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Viewing contents of a .jar file

java
class-implementation
java-doc
jdk-tools
Alex KataevbyAlex Kataev·Dec 3, 2024
TLDR

Want to peek inside a .jar file quickly? Use the jar tf command:

jar tf yourfile.jar

This command shows the content list without extraction. For extracting the files, replace tf with xf:

jar xf yourfile.jar # You're now a digital archeologist!

Don't forget, a .jar file is essentially a ZIP archive. You can use any ZIP tool like WinRAR or 7-Zip to explore it.

No mystery with Java classes

To dive deeper inside the Java classes, 'javap' tool can be your go-to:

javap -c -p MyClass.class # Private members are no longer secrets!

Here, -c provides the disassembled code, while -p unveils private members. Perfect for cases where you need to scrutinize class implementations.

Know your APIs

One cannot overlook the importance of APIs when studying .jar files. JavaDoc shines here. It exhaustively documents APIs, enriching your understanding of what the code can do.

Sith-level exploration

Parsing runtime behaviours with JDK

The power of JDK tools, you have. ('jcmd', 'jdeps', and 'jconsole' it includes). They decode runtime behaviours and dependencies.

IDEs like Eclipse and IntelliJ IDEA? Yes, we have a plugin for that! These plugins navigate through classes and make understanding library structures easier than a walk in the IntelliJ park.

Bring the code back with Jad

Looking at decompiled classes can illuminate the original Java code. Tools like Jad can revert .class files into readable Java code – the Holy Grail if you’re into method and field analysis.

Note: This is a delicate science and should be only used for good!

Listing contents on Unix

On Unix systems, you can use the unzip -l yourfile.jar or zipinfo yourfile.jar commands to inspect the packages. Forget about "where's Waldo", "where's the .jar file" is the new game in terminal town!

Searching made easy

Sometimes, the classes can be harder to find than a four-leaf clover. If you’re looking for a class by its name, refer to the following Stackoverflow thread "Find a class in a pile of .jar files":

https://stackoverflow.com/q/275120

Shell scripts or commands like grep, find or other specialized tools will help you find that needle in the haystack.

Dealing with stubborn JAR files

When the JAR files play hard to retrieve

Dealing with corrupted, obfuscated, or proprietary JAR files? Hex editors or specialized software might be just what you need.

Windows paths are long, but your patience doesn't have to be

Encountered the dreaded "path too long" error on Windows? Use tools like 7-Zip, which can navigate long file paths as easily as a hot knife through butter.

Security? Checked!

Security restrictions can bar you from viewing or decompiling classes. Remember the idiom, "Curiosity killed the cat"? Don't let your curiosity kill your computer!