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Google App Engine With Java And Groovy


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Building a "recommended books" application on Google App Engine for Java "early look", using Groovy to help out on the XML processing.

Published in: Technology, News & Politics
  • Nice !! Download 100 % Free Ebooks, PPts, Study Notes, Novels, etc @
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  • Google played the same game with their Android development kit, i.e., they're supporting a non-standard JVM that doesn't implement any of the editions (not even ME). I can only assume their motivation is based on their own needs. Once they decided not to support relational databases for scaling reasons (no joins allowed), the precedent was set and they could do whatever they wanted.

    That said, I don't have any inside information. You might check out the rather extensive message boards for GAE to find clues.

    Thanks for your comment and I'm glad the presentation was useful for you. :)
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  • Nice prez, Ken.
    From a platform perspective, one could agree to limiting the use of sockets, threads, and System-APIs. A couple of questions come to mind, though -
    What appears to be the reasoning behind limiting the support of other standard JEE APIs? What's the likelihood of these being supported anytime on future?
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Google App Engine With Java And Groovy

  1. 1. Java and Groovy on Google App Engine ---> Ken Kousen
  2. 2. Google App Engine Google's "cloud computing" solution     Run applications on Google's scalable infrastructure     Pay based on resources used         storage, bandwidth             measured by gigabyte     For free,          up to 500 MB of storage and         up to 5 million page views/month
  3. 3. Running Java on GAE     Original GAE version:         Python interpreter and standard libraries     New, "Early Look" version:         JVM available             So Java works, as well as other languages                 that compile to the JVM                 i.e., Groovy, Scala, JRuby, ...     
  4. 4. Java "Early Look" Need to register at      Originally expected 10K developers     Demand was so high, increased to 25K     Now open to ALL Download SDK Download Eclipse plugin (optional) Can run locally or to     If Google Apps user, can map local http address         (example later)
  5. 5. Sandbox Environment Limited access to underlying OS     Manage app through application console     No writing to file system         Can read files uploaded by app     Datastore available (discussed below)     Services available (described next)
  6. 6. Welcome to 1999 Let's go back to those thrilling days of yesteryear...         Ricky Martin,         Livin' La Vida Loca     Jar-Jar Binks                      Bill and Monica   
  7. 7. Also in 1999 On Dec. 17th, Sun released Servlet 2.2 specification     Established structure of a WAR file     Ever since then, you could deploy a WAR file         to an application server     Unfortunately, GAE doesn't know from WAR files
  8. 8. WAR, huh, ... what is it good for? Actually, that's not quite true     GAE does know about war structure,         just not war files     gae_app         src             java code         war             normal war stuff, including classes and lib dirs             WEB-INF                 web.xml, etc
  9. 9. GAE Limitations GAE running on Java 6, but with some limitations Once a request is sent to the client, no further processing can be done Request will be terminated if longer than 30 sec to complete, throwing an exception Also, No sockets No threads or timers No JNI System.gc(), System.exit(...), etc, do nothing Security issues, esp. with class loaders
  10. 10. GAE War Quirks Sample web.xml file     Has DTD based on Web App 2.3     But also includes xmlns and version attributes         (version = 2.5, no less) It's confused
  11. 11. Scalability About 30 active dynamic requests simultaneously Average server-side req processing time is 75 ms        --> about 400 requests/sec without additional latency     (note static files not affected by this limit)
  12. 12. GAE Services URL Fetch     URL wrapper that uses Google infrastructure to         retrieve resources Mail     Send email Memcache     "high performance in-memory key-value cache" Image Manipulation     Resize, copy, rotate, flip JPEG and PNG images User     Detect if user is logged in and is administrator
  13. 13. Welcome to the 2300s     Maybe by then we'll have moved beyond relational DBs         (but I doubt it...)
  14. 14. Datastore Distributed data storage     transactional Filtering and sorting by property value type NOT a traditional relational database     Google uses the term "schemaless" Uses optimistic concurrency control with retries
