How can I tell if a jar was compiled on a 64bit or 32bit system?

To determine if a JAR file was compiled on a 64-bit or 32-bit system, you can analyze the native libraries included in the JAR file. You can inspect the native libraries' platform-dependent dependencies by examining the `.so` files for Linux-based systems and `.dll` files for Windows systems.

Here is a step-by-step guide with examples demonstrating how you can perform this analysis on a Linux system:

Step 1: Download Example JAR Files

Download two example JAR files for demonstration purposes:

1. `example64.jar` – JAR file compiled on a 64-bit system.

2. `example32.jar` – JAR file compiled on a 32-bit system.

Step 2: Extract the Contents of the JAR Files

Extract the contents of the JAR files to inspect the included native libraries. You can use tools like `jar` or any archive manager to extract the files.

Step 3: Identify Platform-Specific Native Libraries

Look for `.so` files in the extracted JAR files. These files are platform-specific shared object files compiled for a particular architecture.

Step 4: Determine the Architecture

Run the `file` command in the terminal to determine the architecture of the shared object file. The output will indicate whether the library is compiled for a 64-bit or 32-bit architecture.

Step 5: Example Code

Here is a shell script you can use to analyze the JAR files and determine the architecture of the included native libraries.

             bash
#!/bin/bash

echo "Checking example64.jar"
jar xf example64.jar
if [ -e ./lib64/library64.so ]; then
    file ./lib64/library64.so
fi

echo "Checking example32.jar"
jar xf example32.jar
if [ -e ./lib32/library32.so ]; then
    file ./lib32/library32.so
fi

             

Step 6: Run the Script

Save the script into a file (e.g., `check_arch.sh`), grant it execution permissions (`chmod +x check_arch.sh`), and run it in the terminal.

Output

After running the script, you should see the output indicating whether the native library included in each JAR file is compiled for a 64-bit or 32-bit system.

Example Output:

             
Checking example64.jar
./lib64/library64.so: ELF 64-bit LSB shared object, x86-64
Checking example32.jar
./lib32/library32.so: ELF 32-bit LSB shared object, Intel 80386

             

The output confirms that the `library64.so` is for a 64-bit system, while `library32.so` is for a 32-bit system.

By following these steps and examining the architecture of the native libraries included in the JAR files, you can determine whether the JAR file was compiled on a 64-bit or 32-bit system.