Object Serialization and IO Error

Question

Hi,
I am trying to serialize 3 hashtable objects, with serializable keys and elements, on to disk. Here is a snippet of the code disk management code:
     public void loadData(StoreManager s_man) {
          // read from disk
          Hashtable o = (Hashtable)readObjects();
          Hashtable c = (Hashtable)readClasses();
          Hashtable i = (Hashtable)readIndex();
          //Hashtable e = (Hashtable)readEnv();
          Integer id = (Integer)readEnv();
          // set the store manager objects
          s_man.setObjects(o);
          s_man.setClasses(c);
          s_man.setIndex(i);
          Env.setCurrentID(id);
Here is what the readObject method looks like:
     * Deserialize disk data and return Object data.
     public synchronized Object readObjects() {
          if (!objectdatafile.exists())
               return null;
          Object o = new Object();
          try {
               FileInputStream istream = new FileInputStream(objectdatafile);
               ObjectInputStream pack = new ObjectInputStream(istream);
               o = pack.readObject();
               istream.close();
          catch (Exception e) {
               e.printStackTrace();
Occasionally, when starting the program (i.e. when it initially reads all data from disk), I am getting the following exceptions:
java.io.EOFException
at java.io.ObjectInputStream$BlockDataInputStream.peekByte(ObjectInputStream.java:2426)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1238)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:325)
at java.util.Hashtable.readObject(Hashtable.java:799)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.
java:42)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
sorImpl.java:28)
at java.lang.reflect.Method.invoke(Method.java:327)
at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:812
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1736)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1
639)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1267)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:325)
at DiskManager.readObjects(DiskManager.java:165)
at DiskManager.loadData(DiskManager.java:42)
at LoadDataAction.run(LoadDataAction.java:30)
at java.lang.Thread.run(Thread.java:539)
java.lang.ClassCastException: java.lang.Object
at DiskManager.loadData(DiskManager.java:42)
at LoadDataAction.run(LoadDataAction.java:30)
at java.lang.Thread.run(Thread.java:539)
I would like to repeat that I am not getting this error everytime, but about once every two runs. Please share your feelings about possible errors I am making or if there is an inherent bug with serialization of hashtables.
Thanks

Answer 1

the java.io.EOFException looks like you did not properly close the stream on writing. to me this seems like there is an error in the writing code rather than the reading code. although there are some things you can improve...
robert