Question

我编写了一个应该打印出“Hello World”的servlet，但它无法正常工作。

我在startup.sh中运行/usr/share/tomcat8/bin/startup.sh启动tomcat，我的程序位于/usr/share/tomcat8/webapps/hello/WEB-INF/classes/HelloWorld.class文件夹中。

这是我的web.xml：

<servlet>
   <servlet-name>HelloWorld</servlet-name>
   <servlet-class>HelloWorld</servlet-class>
</servlet>

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

这是我的源代码：

import java.io.*;
import javax.servlet.http.*;
import javax.servlet.ServletException;

public class HelloWorld extends HttpServlet
{

    static final long serialVersionUID = 42L;

    public void doGet(HttpServletRequest request,
                  HttpServletResponse response)
            throws IOException, ServletException
    {
            response.setContentType("text/html");
            PrintWriter out = response.getWriter();
            out.println("<html>");
            out.println("<head>");
            out.println("\t<title>Test</title>");
            out.println("</head>");
            out.println("<body>");
            out.println("<b>Hello World!</b>");
            out.println("</body>");
            out.println("</html>");
    }
}

我使用以下命令编译它：

javac -classpath %J2EE_HOME%\lib\j2ee.jar -classpath ../../../../lib/servlet-api.jar HelloWorld.java

没有编译错误，但是当我访问ipaddress:8080/hello/HelloWorld时，我得到以下错误代码：

exception

java.lang.NullPointerException
    org.apache.catalina.loader.WebappClassLoaderBase.binaryNameToPath(WebappClassLoaderBase.java:2562)
    org.apache.catalina.loader.WebappClassLoaderBase.findLoadedClass0(WebappClassLoaderBase.java:2730)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1208)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1166)
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:528)
    org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1099)
    org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:670)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1520)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1476)
    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.lang.Thread.run(Thread.java:745)

尝试打开它时的Servlet异常

0 个答案: