java io InvalidClassException local class incompatible

Question

I created client and server and then added a class in client side for serializing purposes  then simply just went to the folder of the client in my hard drive and copy paste it to the server correponding location  both classname class and classname java respectively  It worked well in my own laptop but when I wanted to continue my work on other system   when I opened the projects folders and after client tries to connect to the server  the following error appears  Exception in thread  quot main quot  java io InvalidClassException  projectname clasname  local class incompatible  stream classdesc serialVersionUID   -6009442170907349114  local class serialVersionUID   6529685098267757690     at java io ObjectStreamClass initNonProxy ObjectStreamClass java 562      at java io ObjectInputStream readNonProxyDesc ObjectInputStream java 1582      at java io ObjectInputStream readClassDesc ObjectInputStream java 1495      at java io ObjectInputStream readOrdinaryObject ObjectInputStream java 1731      at java io ObjectInputStream readObject0 ObjectInputStream java 1328      at java io ObjectInputStream readObject ObjectInputStream java 350   What is going on  Is it because I ran the program with an older version of the IDE  EDIT import java io Serializable  import java net URL   public class KeyAdr implements Serializable     private static final long serialVersionUID   6529685098267757690L     public URL adr    public String key

User · Answer

One thing that could have happened    1  you create your serialized data with a given library A  version X  2  you then try to read this data with the same library A  but version Y    Hence  at compile time for the version X  the JVM will generate a first Serial ID  for version X  and it will do the same with the other version Y  another Serial ID    When your program tries to de-serialize the data  it can t because the two classes do not have the same Serial ID and your program have no guarantee that the two Serialized objects correspond to the same class format   Assuming you changed your constructor in the mean time and this should make sense to you

User · Answer

I believe this happens because you use the different versions of the same class on client and server  It can be different data fields or methods

User · Answer

If a class does not explicitly define a private static final long serialVersionUID in the code it will be autogenerated  and there is no guarantee that different machines will generate the same id  it looks like that is exactly what happened  Also if the classes are different in any way  using different versions of the class  the autogenerated serialVersionUIDs will also be different   From the Serializable interface s docs      If a serializable class does not explicitly declare a serialVersionUID  then the serialization runtime will calculate a default serialVersionUID value for that class based on various aspects of the class  as described in the Java TM  Object Serialization Specification  However  it is strongly recommended that all serializable classes explicitly declare serialVersionUID values  since the default serialVersionUID computation is highly sensitive to class details that may vary depending on compiler implementations  and can thus result in unexpected InvalidClassExceptions during deserialization  Therefore  to guarantee a consistent serialVersionUID value across different java compiler implementations  a serializable class must declare an explicit serialVersionUID value  It is also strongly advised that explicit serialVersionUID declarations use the private modifier where possible  since such declarations apply only to the immediately declaring class--serialVersionUID fields are not useful as inherited members  Array classes cannot declare an explicit serialVersionUID  so they always have the default computed value  but the requirement for matching serialVersionUID values is waived for array classes    You should define a serialVersionUID in the class definition  e g    class MyClass implements Serializable       private static final long serialVersionUID   6529685098267757690L

User · Answer

The exception message clearly speaks that the class versions  which would include the class meta data as well  has changed over time  In other words  the class structure during serialization is not the same during de-serialization  This is what is most probably  going on

User · Answer

Serialisation in java is not meant as long term persistence or transport format -  it is too fragile for this   With the slightest difference in class bytecode and JVM  your data is not readable anymore  Use XML or JSON data-binding for your task  XStream is fast and easy to use  and there are a ton of alternatives

User · Answer

If you are using oc4j to deploy the ear   Make sure you set in the project the correct path for deploy home   You can fiind deploy home in common properties file  The oc4j needs to reload the new created class in the ear so that the server class and the client class have the same serialVersionUID

User · Answer

If you are using the Eclipse IDE  check your Debug Run configuration  At Classpath tab  select the runner project and click Edit button  Only include exported entries must be checked

[java] java.io.InvalidClassException: local class incompatible:

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