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Then the program closes the socket and terminates.
The next program is an extremely simple web browser program. More correctly, the next program is a simple HTTP client implemented using sockets. A completelisting of the program is provided in Listing 14 .
The program implements just enough of the HTTP protocol to make it capable of getting a file froman HTTP server. Considerably more programming effort would be required to turn it into a useful browser.
Beginning of the program named Java4660c
As shown in Listing 8 , the program begins by defining the name of a server and the number of the HTTP port on that server. Although the standard portnumber for HTTP servers is port 80, this program is written to access a Tomcat server as localhost using port 8080.
| Listing 8 - Beginning of the program named Java4660c. |
|---|
import java.net.*;
import java.io.*;class Java4660c{
public static void main(String[]args){
String server = "localhost";int port = 8080; //http port on localhost
try{//Get a socket, connected to the specified server
// on the specified port.Socket socket = new Socket(server,port); |
Then the program opens a socket to the specified server on the specified port.
Create input and output streams
As shown in Listing 9 , the program creates input and output stream objects for transferring data between the client and the server .
| Listing 9 - Create input and output streams. |
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//Get an input stream from the socket
BufferedReader inputStream =new BufferedReader(new InputStreamReader(
socket.getInputStream()));//Get an output stream to the socket. Note
// that this stream will autoflush.PrintWriter outputStream =
new PrintWriter(new OutputStreamWriter(socket.getOutputStream()),true); |
The output stream will autoflush , which is critical. If the output stream isn't flushed, the server will not respondproperly. (Presumably it may not receive all of the data until the stream is flushed.)
Send a GET command
The HTTP protocol provides several different commands or requests that the client can send to the server. This program implements only the GET command. This is a request by the client to find and download a specified file.
Then, as shown in Listing 10 , acting as an HTTP client, the program sends a GET command to the server specifying a particular path and file name. The GET command is part of the HTTP application protocol.
| Listing 10 - Send a GET command. |
|---|
outputStream.println("GET /Java4570b.jsp"); |
Fetch and send
This causes the server to attempt to fetch the specified file and send it to the client. If the server is being properly supported on the specific port, itwill send something, although that something could be an error message.
Note that the request includes not only the file name, but also the path to that file relative to the directory that the HTTP server software considers tobe the pseudo-root . This is probably not the actual root directory on the server computer, but rather is a logical root.
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