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How to fix java.lang.NoSuchMethodException: Servlets.MyServlet.() at java.base/java.lang.Class.getConstructor0

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2024-02-09 11:33:18498browse

PHP editor Zimo will answer your question on how to fix "java.lang.NoSuchMethodException: Servlets.MyServlet.() at java.base/java.lang.Class.getConstructor0". This error usually occurs in Java programs and means that the specified constructor cannot be found. To solve this problem, you can check whether the constructor in the code exists, whether the parameters are correct, and whether the classpath is correctly configured. In addition, you can also consider upgrading the Java version or using other available constructors. With these methods, you should be able to successfully fix this error and get the program running normally.

Question content

I have a form in a jsp page and I'm trying to connect to the servlet myservlet. I'm using tomcat 10.x. I keep getting the following error: 

http status 500 – internal server error

type exception report

message error instantiating servlet class [servlets.myservlet]

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

exception

jakarta.servlet.servletexception: error instantiating servlet class [servlets.myservlet]
    org.apache.catalina.authenticator.authenticatorbase.invoke(authenticatorbase.java:482)
    org.apache.catalina.valves.errorreportvalve.invoke(errorreportvalve.java:93)
    org.apache.catalina.valves.abstractaccesslogvalve.invoke(abstractaccesslogvalve.java:673)
    org.apache.catalina.connector.coyoteadapter.service(coyoteadapter.java:340)
    org.apache.coyote.http11.http11processor.service(http11processor.java:391)
    org.apache.coyote.abstractprocessorlight.process(abstractprocessorlight.java:63)
    org.apache.coyote.abstractprotocol$connectionhandler.process(abstractprotocol.java:896)
    org.apache.tomcat.util.net.nioendpoint$socketprocessor.dorun(nioendpoint.java:1744)
    org.apache.tomcat.util.net.socketprocessorbase.run(socketprocessorbase.java:52)
    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:1589)
root cause

java.lang.nosuchmethodexception: servlets.myservlet.<init>()
    java.base/java.lang.class.getconstructor0(class.java:3641)
    java.base/java.lang.class.getconstructor(class.java:2324)
    org.apache.catalina.authenticator.authenticatorbase.invoke(authenticatorbase.java:482)
    org.apache.catalina.valves.errorreportvalve.invoke(errorreportvalve.java:93)
    org.apache.catalina.valves.abstractaccesslogvalve.invoke(abstractaccesslogvalve.java:673)
    org.apache.catalina.connector.coyoteadapter.service(coyoteadapter.java:340)
    org.apache.coyote.http11.http11processor.service(http11processor.java:391)
    org.apache.coyote.abstractprocessorlight.process(abstractprocessorlight.java:63)
    org.apache.coyote.abstractprotocol$connectionhandler.process(abstractprotocol.java:896)
    org.apache.tomcat.util.net.nioendpoint$socketprocessor.dorun(nioendpoint.java:1744)
    org.apache.tomcat.util.net.socketprocessorbase.run(socketprocessorbase.java:52)
    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:1589)
note the full stack trace of the root cause is available in the server logs.

apache tomcat/10.1.18

I know it didn't find the servlet(?) at the given location, but I'm not sure how to fix that. Any help would be greatly appreciated.

This is my file:

index.jsp

<html>
<body>
<h2>hello world!</h2>
<form action="myservlet" method="get">
    <input type="submit" value="enter">
</form>
</body>
</html>

myservlet.java

package servlets;

import jakarta.servlet.servletexception;
import jakarta.servlet.annotation.webservlet;
import jakarta.servlet.http.httpservlet;
import jakarta.servlet.http.httpservletrequest;
import jakarta.servlet.http.httpservletresponse;

import java.io.ioexception;

@webservlet("/myservlet")
public class myservlet extends httpservlet {

    myservlet(){
        super();
    }

    @override
    protected void doget(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        super.doget(req, resp);
    }

    @override
    protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
        super.dopost(req, resp);
    }
}

pom.xml

<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/maven-v4_0_0.xsd">
  <modelversion>4.0.0</modelversion>
  <groupid>org.example</groupid>
  <artifactid>baseproject</artifactid>
  <packaging>war</packaging>
  <version>1.0-snapshot</version>
  <name>baseproject maven webapp</name>
  <url>http://maven.apache.org</url>
  <dependencies>
    <dependency>
      <groupid>junit</groupid>
      <artifactid>junit</artifactid>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupid>jakarta.servlet</groupid>
      <artifactid>jakarta.servlet-api</artifactid>
      <version>6.0.0</version>
      <scope>provided</scope>
    </dependency>
  </dependencies>
  <build>
    <finalname>baseproject</finalname>
  </build>
</project>

I tried removing '@webservlet("/myservlet")' from myservlet.java and manually adding servlet and servlet mapping to web.xml like this: 

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
  
  <servlet>
    <servlet-name>MyServlet</servlet-name>
    <servlet-class>Servlets.MyServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>MyServlet</servlet-name>
    <url-pattern>/MyServlet</url-pattern>
  </servlet-mapping>

</web-app>

However, this still results in a 500 error.

Solution

Expose the servlet's constructor so that tomcat can run it. 

public MyServlet() {
    super();
}

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