How to compress files in ZIP format

Java has "java.util.zip" library to implement the data compression in ZIp format. The overall concept is quite straightforward.

1. Read file with "FileInputStream"
2. Add the file name to "ZipEntry" and output it to "ZipOutputStream"

Simple ZIP example

In this example, it will read a file "C:\\spy.log" and compress it to "C:\\MyFile.zip"

import java.io.FileInputStream;
 import java.io.FileOutputStream;
import java.io.IOException;
 import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;
  
public class App 
{	
    public static void main( String[] args )
     {
    	byte[] buffer = new byte[1024];
  
    	try{
 
    		FileOutputStream fos = new FileOutputStream("C:\\MyFile.zip");
     		ZipOutputStream zos = new ZipOutputStream(fos);
     		ZipEntry ze= new ZipEntry("spy.log");
     		zos.putNextEntry(ze);
    		FileInputStream in = new FileInputStream("C:\\spy.log");
  
    		int len;
    		while ((len = in.read(buffer)) > 0) {
     			zos.write(buffer, 0, len);
     		}
 
    		in.close();
     		zos.closeEntry();
 
    		//remember close it
     		zos.close();
 
    		System.out.println("Done");
  
    	}catch(IOException ex){
     	   ex.printStackTrace();
    	}
     }
}

Advance ZIP example – Recursively

In this example, it will read all files from folder "C:\\testzip" and compress it to "C:\\MyFile.zip". It will recursively zip a directory structure.

import java.io.File;
 import java.io.FileInputStream;
import java.io.FileOutputStream;
 import java.io.IOException;
import java.util.ArrayList;
 import java.util.List;
import java.util.zip.ZipEntry;
 import java.util.zip.ZipOutputStream;
 
public class AppZip
 {
    List<String> fileList;
     private static final String OUTPUT_ZIP_FILE = "C:\\MyFile.zip";
     private static final String SOURCE_FOLDER = "C:\\testzip";
  
    AppZip(){
	fileList = new ArrayList<String>();
     }
 
    public static void main( String[] args )
     {
    	AppZip appZip = new AppZip();
     	appZip.generateFileList(new File(SOURCE_FOLDER));
     	appZip.zipIt(OUTPUT_ZIP_FILE);
    }
  
    /**
     * Zip it
     * @param zipFile output ZIP file location
     */
    public void zipIt(String zipFile){
  
     byte[] buffer = new byte[1024];
  
     try{
 
    	FileOutputStream fos = new FileOutputStream(zipFile);
     	ZipOutputStream zos = new ZipOutputStream(fos);
  
    	System.out.println("Output to Zip : " + zipFile);
  
    	for(String file : this.fileList){
  
    		System.out.println("File Added : " + file);
     		ZipEntry ze= new ZipEntry(file);
         	zos.putNextEntry(ze);
 
        	FileInputStream in = 
                        new FileInputStream(SOURCE_FOLDER + File.separator + file);
  
        	int len;
        	while ((len = in.read(buffer)) > 0) {
         		zos.write(buffer, 0, len);
         	}
 
        	in.close();
     	}
 
    	zos.closeEntry();
     	//remember close it
    	zos.close();
  
    	System.out.println("Done");
     }catch(IOException ex){
        ex.printStackTrace();   
    }
    }
 
    /**
     * Traverse a directory and get all files,
     * and add the file into fileList  
      * @param node file or directory
     */
    public void generateFileList(File node){
  
    	//add file only
	if(node.isFile()){
 		fileList.add(generateZipEntry(node.getAbsoluteFile().toString()));
 	}
 
	if(node.isDirectory()){
 		String[] subNote = node.list();
 		for(String filename : subNote){
 			generateFileList(new File(node, filename));
 		}
	}
 
    }
 
    /**
      * Format the file path for zip
     * @param file file path
     * @return Formatted file path
     */
    private String generateZipEntry(String file){
     	return file.substring(SOURCE_FOLDER.length()+1, file.length());
     }
}