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JavaInfo

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#!/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] >> 16; ## no critic [Use of bitwise operator]: indeed
my $major = $fields[1] & 0xFFFF; ## 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);
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