How to Modify a Jar’s Source in Eclipse and Replace the Original Jar
This guide shows how to locate a jar’s source code in Eclipse, edit it (e.g., add a log statement), export the modified project as a new jar—using the FatJar plugin when third‑party dependencies exist—and replace the original jar in a Java application to see the changes.
Scenario
In a Java application a JAR located in the lib directory needs to be modified. The source code of that JAR is available.
Implementation steps
Open the source project in Eclipse, locate the class to change, and edit the code (for example, insert a line that prints a log message).
Export the project as a JAR:
If the project has no external dependencies, use Export → JAR file and the resulting JAR can replace the original.
If the project depends on third‑party JARs, install the FatJar plug‑in (compatible with Eclipse 4.3) from the Eclipse Marketplace, then run the FatJar wizard to produce a “fat” JAR that bundles all required libraries. Tutorial URL: https://blog.csdn.net/BADAO_LIUMANG_QIZHI/article/details/110123747
Copy the newly built JAR into the application’s lib directory, overwriting the old file.
Restart or reload the application; the modified behavior (e.g., the added log output) becomes visible.
Signed-in readers can open the original source through BestHub's protected redirect.
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Resources and tutorials for programmers' advanced learning journey. Advanced tracks in Java, Python, and C#. Blog: https://blog.csdn.net/badao_liumang_qizhi
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