In this chapter, we create a simple web application with the Maven Archetype plugin. We’ll run this web application in a Servlet container named Jetty, add some dependencies, write a simple Servlet, and generate a WAR file. At the end of this chapter, you will be able to start using Maven to accelerate the development of web applications.
The example in this chapter is generated with the Maven Archetype plugin. While you should be able to follow the development of this chapter without the example source code, we recommend downloading a copy of the example code to use as a reference. This chapter’s example project may be downloaded with the book’s example code at:
http://books.sonatype.com/mvnex-book/mvnex-examples.zip
Unzip this archive in any directory, and then go to the
ch-simple-web directory. There you will see a directory named
simple-webapp, which contains the Maven project developed in this
chapter.
We’ve purposefully kept this chapter focused on Plain-Old Web Applications (POWA)—a Spring Framework; and the other that uses Plexus.
To create your web application:
$ mvn archetype:generate -DgroupId=org.sonatype.mavenbook.simpleweb \
-DartifactId=simple-webapp \
-Dpackage=org.sonatype.mavenbook \
-Dversion=1.0-SNAPSHOT
...
[INFO] [archetype:generate {execution: default-cli}]
Choose archetype:
...
19: internal -> maven-archetype-webapp (A simple Java web application)
...
Choose a number: (...) 15: : 19
Confirm properties configuration:
groupId: org.sonatype.mavenbook.simpleweb
artifactId: simple-webapp
version: 1.0-SNAPSHOT
package: org.sonatype.mavenbook.simpleweb
Y: : Y
[INFO] Parameter: groupId, Value: org.sonatype.mavenbook.simpleweb
[INFO] Parameter: packageName, Value: org.sonatype.mavenbook.simpleweb
[INFO] Parameter: package, Value: org.sonatype.mavenbook.simpleweb
[INFO] Parameter: artifactId, Value: simple-webapp
[INFO] Parameter: basedir, Value: /private/tmp
[INFO] Parameter: version, Value: 1.0-SNAPSHOT
...
[INFO] BUILD SUCCESSFUL
Once the Maven Archetype plugin creates the project, change
directories into the simple-webapp directory and take a look at the
pom.xml. You should see something close to the following.
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.sonatype.mavenbook.simpleweb</groupId>
<artifactId>simple-webapp</artifactId>
<packaging>war</packaging>
<version>1.0-SNAPSHOT</version>
<name>simple-webapp Maven Webapp</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<finalName>simple-webapp</finalName>
</build>
</project>
Next, you will need to configure the Maven Compiler plugin to target Java 5. To do this, add the plugins element to the initial POM as shown in POM for the simple-webapp Project with Compiler Configuration.
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.sonatype.mavenbook.simpleweb</groupId>
<artifactId>simple-webapp</artifactId>
<packaging>war</packaging>
<version>1.0-SNAPSHOT</version>
<name>simple-webapp Maven Webapp</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<finalName>simple-webapp</finalName>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>1.5</source>
<target>1.5</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
Notice the packaging element contains the value war. This packaging
type is what configures Maven to produce a web application archive in
a WAR file. A project with war packaging is going to create a WAR
file in the target/ directory. The default name of this file is
${artifactId}-${version}.war. In this project, the default WAR
would be generated in target/simple-webapp-1.0-SNAPSHOT.war. In the
simple-webapp project, we’ve customized the name of the generated
WAR file by adding a finalName element inside of this project’s build
configuration. With a finalName of simple-webapp, the package
phase produces a WAR file in target/simple-webapp.war.
<project>
[...]
<build>
<finalName>simple-webapp</finalName>
<plugins>
<plugin>
<groupId>org.mortbay.jetty</groupId>
<artifactId>maven-jetty-plugin</artifactId>
</plugin>
</plugins>
</build>
[...]
