8039165: [Doc] MessageFormat null locale generates NullPointerException

Reviewed-by: naoto, iris
Backport-of: c6396dceb9a64578d5b335af27ad1d968190a1fa

src/java.base/share/classes/java/text/MessageFormat.java

@@ -390,11 +390,19 @@ public MessageFormat(String pattern) {
      * Patterns and their interpretation are specified in the
      * <a href="#patterns">class description</a>.
      *
+     * @implSpec The default implementation throws a
+     * {@code NullPointerException} if {@code locale} is {@code null}
+     * either during the creation of the {@code MessageFormat} object or later
+     * when {@code format()} is called by a {@code MessageFormat}
+     * instance with a null locale and the implementation utilizes a
+     * locale-dependent subformat.
+     *
      * @param pattern the pattern for this message format
      * @param locale the locale for this message format
      * @throws    IllegalArgumentException if the pattern is invalid
      * @throws    NullPointerException if {@code pattern} is
-     *            {@code null}
+     *            {@code null} or {@code locale} is {@code null} and the
+     *            implementation uses a locale-dependent subformat.
      * @since 1.4
      */
     public MessageFormat(String pattern, Locale locale) {
@@ -843,7 +851,10 @@ public Format[] getFormats() {
      * @throws    IllegalArgumentException if an argument in the
      *            {@code arguments} array is not of the type
      *            expected by the format element(s) that use it.
-     * @throws    NullPointerException if {@code result} is {@code null}
+     * @throws    NullPointerException if {@code result} is {@code null} or
+     *            if the {@code MessageFormat} instance that calls this method
+     *            has locale set to null, and the implementation
+     *            uses a locale-dependent subformat.
      */
     public final StringBuffer format(Object[] arguments, StringBuffer result,
                                      FieldPosition pos)
@@ -889,7 +900,10 @@ public static String format(String pattern, Object ... arguments) {
      * @throws    IllegalArgumentException if an argument in the
      *            {@code arguments} array is not of the type
      *            expected by the format element(s) that use it.
-     * @throws    NullPointerException if {@code result} is {@code null}
+     * @throws    NullPointerException if {@code result} is {@code null} or
+     *            if the {@code MessageFormat} instance that calls this method
+     *            has locale set to null, and the implementation
+     *            uses a locale-dependent subformat.
      */
     public final StringBuffer format(Object arguments, StringBuffer result,
                                      FieldPosition pos)

test/jdk/java/text/Format/MessageFormat/MessageFormatExceptions.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright (c) 2011, 2023, 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.
+ */
+
+/*
+ * @test
+ * @summary Validate some exceptions in MessageFormat
+ * @bug 6481179 8039165
+ * @run junit MessageFormatExceptions
+ */
+
+import java.text.MessageFormat;
+import java.util.Locale;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class MessageFormatExceptions {
+
+    // MessageFormat should throw NPE when constructed with a null pattern
+    @Test
+    public void nullPatternTest() {
+        assertThrows(NullPointerException.class, () -> new MessageFormat(null));
+        assertThrows(NullPointerException.class, () -> new MessageFormat(null, Locale.US));
+        assertThrows(NullPointerException.class,
+                () -> MessageFormat.format(null, new Object[] { "val0", "val1" }));
+    }
+
+    // 8039165: When MessageFormat is constructed with a null locale a NPE
+    // can potentially be thrown depending on the subformat created. Either
+    // during the creation of the object itself, or later when format() is called.
+    // The following are some examples.
+    @Test
+    public void nullLocaleTest() {
+        // Fails when constructor invokes applyPattern()
+        assertThrows(NullPointerException.class,
+                () -> new MessageFormat("{0, date}", null));
+        // Fail when constructor invokes applyPattern()
+        assertThrows(NullPointerException.class,
+                () -> new MessageFormat("{0, number}", null));
+        // Fail when object calls format()
+        assertThrows(NullPointerException.class,
+                () -> new MessageFormat("{0}", null).format(new Object[]{42}));
+        // Fail when object calls format(), but locale is set via .setLocale()
+        MessageFormat msgFmt = new MessageFormat("{0}");
+        msgFmt.setLocale(null);
+        assertThrows(NullPointerException.class, () -> msgFmt.format(new Object[]{42}));
+        // Does not always fail if locale is null
+        assertDoesNotThrow(() ->
+                new MessageFormat("{0}", null).format(new Object[]{"hello"}));
+
+    }
+
+    // 6481179: Invalid format type should be provided in error message of IAE
+    @Test
+    public void formatMsgTest() {
+        IllegalArgumentException iae = assertThrows(IllegalArgumentException.class,
+                () -> MessageFormat.format("Testdata {1,invalid_format_type}", new Object[] { "val0", "val1" }));
+        assertEquals("unknown format type: invalid_format_type", iae.getMessage());
+    }
+}