19.7 Java4650: the urlconnection class

Table of contents

• Preface
  • Viewing tip
    • Figures
    • Listings
• General background information
• Discussion and sample code
• Run the program
• What's next?
• Miscellaneous
• Complete program listing

Preface

This module is one in a collection of modules designed for teaching INEW 2338 Advanced Java (Web) at Austin Community College in Austin, TX. More specifically, it is one in asub-collection of modules designed for teaching network programming in that course. The purpose of this module is to introduce the student to the URLConnection class.

Viewing tip

I recommend that you open another copy of this module in a separate browser window and use the following links to easily find and view the Figuresand Listings while you are reading about them.

Figures

• Figure 1 . Partial program output.

Listings

• Listing 1 . Beginning of the program.
• Listing 2 . Get a URLConnection object.
• Listing 3 . Get information about the URL.
• Listing 4 . The program named Java4650a.

General background information

I don't plan to say very much about the URLConnection class. It is an abstract class that can be extended , and it has a protected constructor that takes a URL object as a parameter.

It has variables or fields that contain useful information about a connection.

It has many methods that can be used to examine and manipulate an object of the class in a variety of different ways.

If you plan to use the URL class for the higher-lever capabilities that it offers, and you plan to write content handlers and protocol handlers , you will probably need to become very familiar with this class. In that case, you will probably want to get a copy of a good Java networkingbook, such as Java Network Programming , by Elliotte Rusty Howard, and study the use of this class in depth.

My objective here is simply to make you aware of the existence of the class and its many methods, and to provide some examples of how you can get and use anobject of the class to obtain higher-level information about a connection.

Discussion and sample code

This program illustrates connecting to a URL and creating a URLConnection object.

The program uses the URLConnection object to obtain and display some of the "higher level" information about the UR L:

• the URL
• the date last modified
• the content type

The computer must be online for this program to run properly. Otherwise, it will throw an exception of type UnknownHostException .

Partial program output

Figure 1 shows part of the output from the program. The first three lines of output correspond to the items in the above list , and are the items that we will be primarily interested in for this module.