Question

Can I write a generic method to trim all strings within an complex object (object containing other objects)? Should java reflection api be used to achieve this?Thanks.

I have provided a sample below. However in reality there could be multiple objects within objects. Each object might contain a collection of String or collection of other objects which may contain String. Is there a way to trim the Strings – ones directly with the objects and ones within collection.

public class School{
   private List<Course> courses;
   private List<Student> students;       
   // Getters and Setters
}

public class Course{
   private String name;
   private String xxx;
   private String yyy;
   private List<String> zzzList;
}

public class Student{
   private Map<String,String> xxx;
   private List<Course> courseList;
}

Answer 1

Yes, reflection is the way. Basically, you need to:

• get the class of the top level object (with [object].getClass())

• get all the fields of the object (with clazz.getFields() – beware, it works only with public fields)

• check if the field is String (either get field.getType() and check it’s a string, or do a field.get(the object) and a instanceof String)

• if it’s the case, replace the string in the object with the trimmed one, using field.set([your object],[trimmed string])

• if the field is an object but not a string, call your method recursively

That will do the trick.

—- just seen your update

Trimming strings in collection will be more tricky, since the strings are not exposed as public fields of the collection (List for example).

You will need something more clever, that will check if an object is an instance of List, or Map, or etc… (or a derived class!).
Main problem is also that java generics are done with erasing type at compile type. So you cannot know that your field is List[String] or List[Integer] or whatever. Every List[?] becomes List.

Still you can try to do it like that:

• if field type is List
• iterate through the list values
• if a value is instanceof String, you have to remove it from the list and insert in place the trimmed version
• if a value is an object, there you go again recursively with your method.

Not very interesting in real life samples, but more on a library side maybe.
Long way to go though!