Fix DateFormat time zone is not restored and add Test.

gson/src/main/java/com/google/gson/internal/bind/DefaultDateTypeAdapter.java

@@ -187,10 +187,13 @@ private Date deserializeToDate(JsonReader in) throws IOException {
     // Needs to be synchronized since JDK DateFormat classes are not thread-safe
     synchronized (dateFormats) {
       for (DateFormat dateFormat : dateFormats) {
+        TimeZone originalTimeZone = dateFormat.getTimeZone();
         try {
           return dateFormat.parse(s);
         } catch (ParseException ignored) {
           // OK: try the next format
+        } finally {
+          dateFormat.setTimeZone(originalTimeZone);
         }
       }
     }

gson/src/main/java/com/google/gson/internal/sql/SqlDateTypeAdapter.java

@@ -29,6 +29,7 @@
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.Date;
+import java.util.TimeZone;
 
 /**
  * Adapter for java.sql.Date. Although this class appears stateless, it is not. DateFormat captures
@@ -59,6 +60,7 @@ public java.sql.Date read(JsonReader in) throws IOException {
       return null;
     }
     String s = in.nextString();
+    TimeZone originalTimeZone = format.getTimeZone(); // Save the original time zone
     try {
       Date utilDate;
       synchronized (this) {
@@ -68,6 +70,8 @@ public java.sql.Date read(JsonReader in) throws IOException {
     } catch (ParseException e) {
       throw new JsonSyntaxException(
           "Failed parsing '" + s + "' as SQL Date; at path " + in.getPreviousPath(), e);
+    } finally {
+      format.setTimeZone(originalTimeZone); // Restore the original time zone after parsing
     }
   }
 

gson/src/main/java/com/google/gson/internal/sql/SqlTimeTypeAdapter.java

@@ -30,6 +30,7 @@
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.Date;
+import java.util.TimeZone;
 
 /**
  * Adapter for java.sql.Time. Although this class appears stateless, it is not. DateFormat captures
@@ -60,6 +61,7 @@ public Time read(JsonReader in) throws IOException {
       return null;
     }
     String s = in.nextString();
+    TimeZone originalTimeZone = format.getTimeZone(); // Save the original time zone
     try {
       synchronized (this) {
         Date date = format.parse(s);
@@ -68,6 +70,8 @@ public Time read(JsonReader in) throws IOException {
     } catch (ParseException e) {
       throw new JsonSyntaxException(
           "Failed parsing '" + s + "' as SQL Time; at path " + in.getPreviousPath(), e);
+    } finally {
+      format.setTimeZone(originalTimeZone); // Restore the original time zone
     }
   }
 

gson/src/test/java/com/google/gson/internal/bind/DefaultDateTypeAdapterTest.java

@@ -18,9 +18,11 @@
 
 import static com.google.common.truth.Truth.assertThat;
 import static com.google.common.truth.Truth.assertWithMessage;
+import static junit.framework.TestCase.assertEquals;
 import static org.junit.Assert.fail;
 
 import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
 import com.google.gson.TypeAdapter;
 import com.google.gson.TypeAdapterFactory;
 import com.google.gson.internal.bind.DefaultDateTypeAdapter.DateType;
@@ -223,6 +225,32 @@ public void testUnexpectedToken() throws Exception {
     }
   }
 
+  @Test
+  public void testGsonDateFormat() {
+    TimeZone originalTimeZone = TimeZone.getDefault();
+    // Set the default timezone to UTC
+    TimeZone.setDefault(TimeZone.getTimeZone("UTC"));
+    try {
+      Gson gson = new GsonBuilder().setDateFormat("yyyy-MM-dd HH:mm z").create();
+      Date originalDate = new Date(0);
+
+      // Serialize the date object
+      String json = gson.toJson(originalDate);
+      assertEquals("\"1970-01-01 00:00 UTC\"", json);
+
+      // Deserialize a date string with the PST timezone
+      Date deserializedDate = gson.fromJson("\"1970-01-01 00:00 PST\"", Date.class);
+
+      // Serialize the deserialized date object again
+      String jsonAfterDeserialization = gson.toJson(deserializedDate);
+      // The expectation is that the date, after deserialization, when serialized again should still
+      // be in the UTC timezone
+      assertEquals("\"1970-01-01 08:00 UTC\"", jsonAfterDeserialization);
+    } finally {
+      TimeZone.setDefault(originalTimeZone);
+    }
+  }
+
   private static TypeAdapter<Date> dateAdapter(TypeAdapterFactory adapterFactory) {
     TypeAdapter<Date> adapter = adapterFactory.create(new Gson(), TypeToken.get(Date.class));
     assertThat(adapter).isNotNull();