确保对象的序列化正确完成

Question

Is there a way to ensure that the serialization of an object is done correctly? I created an applet that I serialize with writeObject() method and I have no Exception no error. But when I try to de-serialize it with readObject() I got a NullPointerException. My applet is kinda complex but I ensured that all my fields are serializable.

The class of the objection have nested classes.

Any guess as to what could have happen?

the code below is in my servlet it creates a SerialTree .

` SerialTree st = new SerialTree() ;

     try{
        ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("/home/cof/test8"));

 out.writeUnshared(st);
 out.flush();
 out.close();

}

Here's the stacktrace :

java.lang.NullPointerException at java.awt.Container.readObject(Container.java:3575) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:991) at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1865) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1770) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1346) at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1684) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1340) at java.io.ObjectInputStream.access$300(ObjectInputStream.java:205) at java.io.ObjectInputStream$GetFieldImpl.readFields(ObjectInputStream.java:2125) at java.io.ObjectInputStream.readFields(ObjectInputStream.java:536) at java.awt.Container.readObject(Container.java:3560) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:991) at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1865) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1770) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1346) at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1684) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1340) at java.io.ObjectInputStream.access$300(ObjectInputStream.java:205) at java.io.ObjectInputStream$GetFieldImpl.readFields(ObjectInputStream.java:2125) at java.io.ObjectInputStream.readFields(ObjectInputStream.java:536) at java.awt.Container.readObject(Container.java:3560) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:991) at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1865) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1770) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1346) at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1684) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1340) at java.io.ObjectInputStream.access$300(ObjectInputStream.java:205) at java.io.ObjectInputStream$GetFieldImpl.readFields(ObjectInputStream.java:2125) at java.io.ObjectInputStream.readFields(ObjectInputStream.java:536) at java.awt.Container.readObject(Container.java:3560) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:991) at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1865) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1770) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1346) at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1684) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1340) at java.io.ObjectInputStream.access$300(ObjectInputStream.java:205) at java.io.ObjectInputStream$GetFieldImpl.readFields(ObjectInputStream.java:2125) at java.io.ObjectInputStream.readFields(ObjectInputStream.java:536) at java.awt.Container.readObject(Container.java:3560) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:991) at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1865) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1770) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1346) at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1684) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1340) at java.io.ObjectInputStream.access$300(ObjectInputStream.java:205) at java.io.ObjectInputStream$GetFieldImpl.readFields(ObjectInputStream.java:2125) at java.io.ObjectInputStream.readFields(ObjectInputStream.java:536) at java.awt.Container.readObject(Container.java:3560) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:616) at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:991) at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1865) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1770) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1346) at java.io.ObjectInputStream.readArray(ObjectInputStream.java:1684) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1340) at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1963) at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1887) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1770) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1346) at java.io.ObjectInputStream.readObject(ObjectInputStream.java:368) at arbre.ArbreClient.getHttpObject(ArbreClient.java:92) at arbre.ArbreClient.init(ArbreClient.java:123) at sun.applet.AppletPanel.run(AppletPanel.java:436) at java.lang.Thread.run(Thread.java:636)

here the lines 70 to 106 to the applet itself ,it tries to retrieve a serilaTree object ?

` try{ result = new ObjectInputStream(new FileInputStream("/home/cof/test8"));

}
 catch(NotSerializableException e){

     e.printStackTrace();
 }

 catch(InvalidClassException e){
     e.printStackTrace();
 }
 catch(StreamCorruptedException e){

     e.printStackTrace();
 }
 catch(NotActiveException e){

     e.printStackTrace();
 }
 catch(OptionalDataException  e){

     e.printStackTrace();
 }

Object obj =null;

    try{

obj = result.readObject(); 

    }
    catch(NullPointerException e){

     e.printStackTrace();
    // System.out.println("lalal");
 }
 catch(NotSerializableException e){

     e.printStackTrace();
 }
 catch(InvalidClassException e){

     e.printStackTrace();
 }
 catch(StreamCorruptedException e){

     e.printStackTrace();
 }

Answer 1

To me, it doesn't make sense to ser/deser the type Applet. Try using a different class.

Update: I have read your stacktrace, and what I see is that you tried to deserialize an applet while running an applet. I strongly suspect this to be the reason of your problem. Try moving all your variables into a different class (call it MySerializableApplet for example, and don't make it extend the class Applet ), then operate your serialisation/deserialization on this one only.