</project>
Once you’ve configured the Maven Jetty Plugin in your project’s
pom.xml, you can then invoke the Run goal of the Jetty plugin to
start your web application in the Jetty Servlet container. Run mvn
jetty:run from the simple-webapp/ project directory as follows:
~/examples/ch-simple-web/simple-webapp $ mvn jetty:run ... [INFO] [jetty:run] [INFO] Configuring Jetty for project: simple-webapp Maven Webapp [INFO] Webapp source directory = \ ~/svnw/sonatype/examples/ch-simple-web/simple-webapp/src/main/webapp [INFO] web.xml file = \ ~/svnw/sonatype/examples/ch-simple-web/\ simple-webapp/src/main/webapp/WEB-INF/web.xml [INFO] Classes = ~/svnw/sonatype/examples/ch-simple-web/\ simple-webapp/target/classes 2007-11-17 22:11:50.532::INFO: Logging to STDERR via org.mortbay.log.StdErrLog [INFO] Context path = /simple-webapp [INFO] Tmp directory = determined at runtime [INFO] Web defaults = org/mortbay/jetty/webapp/webdefault.xml [INFO] Web overrides = none [INFO] Webapp directory = \ ~/svnw/sonatype/examples/ch-simple-web/simple-webapp/src/main/webapp [INFO] Starting jetty 6.1.6rc1 ... 2007-11-17 22:11:50.673::INFO: jetty-6.1.6rc1 2007-11-17 22:11:50.846::INFO: No Transaction manager found 2007-11-17 22:11:51.057::INFO: Started [email protected]:8080 [INFO] Started Jetty Server
|
Warning
|
If you are running the Maven Jetty Plugin on a Windows
platform you may need to move your local Maven repository to a
directory that does not contain spaces. Some readers have reported
issues on Jetty startup caused by a repository that was being stored
under C:\Documents and Settings\<user>. The solution to this
problem is to move your local Maven repository to a directory that
does not contain spaces and redefine the location of your local
repository in ~/.m2/settings.xml.
|
After Maven starts the Jetty Servlet container, load the URL
http://localhost:8080/simple-webapp/
in a web browser. The simple index.jsp generated by the Archetype is
trivial; it contains a second-level heading with the text "Hello
World!". Maven expects the document root of the web application to be
stored in src/main/webapp. It is in this directory where you will
find the index.jsp file shown in Contents of src/main/webapp/index.jsp.
<html>
<body>
<h2>Hello World!</h2>
</body>
</html>
In src/main/webapp/WEB-INF, we will find the smallest possible web
application web.xml, shown in this next example:
<!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>
<display-name>Archetype Created Web Application</display-name>
</web-app>
A web application with a single JSP page and no configured servlets is
next to useless. Let’s add a simple servlet to this application and
make some changes to the pom.xml and web.xml to support this
change. First, we’ll need to create a new package under
src/main/java named org.sonatype.mavenbook.web:
$ mkdir -p src/main/java/org/sonatype/mavenbook/web $ cd src/main/java/org/sonatype/mavenbook/web
Once you’ve created this package, change to the
src/main/java/org/sonatype/mavenbook/web directory and create a
class named SimpleServlet in SimpleServlet.java, which contains
the code shown in the SimpleServlet class:
package org.sonatype.mavenbook.web;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class SimpleServlet extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
PrintWriter out = response.getWriter();
out.println( "SimpleServlet Executed" );
out.flush();
out.close();
}
}
Our SimpleServlet class is just that: a servlet that prints a simple
message to the response’s Writer. To add this servlet to your web
application and map it to a request path, add the servlet and
servlet-mapping elements shown in the following web.xml to your
project’s web.xml file. The web.xml file can be found in
src/main/webapp/WEB-INF.
