DecompressibleInputStream.java

/**
 * <a href="http://www.openolat.org">
 * OpenOLAT - Online Learning and Training</a><br>
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License"); <br>
 * you may not use this file except in compliance with the License.<br>
 * You may obtain a copy of the License at the
 * <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache homepage</a>
 * <p>
 * Unless required by applicable law or agreed to in writing,<br>
 * software distributed under the License is distributed on an "AS IS" BASIS, <br>
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. <br>
 * See the License for the specific language governing permissions and <br>
 * limitations under the License.
 * <p>
 * Initial code contributed and copyrighted by<br>
 * frentix GmbH, http://www.frentix.com
 * <p>
 */
package org.olat.ims.qti.process;

import java.io.IOException;
import java.io.InputStream;
import java.io.InvalidClassException;
import java.io.ObjectInputStream;
import java.io.ObjectStreamClass;

import org.olat.core.logging.OLog;
import org.olat.core.logging.Tracing;

/**
 * 
 * http://stackoverflow.com/questions/795470/how-to-deserialize-an-object-persisted-in-a-db-now-when-the-object-has-different
 * 
 * @author jorge, java forums
 *
 */
public class DecompressibleInputStream extends ObjectInputStream {
	
	private static final OLog log = Tracing.createLoggerFor(DecompressibleInputStream.class);

    public DecompressibleInputStream(InputStream in) throws IOException {
        super(in);
    }

    @Override
    protected ObjectStreamClass readClassDescriptor() throws IOException, ClassNotFoundException {
        ObjectStreamClass resultClassDescriptor = super.readClassDescriptor(); // initially streams descriptor
        Class<?> localClass = Class.forName(resultClassDescriptor.getName()); // the class in the local JVM that this descriptor represents.
        if (localClass == null) {
            log.error("No local class for " + resultClassDescriptor.getName());
            return resultClassDescriptor;
        }
        ObjectStreamClass localClassDescriptor = ObjectStreamClass.lookup(localClass);
        if (localClassDescriptor != null) { // only if class implements serializable
            final long localSUID = localClassDescriptor.getSerialVersionUID();
            final long streamSUID = resultClassDescriptor.getSerialVersionUID();
            if (streamSUID != localSUID) { // check for serialVersionUID mismatch.
                final StringBuilder s = new StringBuilder("Overriding serialized class version mismatch: ");
                s.append("local serialVersionUID = ").append(localSUID).append(" stream serialVersionUID = ").append(streamSUID);
                Exception e = new InvalidClassException(s.toString());
                log.warn(s.toString(), e);
                resultClassDescriptor = localClassDescriptor;
            }
        }
        return resultClassDescriptor;
    }
}