Image:LineIterator.java

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import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.util.Iterator;
import java.util.NoSuchElementException;
 
/**
 * Iterator over each line of a resource : file, url, ...
 */
public final class LineIterator implements Iterator
{
    private final BufferedReader in;
    private String next;
    
    /**
     * Create a new line iterator on a resource
     * @param resource The resource
     * @throws IOException The iterator could not be created
     */
    public LineIterator(final URL resource) throws IOException 
    {
        super();
        in = new BufferedReader(new InputStreamReader(resource.openStream()));
        next = in.readLine();
    }
 
    /**
     * @see java.util.Iterator#hasNext()
     */
    public boolean hasNext()
    {
        return next != null;
    }
 
    /**
     * @see java.util.Iterator#next()
     */
    public Object next()
    {
        // If there is no next element we throw an exception as stated in the interface
        if (next == null)
        {
            throw new NoSuchElementException();
        }
        
        // prefetch next line for optimization
        final String current = next;
        try
        {
            next = in.readLine();
        }
        catch (final IOException e)
        {
            next = null;
        }
        
        // If an error occured or if the stream has no new line
        if (next == null)
        {
            try
            {
                in.close();
            }
            catch (IOException e1)
            {
                // nothing to do
            }
        }
        
        return current;
    }
 
    /**
     * @see java.util.Iterator#remove()
     */
    public void remove()
    {
        throw new UnsupportedOperationException(); 
    }
    
    /**
     * TEST METHOD
     * @param args args
     */
    public static void main(String args[]) throws MalformedURLException, IOException
    {
        final NumberFormat nf = new DecimalFormat();
        int count;
        
        nf.setMinimumIntegerDigits(4);
        nf.setGroupingUsed(false);
        nf.setParseIntegerOnly(true);
        
        // Example to retreive each lines of a caracter file :
        count = 0;
        final URL resource1 = new File("./src/LineIterator.java").toURL();
        for(final Iterator i = new LineIterator(resource1); i.hasNext();)
        {
            System.out.println("Line " + nf.format(++count) + ": " + i.next());
        }
        
        // Example to retreive each lines of a web resource :
        count = 0;
        final URL resource2 = new URL("http://www.labunix.uqam.ca/~charki/INF4482/index.html");
        for(final Iterator i = new LineIterator(resource2); i.hasNext();)
        {
            System.out.println("Line " + nf.format(++count) + ": " + i.next());
        }
    }
} 

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