Check an replace null values in multiple variables java

Question

I'm trying to find an easy way to perform multiple null checks/ replacements in multiple variables in Java.

I have an object with about 20 String variables. In the constructor I want to check if any of the variable values are null. If they are null I want to replace them with an empty String. I could perform a series of if statements but I feel like there must be a cleaner way to do this.

Answer 1

Unless you want to resort to reflection (which I strongly discourage) your best bet is probably to create a helper method (return s == null ? "" : s) and do

field1 = nullToEmpty(field1);
field2 = nullToEmpty(field2);
...

If you already depend on Apache Commons or Guava you can use StringUtils.defaultString or Strings.nullToEmpty.

Answer 2

I agree with aioobe, using reflection is something you should avoid like the plague. But if you are blessed with a project where for example you have to mock a REST interface manually and the objects that come via this interface have tons of Integer, String, Double etc. inside I think you have no other choice.

Here is a generic method that replaces all null pointers it can find in an object with its scalar default values, fills String fields with an empty string and does so recursively if the objects it finds have a parameterless default constructor. Hope this helps other people in the same situation as well.

static void fillNullObjects(Object object) {
    Field[] fields = object.getClass().getDeclaredFields();
    for (Field field : fields) {
        try {
            field.setAccessible(true);
            if (field.get(object) != null) {
                continue;
            }
            else if (field.getType().equals(Integer.class)) {
                field.set(object, 0);
            }
            else if (field.getType().equals(String.class)) {
                field.set(object, "");
            }
            else if (field.getType().equals(Boolean.class)){
                field.set(object, false);
            }
            else if (field.getType().equals(Character.class)) {
                field.set(object, '\u0000');
            }
            else if (field.getType().equals(Byte.class)) {
                field.set(object, (byte) 0);
            }
            else if (field.getType().equals(Float.class)) {
                field.set(object, 0.0f);
            }
            else if (field.getType().equals(Double.class)) {
                field.set(object, 0.0d);
            }
            else if (field.getType().equals(Short.class)) {
                field.set(object, (short) 0);
            }
            else if (field.getType().equals(Long.class)) {
                field.set(object, 0L);
            }
            else if (field.getType().getDeclaredFields().length > 0){
                for (Constructor<?> constructor : field.getClass().getConstructors()) {
                    if (constructor.getParameterTypes().length == 0) {
                        field.set(object, constructor.newInstance());
                        fillNullObjects(field.get(object));
                    }
                }
            }
       } catch (IllegalAccessException | InstantiationException | InvocationTargetException e) {
            e.printStackTrace();
        }
    }
}