WAR + Gradle：ClassNotFound异常

Question

我正在尝试为Tomcat 8 + JDK 1.8编译一个简单的WAR。当我尝试用gradle构建它时，我得到一个未找到类的异常。详情如下：

Eclipse中的文件夹结构： enter image description here

Hello.java：

   package main;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Hello
 */
public class Hello extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public Hello() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub

        response.getWriter().append("{\"message\":\"Hello!\",\"exit\":\"0\"}");
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

的build.gradle：

task wrapper(type: Wrapper) {
gradleVersion = "3.2.1"
}

repositories{
    mavenCentral()
}

allprojects {
    apply plugin: 'java'
    apply plugin: 'war'
    version="1.0"
    println("VERSION:")
    println(version)


    war.destinationDir= file("build\\com\\HelloWorldServlet\\$version")

}

war{
    baseName='HelloWorldServlet'

}

Tomcat错误：

30-Nov-2016 09:34:07.361 SEVERE [http-apr-8080-exec-114] 
org.apache.catalina.core.StandardWrapperValve.invoke Allocate exception for servlet main.Hello
 java.lang.ClassNotFoundException: main.Hello
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1333)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1167)
    at org.apache.catalina.core.DefaultInstanceManager.loadClass(DefaultInstanceManager.java:518)
    at org.apache.catalina.core.DefaultInstanceManager.loadClassMaybePrivileged(DefaultInstanceManager.java:499)
    at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:118)
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1091)
    at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:817)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:135)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:509)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1104)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:684)
    at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2508)
    at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2497)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

WEB.XML：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>HelloWorldServlet</display-name>

    <servlet>
        <servlet-name>HelloWorldServlet</servlet-name>
        <servlet-class>Hello</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>HelloWorldServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

</web-app>

还为Web.xml尝试了这个：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>HelloWorldServlet</display-name>

    <servlet>
        <servlet-name>HelloWorldServlet</servlet-name>
        <servlet-class>main.Hello</servlet-class> <-- Also tried src.main.Hello
    </servlet>

    <servlet-mapping>
        <servlet-name>HelloWorldServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

部署WAR的结构：

-> HelloWorldServlet
   ->META-INF
      -> MANIFEST.MF
      -> war-tracker
   ->WEB-INF
      ->classes
         ->Hello.class