Lab 10. Google App Engine. Tomas Lampo. November 11, 2010

Transcription

1 Lab 10 Google App Engine Tomas Lampo November 11, 2010 Today, we will create a server that will hold information for the XML parsing app we created on lab 8. We will be using Eclipse and Java, but we will also use Objective C. 1. Open Eclipse and make sure that you have installed the Google Plugin ( 2. Click File New Web Application Project and create a project named mynews. Package name should be mynews. 3. Google generates automatically for you a dense folder structure. For this project, we will ignore whatever is in the test package, as well as the packages mynews.client, mynews.server and mynews.shared. 4. Right click the mynews package and add a New Class, called ArticlesServlet. A servlet is nothing but a HTTP request manager, that receives information and then yields a document in a given format. It should look like this: package mynews; import java.io.ioexception; import java.text.simpledateformat; import java.util.list; import javax.jdo.persistencemanager; 1

2 import javax.servlet.http.*; public class ArticlesServlet extends HttpServlet { public void doget(httpservletrequest req, HttpServletResponse resp) throws IOException { resp.setcontenttype("text/plain"); resp.getwriter().println("hello, World!"); What this class does, is that it receives a GET request and creates a plain text document that says Hello, World!. 5. So now we have the servlet ready, but how do we access it on the server? Well, we need to map an address on the server to it. The only way to do that is by modifying the file war/web-inf/web.xml. Make sure you re working in Source Mode (click the Source tab), so it will be easier to modify. Again, Google already populated the file for you. We want to connect the servlet we created with the url YOURSERVER/articles. <servlet> <servlet-name>articlesservlet</servlet-name> <servlet-class>mynews.articlesservlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>articlesservlet</servlet-name> <url-pattern>/articles</url-pattern> </servlet-mapping> Can you understand how it works? 6. Test your server. Go back to the servlet Class we created and then select Run Run As Web Application. 2

3 If there are no errors in your code, this will create a local server in your computer, in port Visit the url and you should see the Hello, World! string. 7. That s all you need to create a basic website with the Google App Engine! We will now create a new class that describes the Article object, and tell the server that this class can actually hold objects, acting like a database. Right click the mynews package and add a new class. Call it Article. 8. You should already be familiar with Java, so here s a quick explanation of what the Article object has: String title String content String author Date date But, since this class actually will act like a database, we need to add some special tags: package mynews; import java.util.date; import com.google.appengine.api.datastore.key; import javax.jdo.annotations.idgeneratorstrategy; import javax.jdo.annotations.persistencecapable; import javax.jdo.annotations.persistent; import public class = IdGeneratorStrategy.IDENTITY) private Key key; 3

4 @Persistent private String author; Can you see how author looks? Do the same for the title, content and date. Using Eclipse, generate the Getters for all the variables, and Setters for all the variables except key. You should also generate an Article creator method that receives the author, title and content, and assigns the current date automatically to the object. 9. Create a new class and call it PMF. This class will be the Database Manager. Its contents should look like this: package mynews; import javax.jdo.jdohelper; import javax.jdo.persistencemanagerfactory; public final class PMF { private static final PersistenceManagerFactory pmfinstance = JDOHelper.getPersistenceManagerFactory("transactions-optional"); private PMF() { public static PersistenceManagerFactory get() { return pmfinstance; Include this class whenever you need to make database calls in Google App Engine. 10. From now on, you should be able to continue on your own. I will provide clues for the complicated parts, but you should provide the rest of the code yourself. You are going to modify the ArticlesServlet class you created so it generates an XML document with a format that can populate the app you created in Lab8. For this, you will this: 4

5 PersistenceManager pm = PMF.get().getPersistenceManager(); resp.setcontenttype("text/xml"); //Our file will be in XML format resp.getwriter().println("<?xml version=\"1.0\" encoding=\"utf-8\"?>"); //Prints the XML document header. String query = "select from " + Article.class.getName() + ""; //Query for getting all the articles List<Article> articles = (List<Article>) pm.newquery(query).execute(); //The articles container. /*Provide code that will print all the articles with the correct format for your app. Resulting XML should look like this: <?xml version="1.0" encoding="utf-8"?> <articles> <item> <title>new 1</title> <pubdate>thu, 11 Nov :37:20 UTC</pubDate> <description>content 1</description> <author>tomas Lampo</author> </item>... </articles>!!!make sure you re printing the date in the right format. Use a date formatter for that. */ 11. Create a Servlet that allows you to add new articles to the server. Whenever you make a call like this: It should save an article in the server with the given information. You will need to have this code: resp.setcontenttype("text/plain"); String title = req.getparameter("title"); 5

6 /* Get the author and the content.*/ Article a = new Article(author, title, content); String ans = "NO"; PersistenceManager pm = PMF.get().getPersistenceManager(); try { pm.makepersistent(a); finally { ans = "YES"; pm.close(); resp.getwriter().println(ans); That s it! Remember to add this servlet to the web.xml file and test your servlets! 12. Finally, upload your app to the Google server. Go to and create a new application. Then, go back to Eclipse and select the little Airplane/Engine button. Whatever you do, do not click the Cancel button once the upload process started. You will block your app on the server forever. Believe me. Now that we know that, let s upload the app to the server. Input your Google and password and click the App Engine Project Settings blue link. Remember the App ID you used on the server? It must match the app ID on the setting. Click the Deploy button and watch how Eclipse uploads your app for you (Warning. This process is super slow. Again: Do not click the cancel button). 13. Let s go back to programming the iphone. You re almost done! Duplicate your Lab8 folder and open your Lab8 project in XCode. Modify the AppDelegate Class so your app connects to the new URL in your server. Also modify the ParseOperation class to match the new tags you used in your XML document. 6

7 14. Upload 3 random articles in your server by modifying the URL to match your server s address and having your name as the author, instead of mine Did the articles appear in your app? 7