Cho em hỏi là làm cách nào để giảm kích thước file sau khi nén ạ.

Em nén xong thì kích thước file tài liệu bằng tất kích thước các file cộng lại. Code:

public void zipFiles(){

    FileOutputStream fos = null;
    ZipOutputStream zipOut = null;
    FileInputStream fis = null;
    try {
        File folder = new File("D:\\Data\\attachment");
        File[] attachFiles = folder.listFiles();

        fos = new FileOutputStream("C:\\Users\\admin\\Desktop\\tai-lieu\\testing.zip");
        zipOut = new ZipOutputStream(new BufferedOutputStream(fos));
        for(File file: attachFiles){
            fis = new FileInputStream(file);
            ZipEntry ze = new ZipEntry(file.getName());
            System.out.println("Zipping the file: "+file.getName());
            zipOut.putNextEntry(ze);
            byte[] tmp = new byte[1024];
            int size = 0;
            while((size = fis.read(tmp)) != -1){
                zipOut.write(tmp, 0, size);
            }
            zipOut.flush();
            fis.close();
        }
        zipOut.close();
        System.out.println("Done... Zipped the files...");
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } finally{
        try{
            if(fos != null) fos.close();
        } catch(Exception ex){

        }
    }
}