vb.net barcode maker Ajax: A Beginner s Guide in Java

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Ajax: A Beginner s Guide
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onreadystatechange readyState responseBody responseStream responseText responseXML status statusText
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Contains the name of the event handler that should be called when the value of the readyState property changes Read/write Contains state of the request Read-only Contains a response body, which is one way HTTP responses can be returned Read-only Contains a response stream, a binary stream to the server Read-only Contains the response body as a string Read-only Contains the response body as XML Read-only Contains the HTTP status code returned by a request Read-only Contains the HTTP response status text Read-only
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abort getAllResponseHeaders getResponseHeader open send setRequestHeader
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Aborts the HTTP request Returns all the HTTP headers Returns the value of an HTTP header Opens a request to the server Sends an HTTP request to the server Sets the name and value of an HTTP header
Table 3-2
XMLHttpRequest Object Methods for Internet Explorer
Property
channel readyState responseText responseXML status statusText
Description
Contains the channel used to perform the request Read-only Contains the state of the request Read-only Contains the response body as a string Read-only Contains the response body as XML Read-only Contains the HTTP status code returned by a request Read-only Contains the HTTP response status text Read-only
Table 3-3
XMLHttpRequest Object Properties for Mozilla, Firefox, and Netscape Navigator
3:
Creating Ajax Applications
Method
abort getAllResponseHeaders getResponseHeader openRequest overrideMimeType
Description
Aborts the HTTP request Returns all the HTTP headers Returns the value of an HTTP header Native (nonscript) method to open a request Overrides the MIME type the server returns
Table 3-4
XMLHttpRequest Object Methods for Mozilla, Firefox, and Netscape Navigator
Property
onreadystatechange readyState responseText responseXML status statusText
Description
Contains the name of the event handler that should be called when the value of the readyState property changes Read/write Contains state of the request Read-only Contains the response body as a string Read-only Contains the response body as XML Read-only Contains the HTTP status code returned by a request Read-only Contains the HTTP response status text Read-only
Table 3-5
XMLHttpRequest Object Properties for Apple Safari
Method
abort getAllResponseHeaders getResponseHeader open send setRequestHeader
Description
Aborts the HTTP request Returns all the HTTP headers Returns the value of an HTTP header Opens a request to the server Sends an HTTP request to the server Sets the name and value of an HTTP header
Table 3-6
XMLHttpRequest Object Methods for Apple Safari
Ajax: A Beginner s Guide
Now that we have an XMLHttpRequest object, what do we do with it You can start by opening it, which lets you configure it in preparation for connecting to the server and downloading data
Opening the XMLHttpRequest Object
When ajaxhtml first loads in the browser, it tries to create an XMLHttpRequest object When the user clicks the button to fetch data from the server using Ajax, the getData function is called, and the first thing it does is check whether an XMLHttpRequest object was created successfully:
<script language = "javascript"> var XMLHttpRequestObject = false; if (windowXMLHttpRequest) { XMLHttpRequestObject = new XMLHttpRequest(); } else if (windowActiveXObject) { XMLHttpRequestObject = new ActiveXObject("MicrosoftXMLHTTP"); } function getData(dataSource, divID) { if(XMLHttpRequestObject) { } } </script>
In case an XMLHttpRequest object couldn t be created, you can add code to explain to the user that their browser can t do Ajax, as follows:
function getData(dataSource, divID) { if(XMLHttpRequestObject) { } else { var obj = documentgetElementById(divID); objinnerHTML = "Sorry, your browser is not Ajax-enabled"; } }
3:
Creating Ajax Applications
It s time to open the XMLHttpRequest object Doing so lets you configure the XMLHttpRequest object with, for example, the URL that it is to contact when you connect to the server Here s how you use the XMLHttpRequest object s open method in general (as always, items in square brackets are optional, and items in italics are placeholders that you fill in yourself):
open("method", "URL"[, asyncFlag[, "userName"[, "password"]]])
The following table explains what the various arguments mean:
method URL asyncFlag userName password The HTTP method used to open the connection, such as GET, POST, PUT, HEAD, or PROPFIND The requested URL A Boolean value indicating whether the call is asynchronous The default is true The username of your account The password used to connect to your account
The following code shows how ajaxhtml uses the XMLHttpRequest object s open method In this case, it uses the HTTP GET method to contact the server (that s the normal way of contacting servers we ll see more about that later in this chapter, in the discussion of another option, the POST method), and passes the URL of the file it s looking for, which is passed to the getData function as the dataSource argument
function getData(dataSource, divID) { if(XMLHttpRequestObject) { XMLHttpRequestObjectopen("GET", dataSource); } }
Using the open method like this configures the XMLHttpRequest object it does not connect, or open, any connection to the server The actual connection process is coming up in a few pages Note that the URL that the XMLHttpRequest object has been configured to access is simply the name of a file, datatxt, as you see here in the call made to getData when the button is clicked:
<body> <H1>An Ajax example</H1> <form> <input type = "button" value = "Fetch the message" onclick = "getData('datatxt', 'targetDiv')"> </form>
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