query to website

[eternalLearner]

i am writing an client application that connects to the server and then sends data to server.
but, the problem is that i get a java.net.Connec tException: Connection refused error.
The code i have written is :

//package bdn;
/*  The java.net package contains the basics needed for network operations. */
import java.net.*;
/* The java.io package contains the basics needed for IO operations. */
import java.io.*;
/** The SocketClient class is a simple example of a TCP/IP Socket Client.
 *
 */
 
public class SocketClient {
     public static void main(String[] args) {
        /** Define a host server */
        //find the ip address by ping cmd in unix
        String host = "211.65.63.147";
        /** Define a port */
        int port = 8080;
 
        StringBuffer instr = new StringBuffer();
        String TimeStamp;
        System.out.println("SocketClient initialized");
 
        try {
          /** Obtain an address object of the server */
          InetAddress address = InetAddress.getByName(host);
          /** Establish a socket connetion */
          Socket connection = new Socket(address, port);
          /** Instantiate a BufferedOutputStream object */
          BufferedOutputStream bos = new BufferedOutputStream(connection.
              getOutputStream());
 
          /** Instantiate an OutputStreamWriter object with the optional character
           * encoding.
           */
          OutputStreamWriter osw = new OutputStreamWriter(bos, "US-ASCII");
 
        }
        catch (Exception g) {
        System.out.println("Exception: " + g);
            }
 
    }
 
 
}
 

please let me know wat could be the problem.

[JosAH]

Why don't you use a URL and a URLConnection for this purpose?

kind regards,

Jos

[eternalLearner]

hmm ok,
but i wrote this code using url,but even this doesnot work ?

import java.io.Buffere dReader;
import java.io.InputSt ream;
import java.io.InputSt reamReader;
import java.net.URL;

public class Sample1 {

public static void main(String[] args) {

try {
//String url =
// "https://services.nature serve.org/" +
// "idd/rest/ns/v1.1/globalSpecies/comprehensive";
String url = "http://www.bioinf.seu. edu.cn/miRNA/index.html";
String uid = "ELEMENT_GLOBAL .2.100925";
String nsAccessKeyId = "72ddf45a-c751-44c7-9bca-8db3b4513347";
String Query = "seqences=/>Example \nCUUGGGAAUGGCA AGGAAACCGUUACCA UUACUGAGUUUAGUA AUGGUAAUGGUUCUC UUGCUAUACCCAGA" ;


String request = url;
request = request + "?";
//request = request + "uid=" + uid;
//request = request + "&";
//request = request + "NSAccessKeyId= " + nsAccessKeyId;
request = request + Query;

URL serviceURL = new URL(request);
InputStream is = serviceURL.open Stream();
//InputStreamRead er isr = new InputStreamRead er(is,"UTF-8");
InputStreamRead er isr = new InputStreamRead er(is);
BufferedReader br = new BufferedReader( isr);

StringBuffer response = new StringBuffer();
String nextLineFromSer vice = br.readLine();
while (nextLineFromSe rvice != null) {
response.append (nextLineFromSe rvice);
nextLineFromSer vice = br.readLine();
}

System.out.prin tln(response);
}
catch (Exception e) {
System.out.prin tln(e);
}

}
}

[JosAH]

I can't contact that site either (using my browser). Are you sure the url address is correct?

kind regards,

Jos

[eternalLearner]

the site is down i guess.
earlier i was able to connect to the website using browser.
but ,do u think my program is correct ?

[JosAH]

@eternalLearner
Try it with a simple url, e.g. http://www.google.com and see what happens.

kind regards,

Jos

[chaarmann]

@eternalLearner
Yes, it is.
But you can enhance it. This is what I am using:

   String url = "http://www.google.com";
StringBuilder response = new StringBuilder(10000);
   BufferedReader reader = new BufferedReader(new InputStreamReader(new URL(url).openStream()));
   String line;
   while ((line = reader.readLine()) != null) response.append(line);
   String html = response.toString();
 

BufferedReader is faster than StringBuffer. You should use StringBuffer only in multithreaded environment (what you don't have), and if you need to synchronize.

Also note that if you call "s= new StringBuffer()" or
"s=new StringBuilder() ", the initial capacity is only 16 characters, so it will need to allocate memory many times to hold an average response of around 7000 bytes in my case. Memory allocation itself is very costly, independent of how many memory you allocate (if it's not some megabytes).
So just estimate the maximum size of your returned webpage (in my case 10000) and use that for initial capacity.

[JosAH]

@chaarmann
It isn't; in Java object allocation is no more than a test, an increment of a pointer and the return of the old pointer value. It isn't like a C-like malloc or a C++-like new operator. Garbage collection can be expensive.

kind regards,

Jos

ps. There's also the StringBuilder class that doesn't synchronize on its buffer.

[chaarmann]

@JosAH
But isn't there a difference between memory allocation and object allocation in Java? I mean to allocate a new object, you can just re-use an old unused object by modifying the pointer (or pointing to a re-usable template if you keep object structure and its data structure separate). But memory allocation goes down deep into the operation system, from chip-cache to first-level cache to second level cache and so on up to saving memory to disk if there is no space available etc. Usually if you need more memory then you need to copy the whole string into a new string. You cannot just increase a pointer and keep the string, because there is usually already some other data allocated at the end of this string. I admit that I don't know how Java handles memory and I know it well from C++. So how should that be possible in Java theoretically? I thought this problem is universal.
Also I know that if you allocate small amounts of memory many times, you get memory fragmentation. Then you need to search through the memory map to find a suitable gap. Assuming the average returned html page is 7000 characters long, then you have to find a new gap 9 times:
16 --> 32 --> 64 --> 128 --> 256 --> 512 --> 1024 --> 2048 --> 4096 --> 8192
Don't you think that's costly?

@JosAH
That's what I wanted to express. It's good that you pinpointed this error in my previous post. I wrote: "BufferedRe ader is faster than StringBuffer",
but wanted to write: "StringBuilder is faster than StringBuffer". That's why I used it in my program.
Quotation from Javadocs, StringBuffer class:
"As of release JDK 5, this class has been supplemented with an equivalent class designed for use by a single thread,StringBu ilder. The StringBuilder class should generally be used in preference to this one, as it supports all of the same operations but it is faster, as it performs no synchronization . "

[chaarmann]

I read an interesting article about java memory allocation, especially about the generational garbage collector.
Quotation: "allocating a new object is nothing more than checking to see if there's enough space left in the heap and bumping a pointer if there is. No searching free lists, best-fit, first-fit, lookaside lists -- just grab the first N bytes out of the heap and you're done."

But doesn't that involve copying the old string to the new location every time?