Unzipping zip files is fairly easy in Java as shown below.

Java Code:
import java.io.*;
import java.util.*;
import java.util.zip.*;
import java.text.*;

class UnZip {
  public static void main(String args[]) throws IOException {
    InputStream in = 
      new BufferedInputStream(new FileInputStream(args[0]));
    ZipInputStream zin = new ZipInputStream(in);
    ZipEntry e;

    while((e=zin.getNextEntry())!= null) {
      if (args.length > 1) {
        if (e.getName().equals(args[1])) {
           unzip(zin, args[1]);
           break;
          }
        }
       unzip(zin, e.getName());
      }
    zin.close();
    }
    
  public static void unzip(ZipInputStream zin, String s) 
     throws IOException {
    System.out.println("unzipping " + s);
    FileOutputStream out = new FileOutputStream(s);
    byte [] b = new byte[512];
    int len = 0;
    while ( (len=zin.read(b))!= -1 ) {
      out.write(b,0,len);
      }
    out.close();
    }
}