Java HTTP library

Being in need to issue POST requests from within a Java application, and wanting re-usable code, I created a very simple Java library for issuing POST and GET requests to a remote server.

POST source codeGET source code

Usage (POST example):

POST post = new POST();
post.postRequest("", "param1=foo&param2=bar", "Mozilla/5.0");

In other words, the arguments are:


The output can be manipulated as desired, depending on what you response you except you should use a corresponding element/object.

Java libary in Android project

If you have developed your Java library that you would like to use within your Android project, or you want to use an existing Java library, make sure that the library itself is compiled with Java 1.6 rather than 1.7. Have been always forgetting that and have wondering for a couple of days why am I getting “NoClassDefFoundError” error.

Java encrypt class

A simple implementation of an encryption class to be used in Java applications for either encrypting strings and calculating files’ fingerprint.

import java.math.BigInteger;

public class Encrypt {

   private FileInputStream fis;

   public Encrypt() { }

   public String encryptString(String input, String salt, String algorithm) {
      String output = null;
      String fullInput = null;

      if (!salt.equals(null)) {
         fullInput = salt + input;
      } else {
         fullInput = input;

      try {
         MessageDigest digest = MessageDigest.getInstance(algorithm);
         digest.update(fullInput.getBytes(), 0, fullInput.length());
         output = new BigInteger(1, digest.digest()).toString(16);
      } catch (NoSuchAlgorithmException ex) {
      return output;

   // Based on:
   public String calculateFingerprint(String fileName, String algorithm) {
      StringBuffer sb = new StringBuffer();
      try {
         MessageDigest md = MessageDigest.getInstance(algorithm);
         fis = new FileInputStream(fileName);
         byte[] dataBytes = new byte[1024];
         int nread = 0;
         while ((nread = != -1) { md.update(dataBytes, 0, nread); }
         byte[] mdbytes = md.digest();
         for (int i = 0; i < mdbytes.length; i++) {
            sb.append(Integer.toString((mdbytes[i] & 0xff) + 0x100, 16).substring(1));
      } catch (Exception ex) {
      return sb.toString();

Link to GiHub repository. The class is intended to be used as a library within Java applications.

Example for encrypting a string:

Encrypt en = new Encrypt();
String encryptedString = en.encryptString(textField.getText().toString(), \
"salt goes here if you want", "md5")));

Example for calculating the fingerprint of a file:

Encrypt en = new Encrypt();
String fingerPrint = en.calculateFingerprint("/path/to/file", sha1);

Android SQLite Adapter class

Working with an SQLite database on Android can require some times more effort than what you should really give. For instance, if you ship a pre-configured and populated database with an application, you would need first to copy over the database to the specific database directory and then open it for reading and/or writing data to it. The SQLiteOpenHelper class provides a few methods that make life a bit easier but it does not provide a copy method for handling this issue. In addition to this, a check method would be required before copying the database and so on. Following on this, I implemented a SQLite adapter class to cover my needs as bellow:

– Copy database to the correct directory.
– Open and close the database.
– Execute raw SQL query.
– Execute SQL query for string, int, long, double.
– Drop table.
– Return count of a table.
– Download a db copy from Internet and replace local one.

Source code at GitHub.


Last week I was in Athens for the 4th International Conference from Scientific Computing to Computational Engineering. Many interesting talks from a wide range of areas. My talk was about “HPC Applications Performance on Virtual Clusters“. The main outcome from my perspective, we need to investigate GPU virtualisation. There are more and more scientists/researchers that want to exploit such systems and in the near future we’ll need to deploy virtualised GPU systems in the same way we do with CPUs.

My paper
My presentation

Basic HTTP authentication with Java

Opening a URL in Java is pretty much straightforward by using the class. If the URL trying to be accessed is password protected (by Apache’s AuthType for example), you will need to authenticate before trying to open the URL. The easiest way to authenticate is by using the Authenticator ( class which is available on Java 1.2 and higher:

final String theUsername = username;
final String thePassword = password;

Authenticator.setDefault(new Authenticator() {
     protected PasswordAuthentication getPasswordAuthentication() {
           return new PasswordAuthentication(theUsername, thePassword.toCharArray());