When one clicks on an URL link in a browser page, a request is sent to the computer at the domain indicated. If no port is included, the default port 80 is used. The Web server is watching this port and when a request arrives it will open a socket for this client and provide the Web page or other service requested.

Other types of servers use other ports to provide services such as database access, email, etc. Also, as mentioned earlier, servers can be created with RMI, thus directly calling methods in the server program itself. Here, though, we will concentrate on socket type servers, such as web servers.

Web serving is a stateless interaction, meaning that it breaks off the connection after answering the request and does not maintain any further connection information about that client. Each interaction will require a new connection. (An on line store might use a cookie file on the browser platform and the IP address of the requestor to maintain information about an interaction for a given period of time.)

Note that servers for other types of protocols, such as FTP, can maintain a connection as long as necessary.

The Java Standard Edition offers lots of resources to create and run your own server such as a HTTP (web) server. The Enterprise Edition offers many advanced tools and features but the J2SE provides sufficient resources to build useful servers.

We will create a micro HTTP server that illustrates all the basic components of a web server. Such a server could run in an embedded processor and provide information on, say, a sensor or display data from a scientific instrument. See the references for similar server projects.

Note that since you customize the server as you wish, you don't have to break off the connection (that is, close the socket) immediately as with standard Web servers. We discuss in Chapter 15 a client/server system using sockets that can maintain a continual connection.

Our little web server needs to

• Create a ServerSocket instance that watches for incoming client requests.
  
  
• Create a Socket to connect with a client.
  
  
• Spin off a thread to handle the client's request
  
  
• Use stream I/O to receive the clients' requests and to send responses.

The following pages will discuss each of these functions.

	Part I	Part II	Part III
Java Core	1  2  3  4  5  6  7  8  9  10  11  12	13 14 15 16 17 18 19 20 21	22 23 24
Supplements	1  2  3  4  5  6  7  8  9  10  11  12
Tech	1  2  3  4  5  6  7  8  9  10  11  12
Physics	1  2  3  4  5  6  7  8  9  10  11  12

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