Language Java Nosugar Comms Code Urldemo.java

// 
//	UrlDemo class
//	part of the set of documents known as Java no sugar.
//	Copyright (c) 1996 Sunil Gupta, sunil@magnetic.demon.co.uk
//	placed into the public domain by the author
//
import java.awt.*;
import java.io.*;
import java.net.*;
import java.applet.*;

	
public class UrlDemo extends Applet
{
	//*******************************************************************
	// GLOBALS
	//*******************************************************************
	static final String USERDEF="USERDEF";
	static final String HOSTPARAM="HOST";

	//*******************************************************************
	// instance variables
	//*******************************************************************
	TextArea textarea;
	TextField textfield;
	Button btn_doit;
	boolean user_url = false;
	String url_string = null;
	
	//*******************************************************************
	// applet methods
	//*******************************************************************
	public void init()
	{
		GridBagConstraints c;
		GridBagLayout layout;
		String param;
		int gridy=0;
		
		//-----FIGURE OUT WHICH URL to use-------------------------
		param =  getParameter(HOSTPARAM);
		if (param != null)
		{
			if (param.equals(USERDEF))
				user_url = true;
			else
				url_string = param;
		}
		
		//--------BUILD THE USER INTERFACE-------------------------
		layout = new GridBagLayout();
		this.setLayout( layout );
		
		//------------------------add the text area----------------
		if (user_url)
		{
			textfield = new TextField(30);
			c = new GridBagConstraints();
			c.gridx = 0; c.gridy = 0; c.gridwidth=2; c.gridheight=1;
			c.fill = GridBagConstraints.BOTH;
			layout.setConstraints(textfield,c);
			this.add(textfield);
			gridy++;
		}
		
		//---------------------------------------------------------
		textarea = new TextArea();
		c = new GridBagConstraints();
		c.gridx = 0; c.gridy = gridy; c.gridwidth=2; c.gridheight=2;
		c.fill = GridBagConstraints.BOTH;
		layout.setConstraints(textarea,c);
		this.add(textarea);
				
		//------------------------add button--------------------
		btn_doit = new Button("query");
		c = new GridBagConstraints();
		c.gridx = 2; c.gridy = 0; c.gridwidth=1; c.gridheight=1;
		c.fill = GridBagConstraints.HORIZONTAL;
		layout.setConstraints(btn_doit,c);
		this.add(btn_doit);
	}


	public boolean action(Event event, Object arg)
	{
		
		if (event.target == btn_doit)
		{
			do_date_url();
			return true;
		}
		return (false)	;
	}
	
	//
	// date is a safe choice since most httpd's implement this
	//
	private void do_date_url()
	{
		URL applet_url, cgi_url;
		String protocol, data_line;
		DataInputStream stream;
		
		//------------------------------------------------------------------
		// clear out any text
		//
		textarea.setText("");
		
		//------------------------------------------------------------------
		// make sure applet is running from httpd
		//
		applet_url = this.getDocumentBase();
		protocol = applet_url.getProtocol();
		if ( ! protocol.equals("http") )
		{
			textarea.appendText(
				"This applet must be run from a server\n" +
				"net.paranoid.geeks have crippled Java applets which\n" +
				"can only make network connections to the machine\n" +
				"from whence it came.\n"	);
			return;
		}
		textarea.appendText("Applet is on a server\n");

		
		//------------------------------------------------------------------
		// BUILD URL
		//
		try
		{
			if (user_url)
			{
				cgi_url = new URL( textfield.getText());
			}
			else if ( url_string != null)
			{
				cgi_url = new URL( url_string);
			}
			else
			{
				cgi_url = new URL("http", applet_url.getHost(), applet_url.getPort(),"/cgi-bin/date");
			}
		}
		catch (MalformedURLException e)
		{
			textarea.appendText("Error parsing   " + e +"\n");
			return;
		}
		catch (SecurityException e)
		{
			textarea.appendText("Security violation detected: " + e +"\n");
			return;
		}
		
		textarea.appendText( "Attempting to use URL " + cgi_url.toString()+ "\n");

		//------------------------------------------------------------------
		// could use getContents, but dont understand how to use it.
		//
		textarea.appendText("\nthe output from the cgi-program is\n\n");
		try
		{
			stream = new DataInputStream(cgi_url.openStream());
			while ( (data_line = stream.readLine()) != null)
			{
				textarea.appendText(data_line +"\n");
			}
				stream.close();
			}
			catch(IOException e)
			{
			textarea.appendText("error reading data from url : "+ e);
			}
	}
}

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