5035850: (str) String.CASE_INSENSITIVE_ORDER should override readResolve()

Summary: Fix to ensure singleton property of String.CaseInsensitiveComparator is maintained through de/serialization.
Reviewed-by: alanb, forax, smarks, dholmes
Contributed-by: darryl.mocek@oracle.com

src/share/classes/java/lang/String.java

@@ -1245,6 +1245,9 @@ public final class String
             }
             return n1 - n2;
         }
+
+        /** Replaces the de-serialized object. */
+        private Object readResolve() { return CASE_INSENSITIVE_ORDER; }
     }
 
     /**

test/java/lang/String/CaseInsensitiveComparator.java

+/*
+ * Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * This test tests that the String.CaseInsensitiveComparator.readResolve method
+ * deserializes String.CASE_INSENSITIVE_ORDER into an object which satisfies the
+ * equals method.
+ *
+ * @test
+ * @bug 5035850
+ * @summary Test for String.CaseInsensitiveComparator.readResolve
+ */
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+
+public class CaseInsensitiveComparator {
+    public static void main(String[] args) throws Exception {
+        Object result;
+
+        try (ByteArrayOutputStream outBuffer = new ByteArrayOutputStream();
+                ObjectOutputStream out = new ObjectOutputStream(outBuffer))
+        {
+            out.writeObject(String.CASE_INSENSITIVE_ORDER);
+            out.close();
+
+            try (ByteArrayInputStream inBuffer = new ByteArrayInputStream(outBuffer.toByteArray());
+                    ObjectInputStream in = new ObjectInputStream(inBuffer))
+            {
+                result = in.readObject();
+            }
+        }
+
+        if (!String.CASE_INSENSITIVE_ORDER.equals(result)) {
+            throw new Exception("Value restored from serial form does not equal original!");
+        }
+
+        if (!result.equals(String.CASE_INSENSITIVE_ORDER)) {
+            throw new Exception("Value restored from serial form does not equal original!");
+        }
+
+        if (String.CASE_INSENSITIVE_ORDER != result) {
+            throw new Exception("Value restored from serial form does not equal original!");
+        }
+    }
+}