严重：为servlet分配异常，尝试从JSP页面调用servlet时出错

Question

When I run the jsp on the tomcat server and it runs ok, but when I click submit it throws the following error, I have checked over everything and I am not sure where to go from here because it seems like it should work, any help would be much appreciated, Thank you.

Error Stack Trace:

SEVERE: Allocate exception for servlet RegistrationServlet
java.lang.ClassNotFoundException: logon.RegistrationServlet.java
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1720)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1571)
at org.apache.catalina.core.DefaultInstanceManager.loadClass(DefaultInstanceManager.java:529)
at org.apache.catalina.core.DefaultInstanceManager.loadClassMaybePrivileged(DefaultInstanceManager.java:511)
at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:139)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1148)
at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:864)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:134)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:315)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

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" 
xmlns:web="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_2_5.xsd" 
id="WebApp_ID" version="2.5">
<display-name>RegistrationTest</display-name>
 <servlet>
        <display-name>RegistrationServlet</display-name>
        <servlet-name>RegistrationServlet</servlet-name>
        <servlet-class>logon.RegistrationServlet</servlet-class>
 </servlet>
 <servlet-mapping>
     <servlet-name>RegistrationServlet</servlet-name>
     <url-pattern>/RegistrationServlet</url-pattern>
 </servlet-mapping>
</web-app>

The JSP page:

<h2>Signup Details</h2>
        <form name="actionForm" action="RegistrationServlet" method ="post">
        <br/>Username:<input type="text" name="name">
        <br/>Password:<input type="password" name="password">
        <br/>Email:<input type="text" name="email">
        <br/><input type="submit" value="Submit">
        </form>

The Servlet:

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 RegistrationServlet
 */
@WebServlet("/RegistrationServlet")
public class RegistrationServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

public RegistrationServlet() {
    super();

}


protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

}


protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    try{
        System.out.println("In the registration Servlet");
        User user = new User();
        user.setName(request.getParameter("name"));
        user.setPassword(request.getParameter("password"));
        user.setEmail(request.getParameter("email"));
        RegisterUser.addUser(user);
        //response.sendRedirect("welcome.jsp");        
    } catch (Throwable exc)
    {
        System.out.println(exc);
    }
}

}

Answer 1

For anybody that has a similar problem in the future, after cleaning the project, ensure that the build automatically box is checked under the project drop down menu as this is required to rebuild after clean, mine was unchecked by default for some reason.

Also I made a small error in the code, I used annotations (@webservlet) in my servlet and I also added the servlet to my web.xml which caused a conflict. This is now done automatically with annotations.

Answer 2

I also got the same exception and resolved just by putting full qualified calssname in the web.xml fle. $fully qualified class name$