<< Chapter < Page Chapter >> Page >

The program named Java4650a

I will explain this program in fragments. A complete listing of the program is provided in Listing 4 .

The URLConnection class is abstract , and therefore cannot be instantiated directly. However, it can be extended , and it has a protected constructor that requires a URL object as a parameter.

A common way to get a URLConnection object is to call a method on a URL object that returns an object of a subclass of the URLConnection class. That is the case in the sample program for this module.

I will ignore the exception handling code in the discussion of this program.

All of the code in the sample program is contained in the main method of the controlling class.

Beginning of the program

The beginning of the program and the beginning of the main method is shown in Listing 1 .

Listing 1 - Beginning of the program.
import java.net.*; import java.io.*;import java.util.*; class Java4650a{public static void main(String[] args){String dataLine; try{//Get a URL object URL url = new URL("http://www.austincc.edu/baldwin/page1.html");

Get a URL object

The code at the bottom of Listing 1 instantiates a URL object. This is essentially the same code that you saw in an earlier module, but you need to see it again here in order to understand the code thatfollows it.

URLConnection object

The code in Listing 2 gets a URLConnection object by calling the openConnection method on the URL object instantiated earlier.

Listing 2 - Get a URLConnection object.
URLConnection urlConnection = url.openConnection();

Get information about the URL

The code in Listing 3 calls three methods on the URLConnection object to obtain three of the higher-level informational aspects of the URL:

  • the URL
  • the date that the file was last modified
  • the content type of the file
Listing 3 - Get information about the URL.
System.out.println(urlConnection.getURL()); Date lastModified = new Date(urlConnection.getLastModified()); System.out.println(lastModified);System.out.println(urlConnection.getContentType());

The result of these three inquiries is shown as the first three lines of text in Figure 1 .

The remaining code

Following this, the program uses the URL object to get an input stream and to display the contents of the file. However, this essentially duplicates a portionof the program in an earlier module, so I won't discuss it further here.

Run the program

I encourage you to copy the code from Listing 4 . Compile the code and execute it. Experiment with the code, making changes, and observing the results of your changes. Make certain that youcan explain why your changes behave as they do.

What's next?

In the next module, I will show you how to download a simple HTML file and to render it in a way that is similar to how it would be rendered in a browser.


This section contains a variety of miscellaneous information.

Housekeeping material
  • Module name: Java4650: The URLConnection Class
  • File: Java4650.htm
  • Published: 03/02/14
  • Revised: 02/07/16

Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.

I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.

In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.

Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.

Complete program listing

Listing 4 - The program named Java4650a.

/*File Java4650a.java Copyright 1998, R.G.Baldwin Revised 01/05/14Illustrates connecting to a URL and creating a URLConnection object.Uses the URL object to obtain and display the URL, the date last modified, and the content type.Also uses the URLConnection object to obtain an input stream object. Then uses this object to read anddisplay the file. **********************************************************/import java.net.*; import java.io.*;import java.util.*; class Java4650a{public static void main(String[] args){String dataLine; try{//Get a URL object URL url = new URL("http://www.austincc.edu/baldwin/page1.html"); //Open a connection to the URL and get a// URLConnection object. URLConnection urlConnection = url.openConnection();//Use the connection to get and display the URLSystem.out.println(urlConnection.getURL());//Use the connection to get and display the date last // modified.Date lastModified = new Date( urlConnection.getLastModified());System.out.println(lastModified);//Use the connection to get and display the content // type.System.out.println(urlConnection.getContentType());//Use the connection to get an InputStream object. // Use the InputStream object to instantiate a// DataInputStream object. BufferedReader htmlPage =new BufferedReader(new InputStreamReader( url.openStream()));//Use the DataInputStream object to read and display// the file one line at a time. while((dataLine = htmlPage.readLine()) != null){System.out.println(dataLine); }//end while loop}//end try catch(Exception e){e.printStackTrace(); }//end catch}//end main }//end class Java4650a


Questions & Answers

how can chip be made from sand
Eke Reply
is this allso about nanoscale material
are nano particles real
Missy Reply
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
where is the latest information on a no technology how can I find it
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
has a lot of application modern world
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now

Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Object-oriented programming (oop) with java' conversation and receive update notifications?