Find a class somewhere inside dozens of JAR files?

java

prompt-engineering

best-practices

tools

byAlex Kataev·Sep 28, 2024

While on your journey to discover YourClass.class in the plethora of JAR files, a combination of jar and grep commands acts as your Swiss knife of productivity. On a Unix-like system, you can execute the following:

for jar in *.jar; do jar -tf "$jar" | grep -Hs YourClass.class && echo "$jar"; done

This compact one-liner locates YourClass.class amongst all JARs in your current directory. It neatly prints out the name of the JAR that has your desired class.

Go with the customs (echo "enjoy your productivity!")

Optimizing your search strategy across colossal JAR libraries is like finding the most efficient route through a dense jungle. Take your steps wisely!

Bash Scripting: A script that traverses through the array of JARs and directly extracts class names can be a real time-saver (and also a life-saver!). Here's an example of what this script might look like:

#!/bin/bash
# This script guarantees both; your class and calmness!
search_class() {
  search_pattern=$1
  for jar in $(find . -name '*.jar'); do
    if jar -tvf "$jar" | grep -Hs "$search_pattern"; then
      echo "Found in: $jar"
    fi
  done
}

# Invoke the function and keep the aspirin aside!
search_class "YourClass.class"

Git Bash or Cygwin: These are some helpful sidekicks when you're fighting this battle on a Windows system to run Unix-like commands.

Summon the power tools (echo "Superman time!")

Some tasks demand specialized weapons. Let's gear up:

Eclipse: If you set up a Java project in Eclipse, your IDE can easily scan through all the attached JARs and find the required class for you.
Jar-explorer: This open-source tool designed just for this peril, can simplify your quest. URL: Jar-explorer
Java Decompiler: This is your microscope to peek inside obfuscated or nested classes.

Command variations for optimizing outputs (echo "Now, you speak my language!")

Your choice of commands might differ based on your operating system:

Windows: The for /R loop command should be your go-to tool for this task. This loop might sound geeky but it's extremely handy!

for /R %i in (*.jar) do @jar -tvf "%i" | findstr /C:"YourClass.class" && echo %i

Unix-like OS: When you are in Unix territory, remember to consider the effect of escaped characters and case sensitivity.

find . -name "*.jar" -exec jar -tvf {} \; 2>/dev/null | grep 'YourClass.class'

Prep for possible hurdles

While the solution seems all rosy on the surface, you may encounter some common obstacles:

Too many JARs: Try creating symbolic links to JARs in a single directory to avoid scattered JAR paths across the file system.
Complex file names: Complex file names? No worries! Make use of command shortcuts like {} in find commands or %i on Windows to handle them flawlessly.

Decipher your JAR findings

Once you've hunted down the class, you might want to delve deeper:

Inspect the class content: Use jar xf to extract the class file and then, use a decompiler to sneak a peek inside.
Resolve dependencies: The class you found might be dependent on other classes or JARs. Be prepared to repeat the process or consult Maven's pom.xml or Gradle scripts to resolve dependencies.

Turbocharge your search skills

Executing the basics and still feeling stuck? Try these advanced techniques:

Combo of 'locate' and 'grep': To speed up the initial file search, you can combine locate to find all JARs and pipe its output to grep.
Regular Expressions: If class names follow a pattern, why not let grep fitted with regular expressions locate your classes?