  15. 15. GAE and Persistence GAE doesn't know from relational     All persistence defined by @annotations on classes         JDO            O'Reilly book (c) 2003          JPA             But JDO is the default                  (wait, what? JDO? what's up with that?)
  16. 16. GAE Persistence GAE object datastore based on BigTable     BigTable is a massively scalable,         distributed storage system         used by Google for lots of things     For Java, API uses DataNucleus bytecode enhancer     (No, I'd never heard of it either...)
  17. 17. Software Development Kit App Engine SDK     Includes web server (jetty)     Emulates all the GAE services SDK includes an upload tool to deploy app to GAE Command line tools included
  18. 18. Project Development Supports Java 5 and Java 6 (Standard Edition)     GAE deployment is Java 6 Google Plugin for Eclipse     version for 3.3 (Europa)     version for 3.4 (Ganymede)
  19. 19. Project Development SDK comes as a zip file     Includes sample applications     Some use GWT:  Google Web Toolkit         How to do Ajax without doing Ajax             by doing it in Java     GWT also comes with the Eclipse plugin
  20. 20. Demo: Recommended Books Warning: User Interface Poisoning Hazard Ahead
  21. 21. Entity Class @PersistenceCapable(identityType = IdentityType.APPLICATION) public class Book { @PrimaryKey         @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Long id; @Persistent private String asin; @Persistent private String recommendation;
  22. 22. Entity Class // Other attributes populated by XML response (not persistent!) private String title; private String author;  // multiple are separated by commas private String formattedPrice; private String mediumImageURL; private String detailPageURL;     // contructors, getter and setter methods     // equals, hashCode, toString overrides as desired }
  23. 23. Entity Class Book represents book at Amazon provides Product Advertising API     formerly Amazon Associates Service RESTful (sort of) web service     Append parameters to request         URL = base?Service=AWSECommerceService             &Operation=ItemLookup             &ASIN=...isbn...   // ... etc ...
  24. 24. Amazon Web Service Input URL --> Output XML
  25. 25. Amazon Web Service As of May, 2009     Renamed Product Advertising API (ugh) As of August, 2009     All REST requests must be digitally signed     Sample code given in Java         Uses javax.crypto classes and Apache Commons Codec     
  26. 26. DAO Interface public interface BookDAO { Book findById(Long id); Book findByAsin(String asin); Set<Book> findAllBooks(); Long addBook(Book b); boolean removeBook(Long id); }
  27. 27. DAO Implementation public class JdoBookDAO implements BookDAO {   private PersistenceManagerFactory pmf = PMF.get();   @Override   public Long addBook(Book b) { Book book = findByAsin(b.getAsin()); if (book != null) {     return book.getId(); } PersistenceManager pm = pmf.getPersistenceManager();
  28. 28. DAO Implementation try {     pm.currentTransaction().begin();     pm.makePersistent(b);     pm.currentTransaction().commit(); } finally {     if (pm.currentTransaction().isActive()) { pm.currentTransaction().commit();     }             pm.close(); } return b.getId();     }
  29. 29. DAO Implementation public Set<Book> findAllBooks() { Set<Book> results = new HashSet<Book>(); PersistenceManager pm = pmf.getPersistenceManager(); Query q = pm.newQuery(Book.class); q.setOrdering("asin desc"); try {     List<Book> books = (List<Book>) q.execute();     for (Book b : books) {         results.add(b);     } } finally {     pm.close(); } return results;     }
  30. 30. Use Cases Servlet implementations of use cases     List all books     Add a new book     Remove a book Each is mapped in web.xml file Each goes through a service class to fill in book details Each forwards to JSP
  31. 31. List All Books     public void doGet(     HttpServletRequest req, HttpServletResponse resp)  throws IOException, ServletException { AmazonBookService service = new AmazonBookService(); Set<Book> books = (Set<Book>) service.getBooks(); req.setAttribute("books", books); req.getRequestDispatcher("books.jsp").forward(req, resp);     } What is that AmazonBookService?     It converts XML to Book instances     Enter Groovy...
  32. 32. Amazon Book Service Class implemented in Groovy: class AmazonBookService { def baseUrl = '' def params = ['Service':'AWSECommerceService',              'Operation':'ItemLookup',              'AWSAccessKeyId':'... long ugly key ...',              'AssociateTag':'kouitinc-20',              'ResponseGroup':'Medium'] BookDAO dao = DAOFactory.instance.bookDAO
  33. 33. Amazon Book Service def getBooks() { def books = dao.findAllBooks() books.each { book -> book = fillInBookDetails(book) } return books }
