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JAR Extractor

The JarExtractor class provides utilities for extracting content from JAR (Java Archive) files. It offers secure methods to extract both individual files and entire folders from JAR archives.

Usage Examples​

Extracting Folders from JAR Files​

// Extract a folder from a JAR file
File jarFile = new File("path/to/library.jar");
String folderPathInJar = "resources/templates/"; // Path inside the JAR
File targetDirectory = new File("path/to/output/templates");

boolean success = JarExtractor.extractFolderFromJar(
    jarFile, 
    folderPathInJar, 
    targetDirectory
);

if (success) {
    System.out.println("Folder extracted successfully!");
} else {
    System.err.println("Failed to extract folder from JAR.");
}

Extracting Individual Files​

// Extract a single file from a JAR
File jarFile = new File("path/to/library.jar");
String filePathInJar = "resources/config/default.properties"; // File path inside the JAR
File outputFile = new File("path/to/output/default.properties");

JarExtractor.extractFileFromJar(
    jarFile, 
    filePathInJar, 
    outputFile
);

Key Features​

Security Considerations​

The JarExtractor class implements several security measures to prevent common vulnerabilities:

  1. Path Traversal Protection: Validates all extracted paths to prevent directory traversal attacks.
  2. Safe Extraction: Uses atomic file operations and temporary files for reliable extraction.
  3. Error Recovery: Cleans up target directories if extraction fails.

Folder Extraction Process​

When extracting a folder from a JAR file, the process follows these steps:

  1. Validates the target directory
  2. Creates the target directory if needed
  3. Performs security validation on all entries
  4. Creates necessary directory structures
  5. Extracts files with safe copy operations

Error Handling​

The extraction methods include comprehensive error handling for common scenarios:

  • Missing JAR files
  • Invalid target directories
  • Path traversal attempts
  • File system permission issues
  • IO errors during extraction

Use Cases​

The JarExtractor is particularly useful in these scenarios:

  1. Runtime Resource Access: Extracting configuration files or templates from application JARs.
  2. Plugin Systems: Extracting plugin content from plugin JAR files.
  3. Resource Updates: Updating resource files without rebuilding the entire application.
  4. Testing: Extracting test data or resources from test libraries.
  5. Installation Processes: Extracting initial configuration or resources during application installation.

Implementation Details​

Directory Handling​

When extracting directories, the JarExtractor handles both directory entries and file entries:

  • Directory entries are created as directories in the target location
  • Files are extracted with their relative paths maintained
  • Existing directories with the same name are safely cleaned up before extraction

Logging​

The JarExtractor logs operation status to standard output and standard error, helping to track the extraction process and diagnose any issues that might occur.