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The Java platform 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-compatible browsers use
this ability of the Java platform to the extreme to transport and run
applets over the Internet.
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.
Security considerations: Note that communications over the network are subject to approval by
the current security manager.
Providing Your Own Security Manager
describes what a security manager is and how to write a
customized security manager for your applications.
For general information about the security features
provided by the JDK, refer to
Security in Java 2 SDK 1.2.
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
Practical Considerations when Writing Applets for information about the security
restrictions placed on applets.
