Who is responsible for XML?

XML is a project of the World Wide Web Consortium (W3C), and the development of the specification is supervised by an XML Working Group. A Special Interest Group of co-opted contributors and experts from various fields contributed comments and reviews by email.

XML is a public format: it is not a proprietary development of any company, although the membership of the WG and the SIG represented companies as well as industrial research and academic institutions. The v1.0 specification was accepted by the W3C as a Recommendation on Feb 10, 1998.

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Why is XML such an important development?

It removes two constraints which were holding back Web developments:

dependence on a single, inflexible document type (HTML) which was being much abused for tasks it was never designed for;

the complexity of full SGML, whose syntax allows many powerful but hard-to-program options.

XML allows the flexible development of user-defined document types. It provides a robust, non-proprietary, persistent, and verifiable file format for the storage and transmission of text and data both on and off the Web; and it removes the more complex options of SGML, making it easier to program for.

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Aren't XML, SGML, and HTML all the same thing?

Not quite; SGML is the mother tongue, and has been used for describing thousands of different document types in many fields of human activity, from transcriptions of ancient Irish manuscripts to the technical documentation for stealth bombers, and from patients' clinical records to musical notation. SGML is very large and complex, however, and probably overkill for most common office desktop applications.

XML is an abbreviated version of SGML, to make it easier to use over the Web, to make it easier for you to define your own document types, and to make it easier for programmers to write programs to handle them. It omits all the complex and less-used options of SGML in return for the benefits of being easier to write applications for, easier to understand, and more suited to delivery and interoperability over the Web. But it is still SGML, and XML files may still be processed in the same way as any other SGML file (see the question on XML software).

HTML is just one of many SGML or XML applications—the one most frequently used on the Web.

Technical readers may find it more useful to think of XML as being SGML−− rather than HTML++.


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How can I read the status code of a HTTP request?

If you use the URL.openStream() method, there's no way to determine whether a request was successful or not. The only alternative is to use the URL.openConnection() method, which returns a URLConnection instance. The URLConnection is an abstract class, meaning that it provides a template of methods which other classes will implement. Even though the URL.openConnection() method returns a URLConnection instance, it is actually returning a concrete implementation of that class.

When a request is made for a resource using the Hypertext Transfer Protocol, the implementation of URLConnection that is returned is a java.net.HttpURLConnection. This class defines additional methods, one of which allow you to access the response status code. To find out the status of a request, you need to cast the URLConnection to a HttpURLConnection, and invoke the int HttpUrlConnection.getResponseCode() method.

URL url = new URL ( some_url );
URLConnection connection = url.openConnection();

connection.connect();

// Cast to a HttpURLConnection
if ( connection instanceof HttpURLConnection)
{
HttpURLConnection httpConnection = (HttpURLConnection) connection;

int code = httpConnection.getResponseCode();

// do something with code .....
}
else
{
System.err.println ("error - not a http request!");
}


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How can I create an event handling mechanism in Java? I'm used to ActiveX controls, which fire asynchronous events (i.e. when a control is finished a

The most common mechanism for this is the callback, where one class calls the method of another to notify it of an action or event. The class to be notified defines methods that will respond to specific events, such as when a mouse is clicked, dragged, or released. The AWT makes heavy use of this, with Listener interfaces. A class implements the event handling methods of a listener, and can then be registered with a component that generates these types of events. Classes that are event sources provide methods which register a listener, and at a later time when the event is generated, will invoke listener methods. The Abstract Windowing Toolkit (AWT) and Swing APIs would be a good place to start, to see if this suits your needs.


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How can I poll a remote server, to see if it is still available? I'd like to check to see if the server has crashed, and if so, record the time.

If your application is a TCP server, the easiest way to do this is for a client to connect to it, using the java.net.Socket class. When the Socket is connected, if the server is down an IOException will be thrown, indicating that the server is not accepting connections.

However, this may not be a sufficient test for mission critical applications. What if the server has stalled, and will accept connections but not respond to them? In this situation, you'll need to write a valid request to the server (using the appropriate network protocol, such as HTTP or FTP). It doesn't matter what type of request is made, or what data is really returned (unless it is an error message). The only purpose of the request is to see if the server will response, and is still available for use.


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Who created Java?

Java is still a relatively new language, so it is quite amusing to some to think that Java has a "history" behind it. One of the most frequent questions I've been getting lately though is about the origins of Java.

Java was created by engineers working at Sun Microsystems. The figure that stands out most of all is James Gosling, widely regarded as the "father" of Java. James and his team were working on a language whose original name was Oak. Oak was designed for embedded devices, such as mobile phones. The first publicly available version of Java, however, was as Java applets, in the original HotJava browser. From there, Java grew to what it is today.


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