);
            if(value == null) {
                return f.getName();
            }
        }
        return null;
     }

Doing something like this will require a testing more complete than just if(value == null) because I imagine that you can have attributes of several types and each type will have a specific validation.

If you decide to go this way you can use an annotation to identify the attributes to validate and the use :

Annotation[] ans =  f.getAnnotations();

To check if your annotation is present on the attribute and thus validate only the required fields

VGR · Accepted Answer · 2017-12-21 16:00:11Z

2

It’s best to avoid reflection. Instead of trying to find the name automatically, pass it as an argument:

public String validateForNull(String attributeValue,
                              String attributeName) {

    if (attributeValue == null || attributeValue.isEmpty()) {
        return attributeName;
    }
    return null;
}

// ...

String emptyAttribute =
    validateForNull(myclass.getAppName(), "appName");

answered Dec 21, 2017 at 16:00

VGR

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