Click here to close now.


Java IoT Authors: Mike Kavis, Liz McMillan, Elizabeth White, Cloud Best Practices Network, Adrian Bridgwater

Related Topics: Java IoT

Java IoT: Article

Reading Data from the Internet

Lesson 6, Java Basics

To read local file streams, a program has to specify the file's location, i.e. "c:\practice\training.html". The same procedure is valid for reading of the remote files: just open the stream over the network. Java has a class URL that will help you to connect to a remote computer on the Internet.

At first, create an instance of the class URL:

  URL xyz = new URL("");
catch(MalformedURLException e){

The MalformedURLException could be thrown if a non-valid URL has been used, for example missed protocol if you forgot to start URL with http://, extra spaces, etc. The MalformedURLException does not indicate that the remote machine has problems - just check the spelling of the URL.

Creation of the URL object does not establish the connection with the remote machine: you'll still need to open a stream to read it. Usually you have to perform the following steps to read a file from the Internet:

Step 1. Create and instance of the class URL

Step 2. Create an instance of the class URLConnection and open a connection using the URL instance from step 1.

Step 3. Get a reference to an input stream of this object by calling the method URLConnection.getInputStream()

Step 4. Read the data from the stream (use the buffered reader to speed up the process).

Since the streams from the package are being used here for the read/write operations, you'll have to handle I/O exceptions.

The server you are trying to connect to has to be up and running and, in case of using http protocol, the special software (Web Server) has to be "listening to" the port that you specified in the URL instance. By default, Web servers are listening to the port number 80.

The program below reads and prints on the system console the content of the file index.html from Obviously, to test this program your computer has to be connected to the Internet.

public class WebSiteReader {
  public static void main(String args[]){
       String nextLine;
       URL url = null;
       URLConnection urlConn = null;
       InputStreamReader  inStream = null;
       BufferedReader buff = null;
          // Create the URL obect that points
          // at the default file index.html
          url  = new URL("" );
          urlConn = url.openConnection();
         inStream = new InputStreamReader( 
           buff= new BufferedReader(inStream);
       // Read and print the lines from index.html
        while (true){
            nextLine =buff.readLine();  
            if (nextLine !=null){
     } catch(MalformedURLException e){
       System.out.println("Please check the URL:" + 
                                           e.toString() );
     } catch(IOException  e1){
      System.out.println("Can't read  from the Internet: "+ 
                                          e1.toString() ); 

The class WebSiteReader explicitly creates the URLConnection object. Strictly speaking we could get away just with the class URL:

URL url = new URL("");
InputStream in = url.getInputStream();
Buff= new BufferedReader(new InputStreamReader(in));

The reason why you may consider using the URLConnection class is that it could give you some additional control over the I/O process. For example, by calling its method setDoInput(true) you could allow (or disallow) downloads.

Connecting Through HTTP Proxy Servers

Most of the companies use firewalls for security reasons and their employees reach the Internet through the HTTP proxy server. Check the settings of your Internet browser to find out the host name and port number of the proxy server. If you are using Microsoft Internet Explorer check the menu Internet Options | Connections | LAN Setting. Netscape Navigator has proxy settings under Preferences | Advanced | Proxies.

While Java Applets know parameters of the proxy servers because they live inside the browser that has the proper settings, Java applications should set the parameters of the proxy server, for example:

   System.setProperty("http.proxyPort", 8080);

If you do not want to hardcode these value, pass them to the program from the command line:

c:\practice>java  -Dhttp.proxyPort=8080  WebSiteReader

If you run this program without specifying the proxy settings, you'll get the UnknownHostException.

How to Download Files From the Internet

By using the class URL with input streams, we should be able to download practically any file (images, music, binary files) from the unsecured Internet site. The trick is in proper opening of the file stream. Let‚s write the class FileDownload that takes a URL and the file name as a command line arguments and copies remote file on your local disk.


class FileDownloader{

  public static void main(String args[]){
    if (args.length!=2){
        "Proper Usage: java FileDownloader RemoteFileURL LocalFileName");

  DataInputStream in=null;
  DataOutputStream out=null;
  FileOutputStream fOut=null;

    URL remoteFile=new URL(args[0]);
    URLConnection fileStream=remoteFile.openConnection();

    // Open the input streams for the remote file 
    fOut=new FileOutputStream(args[1]);

