Getting started with GWT

[In Progress]

Setting up your pom.xml

You will need the following dependencies to get started:

    <dependencies>
        <dependency>
            <groupId>org.atmosphere</groupId>
            <artifactId>atmosphere-gwt-client</artifactId>
            <version>{version}</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.atmosphere</groupId>
            <artifactId>atmosphere-gwt-server</artifactId>
            <version>{version}</version>
        </dependency>
        <dependency>
            <groupId>com.google.gwt</groupId>
            <artifactId>gwt-user</artifactId>
            <version>2.4.0</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>com.google.gwt</groupId>
            <artifactId>gwt-servlet</artifactId>
            <version>2.4.0</version>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-jdk14</artifactId>
            <version>1.6.1</version>
        </dependency>
    </dependencies>

The atmosphere-gwt-client has scope provided because these Java classes will be transformed to javascript and are included into the resulting war package.You should select the slf4j package for the logging framework that you will use. Here we selected the jdk14 bridge for java.util.logging. You can define the following properties for convenience and we will refer to them in this document:

    <properties>
        <gwtModule>org.atmosphere.samples.GWTDemo</gwtModule>
        <gwt.compiler.force>false</gwt.compiler.force>
        <gwt.draftCompile>false</gwt.draftCompile>
        <gwt.style>OBF</gwt.style>
        <outputDir>${war.target}/WEB-INF/classes</outputDir>
    </properties>

<gwtModule> defines the basename and package of your main .gwt.xml file. So in the case of the gwt-demo it is located in src/main/resources/org/atmosphere/samples/GWTDemo.gwt.xml

Next you will need to define and configure the maven-gwt-plugin. This can be done in multiple ways, but what has worked well for the samples is the following:

    <build>
        <outputDirectory>${outputDir}</outputDirectory>
        <plugins>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>gwt-maven-plugin</artifactId>
                <version>${gwt-version}</version>
                <configuration>
                    <module>${gwtModule}</module>
                    <gwtVersion>${gwt-version}</gwtVersion>
                    <runTarget>http://localhost:8888/gwtDemo/gwtDemo.jsp</runTarget>
                    <noServer>false</noServer>
                    <sourcesOnPath>true</sourcesOnPath>
                    <hostedWebapp>${war.target}</hostedWebapp>
                </configuration>
                <executions>
                    <execution>
                        <configuration>
                            <extraJvmArgs>-Xmx512m</extraJvmArgs>
                        </configuration>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>

            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.3.2</version>
                <configuration>
                    <encoding>UTF-8</encoding>
                    <source>1.6</source>
                    <target>1.6</target>
                </configuration>
            </plugin>

            <plugin>
                <artifactId>maven-clean-plugin</artifactId>
                <version>2.4</version>
                <configuration>
                    <filesets>
                        <fileset>
                            <directory>${outputDir}</directory>
                        </fileset>
                        <fileset>
                            <directory>${war.target}/gwtDemo</directory>
                        </fileset>
                        <fileset>
                            <directory>${war.target}/WEB-INF/lib</directory>
                            <includes>
                                <include>*.jar</include>
                            </includes>
                        </fileset>
                        <fileset>
                            <directory>${war.target}/WEB-INF/deploy</directory>
                        </fileset>
                        <fileset>
                            <directory>${basedir}/src/main</directory>
                            <includes>
                                <directory>gwt-unitCache/**</directory>
                            </includes>
                        </fileset>
                    </filesets>
                </configuration>
            </plugin>

        </plugins>
    </build>

You will need to adapt this to your own project specifics.

Setting up your AtmosphereServlet

After setting up your AtmosphereServlet in your web.xml you will need to add the following init parameter to you servlet:

<init-param>
    <!-- prevent deadlocks -->
    <param-name>org.atmosphere.disableOnStateEvent</param-name>
    <param-value>true</param-value>
</init-param>

Which is described here Configuring Atmosphere using the web.xml Simply put: you are in trouble if you dont use this parameter :-)

Setting up your .gwt.xml

You will need to add the following to your .gwt.xml file apart from the usual stuff you need in there

<inherits name="org.atmosphere.gwt.Client"/>
<inherits name="com.google.gwt.logging.Logging"/>
<set-property name="gwt.logging.logLevel" value="INFO"/>
<set-property name="gwt.logging.popupHandler" value="DISABLED"/>

Of course you are free to setup the GWT logging differently.

Setting up your client code

... TODO ...

AtmosphereListener Javadoc

    void onConnected(int heartbeat,
               int connectionID)
    The connection has been established
    Parameters:
    heartbeat - This is the interval with which the server will send heartbeats
    connectionID - This is the unique number that identifies this connection

    void onBeforeDisconnected()
    Send just before the connection is stopped (this can happen also because the window is being closed)

    void onDisconnected()
    The connection has disconnected. When the disconnect was unexpected the connecting will be refreshed.

    void onError(Throwable exception,
           boolean connected)
    An error has occurred.
    Parameters:
    exception -
    connected - This will indicate whether the connection is still alive

    void onHeartbeat()
    The connection has received a heartbeat. When a heartbeat is not received at the expected time, the connection is
    assumed to be dead and a new one is established.

    void onRefresh()
    The connection will be refreshed by the client. This will occur to prevent data from accumulating in the clients comet
    implementation and slowing down message processing. Normally you don't need to do anything with this event. It signals
    the start of a scheduled reconnection. A new connection will be established and the current connection is only dropped
    when the new connection has become alive.

    void onAfterRefresh()
    You will receive this after a connection has been refreshed or re-established and is ready to process new events.

    void onMessage(List<?> messages)
    A batch of messages from the server has arrived.
    Parameters:
    messages -

Running the GWT shell while deployed in a JavaEE container of your choice

What you should do is specify true in the configuration of the maven-gwt-plugin and deploy the war to your tomcat server. After the war is deploy you should run "mvn gwt:run" and the shell will start without starting the build-in jetty. Now you type the url of your page that is hosted by tomcat and add "?gwt.codesvr=127.0.0.1:9997" to the url. This will redirect the javascript to the gwt shell.

Read more about the GWT Maven Plugin

Tips & Tricks

Spinning cursor in Chrome (Webkit) browsers

Try and start the client (AtmosphereClient.start()) [scheduleDeferred](http://google-web-toolkit.googlecode.com/svn/javadoc/2.0/com/google/gwt/core/client/Scheduler.html#scheduleDeferred(com.google.gwt.core.client.Scheduler.ScheduledCommand\))