  34. 34. Amazon Book Service def fillInBookDetails(Book book) { def queryString = params.collect { k,v -> "$k=$v" }.join('&') def url = "${baseUrl}?${queryString}&ItemId=${book.asin}" def response = new XmlSlurper().parse(url) def item = response.Items.Item book.title = item.ItemAttributes.Title =              item.ItemAttributes.Author.collect { it }.join(', ') book.formattedPrice =              item.ItemAttributes.ListPrice.FormattedPrice book.mediumImageURL = item.MediumImage.URL book.detailPageURL = item.DetailPageURL return book     }
  35. 35. One annoying thing For Groovy classes,     GAE needs all compiled classes in         war/WEB-INF/classes/ ...         (normal for WAR files)     But couldn't get that and Groovy Eclipse plugin         to keep them in classpath at same time     Had to manually copy compiled classes to proper dir     Grrr... but at least it worked  (probably Eclipse issue)
  36. 36. JSP books.jsp displays all the books in the request <%@ taglib prefix="c" uri="" %> <%@ page isELIgnored="false" %> ...       <c:forEach items="${books}" var="book">        <tr>             <td><a href="${book.detailPageURL}">                  <img alt="${book.title} picture"                         src="${book.mediumImageURL}">                  </a></td>         
  37. 37. JSP     <td>         <ul>             <li>ISBN: ${book.asin}</li>             <li style="font-weight: bold;">             <a href="${book.detailPageURL}">${book.title}</a></li>             <li style="font-style: italic;">${}</li>             <li>${book.formattedPrice}</li>         </ul>     </td>     <td>${book.recommendation}</td>
  38. 38. Resulting Display
  39. 39. Admin Capabilities Use GAE UserService class UserService us = UserServiceFactory.getUserService();      if (us.isUserLoggedIn()) {       <p><a href="<%=          us.createLogoutURL("/listbooks") %>">Logout</a></p>     } else {     <p><a href="<%=          us.createLoginURL("/listbooks") %>">Login</a></p>     } Yeah, ugly scriptlet code, but so be it
  40. 40. Admin Capabilities If logged in user and user is registered admin,     Can add new books     Can delete existing books Otherwise links aren't available Probably best to make a custom JSP tag out of this     Or use a real security solution         JSecurity, Spring Security, etc. Easy enough for a demo, though
  41. 41. Admin Capabilities Can set billing limit, too     Mine is $2/day,         so don't bother writing those scripts ... :)
  42. 42. Other Services URL fetch service         Just opening a URL means we're using it already         Has more capabilities for alternate request types Mail service     Can only send, not receive     Limits on size, frequency, but seem reasonable Memcache     API implements JCache interface
  43. 43. Memcache Caching capability based on javax.cache package     JCache: JSR 107 (under development)     Cache cache = CacheManager.instance.         cacheFactory.createCache(props)     ...     if (cache.get(book.asin)) {         book = cache.get(book.asin)     } else { book = fillInBookDetails(book) cache.put(book.asin,book)     }
  44. 44. Scheduling CRON jobs supported in cron.xml <?xml version="1.0" encoding="UTF-8"?> <cronentries>     <cron>         <url>/listbooks</url>         <description>Repopulate the cache every day at             5am</description>         <schedule>every day 05:00</schedule>     </cron> </cronentries>
  45. 45. Admin Console Administrative console located at   for non-Google Apps  or if the domain is using Google Apps Current limit of 10 apps per user Can check activity, quotas, etc.
  46. 46. GAE vs. Amazon EC2 Amazon EC2 installs images     You need to configure server, JVM, etc. GAE is a sandbox with provided services     Detailed admin console available     Java persistence framework built in
  47. 47. The Quest for the Holy Grails Grails framework     Spring + Hibernate + Groovy Modular -- built on plugins     Now there's a GAE plugin         Uninstall hibernate, can then use JDO         Some quirks, but it's early yet     Will eventually be the easiest way to build a GAE app
  48. 48. Grails GAE Plugin 1. Create Grails app with matching name     (Workaround available if not possible) 2. Uninstall Hibernate plugin 3. Install app-engine plugin (set APPENGINE_HOME) 4. Set version to 1 (or some other int)     GAE doesn't like decimal version numbers 5. Deploy using package command
  49. 49. Opinionated Conclusions: Bad Stuff Must be able to deploy a WAR file     Hard to take GAE seriously otherwise     Expect this to be easy in release version Must support the full Java EE standard     Sun (Oracle?) is very upset about this...     Also hard to port existing apps otherwise Should support other persistence options     Especially Hibernate     Spring would be nice, too (might be asking a lot)     But non-relational issues will persist (sorry)
  50. 50. Opinionated Conclusions: Good Stuff Easy to use cloud framework     Great entry-level tool Scales like Google Free!      You get a fully-functioning system for free     Did I mention that it's free?     (okay, within limits, but it's free for a while)
  51. 51. Links Google App Engine home Source code     git://  Deployed App URL  GAE Plugin for Grails