Writing and Responding to Pub/Sub Messages

<appengine-web-appxmlns="http://appengine.google.com/ns/1.0">
<threadsafe>true</threadsafe>
<runtime>java8</runtime>
<env-variables>
<env-varname="PUBSUB_TOPIC"value="your-topic"/>
<env-varname="PUBSUB_VERIFICATION_TOKEN"value="your-verification-token"/>
</env-variables>
</appengine-web-app>

@WebServlet(value="/pubsub/push")
publicclass PubSubPushextendsHttpServlet{
@Override
publicvoiddoPost(HttpServletRequestreq,HttpServletResponseresp)
throwsIOException,ServletException{
StringpubsubVerificationToken=System.getenv("PUBSUB_VERIFICATION_TOKEN");
// Do not process message if request token does not match pubsubVerificationToken
if(req.getParameter("token").compareTo(pubsubVerificationToken)!=0){
resp.setStatus(HttpServletResponse.SC_BAD_REQUEST);
return;
}
// parse message object from "message" field in the request body json
// decode message data from base64
Messagemessage=getMessage(req);
try{
messageRepository.save(message);
// 200, 201, 204, 102 status codes are interpreted as success by the Pub/Sub system
resp.setStatus(102);
}catch(Exceptione){
resp.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
}
}
privateMessagegetMessage(HttpServletRequestrequest)throwsIOException{
StringrequestBody=request.getReader().lines().collect(Collectors.joining("\n"));
JsonElementjsonRoot=JsonParser.parseString(requestBody).getAsJsonObject();
StringmessageStr=jsonRoot.getAsJsonObject().get("message").toString();
Messagemessage=gson.fromJson(messageStr,Message.class);
// decode from base64
Stringdecoded=decode(message.getData());
message.setData(decoded);
returnmessage;
}
privateStringdecode(Stringdata){
returnnewString(Base64.getDecoder().decode(data));
}
privatefinalGsongson=newGson();
privateMessageRepositorymessageRepository;
PubSubPush(MessageRepositorymessageRepository){
this.messageRepository=messageRepository;
}
publicPubSubPush(){
this.messageRepository=MessageRepositoryImpl.getInstance();
}
}

/*
 * Copyright 2017 Google Inc.
 *
 * 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.
 */
packagecom.example.appengine.pubsub;
importcom.google.cloud.ServiceOptions ;
importcom.google.cloud.pubsub.v1.Publisher ;
importcom.google.protobuf.ByteString ;
importcom.google.pubsub.v1.ProjectTopicName ;
importcom.google.pubsub.v1.PubsubMessage ;
importjava.io.IOException;
importjavax.servlet.ServletException;
importjavax.servlet.annotation.WebServlet;
importjavax.servlet.http.HttpServlet;
importjavax.servlet.http.HttpServletRequest;
importjavax.servlet.http.HttpServletResponse;
importorg.apache.http.HttpStatus;
@WebServlet(name="Publish with PubSub",value="/pubsub/publish")
publicclass PubSubPublishextendsHttpServlet{
@Override
publicvoiddoPost(HttpServletRequestreq,HttpServletResponseresp)
throwsIOException,ServletException{
Publisher publisher=this.publisher;
try{
String topicId=System.getenv("PUBSUB_TOPIC");
// create a publisher on the topic
if(publisher==null){
ProjectTopicName topicName=
ProjectTopicName .newBuilder()
.setProject(ServiceOptions .getDefaultProjectId())
.setTopic(topicId)
.build();
publisher=Publisher .newBuilder(topicName).build();
}
// construct a pubsub message from the payload
finalString payload=req.getParameter("payload");
PubsubMessage pubsubMessage=
PubsubMessage .newBuilder().setData(ByteString .copyFromUtf8 (payload)).build();
publisher.publish (pubsubMessage);
// redirect to home page
resp.sendRedirect("/");
}catch(Exceptione){
resp.sendError(HttpStatus.SC_INTERNAL_SERVER_ERROR,e.getMessage());
}
}
privatePublisher publisher;
publicPubSubPublish(){}
PubSubPublish(Publisher publisher){
this.publisher=publisher;
}
}