Lecture 10 Fundamentals of GAE Development. Cloud Application Development (SE808, School of Software, Sun Yat-Sen University) Yabo (Arber) Xu

Transcription

1 Lecture 10 Fundamentals of GAE Development Cloud Application Development (SE808, School of Software, Sun Yat-Sen University) Yabo (Arber) Xu

2 Outline GAE Architecture GAE Dev Environment Anatomy of GAE Demo 2 / 44

3 GAE Service Architecture Front-End: Load Balancing & Request Forwarding Static Files: Serving static files, i.e. images/css/js AppServer: Process requests & call services Datastore: central place for data persistence

4 Under the Cover of GAE Reuse of lots Google existing technologies Datastore Service: Bigtable Images Service: Picasa User Service: Google Accounts. Protocol Buffers A RPC protocol to support communication among different service Platform/Language Independent Shared-Nothing Architecture AppServer / AppServer Datastore 4 / 44

5 Dev Environment JDK 6 Google Plugin for Eclipse GAE Java SDK Support Java Servlet Standard 5 / 44

6 GAE Dev Stacks 6 / 44

7 GAE Sandbox Applications run in a restricted "sandbox" environment Limited access to OS. Limitations enable scalability. GAE Applications can execute code, store and query data in the App Engine datastore use the GAE mail, URL fetch and users services, and many others examine the user's web request and prepare the response. GAE Applications cannot: Write to the file system. Use datastore instead. Open a socket or access another host directly. Use URL fetch services instead. Spawn a sub-process or thread. A web request to an application must be handled in a single process within a few seconds. Make other kinds of system calls. 7 / 44

8 GAE SDK Core Packages com.google.appengine.api.datastore com.google.appengine.api.images com.google.appengine.api.mail com.google.appengine.api.memcache com.google.appengine.api.urlfetch com.google.appengine.api.users Scheduled tasks with cron service Java tools for testing/uploading app and downloading logs 8 / 44

9 Anatomy of GAE demo GuestBook 9 / 44

10 GAE Demo: GuestBook Project Directory Structure 10 / 44

11 Java Servlet GAE Applications use Java Servlet API to interact with web servers AServlet is a class that can process and repsond to web requests. src/guestbook/guestbookservlet.java 11 / 44

12 Web Application Deployment Descriptor war/web-inf/web.xml Determines mapping between url/servlet

13 GAE Configuration war/web-inf/appengine-web.xml Configurations on GAE delopyment

14 Run & Test locally Run as Web Application Test URL: HttpRequest Front End AppServer HttpRequest HttpResponse GuestBookServlet

15 JSP Template systems for making complicated pages war/guestbook.jsp

16 More JSP &Servlet Implements guestbook form Map post request to a newservlet

17 More JSP &Servlet Logging behavior can be controlled by logging.properties configuration file ( need to add system-properties in war/web_inf/appengine-web.xml)

18 Data Persistence via JDO JDO: Standard Java Persistence API, implemented by DataNucleus Access Platform Easy to port to other platforms later It tells how to store & retrieve Java Objects through notations

19 PersistenceManagerFactory Each request to datastore needs a instance of PersistanceManager class, so create a singleton wrapper class

20 Store Data via JDO src/guestbook/signguestbookservlet.java

21 JDOQL Perform queries of entities in GAE store Similar to SQL An example: select from guestbook.greeting order by date desc range 0,5

22 JDOQL Perform queries of entities in GAE store

23 Using Static Files For efficiency, Static files such as images, CSS, JS, movies are served directly to browsers All files under war except JSP and WEB-INF are available as static files

24 Local Dev Server 24 / 44

25 OK, now we can start dancing on GAE!