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Why am I getting a NoClassDefFoundError in Java?

Posted by: admin November 2, 2017 Leave a comment

Questions:

I am getting a NoClassDefFoundError when I run my Java application. What is typically the cause of this?

Answers:

This is caused when there is a class file that your code depends on and it is present at compile time but not found at runtime. Look for differences in your build time and runtime classpaths.

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While it’s possible that this is due to a classpath mismatch between compile-time and run-time, it’s not necessarily true.

It is important to keep two or three different exceptions straight in our head in this case:

  1. java.lang.ClassNotFoundException This exception indicates that the class was not found on the classpath. This indicates that we were trying to load the class definition, and the class did not exist on the classpath.

  2. java.lang.NoClassDefFoundError This exception indicates that the JVM looked in its internal class definition data structure for the definition of a class and did not find it. This is different than saying that it could not be loaded from the classpath. Usually this indicates that we previously attempted to load a class from the classpath, but it failed for some reason – now we’re trying to use the class again (and thus need to load it, since it failed last time), but we’re not even going to try to load it, because we failed loading it earlier (and reasonably suspect that we would fail again). The earlier failure could be a ClassNotFoundException or an ExceptionInInitializerError (indicating a failure in the static initialization block) or any number of other problems. The point is, a NoClassDefFoundError is not necessarily a classpath problem.

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Here is the code to illustrate java.lang.NoClassDefFoundError.

NoClassDefFoundErrorDemo.java

public class NoClassDefFoundErrorDemo {
    public static void main(String[] args) {
        try {
            // The following line would throw ExceptionInInitializerError
            SimpleCalculator calculator1 = new SimpleCalculator();
        } catch (Throwable t) {
            System.out.println(t);
        }
        // The following line would cause NoClassDefFoundError
        SimpleCalculator calculator2 = new SimpleCalculator();
    }

}

SimpleCalculator.java

public class SimpleCalculator {
    static int undefined = 1 / 0;
}

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I have found that sometimes I get a NoClassDefFound error when code is compiled with an incompatible version of the class found at runtime. The specific instance I recall is with the apache axis library. There were actually 2 versions on my runtime classpath and it was picking up the out of date and incompatible version and not the correct one, causing a NoClassDefFound error. This was in a command line app where I was using a command similar to this.

set classpath=%classpath%;axis.jar

I was able to get it to pick up the proper version by using:

set classpath=axis.jar;%classpath%;

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NoClassDefFoundError In Java

Definition:

  1. Java Virtual Machine is not able to find a particular class at runtime which was available at compile time.

  2. If a class was present during compile time but not available in java classpath during runtime.

enter image description here

Examples:

  1. The class is not in Classpath, there is no sure shot way of knowing it but many times you can just have a look to print System.getproperty(“java.classpath”) and it will print the classpath from there you can at least get an idea of your actual runtime classpath.
  2. A simple example of NoClassDefFoundError is class belongs to a missing JAR file or JAR was not added into classpath or sometimes jar’s name has been changed by someone like in my case one of my colleagues has changed tibco.jar into tibco_v3.jar and the program is failing with java.lang.NoClassDefFoundError and I were wondering what’s wrong.

  3. Just try to run with explicitly -classpath option with the classpath you think will work and if it’s working then it’s a sure short sign that someone is overriding java classpath.

  4. Permission issue on JAR file can also cause NoClassDefFoundError in Java.
  5. Typo on XML Configuration can also cause NoClassDefFoundError in Java.
  6. when your compiled class which is defined in a package, doesn’t present in the same package while loading like in the case of JApplet it will throw NoClassDefFoundError in Java.

Possible Solutions:

  1. The class is not available in Java Classpath.
  2. If you are working in J2EE environment than the visibility of Class among multiple Classloader can also cause java.lang.NoClassDefFoundError, see examples and scenario section for detailed discussion.
  3. Check for java.lang.ExceptionInInitializerError in your log file. NoClassDefFoundError due to the failure of static initialization is quite common.
  4. Because NoClassDefFoundError is a subclass of java.lang.LinkageError it can also come if one of it dependency like native library may not available.
  5. Any start-up script is overriding Classpath environment variable.
  6. You might be running your program using jar command and class was not defined in manifest file’s ClassPath attribute.

Resources:

3 ways to solve NoClassDefFoundError

java.lang.NoClassDefFoundError Problem patterns

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I was using spring framework with maven and solved this error in my project.

