How to Resolve \"java.lang.ClassNotFoundException\" When Using \"java -jar\" with an Additional Classpath?

Resolving the ClassNotFoundException When Using "java -jar" with an Additional Classpath

When running a JAR file using "java -jar MyFile.jar" and specifying an additional classpath, one may encounter the error "java.lang.ClassNotFoundException." This error suggests that the necessary libraries for running the program are not accessible to the runtime environment.

To address this issue, it's important to understand that the "-jar" option launches the JAR file as a standalone application, meaning that it should contain all the required dependencies internally. Using "-cp" to specify an external classpath is intended for situations where the JAR file is not self-contained.

Therefore, there are two recommended approaches:

1. Manifest Classpath (If the JAR is Self-Contained):

   • Copy the required libraries into the "libs" subfolder.
   • Use Ant's "" task to update the JAR's manifest file to include the "libs" directory in the Class-Path attribute.
   • Run the program using "java -jar MyProgram.jar," and the required libraries will be automatically loaded.

2. Explicit Classpath (If the JAR is Not Self-Contained):

   • Place the main JAR and all dependencies in the same directory.
   • Run the program using "java -cp '.libs/' main.Main," where "." represents the current directory and the star () includes all JAR files in the "libs" directory.

By implementing either of these approaches, the additional libraries will be accessible to the JAR file during execution, resolving the "ClassNotFoundException" error.

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