heron/tools/apiserver/src/java/com/twitter/heron/apiserver/resources/NotFoundExceptionHandler.java

//  Copyright 2017 Twitter. All rights reserved.
//
//  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.twitter.heron.apiserver.resources;

import javax.ws.rs.NotFoundException;
import javax.ws.rs.core.Response;
import javax.ws.rs.ext.ExceptionMapper;
import javax.ws.rs.ext.Provider;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.node.ObjectNode;

@Provider
public class NotFoundExceptionHandler implements ExceptionMapper<NotFoundException> {
  @Override
  public Response toResponse(NotFoundException exception) {
    final ObjectMapper mapper = new ObjectMapper()
        .enable(SerializationFeature.INDENT_OUTPUT)
        .enable(SerializationFeature.WRITE_SINGLE_ELEM_ARRAYS_UNWRAPPED);
    final ObjectNode node = mapper.createObjectNode();
    final ArrayNode arrayNode = node.putArray("paths");
    arrayNode.add("/api/v1/topologies");
    arrayNode.add("/api/v1/version");
    arrayNode.add("/api/v1/file");

    final String response;
    try {
      response = mapper.writeValueAsString(node);
    } catch (JsonProcessingException e) {
      throw new RuntimeException("Error creating page not found response", e);
    }

    return Response.status(Response.Status.NOT_FOUND)
        .entity(response)
        .build();
  }
}