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
@@ -62,7 +63,9 @@ public java.sql.Date read(JsonReader in) throws IOException {
     try {
       Date utilDate;
       synchronized (this) {
+        TimeZone originalTimeZone = format.getTimeZone(); // Save the original time zone
         utilDate = format.parse(s);
+        format.setTimeZone(originalTimeZone); // Restore the original time zone after parsing
       }
       return new java.sql.Date(utilDate.getTime());
     } catch (ParseException e) {

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
@@ -62,7 +63,9 @@ public Time read(JsonReader in) throws IOException {
     String s = in.nextString();
     try {
       synchronized (this) {
+        TimeZone originalTimeZone = format.getTimeZone(); // Save the original time zone
         Date date = format.parse(s);
+        format.setTimeZone(originalTimeZone); // Restore the original time zone
         return new Time(date.getTime());
       }
     } catch (ParseException e) {

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 org.junit.Assert.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 +225,27 @@ public void testUnexpectedToken() throws Exception {
     }
   }
 
+  @Test
+  public void testGsonDateFormat() {
+    // Set the default timezone to UTC
+    TimeZone.setDefault(TimeZone.getTimeZone("UTC"));
+    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);
+  }
+
   private static TypeAdapter<Date> dateAdapter(TypeAdapterFactory adapterFactory) {
     TypeAdapter<Date> adapter = adapterFactory.create(new Gson(), TypeToken.get(Date.class));
     assertThat(adapter).isNotNull();