Networking is the capability of different computers to make connections with each other and to exchange information. In Java, basic networking is supported by classes in the java.net package, including support for connecting and retrieving files by Hypertext Transfer Protocol (HTTP) and File Transfer Protocol (FTP), as well as working at a lower level with sockets. You can communicate with systems on the Net in three simple ways:
Load a web page and any other resource with a uniform resource locator (URL) from an applet.
· Use the socket classes, Socket and ServerSocket, which open standard socket connections to hosts and read to and write from those connections.
· Call getInputStream(), a method that opens a connection to a URL and can extract data from that connection.
· Opening a Stream over the Net
As you learned during Day 15, “Working with Input and Output,” you can pull information through a stream into your Java programs in several ways. The classes and methods you choose depend on the format of the information and what you want to do with it. One of the resources you can reach from your Java programs is a text document on the web, whether it’s a Hypertext Markup Language (HTML) file, Extensible Markup Language (XML) file, or some other kind of plain text document. You can use a four-step process to load a text document off the Web and read it line by line:
1. Create a URL object that represents the resource’s web address.
2. Create a HttpURLConnection object that can load the URL and make a connection to the site hosting it.
3. Use the getContent() method of that HttpURLConnection object to create an InputStreamReader that can read a stream of data from the URL.
4. Use that input stream reader to create a BufferedReader object that can efficiently read characters from an input stream.
There’s a lot of interaction going on between the web document and your Java program. The URL is used to set up a URL connection, which is used to set up an input stream reader, which is used to set up a buffered input stream reader. The need to catch any exceptions that occur along the way adds more complexity to the process.
