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https://issues.apache.org/jira/browse/COLLECTIONS-576?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Thomas Neidhart resolved COLLECTIONS-576.
-----------------------------------------
Resolution: Fixed
Fix Version/s: 4.1
Fixed in r1705620.
Thanks for the report and testcase.
> MultiKey subclassing has deserialization problem since COLLECTIONS-266:
> either declare protected readResolve() or MultiKey must be final
> ----------------------------------------------------------------------------------------------------------------------------------------
>
> Key: COLLECTIONS-576
> URL: https://issues.apache.org/jira/browse/COLLECTIONS-576
> Project: Commons Collections
> Issue Type: Bug
> Components: KeyValue
> Affects Versions: 4.0
> Reporter: Stephan Roch
> Fix For: 4.1
>
>
> MultiKey from collections 4 provides a transient hashCode and a *private*
> readResolve to resolve COLLECTIONS-266: Issue with MultiKey when
> serialized/deserialized via RMI.
> Unfortunately the solution does not work in case of *subclassing*:
> readResolve in MultiKey should be declared *protected* readResolve() to be
> called during deserialization of the subclass. Otherwise MultiKey must be
> final to avoid such subclassing.
> *Testcase*:
> {code:java|title=MultiKeySerializationTest.java}
> package de.ivu.test.common.collections4;
> import static org.junit.Assert.assertEquals;
> import java.io.ByteArrayInputStream;
> import java.io.ByteArrayOutputStream;
> import java.io.IOException;
> import java.io.ObjectInputStream;
> import java.io.ObjectOutputStream;
> import org.apache.commons.collections4.keyvalue.MultiKey;
> import org.junit.Test;
> public class MultiKeySerializationTest {
> @Test
> @SuppressWarnings("unchecked")
> public void testReadResolveEqualHashCode()
> throws IOException, ClassNotFoundException {
> class MultiKey2<A, B>
> extends MultiKey {
> private static final long serialVersionUID = 1928896152249821416L;
> public MultiKey2(A key1, B key2) {
> super(key1, key2);
> }
> public A getFirst() {
> return (A) getKey(0);
> }
> public B getSecond() {
> return (B) getKey(1);
> }
>
> // FIXME: MultiKey should either declare protected readResolve()
> or must be final.
> }
> MultiKey2<String, String> one = new MultiKey2<>("bla", "blub");
> System.out.println(one.hashCode());
> ByteArrayOutputStream byteOut = new ByteArrayOutputStream();
> ObjectOutputStream out = new ObjectOutputStream(byteOut);
> out.writeObject(one);
> out.close();
> byte[] serialized = byteOut.toByteArray();
> ByteArrayInputStream byteIn = new ByteArrayInputStream(serialized);
> ObjectInputStream in = new ObjectInputStream(byteIn);
> MultiKey2<String, String> two = (MultiKey2<String, String>)
> in.readObject();
> System.out.println(two.hashCode());
> assertEquals("hashCode must be equal - please check for protected
> readResolve in MultiKey*", one.hashCode(),
> two.hashCode());
> }
> }
> {code}
> *Fix:*
> {code:java|title=MultiKey.java}
> @@ -274,7 +274,7 @@
> * only stable for the same process).
> * @return the instance with recalculated hash code
> */
> - private Object readResolve() {
> + protected Object readResolve() {
> calculateHashCode(keys);
> return this;
> }
> {code}
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