Copy all values from fields in one class to another through reflection

Question

I have a class which is basically a copy of another class   public class A     int a    String b     public class CopyA     int a    String b      What I am doing is putting values from class A into CopyA before sending CopyA through a webservice call  Now I would like to create a reflection-method that basically copies all fields that are identical  by name and type  from class A to class CopyA   How can I do this   This is what I have so far  but it doesn t quite work  I think the problem here is that I am trying to set a field on the field I am looping through   private  lt T extends Object  Y extends Object gt  void copyFields T from  Y too         Class lt   extends Object gt  fromClass   from getClass        Field   fromFields   fromClass getDeclaredFields         Class lt   extends Object gt  tooClass   too getClass        Field   tooFields   tooClass getDeclaredFields         if  fromFields    null  amp  amp  tooFields    null            for  Field tooF   tooFields                logger debug  toofield name  0 and type  1   tooF getName    tooF getType   toString                 try                      Check if that fields exists in the other method                 Field fromF   fromClass getDeclaredField tooF getName                     if  fromF getType   equals tooF getType                           tooF set tooF  fromF                                   catch  SecurityException e                       TODO Auto-generated catch block                 e printStackTrace                  catch  NoSuchFieldException e                       TODO Auto-generated catch block                 e printStackTrace                  catch  IllegalArgumentException e                       TODO Auto-generated catch block                 e printStackTrace                  catch  IllegalAccessException e                       TODO Auto-generated catch block                 e printStackTrace                                     I am sure there must be someone that has already done this somehow

User · Answer

I solved the above problem in Kotlin that works fine for me for my Android Apps Development:

 object FieldMapper {

fun <T:Any> copy(to: T, from: T) {
    try {
        val fromClass = from.javaClass

        val fromFields = getAllFields(fromClass)

        fromFields?.let {
            for (field in fromFields) {
                try {
                    field.isAccessible = true
                    field.set(to, field.get(from))
                } catch (e: IllegalAccessException) {
                    e.printStackTrace()
                }

            }
        }
    } catch (e: Exception) {
        e.printStackTrace()
    }

}

private fun getAllFields(paramClass: Class<*>): List<Field> {

    var theClass:Class<*>? = paramClass
    val fields = ArrayList<Field>()
    try {
        while (theClass != null) {
            Collections.addAll(fields, *theClass?.declaredFields)
            theClass = theClass?.superclass
        }
    }catch (e:Exception){
        e.printStackTrace()
    }

    return fields
}

}

User · Answer

This is a late post  but can still be effective for people in future    Spring provides a utility BeanUtils copyProperties srcObj  tarObj  which copies values from source object to target object when the names of the member variables of both classes are the same    If there is a date conversion   eg  String to Date   null  would be copied to the target object  We can then  explicitly set the values of the date as required    The BeanUtils from Apache Common throws an error when there is a mismatch of data-types  esp  conversion to and from Date   Hope this helps

User · Answer

I think you can try dozer  It has good support for bean to bean conversion  Its also easy to use  You can either inject it into your spring application or add the jar in class path and its done   For an example of your case      DozerMapper mapper   new DozerMapper    A a  new A    CopyA copyA   new CopyA    a set       set fields of a  mapper map a copyOfA      will copy all fields from a to copyA

User · Answer

I didn t want to add dependency to another JAR file because of this  so wrote something which would suit my needs  I follow the convention of fjorm https   code google com p fjorm  which means that my generally accessible fields are public and that I don t bother to write setters and getters   in my opinion code is easier to manage and more readable actually   So I wrote something  it s not actually much difficult  which suits my needs  assumes that the class has public constructor without args  and it could be extracted into utility class    public Effect copyUsingReflection         Constructor constructorToUse   null      for  Constructor constructor   this getClass   getConstructors            if  constructor getParameterTypes   length    0            constructorToUse   constructor          constructorToUse setAccessible true                     if  constructorToUse    null          try           Effect copyOfEffect    Effect  constructorToUse newInstance            for  Field field   this getClass   getFields                try               Object valueToCopy   field get this                 if it has field of the same type  Effect in this case   call the method to copy it recursively             if  valueToCopy instanceof Effect                  valueToCopy     Effect  valueToCopy  copyUsingReflection                                TODO add here other special types of fields  like Maps  Lists  etc              field set copyOfEffect  valueToCopy               catch  IllegalArgumentException   IllegalAccessException ex                Logger getLogger Effect class getName    log Level SEVERE  null  ex                                 return copyOfEffect          catch  InstantiationException   IllegalAccessException   IllegalArgumentException   InvocationTargetException ex            Logger getLogger Effect class getName    log Level SEVERE  null  ex                     return null

