This chapter is from the book
This chapter is from the book
This chapter is from the book
Deploying Applications
Deploying a GWT application can be as easy as deploying a regular web page. A simple GWT client is made up of HTML and JavaScript files that can be copied to a directory on a web server and loaded into a browser. For example, the Gadget Desktop application in Chapter 6 does not use any server-side code, so its files for deployment are simply its JavaScript files, several image files, and the host HTML file. You can install this application on any web server simply by copying the files.
Deploying to a Web Server
You've seen how to set up development environments with Java tools, run the GWT scripts, and use the GWT jar files, but for a client-side application these files are left on the development machine. You simply need to run the GWT compile script, or click the Compile button in the GWT hosted mode browser, to generate the files needed for deployment. For example, compiling the Gadget Desktop application can be done from the command line. Or it can be compiled from the hosted mode browser, as shown in Figure 4-47. GWT places these files in a directory named after your application inside the www directory for your project, as you can see in Figure 4-48. This is the file list that you would copy to a directory on your web server.
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Figure 4-47 Compiling your application from the GWT hosted mode browser
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Figure 4-48 The GWT compiler places the files to deploy in www
Deploying a Servlet to a Servlet Container
If you are using GWT-RPC, you will need to deploy your service implementation to a servlet container. Although the GWT hosted mode browser runs an embedded version of Tomcat, deploying to a regular Tomcat instance is somewhat different. If you are deploying to Tomcat, you'll need to add your application to its webapps directory. Figure 4-49 outlines the steps to add your application to Tomcat's directory structure.
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Figure 4-49 Steps to deploy your application to Tomcat
Let's look at the five steps shown in Figure 4-49. First you need to locate the installation directory for Tomcat. Second, you need to create your application directory under the webapps directory. Third, you need to set up your web.xml file in the WEB-INF directory for your application. For the Instant Messenger application, the file looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<web-app>
<servlet>
<servlet-name>messenger</servlet-name>
<servlet-class>com.gwtapps.messenger.server.MessengerServiceImpl</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>messenger</servlet-name>
<url-pattern>/messenger</url-pattern>
</servlet-mapping>
</web-app>
Fourth, copy your servlet class to the class' directory in the WEB-INF directory. Finally, fifth, copy the gwt-servlet.jar file to the lib directory in the WEB-INF directory. The gwt-servlet.jar file has the GWT classes required to support the server-side RPC. You could use gwt-user.jar instead, but gwt-servlet.jar is smaller and therefore preferred. Deployment can be automated by using a build tool such as Ant.
Automating Deployment with Ant
As you can see from the previous section, deployment to a server container often involves many steps of compiling code, copying files, and creating directories. When a task involves many steps like this, it is best to automate the process. Ant is the ideal Java tool for automating build tasks like this. With it you can accomplish all of the previous steps of deploying a GWT web application with one Ant step.
Ant is a command line tool that accepts an XML build file. The build file contains a list of build targets with steps to accomplish build tasks. There is rich support for different types of steps, including copying files, creating directories, and compiling code. The Ant system is also extensible, so you can develop new steps or add new steps from other developers.
Let's run through an example of how to build a GWT application for use on a servlet container with Ant. First, verify that you have Ant installed and in your path. You should be able to type ant –version at the command line, as shown in Figure 4-50.
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Figure 4-50 Verifying Ant is on your system
If you don't have Ant installed, you can download it from http://ant.apache.org. After ensuring that Ant is installed on your development machine, you can write a build.xml file for a project. The following is the build.xml file we will use:
<project default="deploy">
<property name="gwtpath" value="/Users/ryan/lib/gwt-mac-1.4.10"/>
<property name="gwtapipath" value="/Users/ryan/lib/gwt-google-apis-1.0.0"/>
<property name="targetdir" value="${basedir}/www/${app}"/>
<property name="wwwdir" value="${basedir}/www"/>
<property name="srcdir" value="${basedir}/src"/>
<property name="bindir" value="${basedir}/bin"/>
<path id="classpath">
<pathelement location="${gwtapipath}/gwt-google-apis.jar"/>
<pathelement location="${gwtpath}/gwt-user.jar"/>
<pathelement location="${gwtpath}/gwt-dev-mac.jar"/>
<pathelement location="${srcdir}"/>
<pathelement location="${bindir}"/>
</path>
<target name="compile-gwt">
<java classname="com.google.gwt.dev.GWTCompiler" fork="true">
<classpath refid="classpath"/>
<jvmarg value="-XstartOnFirstThread"/>
<arg value="-out"/>
<arg value="${wwwdir}"/>
<arg value="${app}"/>
</java>
</target>
<target name="compile" depends="compile-gwt">
<mkdir dir="${targetdir}/WEB-INF/classes"/>
<javac srcdir="${srcdir}"
destdir="${targetdir}/WEB-INF/classes"
excludes="**/client/*.java">
<classpath refid="classpath"/>
</javac>
</target>
<target name="deploy" depends="compile">
<mkdir dir="${targetdir}/WEB-INF/lib"/>
<copy todir="${targetdir}/WEB-INF/lib" file="${gwtpath}/gwt-servlet.jar"/>
<copy tofile="${targetdir}/WEB-INF/web.xml"
file="${basedir}/${app}.web.xml"/>
</target>
</project>
The file begins by defining a project element with a default target. This target is run when one is not specified on the command line. The first few elements inside the project tag are property definition elements. You can place variables in these elements that will be reused throughout the build file. For example, in this file we have the source directories and jar directories set for use later. Inside the attributes you can see how the properties can be referenced with the ${name} format. Before the targets are defined in the file, we set a path element. This element lists the jar files and directories that are on the classpath. We use this classpath later and can refer to it by its ID.
The first target, compile-gwt, runs the GWT compiler on our GWT module. The module is not specified in this target. Instead the ${app} placeholder is used. We have not defined this as a property, but we can pass in this variable as a command line argument. This gives the build file the flexibility of being used for more than one application. Running this target generates the compiled JavaScript files for the application and copies all of the public files used for the project to the www directory.
The second target, compile, uses the regular javac compiler to compile all of the other Java class files. These are class files that will be needed on the server and will include the GWT-RPC service servlet if one is used. The Ant script copies these class files to the www directory under WEB-INF/classes. This is the standard location for class files for a servlet container web application.
The final target, deploy, copies the required GWT library, gwt-servlet.jar, to the WEB-INF/lib directory. This is the standard location for jar files for a servlet container web application. The target also copies a predefined web.xml file to the www directory. The web.xml file is required to describe the servlets in the web application.
Running the task for the Instant Messenger application in Chapter 9 results in the output shown in Figure 4-51. Once this is complete, we should have a www directory that is ready to be used in a servlet container, and which follows the conventions for servlet containers for file names and locations, as illustrated in Figure 4-52.
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Figure 4-51 Compiling and deploying with Ant
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Figure 4-52 The output from an Ant script