Swagger: java.text.ParseException: Unparseable date error

This question's answer has been resolved. Apparently, I didn't mention any version of GSON in my gradle application file. So, by default it was assuming 2.3.1 version. But, my GSON data was in 2.7 version. That's why it was failing.

If we are using Gson 2.3.1 version, the defaultdatetypeadapter.java has the following methods

    final class DefaultDateTypeAdapter implements JsonSerializer<Date>, JsonDeserializer<Date> {

  // TODO: migrate to streaming adapter

  private final DateFormat enUsFormat;
  private final DateFormat localFormat;
  private final DateFormat iso8601Format;

  DefaultDateTypeAdapter() {
    this(DateFormat.getDateTimeInstance(DateFormat.DEFAULT, DateFormat.DEFAULT, Locale.US),
        DateFormat.getDateTimeInstance(DateFormat.DEFAULT, DateFormat.DEFAULT));
  }

  DefaultDateTypeAdapter(String datePattern) {
    this(new SimpleDateFormat(datePattern, Locale.US), new SimpleDateFormat(datePattern));
  }

  DefaultDateTypeAdapter(int style) {
    this(DateFormat.getDateInstance(style, Locale.US), DateFormat.getDateInstance(style));
  }

  public DefaultDateTypeAdapter(int dateStyle, int timeStyle) {
    this(DateFormat.getDateTimeInstance(dateStyle, timeStyle, Locale.US),
        DateFormat.getDateTimeInstance(dateStyle, timeStyle));
  }

  DefaultDateTypeAdapter(DateFormat enUsFormat, DateFormat localFormat) {
    this.enUsFormat = enUsFormat;
    this.localFormat = localFormat;
    this.iso8601Format = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'", 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
  public JsonElement serialize(Date src, Type typeOfSrc, JsonSerializationContext context) {
    synchronized (localFormat) {
      String dateFormatAsString = enUsFormat.format(src);
      return new JsonPrimitive(dateFormatAsString);
    }
  }

  public Date deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
      throws JsonParseException {
    if (!(json instanceof JsonPrimitive)) {
      throw new JsonParseException("The date should be a string value");
    }
    Date date = deserializeToDate(json);
    if (typeOfT == Date.class) {
      return date;
    } else if (typeOfT == Timestamp.class) {
      return new Timestamp(date.getTime());
    } else if (typeOfT == java.sql.Date.class) {
      return new java.sql.Date(date.getTime());
    } else {
      throw new IllegalArgumentException(getClass() + " cannot deserialize to " + typeOfT);
    }
  }

  private Date deserializeToDate(JsonElement json) {
    synchronized (localFormat) {
      try {
        return localFormat.parse(json.getAsString());
      } catch (ParseException ignored) {
      }
      try {
        return enUsFormat.parse(json.getAsString());
      } catch (ParseException ignored) {
      }
      try {
        return iso8601Format.parse(json.getAsString());
      } catch (ParseException e) {
        throw new JsonSyntaxException(json.getAsString(), e);
      }
    }
  }

  @Override
  public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append(DefaultDateTypeAdapter.class.getSimpleName());
    sb.append('(').append(localFormat.getClass().getSimpleName()).append(')');
    return sb.toString();
  }
}

If you notice deserializeToDate method, it generates 3 formats,

1) Local Format

2) enUsFormat

3) iso8601Format

where

enUsFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'") and

localFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'", Locale.US)

Both localFormat and iso8601Format are same. The value of parameter creationDate was 2017-08-14To2:42:59.528Z. For some reason, it was not getting parsed through either of the 3 formats.

Later, I realized that I was using wrong GSON version, so I included this line in my build.gradle file and again ran the application.

compile 'com.google.code.gson:gson:2.7'

I ran in debug code and went through each and every step. This time I noticed that defaultdatetypeadapter.java file got changed.

final class DefaultDateTypeAdapter implements JsonSerializer<Date>, JsonDeserializer<Date> {

  // TODO: migrate to streaming adapter

  private final DateFormat enUsFormat;
  private final DateFormat localFormat;

  DefaultDateTypeAdapter() {
    this(DateFormat.getDateTimeInstance(DateFormat.DEFAULT, DateFormat.DEFAULT, Locale.US),
        DateFormat.getDateTimeInstance(DateFormat.DEFAULT, DateFormat.DEFAULT));
  }

  DefaultDateTypeAdapter(String datePattern) {
    this(new SimpleDateFormat(datePattern, Locale.US), new SimpleDateFormat(datePattern));
  }

  DefaultDateTypeAdapter(int style) {
    this(DateFormat.getDateInstance(style, Locale.US), DateFormat.getDateInstance(style));
  }

  public DefaultDateTypeAdapter(int dateStyle, int timeStyle) {
    this(DateFormat.getDateTimeInstance(dateStyle, timeStyle, Locale.US),
        DateFormat.getDateTimeInstance(dateStyle, timeStyle));
  }

  DefaultDateTypeAdapter(DateFormat enUsFormat, DateFormat localFormat) {
    this.enUsFormat = enUsFormat;
    this.localFormat = localFormat;
  }

  // These methods need to be synchronized since JDK DateFormat classes are not thread-safe
  // See issue 162
  @Override
  public JsonElement serialize(Date src, Type typeOfSrc, JsonSerializationContext context) {
    synchronized (localFormat) {
      String dateFormatAsString = enUsFormat.format(src);
      return new JsonPrimitive(dateFormatAsString);
    }
  }

  @Override
  public Date deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
      throws JsonParseException {
    if (!(json instanceof JsonPrimitive)) {
      throw new JsonParseException("The date should be a string value");
    }
    Date date = deserializeToDate(json);
    if (typeOfT == Date.class) {
      return date;
    } else if (typeOfT == Timestamp.class) {
      return new Timestamp(date.getTime());
    } else if (typeOfT == java.sql.Date.class) {
      return new java.sql.Date(date.getTime());
    } else {
      throw new IllegalArgumentException(getClass() + " cannot deserialize to " + typeOfT);
    }
  }

  private Date deserializeToDate(JsonElement json) {
    synchronized (localFormat) {
      try {
        return localFormat.parse(json.getAsString());
      } catch (ParseException ignored) {}
      try {
        return enUsFormat.parse(json.getAsString());
      } catch (ParseException ignored) {}
      try {
        return ISO8601Utils.parse(json.getAsString(), new ParsePosition(0));
      } catch (ParseException e) {
        throw new JsonSyntaxException(json.getAsString(), e);
      }
    }
  }

  @Override
  public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append(DefaultDateTypeAdapter.class.getSimpleName());
    sb.append('(').append(localFormat.getClass().getSimpleName()).append(')');
    return sb.toString();
  }
}

If you notice now deserializeToDate method, it generated one different format and the GSON version it was showing was 2.7.

1) localFormat

2) enUsFormat

3) ISO8601Utils

This time, creationDate value got successfully parsed through ISO8601Utils method.

I was struggling to find the solution for last one week. At last, one inclusion of line in build.gradle file made all the difference in the end.

Hope this explanation helps for someone who is facing the same issue in future.