【发布时间】：2021-04-18 13:53:12
【问题描述】：
我一直在徒劳地尝试实现 tomcat 9 的 jakarta servlet，而不是之前的 javax.servlet 实现（据我了解，jakarta 包是前进的方向）。问题是当我将浏览器指向我的 servlet 的 url 时，我收到以下错误...
java.lang.ClassCastException: class cti.nm.web.Index cannot be cast to class javax.servlet.Servlet (cti.nm.web.Index is in unnamed module of loader org.apache.catalina.loader.ParallelWebappClassLoader @48c76607; javax.servlet.Servlet is in unnamed module of loader java.net.URLClassLoader @621be5d1)
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:343)
org.apache.coyote.ajp.AjpProcessor.service(AjpProcessor.java:432)
org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:888)
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1597)
org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.base/java.lang.Thread.run(Thread.java:832)
问题很明显。 Tomcat 试图将我的 jakarta.servlet.http.HttpServlet 转换为 javax.servlet.Servlet，这显然是行不通的。我想不通的是如何告诉它 servlet 实际实现的是什么类。
类本身被声明为 ...
package cti.nm.web;
import jakarta.servlet.http.HttpServlet;
import java.io.IOException;
import java.io.PrintWriter;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
public class Index extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException {
response.setContentType("text/html");
//print a bunch of stuff
}
}
我的web.xml文件如下...
<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">
<display-name>NMWeb</display-name>
<description>
NMWeb Description
</description>
<servlet>
<servlet-name>Index</servlet-name>
<servlet-class>cti.nm.web.Index</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Index</servlet-name>
<url-pattern>/NMWeb</url-pattern>
</servlet-mapping>
</web-app>
我曾希望在部署描述符中使用正确的 jakartaee xml 模式会导致使用正确的类，但显然不是。 WAR 似乎包含正确的罐子......
jakarta.jakartaee-api-9.0.0.jar
tomcat-el-api-10.0.0.jar
tomcat-servlet-api-10.0.0.jar
jakarta.servlet-api-5.0.0.jar
tomcat-jsp-api-10.0.0.jar
pom 被指定为 ...
<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>cti.nm.NMWeb</groupId>
<artifactId>NMWeb</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>war</packaging>
<build>
<sourceDirectory>src</sourceDirectory>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
<plugin>
<artifactId>maven-war-plugin</artifactId>
<version>3.2.3</version>
<configuration>
<warSourceDirectory>WebContent</warSourceDirectory>
</configuration>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<groupId>jakarta.platform</groupId>
<artifactId>jakarta.jakartaee-api</artifactId>
<version>[9.0.0,)</version>
</dependency>
<!-- https://mvnrepository.com/artifact/jakarta.servlet/jakarta.servlet-api -->
<dependency>
<groupId>jakarta.servlet</groupId>
<artifactId>jakarta.servlet-api</artifactId>
<version>[5.0.0,)</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.apache.tomcat/tomcat-jsp-api -->
<dependency>
<groupId>org.apache.tomcat</groupId>
<artifactId>tomcat-jsp-api</artifactId>
<version>[10.0.0,)</version>
</dependency>
</dependencies>
</project>
在网上搜索这个问题的答案已经有好几天了，我似乎找不到这种确切情况的任何其他实例。我应该提一下，这是我手动修改的 Eclipse 生成的 probject。当我部署 war 文件时，使用 maven 和 eclipse 构建会产生相同的结果。
【问题讨论】：
标签： maven tomcat servlets classcastexception