With recent builds of JDK 7, a user subclass of javax.management.QueryEval will no longer
serialize.  The following test program:

import java.io.*;
import javax.management.*;

public class QES extends QueryEval {
    public static void main(String[] args) throws Exception {
	QES qes = new QES();
    	ByteArrayOutputStream bout = new ByteArrayOutputStream();
	ObjectOutputStream oout = new ObjectOutputStream(bout);
	oout.writeObject(qes);
	oout.close();
	ByteArrayInputStream bin = new ByteArrayInputStream(bout.toByteArray());
	ObjectInputStream oin = new ObjectInputStream(bin);
	QES qes2 = (QES) oin.readObject();
	System.out.println("Read: " + qes2);
    }
}

produces the following exception:

Exception in thread "main" java.io.InvalidClassException: QES; QES; no valid constructor
	at java.io.ObjectStreamClass.checkDeserialize(ObjectStreamClass.java:730)
	at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1751)
	at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1347)
	at java.io.ObjectInputStream.readObject(ObjectInputStream.java:369)
	at QES.main(QES.java:13)
Caused by: java.io.InvalidClassException: QES; no valid constructor
	at java.io.ObjectStreamClass.<init>(ObjectStreamClass.java:488)
	at java.io.ObjectStreamClass.lookup(ObjectStreamClass.java:327)
	at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1123)
	at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:343)
	at QES.main(QES.java:9)
Posted Date : 2008-04-22 14:32:05.0

N/A

This is due to the new non-public class javax.management.ToQueryString, which defines a toQueryString() method that is overridden by various other javax.management classes.  Serialization requires the first non-serializable superclass of the serialized class to have a no-arg constructor that is accessible to the serialized class.  A custom subclass will be outside the javax.management package so will not have access to the constructor of javax.management.ToQueryString.  It happens that adding a public constructor to ToQueryString will fix this problem, but that is arguably a bug in the serialization system so we should not rely on it.  We will need to rewrite the code to dispense with ToQueryString, which will probably require an ugly chain of "if instanceof".
Posted Date : 2008-04-22 14:32:05.0