Get all Fields of class including the ones which are other classes

Question

Based on the question Get all Fields of class hierarchy I want to ask the following using -as I suppose- reflection. Lets suppose I have the following Class

package com.foo.bar

public class Employee{ 

    private String firstName; 

    private String id; 

    private Address address; 

// Getters and Setters follow

}

and the Class Address is

package com.foo.bar

public class Address{ 

    private String street; 

    private String streetNum; 

// Getters and Setters follow

}

I want to populate a list with all fields from all classes originating from Employee in the form

Employee.firstName
Employee.id
Employee.Address.street
Employee.Address.streetNum

All the classes I am interested in are either in the same package as Employee class ex com.foo.bar or in specific packages that I am already aware of.

My original thinking is to somehow get all the fields, get the packages from the class of the fields and somehow drill down in multiple levels to get the information I need.

Any help is greatly appreciated.

Thanks

ps. I am using JDK 7

@Seelenvirtuose Of course I could be wrong. This is my initial approach. Any other approach is welcome — Alexius DIAKOGIANNIS, Oct 12 '18 at 09:11
@AlexiusDiakogiannis your plan sounds good to me. Where are you stuck and what have you tried? — jokster, Oct 12 '18 at 09:19
@Seelenvirtuose I am trying to populate the list I am describing in the example above. In my project there are hundreds of similar entities with dozens of fields that fall to this case. The reason I want to populate this list is out of the scope of the question. — Alexius DIAKOGIANNIS, Oct 12 '18 at 09:20
Well ... Your "question" does not explain enough for answering it. What list? What do you mean with "populate"? So ... again ... what exactly are you trying to do? What does not work? And why does it not work? — Seelenvirtuose, Oct 12 '18 at 09:22
@jokster Thanks :) My initial problem is that I cannot know how deep this may go. I am trying to create a recursive function but my code now is all blood and tears so I cannot paste it — Alexius DIAKOGIANNIS, Oct 12 '18 at 09:33
@Seelenvirtuose Please read my question again, I think it is clear enough. :) — Alexius DIAKOGIANNIS, Oct 12 '18 at 09:35

score 2 · Answer 1 · answered Oct 12 '18 at 09:24

Here's a simple way that inspects class declared fields:

static Set<Field> getFields(Class<?> cls) {
    Set<Field> set = new HashSet<>();

    for (Field f : cls.getDeclaredFields()) {
        set.add(f);

        //a filter to avoid standard classes. Update accordingly
        if (f.getType().getName().startsWith("com.foo.bar")) {
            set.addAll(getFields(f.getType()));
        }
    }

    return set;
}

And a simple call:

public static void main(String[] args) {
    Set<Field> all = getFields(Employee.class);
    for (Field f : all) {
        System.out.println(String.format("%s.%s", 
             f.getDeclaringClass().getSimpleName(), f.getName()));
    }
}

With your example classes, the above prints:

Employee.firstName
Employee.address
Address.street
Address.streetNum
Employee.id

And here's an equivalent Java8+ version (only inspecting 2 levels of the tree):

Stream.of(Employee.class.getDeclaredFields())
        .flatMap(f -> Stream.concat(Stream.of(f), 
                Stream.of(f.getType().getDeclaredFields())))
        .filter(f -> f.getDeclaringClass()
                      .getPackage()
                      .getName()
                      .startsWith("com.foo.bar"))
        .map(f -> String.format("%s.%s", 
                    f.getDeclaringClass().getSimpleName(), f.getName()))
        .forEach(System.out::println);

The filter above is used to limit inspected classes to those in the current package (change accordingly). Without it, one gets String's fields, etc.

You may also want to call distinct() to remove duplicates if they may show up.

score 1 · Answer 2 · answered Oct 16 '18 at 14:18

Thank you all, I created a recursive function that does the trick. The function is the following

private void getClassFields(final Class c,final List<String> fields) throws ClassNotFoundException {
    for(Field f : c.getDeclaredFields()){
        if(f.getType().getName().contains("foo.bar")){
            getClassFields(Class.forName(f.getType().getName()),fields);
        }else {
            fields.add(f.getName());
        }
    }
}

Get all Fields of class including the ones which are other classes

2 Answers2