web page to a String

From the link you posted, as I see it.  
URLConnection object is used to obtain the contents of the web page.  
InputStreamReader reads the content and puts it into charArray.
charArray is added to sb  
sb is converted to String
result is printed  

I guess the confusing lines are
 
>while ((numCharsRead = isr.read(charArray)) > 0) {  
this line uses  InputStreamReader's read() method. From the API  we see that we are using the read method that is  inherited from java.io.Reader .   This method reads characters into an array.  It returns the number of characters that it has read, or -1 if the end of the stream has been reached.  In this case numCharsRead is the number returned. So the while statement keeps executing the read until the whole array is read.

>sb.append(charArray, 0, numCharsRead);  
This uses StringBuffer's method append.   charArray is the array to be appended. 0 is the index of the first char to append.  numCharsRead is the number of chars to append.
Actually, from looking at  the API,  we could have used the other append method and simply have used
sb.append(charArray);

i checked the api
http://docs.oracle.com/javase/7/docs/api/java/lang/StringBuffer.html
hwich append they are using

public StringBuffer append(char[] str,
                  int offset,
                  int len)

Appends the string representation of a subarray of the char array argument to this sequence.

Characters of the char array str, starting at index offset, are appended, in order, to the contents of this sequence. The length of this sequence increases by the value of len.

The overall effect is exactly as if the arguments were converted to a string by the method String.valueOf(char[],int,int), and the characters of that string were then appended to this character sequence.

Parameters:
    str - the characters to be appended.
    offset - the index of the first char to append.
    len - the number of chars to append.
Returns:
    a reference to this object.
Throws:
    IndexOutOfBoundsException - if offset < 0 or len < 0 or offset+len > str.length

is this is above one. please advise

we could have used the other append method and simply have used
sb.append(charArray);

How to understand and get the gist of API and decide which one is the best for particular situation. I am not very clear on that. please advise

>is this is above one. please advise  
Yes.  
At the API link that you posted, there are two append methods that accept a char []  as a parameter. In my opinion, the other one should have used because we are appending the whole array.  Furthermore, we should use StringBuilder  instead of StringBuffer.
http://docs.oracle.com/javase/7/docs/api/java/lang/StringBuilder.html   
Maybe the code that you linked  is old code.

when i run this example i see error in my console as below

java.net.ConnectException: Connection timed out: connect
      at java.net.PlainSocketImpl.socketConnect(Native Method)
      at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351)

Furthermore, we should use StringBuilder  instead of StringBuffer.

why do you think so. Please advise

I have not understood gist of this example what author is trying to do. Get google url (www.google.com) and convert to string. why we need character array here. Please advise

>java.net.ConnectException: Connection timed out: connect  
What URL did you try to connect to ?  Did you try just typing the URL into the address bar of your browser?  Could you access the page that way?
I copyed, pasted, compiled and ran the exact code from the page you linked. It worked for me.  

>why do you think so. Please advise
I read the API.http://docs.oracle.com/javase/7/docs/api/java/lang/StringBuilder.html    

A mutable sequence of characters. This class provides an API compatible with StringBuffer, but with no guarantee of synchronization. This class is designed for use as a drop-in replacement for StringBuffer in places where the string buffer was being used by a single thread (as is generally the case). Where possible, it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations.

>I have not understood gist of this example what author is trying to do  
He is demonstrating a way of reading content from a URL.  
>why we need character array here  
We could read and append one character at a time, but it more it faster and more efficient to use array.

>I have not understood gist of this example what author is trying to do  
He is demonstrating a way of reading content from a URL.

content of the URL((say www.aaa.com) or content of the URL page (when url page opens it opens with membership, discounts, shopping, automative, travel etc) that is displayed using the URL. please advise

>content of the URL((say www.aaa.com) or content of the URL page  
A server sends a response back to a client that made the request. That response is the content. It is the source code for a browser.

Yes, you right. I didn't think about it long enough and made a bad suggestion. I am sorry.

Rank: Genius
rrz@871311 Member Since: 05/02/2000 1317 Solution(s) >java.net.ConnectException: Connection timed out: connect  
What URL did you try to connect to ?  Did you try just typing the URL into the address bar of your browser?  Could you access the page that way?

I just tried the example as it is in my eclipse IDE

public class ConvertUrlToString {

	public static void main(String[] args) {

		try {
			String webPage = "http://www.google.com";
			URL url = new URL(webPage);
			URLConnection urlConnection = url.openConnection();

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i was able to access google.com out side ide from my browser without any issue. I tried on my office laptop. do you think that might block connection. I am not sure. please advise

eg. say your stream had the following characters in it...  ABCDEFGHI  and you had a charArray of size 4...

On the first isr.read...
charArray = [A,B,C,D]
numCharsRead = 4
so using either sb.append call the string currently holds...
"ABCD"

On the next isr.read...
charArray = [E,F,G,H]
numCharsRead = 4
so using either sb.append call the string currently holds...
"ABCDEFGH"

On the next (and last) isr.read...
charArray = [I,F,G,H]             (notice that "I" was read in but F G H are still there from before)
numCharsRead = 1
so if we just did sb.append(charArray) we would end up with...
"ABCDEFGHIFGH"
rather than if we use sb.append(charArray, 0 numCharsRead) where numCharsRead = 1 we get...
"ABCDEFGHI"  (correctly!)

I do not understand this example clearly. Can you please elaborate.

>content of the URL((say www.aaa.com) or content of the URL page  
A server sends a response back to a client that made the request. That response is the content. It is the source code for a browser

does it changes the image content also to the string. please advise

I changed to
      String webPage = "http://acme.com/mailto/?id=wa";

Still i am getting similar error


java.net.ConnectException: Connection timed out: connect
      at java.net.PlainSocketImpl.socketConnect(Native Method)
      at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351)


I will try from home laptop later and let you know.

I tried with www.google.com as given in link from home laptop. I got output

*** BEGIN ***
<!doctype html><html itemscope="" itemtype="http://schema.org/WebPage"><head><meta content="Search the world's information, including webpages, images, videos and more. Google has many special features to help you find exactly what you're looking for." name="description"><meta content="noodp" name="robots"><meta itemprop="image" content="/images/google_favicon_128.png"><title>Google</title><script>(function(){
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Select allOpen in new window

So, the code works.