ZipHelper Tutorial

This tutorial provides an overview of the ZipHelper class, which is part of the lightweight-component/aj-util library. The ZipHelper class provides utility methods for ZIP compression and decompression operations.

Introduction

The ZipHelper class contains static methods for working with ZIP files, including compression, decompression, and file type detection.

Main Features

• ZIP extraction with Zip Slip, symbolic-link, entry-count, size, and compression-ratio protection
• File and directory compression (with STORED or DEFLATED options)
• Recursive directory compression
• ZIP file detection by opening and validating the archive structure, including empty ZIPs
• Buffered CRC32 calculation for STORED entries
• Automatic directory creation

Methods

1. Decompression

1. unzip(String save, String zipFile) - Decompress ZIP file to target directory
2. unzip(String save, String zipFile, ExtractionLimits limits) - Decompress with custom resource limits
3. unzipWithChineseFilename(...) - Read legacy GBK entry names

2. Compression

1. zipFile(File[] fileContent, String saveZip, boolean useStore) - Compress files to ZIP
2. zipDirectory(String sourceDir, String saveZip, boolean useStore) - Compress directory to ZIP
3. zipSingleFile(String sourceFile, String saveZip, boolean useStore) - Compress one file

3. Utility Methods

1. initFolder(File file) - Ensure parent directories exist for a file
2. initFolder(String file) - String version of initFolder
3. isZipFile(String filePath) - Check if file is a valid ZIP file

Usage Examples

Decompression

ZipHelper.unzip("C:/extracted", "C:/archive.zip");

Extraction uses conservative default limits. Use the overload with ExtractionLimits when trusted archives require different limits.

File Compression

File[] files = {new File("file1.txt"), new File("file2.txt")};
ZipHelper.zipFile(files, "archive.zip", false); // Use DEFLATED compression

Directory Compression

ZipHelper.zipDirectory("C:/data", "backup.zip", true); // Use STORED (no compression)

Directory compression does not follow symbolic links. The destination ZIP must be outside the source directory.

ZIP File Detection

boolean isZip = ZipHelper.isZipFile("unknown.zip");

Missing files, directories, and malformed archives return false.

Directory Creation

ZipHelper.initFolder("C:/new/path/file.txt"); // Creates C:/new/path if needed

Compression Methods

The class supports two compression methods:

1. DEFLATED (default) - Standard ZIP compression
2. STORED - No compression, files are stored as-is

Error Handling

I/O failures are reported as UncheckedIOException; invalid arguments use IllegalArgumentException. Compression is written to a temporary file and published only after the archive is complete.

Conclusion

The ZipHelper class provides comprehensive utility methods for working with ZIP files, making compression and decompression operations more convenient in Java applications.