Alphageeks IL #2 Google App Engine

Google App Engine
לירן זילכה
מנכ"ל משותף
Liran.zelkha@alunasoft.com

Aluna
Israel’s leading Java/JavaEE and SOA consulting company
Customers:

Installing The SDK
Java 5 & 6 are supported
Download google eclipse plugin from
Or just download and install the SDK
http://dl.google.com/eclipse/plugin/3.4
http://code.google.com/appengine/downloads.html

App Engine Project
A standard JavaEE WAR file

The Servlet
package guestbook;
import java.io.IOException;
import javax.servlet.http.*;
public class GuestbookServlet extends HttpServlet {
public void doGet(HttpServletRequestreq, HttpServletResponseresp)
throws IOException {
resp.setContentType("text/plain");
resp.getWriter().println("Hello, world");
}
}

Web.xml
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE web-app PUBLIC
"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app xmlns="http://java.sun.com/xml/ns/javaee" version="2.5">
<servlet>
<servlet-name>guestbook</servlet-name>
<servlet-class>guestbook.GuestbookServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>guestbook</servlet-name>
<url-pattern>/guestbook</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>/index.html</welcome-file>
</welcome-file-list>
</web-app>

Appengine-web.xml
<?xml version="1.0" encoding="utf-8"?>
<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
<application></application>
<version>1</version>
</appengine-web-app>

Run/Debug
Web server runtime comes with the plugins

Users service
package guestbook;
public class GuestbookServlet extends HttpServlet {
public void doGet(HttpServletRequestreq, HttpServletResponseresp)
throws IOException {
UserServiceuserService = UserServiceFactory.getUserService();
User user = userService.getCurrentUser();
if (user != null) {
resp.setContentType("text/plain");
resp.getWriter().println("Hello, " + user.getNickname());
} else {
resp.sendRedirect(userService.createLoginURL(req.getRequestURI()));
}
}
}

Other Services
Datastore
Database with JDO and JPA access
Memcache
Implements Jcache
URL Fetch
Or just use java.net.URLConnection
Images
Image editing capabilities
Jobs
Google Accounts

Using JPA
<?xml version="1.0" encoding="UTF-8" ?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0">
<persistence-unit name="transactions-optional">
<provider>org.datanucleus.store.appengine.jpa.DatastorePersistenceProvider</provider>
<properties>
<property name="datanucleus.NontransactionalRead" value="true"/>
<property name="datanucleus.NontransactionalWrite" value="true"/>
<property name="datanucleus.ConnectionURL" value="appengine"/>
</properties>
</persistence-unit>
</persistence>

Getting EntityManager
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
public final class EMF {
private static final EntityManagerFactoryemfInstance =
Persistence.createEntityManagerFactory("transactions-optional");
private EMF() {}
public static EntityManagerFactory get() {
return emfInstance;
}
}

Uploading
Register at https://appengine.google.com/
Deploy from your eclipse environment
Access at http://application-id.appspot.com/

App Engine Sandbox
An App Engine application cannot:
write to the filesystem. Applications must use the App Engine datastore for storing persistent data. Reading from the filesystem is allowed, and all application files uploaded with the application are available.
open a socket or access another host directly. An application can use the App Engine URL fetch service to make HTTP and HTTPS requests to other hosts on ports 80 and 443, respectively.
spawn a sub-process or thread. A web request to an application must be handled in a single process within a few seconds. Processes that take a very long time to respond are terminated to avoid overloading the web server.
make other kinds of system calls.