Tag: io

Network I/O Is Unpredictable: Node.js

We’ve seen the importance of callback method in our previous video tutorials. Now lets see how networked I/O Is unpredictable.


http-module-get-method-nodejs-network-io-unpredictability

Here we request/ping for information from 3 different servers and look at its response time. Each time we send a request, we get different response time depending upon how busy the server is, its bandwidth etc.

JavaScript File
app.js

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var http= require("http"),
      urls  = [ "technotip.org",
         "technotip.com",
      "www.capturecaption.com"
       ];
 
for(var i = 0; i < urls.length; i++){
ping( urls[i] );
}
 
function ping( url ){
var start = new Date();
 
http.get({ host: url }, function(res){
console.log("URL :"+url);
console.log("Response Time: "+(new Date() - start)+" ms");
});
}

Here we require http module, which is built into nodejs, and store it inside a local object called http. We also declare and initialize an array with 3 domain names. Using for loop, we loop through each URL present in the urls array and pass it to a method called ping();

Inside ping method, we record client system date in a variable before sending a request to the server(via URL). Now using http objects get method we send request to the server and see it’s response time. get method takes 2 parameter, first parameter is an object which contains host information – the host url { host: url }. Second parameter is a callback method which automatically gets an object which is returned by first parameter {host: url}. Inside the callback method, we subtract the new system date with the one we recorded before requesting for a response, this way we calculate the response time of each URL.

HTTP get method: Node.js


[youtube https://www.youtube.com/watch?v=vktKMtWoPbA]

YouTube Link: https://www.youtube.com/watch?v=vktKMtWoPbA [Watch the Video In Full Screen.]



output
C:\node>node app.js
URL :technotip.com
Response Time: 1462 ms
URL :www.capturecaption.com
Response Time: 1993 ms
URL :technotip.org
Response Time: 2004 ms

C:\node>node app.js
URL :technotip.com
Response Time: 1381 ms
URL :www.capturecaption.com
Response Time: 1702 ms
URL :technotip.org
Response Time: 1871 ms

C:\node>node app.js
URL :technotip.com
Response Time: 1409 ms
URL :www.capturecaption.com
Response Time: 1628 ms
URL :technotip.org
Response Time: 2001 ms

C:\node>node app.js
URL :technotip.com
Response Time: 1512 ms
URL :www.capturecaption.com
Response Time: 1534 ms
URL :technotip.org
Response Time: 1899 ms

Each time we execute the script, we get different response time, and the order of URLs may also differ, as we can’t predict which server will respond first.

Read Keyboard Input: Java

This video tutorial shows how to read user input from Keyboard in Java.

In this tutorial we illustrate using a relatively simple program, where user is asked to input some string and it is read by the program and then out put to the console window. Simple java program.

Import
We have to import io package, so that we can make use of DataInputStream Class present in io package.

    import java.io.*;

Creating Object
Next, we create an object of the inbuilt class DataInputStream. And not that it takes a parameter System.in for reading keyboard inputs.

DataInputStream d = new DataInputStream(System.in);

try catch
To know more about try catch and finally read: Try, Catch and Finally in Java.

Since user can give any kind of unwanted input, we should write those code (which may rise exception) inside the try block.
and write the corresponding catch statement.

try
{
System.out.println("Entered String is: "+d.readLine());
}
catch(Exception e)
{
System.out.println(e);
}

Video Tutorial: Read Keyboard Input: Java


[youtube https://www.youtube.com/watch?v=FzUOZo3AX2Y]

YouTube Link: https://www.youtube.com/watch?v=FzUOZo3AX2Y [Watch the Video In Full Screen.]




Full Source Code:(keyboardInput.java)

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import java.io.*;
 
class keyboardInput
{
public static void main(String args[])
{
DataInputStream d = new DataInputStream(System.in);
 
System.out.println("Enter a string");
try
{
System.out.println("Entered String is: "+d.readLine());
}
catch(Exception e)
{
System.out.println(e);
}
 
}
}

Output:
Enter a string
Microsoft Windows 8
Entered String is: Microsoft Windows 8