java.lang.NullPointerException from org.apache.catalina.loader.WebappClassLoaderBase.loadClass

Question

What causes this? This appears to be a very comon error with myriad causes.

HTTP Status 500 -

type Exception report

message

description The server encountered an internal error that prevented it from fulfilling this request.

exception

java.lang.NullPointerException
    java.util.concurrent.ConcurrentHashMap.putVal(Unknown Source)
    java.util.concurrent.ConcurrentHashMap.putIfAbsent(Unknown Source)
    java.lang.ClassLoader.getClassLoadingLock(Unknown Source)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1149)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1116)
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:510)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:1110)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:785)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1425)
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)
    java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.lang.Thread.run(Unknown Source)
note The full stack trace of the root cause is available in the Apache Tomcat/8.5.3 logs.

Here are the includes:

import java.util.Set;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.Application;

Adding web.xml Please note: I have tried multiple values for the url-pattern and all it seems to do is change the URI on which I get the error. 'Hello' is the class name in the java source.

<?xml version="1.0" encoding="UTF-8"?>
<web-app 
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns="http://java.sun.com/xml/ns/javaee"
        xsi:schemaLocation="
        http://java.sun.com/xml/ns/javaee
        http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">

        <servlet>
        <servlet-name>HelloWorldTomcatService</servlet-name>
        <init-param>
            <param-name>com.package.from.java.file</param-name>
            <param-value>Hello</param-value>
        </init-param>
        </servlet>
    <servlet-mapping>
        <servlet-name>HelloWorldTomcatService</servlet-name>
        <url-pattern></url-pattern>
    </servlet-mapping>
    <session-config>
        <session-timeout>30</session-timeout>
    </session-config>
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>

From the first look it seems to me like an error in servlet or webapp configuration, but it's hard to say without knowing more. Look into catalina.out log file and post the full stack trace, and the web.xml file of your webapp would be also helpful. — Jozef Chocholacek
– Jozef Chocholacek, Commented Jul 22, 2016 at 6:40
I think you need to supply: note The full stack trace of the root cause is available in the Apache Tomcat/8.5.3 logs. — Romain Hippeau
– Romain Hippeau, Commented Jul 22, 2016 at 15:15
@RomainHippeau I was unable to find a more detailes stacktrace in any of the log files. Perhaps there's some setting to enable it, but I managed to muddle through without it eventually. — user1958756
– user1958756, Commented Jul 22, 2016 at 21:27

BalusC · Accepted Answer · 2016-07-22 19:33:57Z

2

java.lang.NullPointerException
    java.util.concurrent.ConcurrentHashMap.putVal(Unknown Source)
    java.util.concurrent.ConcurrentHashMap.putIfAbsent(Unknown Source)
    java.lang.ClassLoader.getClassLoadingLock(Unknown Source)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1149)

This specific one can be caused by a web.xml entry which expects a <xxx-class> such as <servlet-class>, <filter-class> or <listener-class>, but it is actually absent or empty.

And indeed, your <servlet> entry is missing the <servlet-class>. It should refer the FQN of the servlet class you'd like to register under the name as specified by <servlet-name> like below.

<servlet>
    <servlet-name>someServlet</servlet-name>
    <servlet-class>com.example.SomeServlet</servlet-class>
</servlet>

That said, your <init-param><param-name> also doesn't look good if it is actually the JAX-RS servlet you tried to register. Are you sure you're reading the right tutorials/resources as to learning JAX-RS and integrating it in Tomcat? A well known one is provided by Lars Vogel.

answered Jul 22, 2016 at 19:33

BalusC

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1 Comment

user1958756 Over a year ago

I was actually using that tutorial for a while. Eventually I abandoned it and was able to muddle through doing something like what you said.

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