Java Servlet - 實例化 servlet 類的 HTTP 狀態 500 錯誤

Question

我正在嘗試實例化我的 servlet，但我收到了這個 500 狀態錯誤。 我已閱讀其他帖子，但建議的解決方案似乎都不適用於我的錯誤。

我的 SampServlet 類

package com.example;

import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(name = "SampServlet", value = "/SampServlet")
public class SampServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //define that we want to send HTML to our browser
        response.setContentType("text/html");
        // create our PrintWriter that allows us to write out text as well as write HTML to the screen
        PrintWriter out = response.getWriter();
        try {
            out.println("<h3>Testing Servlets</h3>");
        }
        finally {
            out.close();
        }
    }
}

我的 web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <servlet>
        <servlet-name>SampServlet</servlet-name>
        <servlet-class>com.example.SampServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>SampServlet</servlet-name>
        <url-pattern>/SampServlet</url-pattern>
    </servlet-mapping>
</web-app>

項目結構在此處輸入圖像描述

我去 http://localhost:8080/SampServlet 時遇到的錯誤

Message Error instantiating servlet class [com.example.SampServlet]

Description The server encountered an unexpected condition that prevented it from fulfilling the request.

Exception

jakarta.servlet.ServletException: Error instantiating servlet class [com.example.SampServlet]
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:356)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:867)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1716)
    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: javax/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:2527)
    org.apache.catalina.loader.WebappClassLoaderBase.findClass(WebappClassLoaderBase.java:877)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1413)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1257)
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:356)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:867)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1716)
    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: javax.servlet.http.HttpServlet
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1449)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1257)
    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:2527)
    org.apache.catalina.loader.WebappClassLoaderBase.findClass(WebappClassLoaderBase.java:877)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1413)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1257)
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:356)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:867)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1716)
    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.

Answer 1

Tomcat 10.0 及更高版本使用新的 Jakarta EE 包進行代碼。 例如，這意味着javax.servlet.http.HttpServlet現在是jakarta.servlet.http.HttpServlet 。 由於 Oracle 及其對開發社區的敵意，這一變化始於 EE 規范的第 9 版。

您的代碼應該以以下內容開頭：

import jakarta.servlet.*;
import jakarta.servlet.http.*;
import jakarta.servlet.annotation.*;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(name = "SampServlet", value = "/SampServlet")
public class SampServlet extends HttpServlet {

使用新規格。 Tomcat 還有一個開源工具，可以將更大的代碼庫從 EE 8 轉換為 EE 9 規范。