<!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>
<display-name>Archetype Created Web Application</display-name>
<servlet>
<servlet-name>simple</servlet-name>
<servlet-class>
org.sonatype.mavenbook.web.SimpleServlet
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>simple</servlet-name>
<url-pattern>/simple</url-pattern>
</servlet-mapping>
</web-app>
Everything is in place to test this servlet; the class is in
src/main/java and the web.xml has been updated. Before we launch
the Jetty plugin, compile your project by running mvn compile:
~/examples/ch-simple-web/simple-webapp $ mvn compile
...
[INFO] [compiler:compile]
[INFO] Compiling 1 source file to \
~/examples/ch-simple-web/simple-webapp/target/classes
[INFO] -----------------------------------------------------
[ERROR] BUILD FAILURE
[INFO] -----------------------------------------------------
[INFO] Compilation failure
/src/main/java/org/sonatype/mavenbook/web/SimpleServlet.java:[4,0] \
package javax.servlet does not exist
/src/main/java/org/sonatype/mavenbook/web/SimpleServlet.java:[5,0] \
package javax.servlet.http does not exist
/src/main/java/org/sonatype/mavenbook/web/SimpleServlet.java:[7,35] \
cannot find symbol
symbol: class HttpServlet
public class SimpleServlet extends HttpServlet {
/src/main/java/org/sonatype/mavenbook/web/SimpleServlet.java:[8,22] \
cannot find symbol
symbol : class HttpServletRequest
location: class org.sonatype.mavenbook.web.SimpleServlet
/src/main/java/org/sonatype/mavenbook/web/SimpleServlet.java:[9,22] \
cannot find symbol
symbol : class HttpServletResponse
location: class org.sonatype.mavenbook.web.SimpleServlet
/src/main/java/org/sonatype/mavenbook/web/SimpleServlet.java:[10,15] \
cannot find symbol
symbol : class ServletException
location: class org.sonatype.mavenbook.web.SimpleServlet
The compilation fails because your Maven project doesn’t have a dependency on the Servlet API. In the next section, we’ll add the Servlet API to this project’s POM.
To write a servlet, we’ll need to add the Servlet API as a dependency to the project’s POM.
<project>
[...]
<dependencies>
[...]
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<version>2.4</version>
<scope>provided</scope>
</dependency>
</dependencies>
[...]
</project>
It is also worth pointing out that we have used the provided scope for this dependency. This tells Maven that the JAR is "provided" by the container and thus should not be included in the WAR. If you were interested in writing a custom JSP tag for this simple web application, you would need to add a dependency on the JSP 2.0 API. Use the configuration shown in this example:
<project>
[...]
<dependencies>
[...]
<dependency>
<groupId>javax.servlet.jsp</groupId>
<artifactId>jsp-api</artifactId>
<version>2.0</version>
<scope>provided</scope>
</dependency>
</dependencies>
[...]
</project>
Once you’ve added the Servlet specification as a dependency, run mvn clean install followed by mvn jetty:run.
|
Note
|
mvn jetty:run will continue to run the Jetty servlet container
until you stop the process with CTRL-C. If you started Jetty in
Configuring the Jetty Plugin, you will need to stop that process
before starting Jetty a second time.
|
[tobrien@t1 simple-webapp]$ mvn clean install ... [tobrien@t1 simple-webapp]$ mvn jetty:run [INFO] [jetty:run] ... 2007-12-14 16:18:31.305::INFO: jetty-6.1.6rc1 2007-12-14 16:18:31.453::INFO: No Transaction manager found 2007-12-14 16:18:32.745::INFO: Started [email protected]:8080 [INFO] Started Jetty Server
At this point, you should be able to retrieve the output of the SimpleServlet. From the command line, you can use curl to print the output of this servlet to standard output:
~/examples/ch-simple-web $ curl http://localhost:8080/simple-webapp/simple SimpleServlet Executed
After reading this chapter, you should be able to bootstrap a simple web application. This chapter didn’t dwell on the million different ways to create a complete web application. Other chapters provide a more comprehensive overview of projects that involve some of the more popular web frameworks and technologies.