JSP -错误实例化servlet类[com.example.demo.HelloServlet]
JSP -错误实例化servlet类[com.example.demo.HelloServlet]
提问于 2022-09-09 14:24:31
开始使用JSP，尽管它仍然是Java的初学者。
错误就像标题中提到的那样。从错误消息中再读几行：
*
Description The server encountered an unexpected condition that prevented it from fulfilling the request.
Exception
javax.servlet.ServletException: Error instantiating servlet class [com.example.demo.HelloServlet]
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:687)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360)
org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:890)
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1789)
org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.base/java.lang.Thread.run(Thread.java:833)
Root Cause
java.lang.NoClassDefFoundError: jakarta/servlet/http/HttpServlet
java.base/java.lang.ClassLoader.defineClass1(Native Method)
java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1013)
java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)
org.apache.catalina.loader.WebappClassLoaderBase.findClassInternal(WebappClassLoaderBase.java:2472)
org.apache.catalina.loader.WebappClassLoaderBase.findClass(WebappClassLoaderBase.java:875)
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1376)
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1220)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:687)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360)
org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:890)
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1789)
org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.base/java.lang.Thread.run(Thread.java:833)
Root Cause
java.lang.ClassNotFoundException: jakarta.servlet.http.HttpServlet
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1412)
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1220)
java.base/java.lang.ClassLoader.defineClass1(Native Method)
java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1013)
java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)
org.apache.catalina.loader.WebappClassLoaderBase.findClassInternal(WebappClassLoaderBase.java:2472)
org.apache.catalina.loader.WebappClassLoaderBase.findClass(WebappClassLoaderBase.java:875)
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1376)
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1220)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:687)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360)
org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:890)
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1789)
org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.base/java.lang.Thread.run(Thread.java:833)
Note The full stack trace of the root cause is available in the server logs.-
index.jsp
<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %>
<!DOCTYPE html>
<html>
<head>
<title>JSP - Hello World</title>
</head>
<body>
<h1><%= "Hello World!" %>
</h1>
<br/>
<a href="hello-servlet">Hello Servlet</a>
</body>
</html>web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
version="5.0">
<servlet>
<servlet-name>helloServlet</servlet-name>
<servlet-class>com.example.demo.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>helloServlet</servlet-name>
<url-pattern>/hello-servlet</url-pattern>
</servlet-mapping>
</web-app>HelloServlet.java
package com.example.demo;
import java.io.*;
import jakarta.servlet.http.*;
import jakarta.servlet.annotation.*;
@WebServlet(name = "helloServlet", value = "/hello-servlet", urlPatterns = {"/hello-servlet"}, loadOnStartup = 1)
public class HelloServlet extends HttpServlet {
private String message;
public HelloServlet(){
}
public void init() {
message = "Hello World!";
}
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
response.setContentType("text/html");
// Hello
PrintWriter out = response.getWriter();
out.println("<html><body>");
out.println("<h1>" + message + "</h1>");
out.println("</body></html>");
}
public void destroy() {
}
}我在java文件中使用的@WebServlet中添加了urlPatterns = ..., loadOnStartup --在查看了StackOverflow上的一些解决方案之后，但似乎没有什么效果。
有什么可行的解决办法吗？
尝试向Java类添加构造函数，通过添加servlet标记来编辑web.xml，并在java类中添加@WebServlet行，但是没有任何效果。
做了一切让项目结构牢记在心的事情，仍然没有解决方案。只使用一种web映射-- @WebServlet或web.xml --都不起作用。两者都用过了，还是不管用。
我使用的是IntelliJ终极版。
回答 1
Stack Overflow用户
发布于 2022-09-11 14:38:04
解决了！
在尝试使用最新的Jakarta和Tomcat 9服务器(当时我正在使用)时，出现了一个问题。更新的10.0版本解决了这个问题。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/73663634
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