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From "Charles Lamb (JIRA)" <j...@apache.org>
Subject [jira] Created: (HARMONY-6439) NullPointerException thrown in certain Serialization cases
Date Fri, 05 Feb 2010 12:37:27 GMT
NullPointerException thrown in certain Serialization cases
----------------------------------------------------------

                 Key: HARMONY-6439
                 URL: https://issues.apache.org/jira/browse/HARMONY-6439
             Project: Harmony
          Issue Type: Bug
          Components: Classlib
    Affects Versions: 5.0M12
         Environment: Windows
            Reporter: Charles Lamb
            Priority: Minor


Harmony object serialization has an initialization bug that causes NullPointerException when
overriding the ObjectInputStream.readClassDescriptor and ObjectOutputStream.writeClassDescriptor
methods, in order to store the ObjectStreamClass elsewhere.  In Berkeley DB, overriding these
methods is necessary to store the ObjectStreamClass in a separate database, to avoid repeating
it redundantly in every database record.  This type of overriding is supported by the Java
specification, and the problem does not occur in other Java class libraries (specifically,
the bug does not occur on the Sun, IBM and BEA Java platforms).

The attached test demonstrates the problem by simply serializing and deserializing an object
to/from a byte array, when readClassDescriptor and writeClassDescriptor are overridden.  A
NullPointerException occurs because of an uninitialized field during the call to readObject.

C:\temp>java -classpath . ClassDescriptorOverrideBug
java.lang.NullPointerException
        at java.io.ObjectStreamField.resolve(ObjectStreamField.java:336)
        at java.io.ObjectInputStream.readNewClassDesc(ObjectInputStream.java:1838)
        at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:799)
        at java.io.ObjectInputStream.readNewObject(ObjectInputStream.java:2039)
        at java.io.ObjectInputStream.readNonPrimitiveContent(ObjectInputStream.java:902)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:2251)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:2208)
        at ClassDescriptorOverrideBug.doTest(ClassDescriptorOverrideBug.java:49)
        at ClassDescriptorOverrideBug.main(ClassDescriptorOverrideBug.java:29)

Note that this problem only occurs when primitive fields are declared in the serializable
class.

A workaround for this bug is to serialize and deserialize the ObjectStreamClass before it
is used.  Apparently deserialization causes initialization to occur correctly.

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.ObjectStreamClass;
import java.io.OutputStream;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;

/**
 * Demonstrates a Harmony bug in Java serialization, where overriding the
 * ObjectInputStream.readClassDescriptor and
 * ObjectOutputStream.writeClassDescriptor methods, in order to store the
 * ObjectStreamClass elsewhere, causes a NullPointerException.
 */
public class ClassDescriptorOverrideBug {

    private final Map<Integer, ObjectStreamClass> idToDescMap =
        new HashMap<Integer, ObjectStreamClass>();
    private final Map<String, Integer> nameToIdMap =
        new HashMap<String, Integer>();
    private int nextId = 1;

    public static void main(String argv[]) {
        try {
            new ClassDescriptorOverrideBug().doTest();
            System.out.println("SUCCESS");
            System.exit(0);
        } catch (Exception e) {
            e.printStackTrace();
            System.exit(1);
        }
    }

    /* Write/serialize and read/de-serialize an object. */
    void doTest()
        throws IOException, ClassNotFoundException {

        final ByteArrayOutputStream baos = new ByteArrayOutputStream();
        final MyObjectOutputStream oos = new MyObjectOutputStream(baos);
        oos.writeObject(new Data());
        final byte[] bytes = baos.toByteArray();
        final ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
        final MyObjectInputStream ois = new MyObjectInputStream(bais);
        /* NullPointerException is thrown by the readObject call below. */
        ois.readObject();
    }
    
    /* Primitive fields are necessary to cause the NullPointerException. */
    static class Data implements Serializable {
        String field1 = "field1";
        String field2 = "field2";
        int field3 = 333;
        int field4 = 444;
        String field5 = "field5";
    }

    /* Overrides writeClassDescriptor to store ObjectStreamClass in map. */
    class MyObjectOutputStream extends ObjectOutputStream {

        MyObjectOutputStream(OutputStream out)
            throws IOException {

            super(out);
        }

        @Override
        protected void writeClassDescriptor(ObjectStreamClass desc)
            throws IOException {

            final String className = desc.getName();
            final int id;
            if (nameToIdMap.containsKey(className)) {
                /* Known class: get ID from map. */
                id = nameToIdMap.get(className);
            } else {
                /* New class: assign ID and store in maps. */
                id = nextId;
                nextId += 1;
                idToDescMap.put(id, desc);
                nameToIdMap.put(className, id);
            }
            /* Write ID of ObjectStreamClass. */
            writeInt(id);
        }
    }

    /* Overrides readClassDescriptor to get ObjectStreamClass from map. */
    class MyObjectInputStream extends ObjectInputStream {

        MyObjectInputStream(InputStream in)
            throws IOException {

            super(in);
        }

        @Override
        protected ObjectStreamClass readClassDescriptor()
            throws IOException, ClassNotFoundException {

            /* Read the ID and get the ObjectStreamClass from a map. */
            final int id = readInt();
            final ObjectStreamClass desc = idToDescMap.get(id);
            if (desc == null) {
                throw new ClassNotFoundException("id not found: " + id);
            }
            return desc;
        }
    }
} 


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