The Java environment is highly regarded in part because of its
suitability for writing programs that use and interact with the
resources on the Internet and the World Wide Web. In fact,
Java-capable browsers use this ability of the Java environment
to the extreme to transport and run applets over the net.
The Custom Networking and Security trail walks you through the
complexities of writing Internet-aware Java applications and
applets.
Overview of Networking
has two sections.
The first section provides a brief overview of networking to
familiarize you with terms and concepts that you will need to
understand before learning how to use URLs, sockets,
and datagrams. The second section describes the networking
capabilities of the Java environment that you may already be
using without realizing it!
Working with URLs
discusses how your Java programs can use URLs to access information
on the Internet. A Uniform Resource Locator (URL) is an address of
a resource on the Internet. Your Java programs can use URLs to connect
to and retrieve information over the network. This lesson
provides a more complete definition of URL, shows you how to
create and parse URLs, how to open a connection to a URL,
and how to read from and write to those connections.
All About Sockets
explains how you can use sockets so that your programs can communicate
with other programs on the network.
A socket is one end of a two-way communication link between
two programs running on the network. This lesson first shows you
how to read from and write to a socket from a client program communciating
with a standard server program--the echo server.
Also, this lesson walks you through the details of a complete
client/server example showing you how to implement both the client
and the server side of a client/server pair.
All About Datagrams
shows you how to use datagrams to broadcast messages over the network.
The lesson on sockets focuses on "perfect" communication links between
applications running on the network. Perfect communication links guarantee
the arrival of all packets in the order they were sent. While necessary
for some applications, perfect links are overkill for others. These
applications use datagrams instead. The delivery of datagrams is not
guaranteed nor is the order in which they are delivered. This lesson
takes you step-by-step through a client/server example that uses
datagrams to communicate.
Providing Your Own Security Manager
describes Java's security model and how you can build your
own security manager for your Java applications.
Security consideration:
Note that communication over the network are subject to
approval by the current security manager. The example programs
contained in the lessons covering URLs, sockets, and datagrams
in this trail are stand alone applications, which by default have
no security manager. If you convert these applications to applets
they might be unable to communicate over the network depending on
the browser or viewer they are running in. See
Understanding Applet Capabilities and Restrictions
for information about the security restrictions placed on applets.
