@WebServlet annotation not recognized; init doesn't run

问题:

I'm trying to learn annotations. I currently have a webapp that runs an init() when the app is started in Tomcat.

The following code works...

web.xml:

<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://java.sun.com/xml/ns/javaee"          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"          xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"          version="3.0">      <servlet>         <servlet-name>MainServlet</servlet-name>         <servlet-class>com.company.Main</servlet-class>         <load-on-startup>1</load-on-startup>     </servlet> </web-app> 

Main.java:

import java.io.IOException; import javax.servlet.*; import javax.servlet.annotation.WebServlet;  //@WebServlet(name="MainServlet", value="/main.jsp", loadOnStartup=1) public class Main extends GenericServlet {      public Main() { }      @Override     public void init() {         System.out.println("Hello!");     }      @Override     public void destroy() {         System.out.println("Bye!");     }      @Override     public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException { } } 

However, when I uncomment the @WebServlet annotation and comment out the servlet entry in web.xml, the init method doesn't run.

Am I missing something obvious?

In case this will help, this is my pom.xml:

<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>...</groupId>     <artifactId>...</artifactId>     <packaging>war</packaging>     <version>1.0-SNAPSHOT</version>     <name>Name</name>     <url>http://maven.apache.org</url>     <build>         <plugins>             <plugin>                 <groupId>org.apache.maven.plugins</groupId>                 <artifactId>maven-compiler-plugin</artifactId>                 <version>2.0.2</version>                 <configuration>                     <source>1.6</source>                     <target>1.6</target>                 </configuration>             </plugin>         </plugins>     </build>     <dependencies>         <dependency>             <groupId>junit</groupId>             <artifactId>junit</artifactId>             <version>3.8.1</version>             <scope>test</scope>         </dependency>          <dependency>             <groupId>org.springframework</groupId>             <artifactId>spring-core</artifactId>             <version>3.0.5.RELEASE</version>         </dependency>          <dependency>             <groupId>org.springframework</groupId>             <artifactId>spring-tx</artifactId>             <version>3.0.5.RELEASE</version>         </dependency>          <dependency>             <groupId>org.hibernate</groupId>             <artifactId>hibernate-core</artifactId>             <version>3.6.6.Final</version>         </dependency>          <dependency>             <groupId>org.hibernate</groupId>             <artifactId>hibernate-annotations</artifactId>             <version>3.5.6-Final</version>         </dependency>          <dependency>             <groupId>javax</groupId>             <artifactId>javaee-web-api</artifactId>             <version>6.0</version>             <scope>provided</scope>         </dependency>     </dependencies> </project> 

回答1:

Make sure you are running in a servlet 3.0 container - tomcat 7, for example (tomcat 6 does not support servlet 3.0)

Then try specifying <web-app metadata-complete="false" /> - it should be false by default, but try it.

回答2:

Your application might have a web.xml in an old format making JBoss ignore any annotated classes. So if your web.xml looks like:

<!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> 

then change it into:

<web-app xmlns="http://java.sun.com/xml/ns/javaee"          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"          xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"          version="3.0">     <display-name>Archetype Created Web Application</display-name> </web-app> 

This will make sure JBoss handles the war as servlet 3.0 again.

回答3:

According to the Servlet 3.0 spec, the class using the @WebServlet annotation has to extend HttpServlet. That could mean that your GenericServlet just wont do.

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