ServletException: 没有指定 servlet class

Question

我有一个应该非常简单的 "Hello World" servlet，但我无法让它工作。我正在使用 Eclipse、Tomcat 8、Java 7 和 Servlet 3.1。

我看了很多教程和问题，但没有完全帮助。我看到的大多数教程都在谈论通过扩展 HttpServlet 创建 servlet。我让那些工作。现在我想尝试更简洁的注释方法。

我一直在参考本教程，但它并不十分完整，而且似乎有一些不正确或不完整的示例： Packaging and Deploying RESTful Web Services

为什么 com.testing.service.MyApplication 没有加载？

如能帮助运行提供帮助，我们将不胜感激！

这是我的文件：

MyApplication.java

package com.testing.service;

import java.util.HashSet;
import java.util.Set;

import javax.ws.rs.ApplicationPath;
import javax.ws.rs.core.Application;

@ApplicationPath("app")
public class MyApplication extends Application {
    public Set<Class<?>> getClasses() {
        Set<Class<?>> s = new HashSet<Class<?>>();
        s.add(HelloWorldResource.class);
        return s;
    }
}

HelloWorldResource.java

package com.testing.service;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;

@Path("/helloworld")
public class HelloWorldResource {
    @SuppressWarnings("unused")
    private static final long serialVersionUID = 1L;

    @GET
    @Produces("text/plain")
    public String sayHello() {
        return "Hello World!";
    }
}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
    version="3.1">
  <display-name>service</display-name>
  <servlet>
    <servlet-name>com.testing.service.MyApplication</servlet-name>
    <init-param>
        <param-name>javax.ws.rs.Application</param-name>
        <param-value>com.testing.service.MyApplication</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>

</web-app>

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/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.testing</groupId>
  <artifactId>service</artifactId>
  <version>1.0</version>
  <packaging>war</packaging>
  <name>Rest Test</name>
  <dependencies>
    <dependency>
      <groupId>javax.ws.rs</groupId>
      <artifactId>javax.ws.rs-api</artifactId>
      <version>2.0.1</version>
    </dependency>
  </dependencies>  
  <build>
    <pluginManagement>
      <plugins>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>3.1</version>
          <configuration>
            <source>1.7</source>
            <target>1.7</target>
          </configuration>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>

每当我运行Tomcat时，它会显示以下错误：

INFO: Marking servlet com.testing.service.MyApplication as unavailable
Feb 05, 2015 3:28:55 PM org.apache.catalina.core.StandardContext loadOnStartup
SEVERE: Servlet /service threw load() exception
javax.servlet.ServletException: No servlet class has been specified for servlet com.testing.service.MyApplication
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1099)
    at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1041)
    at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:4944)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5230)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1409)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1399)
    at java.util.concurrent.FutureTask.run(FutureTask.java:262)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:744)

Answer 1

我在相关问题的评论中找到了答案。答案由 Alvin Thompson 提供。不幸的是，我没有足够的声誉来支持你的回答。

If you're using a standard Tomcat install (or some other servlet container), you need to include a REST implementation since Tomcat doesn't come with one. If you're using Maven, add this to the dependencies section:
<dependencies>
  <dependency>
    <groupId>org.glassfish.jersey.bundles</groupId>
    <artifactId>jaxrs-ri</artifactId>
    <version>2.13</version>
  </dependency>
  ...
</dependencies>
Then just add an application config class to your project. If you don't have any special configuration needs aside from setting the context path for the rest services, the class can be empty. Once this class is added, you don't need to configure anything in web.xml (or have one at all).

最初发布于此：

How to set up JAX-RS Application using annotations only (no web.xml)?

ServletException: 没有指定 servlet class

ServletException: No servlet class has been specified

java

tomcat

servlets