问题描述
我试图在 Servlet 中创建一个简单的我的第一个应用程序。我将我的 '/hello' url 映射到 HelloServlet。当我尝试访问 /hello 时，我得到了这个。
HTTP Status 500 – Internal Server Error
Type Exception Report
Message Class [com.example.Servlet3.HelloServlet] is not a Servlet
Description The server encountered an unexpected condition that prevented it from fulfilling the request.
Exception
jakarta.servlet.servletexception: Class [com.example.Servlet3.HelloServlet] is not a Servlet
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:543)
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:353)
org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:870)
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1696)
org.apache.tomcat.util.net.socketProcessorBase.run(SocketProcessorBase.java:49)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.base/java.lang.Thread.run(Thread.java:834)
Root Cause
java.lang.classCastException: class com.example.Servlet3.HelloServlet cannot be cast to class jakarta.servlet.Servlet (com.example.Servlet3.HelloServlet is in unnamed module of loader org.apache.catalina.loader.ParallelWebappClassLoader @6b4c53ee; jakarta.servlet.Servlet is in unnamed module of loader java.net.urlclassloader @5c5eefef)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:543)
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:353)
org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:870)
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1696)
org.apache.tomcat.util.net.socketProcessorBase.run(SocketProcessorBase.java:49)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.base/java.lang.Thread.run(Thread.java:834)
Note The full stack trace of the root cause is available in the server logs.
Apache Tomcat/10.0.5
HTTP Status 404 – Not Found
Type Status Report
Description The origin server did not find a current representation for the target resource or is not willing to disclose that one exists.
Apache Tomcat/10.0.5
web.xml 文件
<?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">
<display-name>My Application</display-name>
<servlet>
<servlet-name>FirstServlet</servlet-name>
<servlet-class>com.example.Servlet3.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>FirstServlet</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
</web-app>
HelloServlet.java 代码。
package com.example.Servlet3;
import java.io.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
//@WebServlet(name = "helloServlet",value = "/hello-servlet")
public class HelloServlet extends HttpServlet {
private String message;
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() {
}
}
项目结构 pom.xml 文件。
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.example</groupId>
<artifactId>Servlet3</artifactId>
<version>1.0-SNAPSHOT</version>
<name>Servlet3</name>
<packaging>war</packaging>
<properties>
<maven.compiler.target>1.8</maven.compiler.target>
<maven.compiler.source>1.8</maven.compiler.source>
<junit.version>5.7.0</junit.version>
</properties>
<dependencies>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>4.0.1</version>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-api</artifactId>
<version>${junit.version}</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<version>${junit.version}</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<version>3.3.0</version>
</plugin>
</plugins>
</build>
</project>
我在互联网上搜索了很多，但都是徒劳的。我很沮丧，最后在这里希望得到解决方案。请帮忙。 这个项目是在IntelliJ New->Project->JavaEnterprise WebApplication(Servlet,web.xml)中创建的 Tomcat 服务器启动没有错误。它可以服务静态网页，如上图（项目结构）中的'form.html'文件，但不能服务任何servlet。
解决方法
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