#!/usr/bin/perl

################################################################################

# JavaInfo - Java Class File Version Analyzer

#

# This utility extracts Java version information from compiled class files by

# reading their bytecode headers. It recursively processes files and directories

# to identify Java class files and report their compilation version.

#

# The script reads the first 8 bytes of each file, checks for the Java class

# file magic number (0xCAFEBABE), and extracts the major/minor version numbers

# which indicate the Java version used to compile the class.

#

# Usage: JavaInfo <file or directory> [<file or directory> ...]

#

# Examples:

# JavaInfo MyClass.class

# JavaInfo /path/to/project/bin

# JavaInfo target/classes lib/*.jar

#

# Author: Thomas

# License: See LICENSE file

################################################################################

use strict;

use warnings;

use File::Spec::Functions;

#

# Main entry point - processes all command-line arguments

#

# Parameters:

# @_ - List of file or directory paths to process

#

sub main {

foreach my $node (@_) {

process_node($node);

}

}

#

# Process a filesystem node (file or directory)

#

# Determines whether the given path is a file or directory and dispatches

# to the appropriate handler function.

#

# Parameters:

# $node - Path to the filesystem node to process

#

sub process_node {

my $node = shift();

if (-f $node) {

process_file($node);

} elsif (-d $node) {

process_dir($node);

}

}

#

# Recursively process all files in a directory

#

# Reads all entries in the directory (excluding . and ..) and recursively

# processes each one by calling process_node.

#

# Parameters:

# $dir - Path to the directory to process

#

# Dies on error:

# - If the directory cannot be opened

# - If the directory contents cannot be read

#

sub process_dir {

my $dir = shift();

if (opendir(my $DIR, $dir)) {

if (my @nodes = readdir(DIR)) {

foreach my $node (no_upwards(@nodes)) {

process_node(catfile($dir, $node));

}

} else {

die "$dir: could not read directory ($!)\n";

}

closedir(DIR);

} else {

die "$dir: could not open directory ($!)\n";

}

}

#

# Process a single file and extract Java version information

#

# Reads the first 8 bytes of a file to check if it's a valid Java class file

# (identified by the magic number 0xCAFEBABE) and extracts version information

# from the bytecode header.

#

# Java class file format (first 8 bytes):

# Bytes 0-3: Magic number (0xCAFEBABE)

# Bytes 4-5: Minor version

# Bytes 6-7: Major version

#

# Version mapping:

# Major 45 (minor <=3): Java 1.0.2

# Major 45 (minor >3): Java 1.1.8

# Major 46: Java 1.2.2

# Major 47: Java 1.3.1

# Major 48: Java 1.4.2

# Major 49+: Java (major - 44) [e.g., 52 = Java 8, 61 = Java 17]

#

# Parameters:

# $file - Path to the file to process

#

# Dies on error:

# - If the file cannot be opened

# - If the file cannot be read

# - If the file is not a valid Java class file

#

sub process_file {

my $file = shift();

if (open(my $FILE, '<', $file)) {

binmode($FILE);

my $buffer;

if (read(FILE, $buffer, 8)) {

# Unpack the first 8 bytes as two 32-bit unsigned integers (big-endian)

my @fields = unpack('NN', $buffer);

# Check for Java class file magic number (0xCAFEBABE)

if ($fields[0] == 0xCAFEBABE) {

# Extract minor and major version numbers from the second 32-bit value

my $minor = ($fields[1] & 0xFF00) >> 16; ## no critic [Use of bitwise operator]: indeed

my $major = $fields[1] & 0x00FF; ## no critic [Use of bitwise operator]: indeed

my $version = '';

# Map major/minor version to Java release version

if ($major == 45) {

if ($minor <= 3) {

$version = '1.0.2';

} else {

$version = '1.1.8';

}

} elsif ($major == 46) {

$version = '1.2.2';

} elsif ($major == 47) {

$version = '1.3.1';

} elsif ($major == 48) {

$version = '1.4.2';

} elsif ($major >= 49) {

# Java 5 and later: version = major - 44

$version = ($major - 44);

}

print "$file: Java " . $version . " [" . $minor . "/" . $major . "]\n";

} else {

die "$file: not a java class file\n";

}

} else {

die "$file: could not read file ($!)\n";

}

close($FILE);

} else {

die "$file: could not open file ($!)\n";

}

}

main(@ARGV);