• Java serialization doesn't guaranty that a file can be reread when a class has changed
  • File are in binary mode -< they cannot be reread
Currently, the serialVersionUID is automatically generated. It means that serialized file becomes incompatible if:
  • A field change
  • A method signature change

However, it does not change if the contents of a method is modified => it doesn't guaranty the behavior of the class.


  • User must be able to reread project file during time
  • Detect potential changement even if the project can be read

Some Solutions

Use of class serialverionsuid field

  • It improves robustness for simple changes but doesn't support field modifications

The serialVersionUID should be changed when :.

  • a field is added or renamed or removed.
  • the type of a field is changed
  • the name of the package or the class is changed

However, serialVersionUID should not be changed when

  • the scope of a field is changed (private, protected, public).
  • the fields ore reordered.
  • a method is added, rename, pr removed.
  • modify a static fields.

What's happen if the serialversionuid is not changed ?

  • If a field is removed : not error
  • if a field is added : it is null
  • if the type of a field is changed : we get a java.lang.ClassCastException
  • If a class is renamed : we get a java.lang.ClassNotFoundException

Use of java.bean.xmlencode

  • Only usable with java bean standard

XML library


  • These method are robust against class changes (method signature modification, new field or removed field)
  • XML format is human readable. It can be used for external processing or reutilisation


  • XML is verbose, file are huge
  • File doesn't crash if method or fields have change -> it can leads to inconsistency

  • XML solution are attractive but must be associated with a mechanism to detect inconsistency

How to Detect inconsistency change

  • Record SVN version id => all class should declare a SVN revision
  • Record the list of class fields

file size comparison

  • binary : 459 kb
  • xml (xstream) : 6.8 Mb
  • xml.gz (xstream) : 235kb