5.1. Introduction
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.
5.1.1. Downloading this Chapter’s Example
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.
5.2. Defining the Simple Web Application
We’ve purposefully kept this chapter focused on Plain-Old Web Applications (POWA)—a Spring Framework; and the other that uses Plexus.
5.3. Creating the Simple Web Project
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
不同版本的maven菜单可能有些差别，在选择的时候要选择maven-archetype-webapp对应的数字。比如在maven使用3.5.0版本的时候，要选择10.
[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-1WiEDifz-1583571232228)(D:%5C20190919%5Cappcontainer%5C%E5%AD%A6%E4%B9%A0%E7%AC%94%E8%AE%B0%5Cmaven%5Cimage-20200307161819405.png)]
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.
Initial POM for the simple-webapp Project.
<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 8. To do this, add the plugins element to the initial POM as shown in POM for the simple-webapp Project with Compiler Configuration.
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>1.8</source>
<target>1.8</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.
5.4. Configuring the Jetty Plugin
Configuring the Jetty Plugin.
<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] Configuring Jetty for project: simple-webapp Maven Webapp
[INFO] Webapp source directory = D:\maven\simple-webapp\src\main\webapp
[INFO] Reload Mechanic: automatic
[INFO] Classes = D:\maven\simple-webapp\target\classes
[INFO] Logging to org.slf4j.impl.SimpleLogger(org.mortbay.log) via org.mortbay.log.Slf4jLog
[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] web.xml file = D:\maven\simple-webapp\src\main\webapp\WEB-INF\web.xml
[INFO] Webapp directory = D:\maven\simple-webapp\src\main\webapp
[INFO] Starting jetty 6.1.26 ...
[INFO] jetty-6.1.26
[INFO] No Transaction manager found - if your webapp requires one, please configure one.
[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\. 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.
修改maven的setting.xml文件可以修改本地仓库路径，比如如下设置将本地仓库路径设置为d:/maven/repo
<!-- localRepository
| The path to the local repository maven will use to store artifacts.
|
| Default: ${user.home}/.m2/repository
<localRepository>/path/to/local/repo</localRepository>
-->
<localRepository>d:/maven/repo</localRepository>
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.
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:
Contents of src/main/webapp/WEB-INF/web.xml.
<!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>
5.5. Adding a Simple Servlet
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:
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.
Mapping the Simple Servlet.
<!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:
[INFO] Scanning for projects...
[WARNING]
[WARNING] Some problems were encountered while building the effective model for org.sonatype.mavenbook.simpleweb:simple-webapp:war:1.0-SNAPSHOT
[WARNING] 'build.plugins.plugin.version' for org.mortbay.jetty:maven-jetty-plugin is missing. @ line 42, column 12
[WARNING]
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING]
[INFO]
[INFO] -----------< org.sonatype.mavenbook.simpleweb:simple-webapp >-----------
[INFO] Building simple-webapp Maven Webapp 1.0-SNAPSHOT
[INFO] --------------------------------[ war ]---------------------------------
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ simple-webapp ---
[INFO] Deleting D:\maven\simple-webapp\target
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ simple-webapp ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 0 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.3:compile (default-compile) @ simple-webapp ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent!
[INFO] Compiling 1 source file to D:\maven\simple-webapp\target\classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.403 s
[INFO] Finished at: 2020-03-07T16:51:27+08:00
[INFO] ------------------------------------------------------------------------
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.
5.6. Adding J2EE Dependencies
To write a servlet, we’ll need to add the Servlet API as a dependency to the project’s POM.
Add the Servlet 2.4 Specification as a Dependency.
<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:
Adding the JSP 2.0 Specification as a Dependency.
<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 Section 5.4, “Configuring the Jetty Plugin”, you will need to stop that process before starting Jetty a second time.
[INFO] --- maven-jetty-plugin:6.1.26:run (default-cli) @ simple-webapp ---
[INFO] Configuring Jetty for project: simple-webapp Maven Webapp
[INFO] Webapp source directory = D:\maven\simple-webapp\src\main\webapp
[INFO] Reload Mechanic: automatic
[INFO] Classes = D:\maven\simple-webapp\target\classes
[INFO] Logging to org.slf4j.impl.SimpleLogger(org.mortbay.log) via org.mortbay.log.Slf4jLog
[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] web.xml file = D:\maven\simple-webapp\src\main\webapp\WEB-INF\web.xml
[INFO] Webapp directory = D:\maven\simple-webapp\src\main\webapp
[INFO] Starting jetty 6.1.26 ...
[INFO] jetty-6.1.26
[INFO] No Transaction manager found - if your webapp requires one, please configure one.
[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
因为此处发起的为POST请求，可以通过下载软件curl操作，或者通过postman发起post请求。
5.7. Conclusion
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.