    // Open the output streams for saving this file on disk
    out=new DataOutputStream(fOut);

    in=new DataInputStream(fileStream.getInputStream());

    // Read the remote on save save the file
    int data;
    System.out.println("Download of " + args[0] + " is complete." );   
  } catch (Exception e){
  } finally {
     } catch(Exception e){e.printStackTrace();}

To download the Yahoo's main page into c:\temp directory start this program as follows:

java FileDownloader c:\\temp\\yahoo.html

The Stock Quote Program

In this section we'll write the program that can read stock market quotes from the Internet. There are many Internet sites providing stock market quotes, and 20 minutes delayed quotes are free. Wall Street companies subscribe for the real-time market data feed. One of the popular Internet sites is Yahoo and the URL for getting stock prices is Point your Web browser to this site and get the price quote of any stock symbol. Note the URL of the resulting Web page in your browser. For example, if you've selected the symbol IBM, the URL would look like this:

Right click on this page and select the View Source from the popup menu to see the HTML contents of this page: you'll see lots of HTML tags and the information about the IBM's trading will be buried somewhere deep inside the file:

   Last Trade:</TD><TD class=yfnc_tabledata1><BIG><B>95.32</B>

The next step is to modify the URL in our class WebSiteReader to print the content of the page about the symbol IBM:

    url  = new URL("");

You can also store the whole page in a Java String variable instead of printing it. Just change the while loop to look as follows:

        String theWholePage;
        while (txt =buff.readLine() != null ){
             theWholePage=theWholePage + txt;

If you add some smart tokenizing of theWholePage to get rid of all HTML tags and everything but Last Trade value, you can create your own little GUI Stock Quote screen. While this approach is useful to sharpen you tokenizing skills, it may not be the best solution, especially if Yahoo will change the wording of this page. That's why we'll be using another Yahoo's URL that provide stock quotes in a cleaner comma separated values format (CSV).

Here's the URL that should be used for the IBM's symbol:

This URL would produce a string that looks something like this (the price quotes are not real):


The next class StockQuoter prints the price quote for the symbol that is specified as a command line argument.

import java.util.StringTokenizer;

public class StockQuoter {
       String csvString;
       URL url = null;
       URLConnection urlConn = null;
       InputStreamReader  inStream = null;
       BufferedReader buff = null;

     StockQuoter(String symbol){

           url  = new              
                   + symbol + "&f=sl1d1t1c1ohgv&e=.csv" );
           urlConn = url.openConnection();
           inStream = new
           BufferedReader buff= new BufferedReader(inStream);

           // get the quote as a csv string
           csvString =buff.readLine();  

           // parse the csv string
              StringTokenizer tokenizer = new
                          StringTokenizer(csvString, ",");
              String ticker = tokenizer.nextToken();
              String price  = tokenizer.nextToken();
              String tradeDate = tokenizer.nextToken();  
              String tradeTime = tokenizer.nextToken();  

              System.out.println("Symbol: " + ticker + 
                " Price: " + price + " Date: "  + tradeDate 
                + " Time: " + tradeTime);
     } catch(MalformedURLException e){
         System.out.println("Please check the spelling of the URL:" 
         		           + e.toString() );
     } catch(IOException  e1){
      System.out.println("Can't read from the Internet: " + 
                                           e1.toString() ); 
         }catch(Exception e){

  public static void main(String args[]){
       if (args.length==0){
                     "Sample Usage: java StockQuoter IBM");
       StockQuoter sq = new StockQuoter(args[0]);


To see the latest price of IBM stock start the StockQuoter program as follows:

c:\practice>java StockQuoter IBM

In this lesson I tried to show you that working with the streams over the net may be as simple as dealing with files on your local disk. These days Java runs remote-controlled Mars rovers, and this is not a rocket science anymore - just open a Java stream that points at Mars.

More Stories By Yakov Fain

Yakov Fain is a co-founder of two software companies: Farata Systems and SuranceBay. He authored several technical books and lots of articles on software development. Yakov is Java Champion ( He leads leads Princeton Java Users Group. Two of Yakov's books will go in print this year: "Enterprise Web Development" (O'Reilly) and "Java For Kids" (No Starch Press).

Comments (19) View Comments

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.

