Hello,
I have submitted Jira HARMONY-6439 for this issue. Credit to my
colleagues Mark Hayes and Haomian Wang for narrowing this down.
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 Java Edition, 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;
}
}
}
