Compress and Decompress with Java (using zip)

2 thoughts on “Compress and Decompress with Java (using zip)”

1. I’ve just been down the ‘decompress with Java’ road just recently also. Thought perhaps your readers might find the code I hacked useful in some situations. One is for simple ZIP decompression, the other for GZ

   import java.io.*;
   import java.util.*;
   import java.util.zip.*;

   /* UnZIP a file archive. */
   /* Parameter 1: the directory containing the ZIP file. This will also */
   /* be the output directory. */
   /* Parameter 2: the ZIP file name. */
   /* */

   public class UnZIPFile {

   public static void main(String[] args) {

   String dir = args[0];
   String infile = dir + “/” + args[1];
   String outfile;

   ZipInputStream zin;
   FileOutputStream fout;
   ZipEntry ze;
   int length;
   byte [] outBuf = new byte[512];

   try {
   zin = new ZipInputStream(
   new BufferedInputStream(new FileInputStream(infile)));
   System.out.println(“Processing ZIP archive: ” + infile);
   while((ze = zin.getNextEntry()) != null) {
   System.out.println(” Processing entry: ” + ze);
   outfile = dir + “/” + ze;
   fout = new FileOutputStream(outfile);
   while((length = zin.read(outBuf)) != -1) {
   fout.write(outBuf,0,length);
   }
   fout.close();
   System.out.println(” Entry extracted OK to: ” + outfile);
   }
   zin.close();
   System.exit(0); // (remove for servlets!)
   }

   catch (Exception e) {
   System.err.println(“UnZIPFile failed.”);
   System.err.println(e);
   System.exit(-1);
   }
   }
   }

   import java.io.*;
   import java.util.*;
   import java.util.zip.*;
   import java.util.StringTokenizer;

   /* UnGZIP a file archive. */
   /* Parameter 1: the directory containing the GZIP file. This will also */
   /* be the output directory. */
   /* Parameter 2: the GZIP file name. */
   /* Parameter 3: (optional) output file name */
   /* */

   public class UnGZIPFile {

   public static void main(String[] args) {

   String dir = args[0];
   String fileName = args[1];
   String infile = dir + “/” + fileName;
   String outfile;

   GZIPInputStream gzin;
   FileOutputStream fout;
   int length;
   byte [] outBuf = new byte[512];

   if (args.length == 3) { // output file name specified as a parameter
   outfile = dir + “/” + args[2];
   } else { // output file is input file name w/o extension
   StringTokenizer st = new StringTokenizer(fileName, “.”);
   int tokenCount = st.countTokens();
   if (tokenCount == 1) { // no extension, use ‘txt’…
   outfile = dir + “/” + fileName + “.txt”;
   } else {
   outfile = dir + “/”;
   for (int i = 1; i

2. Your code doesn’t take in account ZIP files that have directory entries after the file entries.

   What happens, for example, if I get a file entry “images/color.jpg” and the directory “images” doesn’t exist yet ?

   I think a better option is to get the entry Enumeration from the ZipFile (with entries method) and then take different actions depending whether the entry is a directory or not (verify that with the isDirectory method).

   If the entry is a directory, then we simply create it. If the entry is a file, first we get the directory part from its name and create the directory. Then we get the InputStream from the ZipEntry and write to the file.