Trail: Custom Networking
This trail walks you through the complexities of writing Java applications and applets that can be used on the Internet.
Overview of Networking
has two sections. The first describes the networking capabilities of
the Java platform that you may already be using without realizing that
you are using the network. The second provides a brief overview of
networking to familiarize you with terms and concepts that you should
understand before reading how to use URLs, sockets, and datagrams.
Working With URLs
discusses how your Java programs can use URLs to access information on
the Internet. A URL (Uniform Resource Locator) is the address of a
resource on the Internet. Your Java programs can use URLs to connect to
and retrieve information over a network. This lesson provides a more
complete definition of a URL and shows you how to create and parse a
URL, how to open a connection to a URL, and how to read from and write
to that connection.
All About Sockets
explains how to use sockets so that your programs can communicate with
other programs on the network. A socket is one endpoint of a two-way
communication link between two programs running on the network. This
lesson shows you how a client can connect to a standard server, the
Echo server, and communicate with it via a socket. It then walks you
through the details of a complete client/server example, which shows
you how to implement both the client side and the server side of a
client/server pair.
All About Datagrams
takes you step by step through a simple client/server example that uses
datagrams to communicate. It then challenges you to rewrite the example
using multicast socket instead.
Programmatic Access to Network Parameters
explains why you might want to access network interface parameters
and how to do so. It gives examples of how to list all the
IP addresses assigned to the machine as well as other useful
information such as whether the interface is running.
Working With Cookies
discusses how cookies are used to create a session between a client
and server, and how you can take advantage of cookies in your
HTTP URL connections.
Security considerations: Note that communications over the network are subject to approval by the current security manager. The Security Manager describes what a security manager is and how it impacts your applications. For general information about the security features provided by the JDK, refer to Security Features in Java SE.
The example programs in the following lessons that cover URLs, sockets, and datagrams are standalone applications, which, by default, have no security manager. If you convert these applications to applets, they may be unable to communicate over the network, depending on the browser or viewer in which they are running. See What Applets Can and Cannot Do for information about the security restrictions placed on applets.