User · Answer

If you have spring in the dependencies you can also use org springframework beans BeanUtils    https   docs spring io spring docs current javadoc-api org springframework beans BeanUtils html

User · Answer

The first argument to tooF set   should be the target object  too   not the field  and the second argument should be the value  not the field the value comes from   To get the value  you need to call fromF get   -- again passing in a target object  in this case from     Most of the reflection API works this way  You get Field objects  Method objects  and so on from the class  not from an instance  so to use them  except for statics  you generally need to pass them an instance

User · Answer

Here is a working and tested solution  You can control the depth of the mapping in the class hierarchy   public class FieldMapper        public static void copy Object from  Object to  throws Exception           FieldMapper copy from  to  Object class              public static void copy Object from  Object to  Class depth  throws Exception           Class fromClass   from getClass            Class toClass   to getClass            List lt Field gt  fromFields   collectFields fromClass  depth           List lt Field gt  toFields   collectFields toClass  depth           Field target          for  Field source   fromFields                if   target   findAndRemove source  toFields      null                    target set to  source get from                                       private static List lt Field gt  collectFields Class c  Class depth            List lt Field gt  accessibleFields   new ArrayList lt  gt             do               int modifiers              for  Field field   c getDeclaredFields                      modifiers   field getModifiers                    if   Modifier isStatic modifiers   amp  amp  Modifier isPublic modifiers                         accessibleFields add field                                               c   c getSuperclass              while  c    null  amp  amp  c    depth           return accessibleFields             private static Field findAndRemove Field field  List lt Field gt  fields            Field actual          for  Iterator lt Field gt  i   fields iterator    i hasNext                   actual   i next                if  field getName   equals actual getName                     amp  amp  field getType   equals actual getType                       i remove                    return actual                                  return null

User · Answer

Why don t you use gson library https   github com google gson  you just convert the Class A to json string  Then convert jsonString to you subClass  CopyA   using below code   Gson gson  new Gson    String tmp   gson toJson a   CopyA myObject   gson fromJson tmp CopyA class

User · Answer

Orika s is simple faster bean mapping framework because it does through byte code generation  It does nested mappings and mappings with different names  For more details  please check here Sample mapping may look complex  but for complex scenarios it would be simple   MapperFactory factory   new DefaultMapperFactory Builder   build    mapperFactory registerClassMap mapperFactory classMap Book class BookDto class  byDefault   toClassMap     MapperFacade mapper   factory getMapperFacade    BookDto bookDto   mapperFacade map book  BookDto class

User · Answer

Spring has a built in BeanUtils copyProperties method  But it doesn t work with classes without getters setters  JSON serialization deserialization can be another option for copying fields  Jackson can be used for this purpose  If you are using Spring In most cases Jackson is already in your dependency list   ObjectMapper mapper       new ObjectMapper   configure DeserializationFeature FAIL ON UNKNOWN PROPERTIES  false   Clazz        copyObject   mapper readValue mapper writeValueAsString sourceObject   Clazz class

User · Answer

Without using BeanUtils or Apache Commons public static  lt T1 extends Object  T2 extends Object gt   void copy T1      origEntity  T2 destEntity  throws IllegalAccessException  NoSuchFieldException       Field   fields   origEntity getClass   getDeclaredFields        for  Field field   fields           origFields set destEntity  field get origEntity