Most Recent Comments
Dave Mason 10/18/07 03:00:39 AM EDT

Hello Yakov,
how can I read data in real time from java applet for example:

nitin 11/27/04 02:34:32 AM EST

can any one tell me how can i read the parameters from URL that has been passed by someone ie id someone send id=123 then how can i get it,how the whole process work & last but the mostimp i want to do whole thing through core java.

MIchael Behrens 02/08/04 08:17:43 PM EST

Great Article! Keep''m coming!
There is also a good WebCopy implementation at:
It makes all the web references local - It does not work on HTTPS - I wish I had all the know-how & code to make an equivalent HTTPS WebSiteReader, which would be very handing for testing our query pages.

Ferruccio Spagna 01/31/04 10:13:33 AM EST

I am very happy with your code, Yakov.
I tried it and everything works very well.
Thanks Ferruccio

Yakov Fain 01/31/04 08:59:53 AM EST

In this lesson I do this using HTTP GET request by attaching parameters to the URL after a question mark separated with an ampersand.

Fo HTTP POST, after getting the URLConnection stream, do something like this:

urlConn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

String myData = "myParam1=" + URLEncoder.encode ("abc") +
"&myParam2=" + URLEncoder.encode ("xyz");

DataOutputStream encodedParams = new DataOutputStream (urlConn.getOutputStream ());

encodedParams.writeBytes (myData);
encodedParams.flush ();
encodedParams.close ();

Ferruccio Spagna 01/31/04 08:29:47 AM EST

Ok. What you say occurs when you have a page with a form. Well known. But my question was: you want to read the stream (see your last article) and perhaps manipulate it. You then use the code: url = new""); c = url.openConnection(); dis = new;
and so on.
How can you give the parameters to the cgi with THESE code lines?

Yakov Fain 01/31/04 08:16:45 AM EST

Well, here''s the sample from my book "The Java Tutorial for the Real World".

1. An HTML form has 2 fields to perform a book search:

Find a book

Enter a word from the book title:

2. The servlet FindBooks runs on the server side, gets the parameters and sends back to the browser a page that reads that this book cost $65:

public class FindBooks extends javax.servlet.http.HttpServlet {

public void doGet(HttpServletRequest req,
HttpServletResponse res)
throws ServletException, IOException {
String title;
PrintWriter out = res.getWriter();
title = req.getParameter("booktitle");


out.println("the book "+title+" costs only $65");

out.println("Please enter your credit card number");


Ferruccio Spagna 01/31/04 07:33:44 AM EST

Thank you for your answer. I have several good Java books, but I didn''t find how I can read a CGI URL stream passing POST parameters in the calling instruction anywhere. Tell me please in a few words the way, if it is possible.

Yakov Fain 01/30/04 07:38:59 PM EST


Java Servlets and JavaServer Pages technologies deal with HTTP Post and Get requests, parameters, etc. Wait for my lesson on servlets, or get a good book if you need to know the answer now.

Ferruccio Spagna 01/30/04 06:10:50 PM EST

I add to my above question: how can I pass the parameter values calling the URL?

Ferruccio Spagna 01/30/04 05:59:24 PM EST

What about reading a CGI URL accepting METHOD=POST parameters?

Yakov Fain 01/29/04 11:27:25 PM EST


You can run on the remote machine one of the following: RMI server, SocketServer, a Servlet,FTP server... that has to create an instance of the class that points at your directory. The File.list() will return the list of files in this directory as a String array. Now create instances of File for each of the array elements and call File.lastModify() to check the timestamp. After finding the file with the proper date, send its URL (or a stream reference) to the client for reading.

Dennis Christopher 01/29/04 01:44:43 PM EST

I found the article useful, and above average in clarity.

I am wondering if anyone knows how you set up the
connection to download an (entire) directory of files?
and to check the file dates before doing so?

Josh Davis 01/28/04 12:49:02 PM EST


You should mention that HttpURLConnection may ''hang'' when contacting servers that don''t behave correctly. This can cause a lot of problems in a server side application. The solutions are:
1) Use something other than URL/URLConnection/HttpURLConnection.
2) Set the system properties that control the socket timeouts for the Sun HTTP client.

John Pantone 01/26/04 01:55:42 PM EST

Very useful, clear.

