added a sample Date type adapter for UTC

extras/src/main/java/com/google/gson/typeadapters/UtcDateTypeAdapter.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2011 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.gson.typeadapters;
+
+import java.io.IOException;
+import java.text.DateFormat;
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.Locale;
+import java.util.TimeZone;
+
+import com.google.gson.JsonParseException;
+import com.google.gson.TypeAdapter;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+
+public final class UtcDateTypeAdapter extends TypeAdapter<Date> {
+  private final DateFormat iso8601Format;
+
+  public UtcDateTypeAdapter() {
+    this.iso8601Format = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSXXX", Locale.US);
+    this.iso8601Format.setTimeZone(TimeZone.getTimeZone("UTC"));
+  }
+
+  // These methods need to be synchronized since JDK DateFormat classes are not thread-safe
+  // See issue 162
+  @Override
+  public synchronized void write(JsonWriter out, Date date) throws IOException {
+    if (date == null) {
+      out.nullValue();
+    }
+    out.value(iso8601Format.format(date));
+  }
+
+  // These methods need to be synchronized since JDK DateFormat classes are not thread-safe
+  // See issue 162
+  @Override
+  public synchronized Date read(JsonReader in) throws IOException {
+    try {
+      switch (in.peek()) {
+      case NULL: return null;
+      default: return iso8601Format.parse(in.nextString());
+      }
+    } catch (ParseException e) {
+      throw new JsonParseException(e);
+    }
+  }
+}

extras/src/test/java/com/google/gson/typeadapters/UtcDateTypeAdapterTest.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2011 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.gson.typeadapters;
+
+import java.util.Calendar;
+import java.util.Date;
+import java.util.TimeZone;
+
+import junit.framework.TestCase;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+
+public final class UtcDateTypeAdapterTest extends TestCase {
+  private final Gson gson = new GsonBuilder()
+  .registerTypeAdapter(Date.class, new UtcDateTypeAdapter())
+  .create();
+
+  public void testLocalTimeZone() {
+    Date expected = new Date();
+    String json = gson.toJson(expected);
+    Date actual = gson.fromJson(json, Date.class);
+    assertEquals(expected.getTime(), actual.getTime());
+  }
+
+  public void testDifferentTimeZones() {
+    for (String timeZone : TimeZone.getAvailableIDs()) {
+      Calendar cal = Calendar.getInstance(TimeZone.getTimeZone(timeZone));
+      Date expected = cal.getTime();
+      String json = gson.toJson(expected);
+      // System.out.println(json + ": " + timeZone);
+      Date actual = gson.fromJson(json, Date.class);
+      assertEquals(expected.getTime(), actual.getTime());
+    }
+  }
+}