How to get the fields in an Object via reflection

Question

I have an object  basically a VO  in Java and I don t know its type  I need to get values which are not null in that object    How can this be done

User · Answer

Here s a quick and dirty method that does what you want in a generic way  You ll need to add exception handling and you ll probably want to cache the BeanInfo types in a weakhashmap   public Map lt String  Object gt  getNonNullProperties final Object thingy        final Map lt String  Object gt  nonNullProperties   new TreeMap lt String  Object gt         try           final BeanInfo beanInfo   Introspector getBeanInfo thingy                  getClass             for  final PropertyDescriptor descriptor   beanInfo                  getPropertyDescriptors                  try                   final Object propertyValue   descriptor getReadMethod                            invoke thingy                   if  propertyValue    null                        nonNullProperties put descriptor getName                                propertyValue                                   catch  final IllegalArgumentException e                       handle this please               catch  final IllegalAccessException e                       and this also               catch  final InvocationTargetException e                       and this  too                               catch  final IntrospectionException e               do something sensible here           return nonNullProperties      See these references    BeanInfo  JavaDoc  Introspector getBeanInfo class   JavaDoc  Introspection  Sun Java Tutorial

User · Answer

You can use Class getDeclaredFields   to get all declared fields of the class  You can use Field get   to get the value    In short   Object someObject   getItSomehow    for  Field field   someObject getClass   getDeclaredFields          field setAccessible true      You might want to set modifier to public first      Object value   field get someObject        if  value    null            System out println field getName           value             To learn more about reflection  check the Sun tutorial on the subject     That said  the fields does not necessarily all represent properties of a VO  You would rather like to determine the public methods starting with get or is and then invoke it to grab the real property values   for  Method method   someObject getClass   getDeclaredMethods          if  Modifier isPublic method getModifiers             amp  amp  method getParameterTypes   length    0          amp  amp  method getReturnType      void class          amp  amp   method getName   startsWith  get      method getName   startsWith  is                    Object value   method invoke someObject           if  value    null                System out println method getName           value                         That in turn said  there may be more elegant ways to solve your actual problem  If you elaborate a bit more about the functional requirement for which you think that this is the right solution  then we may be able to suggest the right solution  There are many  many tools available to massage javabeans

User · Answer

I ve an object  basically a VO  in   Java and I don t know its type  I need to get values which are not null in that object     Maybe you don t necessary need reflection for that -- here is a plain OO design that might solve your problem    Add an interface Validation which expose a method validate which checks the fields and return whatever is appropriate   Implement the interface and the method for all VO   When you get a VO  even if it s concrete type is unknown  you can typecast it to Validation and check that easily    I guess that you need the field that are null to display an error message in a generic way  so that should be enough  Let me know if this doesn t work for you for some reason

[java] How to get the fields in an Object via reflection?

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