[FLINK-9173][REST] Improve client error message for parsing failures

- print parsing exception for expected type, not error
- add toString implemented to JsonResponse

flink-runtime/src/main/java/org/apache/flink/runtime/rest/RestClient.java

@@ -217,7 +217,7 @@ private static <P extends ResponseBody> CompletableFuture<P> parseResponse(JsonR
  try {
  P response = objectMapper.readValue(jsonParser, responseType);
  responseFuture.complete(response);
- } catch (IOException ioe) {
+ } catch (IOException originalException) {
  // the received response did not matched the expected response type
 
  // lets see if it is an ErrorResponse instead
@@ -231,7 +231,7 @@ private static <P extends ResponseBody> CompletableFuture<P> parseResponse(JsonR
  responseFuture.completeExceptionally(
  new RestClientException(
  "Response was neither of the expected type(" + responseType + ") nor an error.",
- jpe2,
+ originalException,
  rawResponse.getHttpResponseStatus()));
  }
  }
@@ -328,5 +328,13 @@ public JsonNode getJson() {
  public HttpResponseStatus getHttpResponseStatus() {
  return httpResponseStatus;
  }
+
+ @Override
+ public String toString() {
+ return "JsonResponse{" +
+ "json=" + json +
+ ", httpResponseStatus=" + httpResponseStatus +
+ '}';
+ }
  }
 }