Starting point

In App Engine 101 we covered

  • Working with App Engine in Eclipse
  • The anatomy of a web app
  • Servlets
  • Datastore Entities
  • Datastore JDO
  • JSP
  • Passing parameters

This session

Here, we cover

  • Logging
  • Memcache
  • Blobstore and Image Service
  • Google Cloud Endpoints
  • Signin
  • The App Engine web interface


  • Use java.util.logging approach
  • On dev server, shows in console
  • On live server, shows in admin interface
Logger log = Logger.getLogger(CreateServlet.class.getName());"A log message!");


  • An in-memory cache
  • Store often-used data here, for example:
    • Session data
    • User preferences
    • Queries performed on most pages of a site
    • Classes implementing Serializable
  • Pattern:
    • Check if data is in memcache
    • If it is: use it
    • If not: get from datastore and put in memcache


Make your class Serializable

public class Person implements Serializable

Use code to check and put in cache similar to this

String key = "Person"+id;
MemcacheService syncCache = MemcacheServiceFactory.getMemcacheService();
Person p = (Person) syncCache.get(key);
if (p == null) {"Cache miss for " + key);
  p = pm.getObjectById(Person.class, id);
  syncCache.put(key, p);
} else {"Cache hit for " + key);

Exercise 1: Memcache

  • Amend update.jsp to first check the cache for the Person before reading Datastore

Blobstore and Image Service

Blobstore is a storage service for arbitrary-size binary data

  • No querying on Blobstore
  • Key/value interface

Step 1: Create a form in your JSP that posts to a special Blobstore URL

<%@ page import="" %>
<%@ page import="" %>
<% BlobstoreService blobstoreService = BlobstoreServiceFactory.getBlobstoreService(); %>

<form action="<%= blobstoreService.createUploadUrl("/uploadpicture") %>" 
         method="post" enctype="multipart/form-data">
  <input type="file" name="pictureFile">

Blobstore and Image Service

Step 2: Create a servlet that gets passed the information once uploaded

BlobstoreService blobstoreService = BlobstoreServiceFactory.getBlobstoreService();
ImagesService imagesService = ImagesServiceFactory.getImagesService();

Map<String, List<BlobKey>> blobs = blobstoreService.getUploads(req);

if (blobs.size() == 0) {
} else {
  BlobKey k = blobs.get("pictureFile").get(0);
  // Do something with the blob key

Blobstore and Image Service

Step 3: Use the Image Service to create a serving URL and a thumbnail URL

ServingUrlOptions soOriginal = ServingUrlOptions.Builder.withBlobKey(k);
ServingUrlOptions soThumb = ServingUrlOptions.Builder.withBlobKey(k).imageSize(100);
String origUrl = imagesService.getServingUrl(soOriginal);
String thumbUrl = imagesService.getServingUrl(soThumb);

req.setAttribute("origUrl", origUrl);
req.setAttribute("thumbUrl", thumbUrl);
req.getRequestDispatcher("/create.jsp").forward(req, resp);

Blobstore and Image Service

Step 4: Use the serving URL and thumbnail URL in your JSP page

<% if (request.getAttribute("thumbUrl") != null) { %>
 <img src="<%=request.getAttribute("thumbUrl")%>">
<% } %>

Google Cloud Endpoints

  • We've been creating our own URL structure with servlets
  • We have to manage the semantics of the HTTP methods (POST, GET, etc.)
  • Code for managing entities is spread across servlets/JSP pages

Google Cloud Endpoints can help!

  • Create a RESTful API for your application to manage data
  • Create one class as an API
  • You get libraries for your API for iOS, Android and Javascript

Google Cloud Endpoints

Step 1: Create an endpoint class

Annotate with @Api

@Api(name = "person", version = "v1", description = "Person API")
public class PersonEndpoint {

Google Cloud Endpoints

Step 2: Create API Methods

Annotate with @ApiMethod

@ApiMethod(name = "read", httpMethod = HttpMethod.GET, path = "/person")
public Person readPerson(@Named("id") Long id) {
  PersistenceManager pm = PMF.get().getPersistenceManager();
  Person person = null;
  try {
    person = pm.getObjectById(Person.class, id);
  } finally {
  return person;

Google Cloud Endpoints

Step 3: Create the library

Google Cloud Endpoints

Step 4: Use the library

  function init() {
    var ROOT = '//' + + '/_ah/api';
    gapi.client.load('person', 'v1', function() {
      console.log('Loaded API');
    }, ROOT);
<script src=""></script>

com.samples.exercises.displayPeople = function(datalist) {

Google Cloud Endpoints

Some explanations ...

  • It's the same code as you've written all along
  • The parameters to the method are the same as your request parameters in servlet or JSP
  • @Named tells your method to use the "id" parameter
  • @Nullable tells your method the parameter is optional
  • You can see your API and call the methods at http://localhost:8888/_ah/api/explorer

Exercise 2: Cloud Endpoints

  • Convert your servlets to a Cloud Endpoint
  • Here's a skeleton
@Api(name = "person", version = "v1", description = "Person API")
public class PersonEndpoint {

  @ApiMethod(name = "list", path = "/list", httpMethod = HttpMethod.GET)
  public CollectionResponse listPersons(
      @Nullable @Named("cursor") String cursorString,
      @Nullable @Named("limit") Integer limit) {

  @ApiMethod(name = "create", httpMethod = HttpMethod.POST, path = "/person")
  public Person insertPerson(Person person) {

  @ApiMethod(name = "remove", httpMethod = HttpMethod.DELETE, path = "/person")
  public void removePerson(@Named("id") Long id) {

  @ApiMethod(name = "read", httpMethod = HttpMethod.GET, path = "/person")
  public Person readPerson(@Named("id") Long id) {

Restricting to signed-in users

Signin options (specified when creating your app)

  • Your Google domain (Google Apps)
  • Any Google account
  • OpenID accounts

Specify this in your web.xml


A tour of the App Engine interface and Namekeepr

  • The App Engine management console
  • Namekeepr, a sample application

Useful links

<Thank You!>