尝试运行Servlet时出现Servlet异常

我是servlet的新手。我得到了低于sevlets的例外。

我的web.xml代码。

    <display-name>LoginServlets</display-name>
    <servlet>
        <servlet-name>LoginServlet</servlet-name>
        <servlet-class>LoginServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/login</url-pattern>
    </servlet-mapping>
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
        <welcome-file>default.html</welcome-file>
        <welcome-file>default.htm</welcome-file>
        <welcome-file>default.jsp</welcome-file>
    </welcome-file-list>

调用此servlet的Html窗体。

<body>
    <form action="login" method="get">
        <table>
            <tr>
                <td>UserName</td>
                <td><input type="text" name="username" /></td>
            </tr>
            <tr>
                <td>Password</td>
                <td><input type="password" name="password" /></td>
            </tr>
            <tr>
                <td><input type="submit" value="SignIn" /></td>
            </tr>
        </table>
    </form>
</body>

我得到了例外。

javax.servlet.ServletException: Error instantiating servlet class LoginServlet
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
    org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
    org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:314)
    java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.lang.Thread.run(Unknown Source)

根本原因。

java.lang.ClassNotFoundException: LoginServlet
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1720)
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1571)
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
    org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
    org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:314)
    java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.lang.Thread.run(Unknown Source)

上一天类似的代码运行良好。但我也使用gitSVN，我用相同的代码设置了一个创建新项目。但它不起作用。我也下载了一些示例，但都不起作用。

这是我的LoginServer类。它位于JavaResources->src mypackage 中

package com.loginservlets;
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoginServlet() {
        super();
        // TODO Auto-generated constructor stub
        System.out.println("LoginServlet");
    }
    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        System.out.println("Get");
        response.setContentType("text/html");
        PrintWriter pw = response.getWriter();
        pw.println("HelloWorld");
        out.close();
    }
    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        System.out.println("Post");
    }
}

类的名称是com.loginservlets.LoginServlet。不是LoginServlet。

请注意，在web.xml中声明servlet与用注释声明servlet是多余的。没有理由在web.xml中声明它，因为您可以使用注释进行同样的操作：

@WebServlet("/login")

由于您已经用@WebServlet注释了servlet类定义，因此不需要在web.xml中声明相同的定义。将@WebServlet("/LoginServlet")更改为@WebServlet(urlPatterns = {"/login"})

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