User · Answer

BeanUtils will only copy public fields and is a bit slow  Instead go with getter and setter methods   public Object loadData  RideHotelsService object a  throws Exception           Method   gettersAndSetters   object a getClass   getMethods             for  int i   0  i  lt  gettersAndSetters length  i                      String methodName   gettersAndSetters i  getName                    try                    if methodName startsWith  get                          this getClass   getMethod methodName replaceFirst  get    set     gettersAndSetters i  getReturnType     invoke this  gettersAndSetters i  invoke object a  null                             else if methodName startsWith  is                                  this getClass   getMethod methodName replaceFirst  is    set      gettersAndSetters i  getReturnType      invoke this  gettersAndSetters i  invoke object a  null                                                catch  NoSuchMethodException e                           TODO  handle exception                  catch  IllegalArgumentException e                           TODO  handle exception                                       return null

User · Answer

If you don t mind using a third party library  BeanUtils from Apache Commons will handle this quite easily  using copyProperties Object  Object

User · Answer

public static  lt T gt  void copyAvalableFields  NotNull T source   NotNull T target  throws IllegalAccessException       Field   fields   source getClass   getDeclaredFields        for  Field field   fields            if   Modifier isStatic field getModifiers                     amp  amp   Modifier isFinal field getModifiers                   field set target  field get source                        We read all the fields of the class  Filter non-static and non-final fields from the result  But there may be an error accessing non-public fields  For example  if this function is in the same class  and the class being copied does not contain public fields  an access error will occur  The solution may be to place this function in the same package or change access to public or in this code inside the loop call     field setAccessible  true    what will make the fields available

User · Answer

My solution   public static  lt T  gt  void copyAllFields T to  T from            Class lt T gt  clazz    Class lt T gt   from getClass               OR             Class lt T gt  clazz    Class lt T gt   to getClass            List lt Field gt  fields   getAllModelFields clazz            if  fields    null                for  Field field   fields                    try                       field setAccessible true                       field set to field get from                      catch  IllegalAccessException e                        e printStackTrace                                                     public static List lt Field gt  getAllModelFields Class aClass        List lt Field gt  fields   new ArrayList lt  gt         do           Collections addAll fields  aClass getDeclaredFields             aClass   aClass getSuperclass          while  aClass    null       return fields

User · Answer

public  lt T1 extends Object  T2 extends Object gt  void copy T1 origEntity  T2 destEntity            DozerBeanMapper mapper   new DozerBeanMapper            mapper map origEntity destEntity            lt dependency gt               lt groupId gt net sf dozer lt  groupId gt               lt artifactId gt dozer lt  artifactId gt               lt version gt 5 4 0 lt  version gt           lt  dependency gt

User · Answer

Dozer  UPDATE Nov 19 2012  There s now a new ModelMapper project too

User · Answer

Mladen s basic idea worked  thanks   but needed a few changes to be robust  so I contributed them here   The only place where this type of solution should be used is if you want to clone the object  but can t because it is a managed object   If you are lucky enough to have objects that all have 100  side-effect free  setters for all fields   you should definitely use the BeanUtils option instead    Here  I use lang3 s utility methods to simplify the code  so if you paste it  you must first import Apache s lang3 library   Copy code  static public  lt X extends Object gt  X copy X object  String    skipFields            Constructor constructorToUse   null          for  Constructor constructor   object getClass   getConstructors                  if  constructor getParameterTypes   length    0                    constructorToUse   constructor                  constructorToUse setAccessible true                   break                                  if  constructorToUse    null                throw new IllegalStateException object     must have a zero arg constructor in order to be copied                      X copy          try               copy    X  constructorToUse newInstance                 for  Field field   FieldUtils getAllFields object getClass                       if  Modifier isStatic field getModifiers                           continue                                       Avoid the fields that you don t want to copy  Note  if you pass in  id   it will skip any field with  id  in it  So be careful                  if  StringUtils containsAny field getName    skipFields                         continue                                     field setAccessible true                    Object valueToCopy   field get object                     TODO add here other special types of fields  like Maps  Lists  etc                  field set copy  valueToCopy                             catch  InstantiationException   IllegalAccessException   IllegalArgumentException                   InvocationTargetException e                throw new IllegalStateException  Could not copy     object  e                     return copy

[java] Copy all values from fields in one class to another through reflection

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