java.net.URLConnection example?

[David Llewellyn]

Does anyone know where I can find an example of reading in a text file with a java.net.URLConnection? I've read the doc's on suns java page but I did not find them that much help to be honest. I've also googled for answers using "java.net.URLConnection" as the search, but this didn't provide any help.

cheers

[Carol Enderlin]

Check out this (jdk 5/1.5) Core Java Technologies Tech Tip - Scanning Text wtih java.util.Scanner

The tech tip references this blog entry that shows a BufferedReader version and a Scanner version.
[ March 09, 2005: Message edited by: Carol Enderlin ]

[David Llewellyn]

Thanks carol, that was great info
however, my Java SDK is version 1.4.2, and it doesn't seem to have the scanner utility.....
Ill search some more, but again, thankyou very much that was a great help!

[Horatio Westock]

Hi.

There is an article here that discusses writing a plain-text content handler with URLConnection.

[David Llewellyn]

Thanks Horatio, I'll check that link out in a minute.
At the moment I'm having an annoyance with reading from a DataInputStream.
I'm trying to read in a plain text file, about 85kb, but sometimes it does not read it all....it mostly finishes the file too early.
Here is the code I have:

import java.io.*;
import java.net.*;

class fileReader {//start of class

public static void main (String[] args) {//main method
try{
InputStream fileSource = new URL("http://members.aol.com/davllew/teapot.x3d").openStream();
byte [] buf = new byte[fileSource.available()];
new DataInputStream(fileSource).readFully(buf);
String text = new String(buf);
System.out.println(text);
fileSource.close();
}
catch(IOException e){
System.out.println("Error reading file!");
}

}//main method

}//end of class


Is this a well known problem? and If so, I wonder how to avoid it.
cheers again

[Horatio Westock]

OK, lets have a look at your code:

byte [] buf = new byte[fileSource.available()];

available() isn't the same as length.

new DataInputStream(fileSource).readFully(buf);

The API for readFully(byte[] b) says the following:

"Reads some bytes from an input stream and stores them into the buffer array b. The number of bytes read is equal to the length of b."

As your buffer may not actually be the length of the file, this may not actually read all of it.

As you want to read a text file into a string, the best way to proceed would be to wrap your input string in a buffer, then read lines from the buffer, appending them to a string buffer until the are none left. Then get the string from the contents of the string buffer.

Here's a snippet you can draw inspiration from:

  
StringWriter content = new StringWriter();
 
BufferedReader in = new BufferedReader(
                        new InputStreamReader(
                            url.openStream()));
 
String line;
while( (line = in.readLine()) != null )
{
    content.write( line );
}
 
in.close();
content.close();
 
return content.toString();

[David Llewellyn]

Thanks for that Horatio, its been most helpful
from the snippet I've managed to do what I wanted which is great.
In case your interested, or there's a better way, this is what I'm now doing:

import java.io.*;
import java.net.*;
 
class FileReader2 {//start of class
 
    public static void main (String[] args) {//main method
 
      try{//read from file
          
        StringWriter content = new StringWriter(); 
        URL url = new URL("http://members.aol.com/davllew/teapot.x3d");
        URLConnection urlConnection = url.openConnection();
        BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
        String line;
        
        //read line from bufferedreader and append to to content(stringwriter) 
        //while the bufferedreader returns a line
        while( (line = in.readLine()) != null )
        {
          content.write( line );
        } 
        
        //close down buffered reader and string writer
        in.close();
        content.close(); 
        
        //output the read in text
        String fileText;
        fileText = content.toString();        
        System.out.println(fileText);
        //show success message
        System.out.println("Finished reading file!");
        
      }catch(IOException e){//handle exceptions
          
          System.out.println("Error reading file!");
          
      }//handle exceptions
 
    }//main method
 

}//class

Once again, thankyou very much!