There was a runtime error in the class.
I was reading a property as integer, but when it read the value from the property file, its value was double.
Spring did not give me a full stack trace of on which line the runtime failed.
It simply said NoClassDefFoundError. But when I executed it as a native Java Application (taking it out of MVC), it gave ExceptionInInitializerError which was the true cause and which is how I traced the error.

@xli’s answer gave me insight into what may be wrong in my code.

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I get NoClassFoundError when classes loaded by the runtime class loader cannot access classes already loaded by the java rootloader. Because the different class loaders are in different security domains (according to java) the jvm won’t allow classes already loaded by the rootloader to be resolved in the runtime loader address space.

Run your program with ‘java -javaagent:tracer.jar [YOUR java ARGS]’

It produces output showing the loaded class, and the loader env that loaded the class. It’s very helpful tracing why a class cannot be resolved.

// ClassLoaderTracer.java
// From: https://blogs.oracle.com/sundararajan/entry/tracing_class_loading_1_5

import java.lang.instrument.*;
import java.security.*;

// manifest.mf
// Premain-Class: ClassLoadTracer

// jar -cvfm tracer.jar manifest.mf ClassLoaderTracer.class

// java -javaagent:tracer.jar  [...]

public class ClassLoadTracer 
{
    public static void premain(String agentArgs, Instrumentation inst) 
    {
        final java.io.PrintStream out = System.out;
        inst.addTransformer(new ClassFileTransformer() {
            public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {

                String pd = (null == protectionDomain) ? "null" : protectionDomain.getCodeSource().toString();
                out.println(className + " loaded by " + loader + " at " + new java.util.Date() + " in " + pd);

                // dump stack trace of the thread loading class 
                Thread.dumpStack();

                // we just want the original .class bytes to be loaded!
                // we are not instrumenting it...
                return null;
            }
        });
    }
}

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This is the best solution I found so far.

Suppose we have a package called org.mypackage containing the classes:

  • HelloWorld (main class)
  • SupportClass
  • UtilClass

and the files defining this package are stored physically under the directory D:\myprogram (on Windows) or /home/user/myprogram (on Linux).

The file structure will look like this:
enter image description here

When we invoke Java, we specify the name of the application to run: org.mypackage.HelloWorld. However we must also tell Java where to look for the files and directories defining our package. So to launch the program, we have to use the following command:
enter image description here

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The technique below helped me many times:

System.out.println(TheNoDefFoundClass.class.getProtectionDomain().getCodeSource().getLocation());

where the TheNoDefFoundClass is the class that might be “lost” due to a preference for an older version of the same library used by your program. This most frequently happens with the cases, when the client software is being deployed into a dominant container, armed with its own classloaders and tons of ancient versions of most popular libs.

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In case you have generated-code (EMF etc.) there can be too many static initialisers which consume all stack space. How to increase the Java stack size?.

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I have a same problem I was stock long hr. I found the solution, In my case, there is the static method defined due to that The JVM can not create the another object of that class.
example,
private static HttpHost proxy = new HttpHost(proxyHost, Integer.valueOf(proxyPort), “http”);

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If someone comes here because of java.lang.NoClassDefFoundError: org/apache/log4j/Logger error, in my case it was produced because I used log4j 2 (but I didn’t add all the files that come with it), and some dependency library used log4j 1. The solution was to add the Log4j 1.x bridge: the jar log4j-1.2-api-<version>.jar which comes with log4j 2. More info in the log4j 2 migration.

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Two different checkout copies of the same project

In my case, the problem was Eclipse’s inability to differentiate between two different copies of the same project. I have one locked on trunk (SVN version control) and the other one working in one branch at a time. I tried out one change in the working copy as a JUnit test case, which included extracting a private inner class to be a public class on its own and while it was working, I open the other copy of the project to look around at some other part of the code that needed changes. At some point, the NoClassDefFoundError popped up complaining that the private inner class was not there; double-clicking in the stack trace brought me to the source file in the wrong project copy.

Closing the trunk copy of the project and running the test case again got rid of the problem.

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make sure this matches in the module:app and module:lib

 android {
compileSdkVersion 23
buildToolsVersion '22.0.1'
packagingOptions {

}


defaultConfig {
    minSdkVersion 17
    targetSdkVersion 23
    versionCode 11
    versionName "2.1"

}

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I got this message after removing 2 files from the SRC library, and when I brought them back I kept seeing this Error message.
My solution was:restart Eclipse. Since then I havn’t seen this message again 🙂