Yakov Fain 01/23/04 09:49:54 PM EST

If the proxy requires authentication, set the following properties:

System.setProperty("http.proxyUser", "JLarkin");
System.setProperty("http.proxyPassword", "YourPassword");

You may also try using the class

John Larkin 01/23/04 11:28:08 AM EST

Our proxy server requires a user_id and password.
I am having trouble finding a method to set these.
Any ideas ? Thanks

Selvan Rajan 01/23/04 10:10:41 AM EST

What would be the case to deal with cookies from some of the web sites? Especially it becomes cumbersome, if there is a redirection involved after setting the cookie.
Any ideas?

Debashish 01/23/04 02:07:51 AM EST

In the following para :
Strictly speaking we could get away just with the class URL:
URL url = new URL("");
InputStream in = url.getInputStream();
Buff= new BufferedReader(new InputStreamReader(in));

I think the second line of code should be :
InputStream in = url.openStream();

@ThingsExpo Stories
Today air travel is a minefield of delays, hassles and customer disappointment. Airlines struggle to revitalize the experience. GE and M2Mi will demonstrate practical examples of how IoT solutions are helping airlines bring back personalization, reduce trip time and improve reliability. In their session at @ThingsExpo, Shyam Varan Nath, Principal Architect with GE, and Dr. Sarah Cooper, M2Mi's VP Business Development and Engineering, will explore the IoT cloud-based platform technologies driving this change including privacy controls, data transparency and integration of real time context w...
There will be 20 billion IoT devices connected to the Internet soon. What if we could control these devices with our voice, mind, or gestures? What if we could teach these devices how to talk to each other? What if these devices could learn how to interact with us (and each other) to make our lives better? What if Jarvis was real? How can I gain these super powers? In his session at 17th Cloud Expo, Chris Matthieu, co-founder and CTO of Octoblu, will show you!
Developing software for the Internet of Things (IoT) comes with its own set of challenges. Security, privacy, and unified standards are a few key issues. In addition, each IoT product is comprised of at least three separate application components: the software embedded in the device, the backend big-data service, and the mobile application for the end user's controls. Each component is developed by a different team, using different technologies and practices, and deployed to a different stack/target - this makes the integration of these separate pipelines and the coordination of software upd...
As a company adopts a DevOps approach to software development, what are key things that both the Dev and Ops side of the business must keep in mind to ensure effective continuous delivery? In his session at DevOps Summit, Mark Hydar, Head of DevOps, Ericsson TV Platforms, will share best practices and provide helpful tips for Ops teams to adopt an open line of communication with the development side of the house to ensure success between the two sides.
Mobile messaging has been a popular communication channel for more than 20 years. Finnish engineer Matti Makkonen invented the idea for SMS (Short Message Service) in 1984, making his vision a reality on December 3, 1992 by sending the first message ("Happy Christmas") from a PC to a cell phone. Since then, the technology has evolved immensely, from both a technology standpoint, and in our everyday uses for it. Originally used for person-to-person (P2P) communication, i.e., Sally sends a text message to Betty – mobile messaging now offers tremendous value to businesses for customer and empl...
The IoT market is on track to hit $7.1 trillion in 2020. The reality is that only a handful of companies are ready for this massive demand. There are a lot of barriers, paint points, traps, and hidden roadblocks. How can we deal with these issues and challenges? The paradigm has changed. Old-style ad-hoc trial-and-error ways will certainly lead you to the dead end. What is mandatory is an overarching and adaptive approach to effectively handle the rapid changes and exponential growth.
SYS-CON Events announced today that Sandy Carter, IBM General Manager Cloud Ecosystem and Developers, and a Social Business Evangelist, will keynote at the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA.
The IoT is upon us, but today’s databases, built on 30-year-old math, require multiple platforms to create a single solution. Data demands of the IoT require Big Data systems that can handle ingest, transactions and analytics concurrently adapting to varied situations as they occur, with speed at scale. In his session at @ThingsExpo, Chad Jones, chief strategy officer at Deep Information Sciences, will look differently at IoT data so enterprises can fully leverage their IoT potential. He’ll share tips on how to speed up business initiatives, harness Big Data and remain one step ahead by apply...
WebRTC converts the entire network into a ubiquitous communications cloud thereby connecting anytime, anywhere through any point. In his session at WebRTC Summit,, Mark Castleman, EIR at Bell Labs and Head of Future X Labs, will discuss how the transformational nature of communications is achieved through the democratizing force of WebRTC. WebRTC is doing for voice what HTML did for web content.
