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You can study the JavaMail API in more detail to understand how to do things like sending attachments in your email too. You can do that using the Google App Engine Email Service.

To get the development environment working the plugin also requires access to the unzipped SDK as packaged by Google. The plugin tries to help you set this up (“gae:unpack”) but that failed for me. I was able to get stuff working by manually unzipping the SDK artifact downloaded directly from Google to the following directory: ~/.m2/repository/com/google/appengine/appengine-java-sdk/1.3.0/appengine-java-sdk-1.3.0

You’ll also notice in our appengine-web.xml that we substitute in our application name. By default this comes from the properties section of the pom.xml file (line 11).

protocol

ublic void doGet(HttpServletRequest req, HttpServletResponse resp)     throws IOException {    resp.setContentType("text/plain");    final DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();    final Query query = new Query("Table/Entity Name");    //query.addSort(Entity.KEY_RESERVED_PROPERTY, Query.SortDirection.DESCENDING);    for (final Entity entity : datastore.prepare(query).asIterable()) {        resp.getWriter().println(entity.getKey().toString());        final Map<String, Object> properties = entity.getProperties();        final String[] propertyNames = properties.keySet().toArray(            new String[properties.size()]);        for(final String propertyName : propertyNames) {            resp.getWriter().println("-> " + propertyName + ": " + entity.getProperty(propertyName));        }    }}

Don't bother with GQL for key-based retrieval -- make a key object from the string: k = db.Key('aght52oobW1hZHIOCxIHTWVzc2FnZRiyAQw') and just db.get(k). If you insist on GQL, btw, that k -- a suitably constructed instance of db.Key, NOT a string object!-) -- is also what you need to substitute into the GQL query (by :1 or whatrever).

keys are SERIOUSLY unique -- from a key you can get the entity's .app() (so uniqueness across apps is a given), .kind() (so uniqueness WITHIN the app's no problem either), etc.

This tutorial concerns using Google Accounts to maintain the existence of your users in a Google App Engine application. Google App Engine provides the class UserServiceFactory to facilitate that. UserServiceFactory is then used to generate UserService object, which in turn provides the following features createLoginURL createLogoutURL getCurrentUser isUserAdmin isUserLoggedIn You would use UserService object to generate the login URL for the browser. The browser would be directed/redirected to this URL. On reaching this URL, the Google log-in prompt would be displayed by Google's server.

to write large batch processing jobs without having to think about the plumbing details.

it is a very easy way to perform some operation on every single Entity of a given Kind in your datastore in parallel

What would you have to build for yourself if Mapper weren’t available? Begin querying over every Entity in chained Task Queues Store beginning and end cursors (introduced in 1.3.5) Create tasks to work with chunks of your datastore Write the code to manipulate your data Build an interface to control your batch jobs Build a callback system for your multitudes of parallelized workers to call when the entire task has completed It’s certainly not a trivial amount of work

App Engine apps create a channel on a remote server, and are returned a channel ID which they pass off to the web browser.

All you have to do is set the keys when you allocate the entities: Entity entity = new Entity(key); Or if you had previously pulled the entities from the datastore, the keys should already be set.

Right now, when the user removes the GWT/App Engine nature from the project, if they have a SDK container on their build path, it is collapsed into its individual jars, and they are added to the classpath. In some cases, users do not expect this behavior (for example, if they mistakingly added the wrong nature).

Well java.lang.System is whitelisted, so won't java.lang.System.out.println(...) work?

I have an Entity with an id type of Long, and the id gets filled in after I call makePersistent(). Here is what the code looks like:     GameEntity game = new GameEntity();    log.warning("before makePersistent id is " + game.getId());    pm.makePersistent(game);    log.warning("after makePersistent id is " + game.getId()); Here is a snippet of the GameEntity class: @PersistenceCapable(identityType = IdentityType.APPLICATION)public class GameEntity {    @PrimaryKey    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)    private Long id; And the output shows what you'd expect: WARNING 6428 - before makePersistent id is nullWARNING 6444 - after makePersistent id is 6 UPDATE: It occurred to me belatedly that you might want an actual Key object. You can create that yourself if you have the id: public Key getKey() {    return KeyFactory.createKey(GameEntity.class.getSimpleName(), id);}