Fixing Maven ClassNotFoundException for json-lib by Adjusting Classifier and outputFileNameMapping

The author frequently encounters Maven-related problems and links to two previous articles that discuss common Maven dependency issues and snapshot version usage.

In this post, a new error is presented: a java.lang.ClassNotFoundException: net.sf.json.JSONException stack trace, indicating that the json-lib library could not be loaded at runtime.

The Maven dependency declared is:

<dependency>
    <groupId>net.sf.json-lib</groupId>
    <artifactId>json-lib</artifactId>
    <version>2.4</version>
    <classifier>jdk15</classifier>
</dependency>

Although the jar json-lib-2.4.jar exists in the packaged lib directory, the required classifier makes the correct file name json-lib-2.4-jdk15.jar. Because the packaged jar lacks the jdk15 suffix, the class loader cannot find the needed classes.

The root cause is the project's assembly plugin configuration, which uses a fixed outputFileNameMapping that does not incorporate the classifier:

<outputFileNameMapping>${artifact.artifactId}-${artifact.baseVersion}.${artifact.extension}</outputFileNameMapping>

Since the classifier is omitted, the resulting jar name is wrong. The solution is to modify the mapping to include the classifier when present:

<outputFileNameMapping>${artifact.artifactId}-${artifact.baseVersion}${dashClassifier?}.${artifact.extension}</outputFileNameMapping>

This expression adds the classifier (with a preceding dash) only if it exists, ensuring the jar is named json-lib-2.4-jdk15.jar and the ClassNotFoundException is resolved.

For further details, see the Maven EAR plugin documentation: http://maven.apache.org/plugins/maven-ear-plugin/examples/customize-file-name-mapping.html

About the author: Yin Jihuan, a technology enthusiast and author of "Spring Cloud Microservices – Full‑Stack Technology and Case Analysis" and "Spring Cloud Microservices: Beginner, Practice, and Advanced", founder of the WeChat public account "Yuan Tiandi".