Tuesday, July 06, 2010

REST Client

This is a feature rich rest client what I developed and released to open source under EPL 1.0 for developers to play with web services. It can be used to test any URL for all HTTP methods
  • GET
  • POST
  • PUT
  • HEAD 


Main Features

  1. Simultaneous views of request, response and browser.
  2. Post raw data or file, text content or binary.
  3. Post params in either body or as part of URL (twitter style).
  4. Post multipart form data with same ease as of normal post.
  5. Handle response equally well even if it is binary e.g. image, pdf etc. No gibberish characters anymore.
  6. Play with headers and params.

Min. Requirement

  • Java 1.6
  • Eclipse 3.4 (for plugin)
  • HTTP 1.1 compatibility

Project Home:


Approved by eclipse.org:


Friday, May 28, 2010

Volatillity of "volatile" in Java Multi-threading

Many people say volatile keyword in Java is poorly understood and underused and I am not the exception. I would try to throw some light over it to make it simple to understand.

volatile has its meaning in context of multi-threading. Many explain it as

"If a variable is declared as volatile then it is guaranteed that any thread which reads it see the most recently written value."

Well first we need to understand that each thread has private memory (cache) in addition to access to shared main memory. Thread contains a copy of shared object, present in main memory, in its cache. There is time-to-time synchronization between cached value and value in main memory; it happens on event of obtaining or releasing lock. But this is not true if variable is declared as volatile. Volatile variables are read and written to main memory only. So there is no need of synchronization and any thread trying to read value will read from main memory.

Having said that there is still an open question of dead lock. Well access to volatile variable is like accessing a synchronized block without holding lock.

Monday, March 29, 2010

Ajax - Internal

Objective of this post is to expose behind the scene story of Ajax but lets start with classical definition of Ajax ...

1. What is Ajax?
Ajax is a web technology by which web client (web page) can interact with server asynchronously. Ajax stands for Asynchronous Javascript and XML. The whole story is around an object XMLHttpRequest which is an implementation, available in most browsers, of an interface XMLHttpRequest provided by scripting engine. IE has a different name of this object called XMLHTTP and instantiated as an activeX object. This object can be used by scripts to programmatically connect to their originating server via HTTP synchronously and asynchronously. Its asynchronous capability is exploited by AJAX for interactive communication with server.

2. Example
function ajaxCall(url) {
var req;

try {
req = new XMLHttpRequest();
} catch(e) {
try {
req = new ActiveXObject("Msxml2.XMLHTTP"); // IE 6.0+
} catch(e) {
try {
req = new ActiveXObject("Microsoft.XMLHTTP"); // Older IE
} catch(e) {
throw new Error("Your browser doesn't support AJAX => " + e); // Doesn't support AJAX

req.onreadystatechange = function() {
if(this.readyState == 4) {
var data = req.responseText;
document.getElementById('response').innerHTML = data; // create a div with id 'response'
// $("#response").html(data); // if using jquery
req.open("GET", url, true);

Working with GET
Parameters can be passed as part of URL with GET e.g. http://server.com/getUser?fname=susan&lname=hank

Working with POST (sending JSON object, sending DOM)
With POST send() method can have a Document, DOM string, JSON string or any simple text string.

◆ A new instance of XMLHttpRequest object needs to be created for each new request. This is so because once readyState gets changed it is not reset to 0.
◆ Some browsers don't implement no argument send() method. So it would be better to pass 'null' if there is nothing to pass.

3. XMLHttpRequest Explained

XMLHttpRequest has the following methods

abort()Aborts the current request
getAllResponseHeaders()Returns all of the HTTP headers as a string
getResponseHeader( headerName )Returns the specific value of the given HTTP header.
open( method, URL, async, userName, password )Opens a connection to the given URL using the given Method.
URL - The URL that you wish to connect to.
method - The HTTP method of which you wish to communicate by.
Possible Methods:
  • GET - most common
  • POST
  • HEAD
  • PUT
  • DELETE - least common
async - whether or not the connection should be asynchronous. For Ajax this is always true.
userName - username IF login is required
password - password IF login is required
send( content )Sends the request to the url in the open function. Content is any information that you wish to send to the server. This is typically null but depends on the method specified in the open function.
setRequestHeader( key, value )Adds a key-value pair to the HTTP header to be sent.

XMLHttpRequest has the following properties

onreadystatechangeA reference to an event handler for an event that triggers everytime the object changes state.
readyStateReturns the state of the object as follows:
  • 0 = uninitialized
  • 1 = open
  • 2 = sent
  • 3 = receiving
  • 4 = ready
responseTextThe response from the server contained in a single string.
responseXMLThe response from the server in XML format.
statusThe HTTP status code as a number
statusTextThe HTTP status as a string, ex: "Not Okay" or "Ok"

4. Interface of XMLHttpRequest object

XMLHttpRequest object is the implementation of interface provided by scripting engine as specified by W3C. Below is the interface

interface XMLHttpRequestEventTarget : EventTarget {
// for future use

interface XMLHttpRequest : XMLHttpRequestEventTarget {
// event handler attributes
attribute Function onreadystatechange;

// states
const unsigned short UNSENT = 0;
const unsigned short OPENED = 1;
const unsigned short HEADERS_RECEIVED = 2;
const unsigned short LOADING = 3;
const unsigned short DONE = 4;
readonly attribute unsigned short readyState;

// request
void open(DOMString method, DOMString url);
void open(DOMString method, DOMString url, boolean async);
void open(DOMString method, DOMString url, boolean async, DOMString? user);
void open(DOMString method, DOMString url, boolean async, DOMString? user, DOMString? password);
void setRequestHeader(DOMString header, DOMString value);
void send();
void send(Document data);
void send([AllowAny] DOMString? data);
void abort();

// response
readonly attribute unsigned short status;
readonly attribute DOMString statusText;
DOMString getResponseHeader(DOMString header);
DOMString getAllResponseHeaders();
readonly attribute DOMString responseText;
readonly attribute Document responseXML;

More information is provided by the W3C at http://www.w3.org/TR/XMLHttpRequest/