Home › Java exceptions › NoClassDefFoundError

What it looks like

java.lang.NoClassDefFoundError: org/apache/commons/lang3/StringUtils

Extends LinkageError in java.lang.

What it means

The code compiled against a class, but when the JVM tried to link it at run time the class definition was missing, or its static initialiser had already failed. Unlike ClassNotFoundException it is an Error and it comes from the JVM, not from a lookup you wrote. Two very different problems share this name: a dependency that is missing at run time, and a class whose earlier initialisation threw an exception (look for "Could not initialize class").

Common causes

• A dependency present at compile time but missing at run time, often provided scope or a transitive dependency excluded by mistake.
• A previous ExceptionInInitializerError: the first use failed and every later use reports NoClassDefFoundError: Could not initialize class.
• Different versions of a library at compile and run time.
• A class loader that cannot see the class that another loader loaded.

How to fix it

1. If the message says "Could not initialize class X", find the earlier ExceptionInInitializerError in the log; that is the real cause.
2. Otherwise compare the compile and run-time classpath and check the dependency scope.
3. Run the dependency tree and look for excluded or conflicting versions.
4. Build one executable jar and test it in a clean environment.

Broken and fixed

<dependency>
  <artifactId>commons-lang3</artifactId>
  <scope>provided</scope> <!-- not on the runtime classpath -->
</dependency>

<dependency>
  <artifactId>commons-lang3</artifactId>
  <!-- default compile scope: packaged and available at run time -->
</dependency>

🔎 Unravel the failing code 🔎 Unravel the fix

Debug it faster

Paste the whole stack trace into the stack trace beautifier to hide framework frames, jump to the root cause and find the first line of your own code. It runs in your browser, so the trace never leaves your machine.

Related exceptions