"Matrix is an ambitious open standard and implementation that's set up to break down the fragmentation problems that exist in IP messaging and VoIP communication," explained John Woolf, Technical Evangelist at Matrix, in this interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
WebRTC has had a real tough three or four years, and so have those working with it. Only a few short years ago, the development world were excited about WebRTC and proclaiming how awesome it was. You might have played with the technology a couple of years ago, only to find the extra infrastructure requirements were painful to implement and poorly documented. This probably left a bitter taste in your mouth, especially when things went wrong.
The broad selection of hardware, the rapid evolution of operating systems and the time-to-market for mobile apps has been so rapid that new challenges for developers and engineers arise every day. Security, testing, hosting, and other metrics have to be considered through the process. In his session at Big Data Expo, Walter Maguire, Chief Field Technologist, HP Big Data Group, at Hewlett-Packard, will discuss the challenges faced by developers and a composite Big Data applications builder, focusing on how to help solve the problems that developers are continuously battling.
Nowadays, a large number of sensors and devices are connected to the network. Leading-edge IoT technologies integrate various types of sensor data to create a new value for several business decision scenarios. The transparent cloud is a model of a new IoT emergence service platform. Many service providers store and access various types of sensor data in order to create and find out new business values by integrating such data.
There are so many tools and techniques for data analytics that even for a data scientist the choices, possible systems, and even the types of data can be daunting. In his session at @ThingsExpo, Chris Harrold, Global CTO for Big Data Solutions for EMC Corporation, will show how to perform a simple, but meaningful analysis of social sentiment data using freely available tools that take only minutes to download and install. Participants will get the download information, scripts, and complete end-to-end walkthrough of the analysis from start to finish. Participants will also be given the pract...
WebRTC: together these advances have created a perfect storm of technologies that are disrupting and transforming classic communications models and ecosystems. In his session at WebRTC Summit, Cary Bran, VP of Innovation and New Ventures at Plantronics and PLT Labs, will provide an overview of this technological shift, including associated business and consumer communications impacts, and opportunities it may enable, complement or entirely transform.
SYS-CON Events announced today that Dyn, the worldwide leader in Internet Performance, will exhibit at SYS-CON's 17th International Cloud Expo®, which will take place on November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Dyn is a cloud-based Internet Performance company. Dyn helps companies monitor, control, and optimize online infrastructure for an exceptional end-user experience. Through a world-class network and unrivaled, objective intelligence into Internet conditions, Dyn ensures traffic gets delivered faster, safer, and more reliably than ever.
WebRTC services have already permeated corporate communications in the form of videoconferencing solutions. However, WebRTC has the potential of going beyond and catalyzing a new class of services providing more than calls with capabilities such as mass-scale real-time media broadcasting, enriched and augmented video, person-to-machine and machine-to-machine communications. In his session at @ThingsExpo, Luis Lopez, CEO of Kurento, will introduce the technologies required for implementing these ideas and some early experiments performed in the Kurento open source software community in areas ...
Too often with compelling new technologies market participants become overly enamored with that attractiveness of the technology and neglect underlying business drivers. This tendency, what some call the “newest shiny object syndrome,” is understandable given that virtually all of us are heavily engaged in technology. But it is also mistaken. Without concrete business cases driving its deployment, IoT, like many other technologies before it, will fade into obscurity.
Who are you? How do you introduce yourself? Do you use a name, or do you greet a friend by the last four digits of his social security number? Assuming you don’t, why are we content to associate our identity with 10 random digits assigned by our phone company? Identity is an issue that affects everyone, but as individuals we don’t spend a lot of time thinking about it. In his session at @ThingsExpo, Ben Klang, Founder & President of Mojo Lingo, will discuss the impact of technology on identity. Should we federate, or not? How should identity be secured? Who owns the identity? How is identity ...
The buzz continues for cloud, data analytics and the Internet of Things (IoT) and their collective impact across all industries. But a new conversation is emerging - how do companies use industry disruption and technology enablers to lead in markets undergoing change, uncertainty and ambiguity? Organizations of all sizes need to evolve and transform, often under massive pressure, as industry lines blur and merge and traditional business models are assaulted and turned upside down. In this new data-driven world, marketplaces reign supreme while interoperability, APIs and applications deliver un...