Java recommended solution for deep cloning copying an instance

Question

I m wondering if there is a recommended way of doing deep clone copy of instance in java   I have 3 solutions in mind  but I can have miss some   and I d like to have your opinion  edit  include Bohzo propositon and refine question  it s more about deep cloning than shallow cloning   Do it yourself   code the clone by hand properties after properties and check that mutable instances are cloned too  pro  - control of what will be performed - quick execution cons  - tedious to write and maintain - bug prone  copy paste failure  missing property  reassigned mutable property    Use reflection   With your own reflection tools or with an external helper  like jakarta common-beans  it is easy to write a generic copy method that will do the job in one line  pro  - easy to write - no maintenance cons  - less control of what happens - bug prone with mutable object if the reflection tool does not clone sub objects too - slower execution  Use clone framework   Use a framework that do it for you  like   commons-lang SerializationUtils Java Deep Cloning Library Dozer Kryo  pro  - same as reflection - more control over what will be exactly be cloned  cons  - every mutable instance is fully cloned  even at the end of the hierarchy - could be very slow to execute  Use bytecode instrumentation to write clone at runtime  javassit  BCEL or cglib might be use to generate a dedicated cloner as fast as one hand writed  Someone knows a lib using one of these tools for this purpose    What I have missed here   Which one would you recommend    Thanks

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Use XStream toXML fromXML in memory   Extremely fast and has been around for a long time and is going strong  Objects don t need to be Serializable and you don t have use reflection  although XStream does    XStream can discern variables that point to the same object and not accidentally make two full copies of the instance  A lot of details like that have been hammered out over the years   I ve used it for a number of years and it is a go to  It s about as easy to use as you can imagine   new XStream   toXML myObj    or  new XStream   fromXML myXML    To clone   new XStream   fromXML new XStream   toXML myObj     More succinctly   XStream x   new XStream    Object myClone   x fromXML x toXML myObj

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For deep cloning implement Serializable on every class you want to clone like this  public static class Obj implements Serializable       public int a  b      public Obj int a  int b            this a   a          this b   b            And then use this function   public static Object deepClone Object object        try           ByteArrayOutputStream baOs   new ByteArrayOutputStream            ObjectOutputStream oOs   new ObjectOutputStream baOs           oOs writeObject object           ByteArrayInputStream baIs   new ByteArrayInputStream baOs toByteArray             ObjectInputStream oIs   new ObjectInputStream baIs           return oIs readObject              catch  Exception e            e printStackTrace            return null            like this  Obj newObject    Obj deepClone oldObject

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I d recommend the DIY way which  combined with a good hashCode   and equals   method should be easy to proof in a unit test

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I d suggest to override Object clone    call super clone   first and than call ref   ref clone   on all references that you want to have deep copied  It s more or less Do it yourself approach but needs a bit less coding

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For deep cloning  clones the entire object hierarchy     commons-lang SerializationUtils - using serialization - if all classes are in your control and you can force implementing Serializable  Java Deep Cloning Library - using reflection - in cases when the classes or the objects you want to clone are out of your control  a 3rd party library  and you can t make them implement Serializable  or in cases you don t want to implement Serializable    For shallow cloning  clones only the first level properties     commons-beanutils BeanUtils - in most cases  Spring BeanUtils - if you are already using spring and hence have this utility on the classpath    I deliberately omitted the  do-it-yourself  option - the API s above provide a good control over what to and what not to clone  for example using transient  or String   ignoreProperties   so reinventing the wheel isn t preferred

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Since version 2 07 Kryo supports shallow deep cloning   Kryo kryo   new Kryo    SomeClass someObject       SomeClass copy1   kryo copy someObject   SomeClass copy2   kryo copyShallow someObject     Kryo is fast  at the and of their page you may find a list of companies which use it in production

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For complicated objects and when performance is not significant i use gson to serialize the object to json text  then deserialize the text to get new object   gson which based on reflection will works in most cases  except that transient fields will not be copied and objects with circular reference with cause StackOverflowError   public static  lt ObjectType gt  ObjectType Copy ObjectType AnObject  Class lt ObjectType gt  ClassInfo        Gson gson   new GsonBuilder   create        String text   gson toJson AnObject       ObjectType newObject   gson fromJson text  ClassInfo       return newObject    public static void main String   args        MyObject anObject         MyObject copyObject   Copy o  MyObject class

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Depends   For speed  use DIY  For bulletproof  use reflection   BTW  serialization is not the same as refl  as some objects may provide overridden serialization methods  readObject writeObject  and they can be buggy

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Joshua Bloch s book has a whole chapter entitled  Item 10  Override Clone Judiciously  in which he goes into why overriding clone for the most part is a bad idea because the Java spec for it creates many problems     He provides a few alternatives    Use a factory pattern in place of a constructor        public static Yum newInstance Yum yum    Use a copy constructor        public Yum Yum yum      All of the collection classes in Java support the copy constructor  e g  new ArrayList l

[java] Java: recommended solution for deep cloning/copying an instance

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