Query system for an environment variable value using C/C++

Today one of my colleague asked me how to query an environment variable using C++. The solution is simple, just use getenv() method. See the below code.

#include <iostream>
#include <cstdlib>
#include <string>

using namespace std;
#pragma warning(disable: 4996) // disable warning for getenv()

int main()
{
 char *pointer = NULL;

 string str;
 cout<<"Enter the environment variable: ";

 while (cin>>str) {
  if(str.compare("exit") == 0) break;
  if(pointer = getenv(str.c_str())) {
   cout<<endl<<"Value of \""<<str<<"\" Variable: "<<pointer<<endl<<endl<<"Enter the environment variable: ";
  }else {
   cout<<"No such variables defined."<<endl<<"Enter the environment variable: ";
  }
 }
}

HttpServer - The Oracle JDK 1.6 Hidden Feature

I have seen this class many a times, but never encountered a scenario to use it. Recently in one of my application I needed to embedded a HTTP server. So I thought, Why not give this class a try !!

HTTP server infrastructure/framework is very simple to implement and is bundled only with the Oracle JDK 1.6. Following are the main classes:

1. HttpServer
2. HttpContext
3. HttpExchange

See this link for sun.* package discussions.

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.InetSocketAddress;
import java.net.URLDecoder;
import java.util.List;
import java.util.concurrent.Executors;

import com.sun.net.httpserver.Headers;
import com.sun.net.httpserver.HttpExchange;
import com.sun.net.httpserver.HttpHandler;
import com.sun.net.httpserver.HttpServer;

public class JavaServer 
{
 public static final String nl = System.getProperty("line.separator");

 public static void main(String[] args) throws Exception 
 {
  if(args.length != 2)
  {
   printUsage();
   System.exit(-1);
  }
  String strPort = null;
  String strAddress = null;

  for (int i = 0; i < args.length; i++) 
  {
   if(args[i].startsWith("-p")){
    strPort = args[i].substring(2, args[i].length()).trim();
   }else if(args[i].startsWith("-a")){
    strAddress = args[i].substring(2, args[i].length()).trim();
   }else
    throw new IllegalArgumentException("Unknown command '" + args[i]+ "'");
  }

  if(strAddress.length() == 0 || strPort.length() == 0)
   throw new IllegalArgumentException("Port = " + strPort + ", IP = " + strAddress);

  int port = Integer.parseInt(strPort);
  InetSocketAddress address = new InetSocketAddress(strAddress, port);

  System.out.println("Going to run server on '" + address + "'");

  new JavaServer().start(address);
 }

 private static void printUsage() {
  System.out.println("$JavaServer -p<Port> -a<IP Address>");
 }

 private HttpServer server;

 public void start(InetSocketAddress address) throws IOException
 {
  server = HttpServer.create(address, 0); 
  server.setExecutor(Executors.newCachedThreadPool());
  server.createContext("/", new RootHandler());
  server.start();
 }
}

class RootHandler implements HttpHandler 
{
 private static final int BUFFER_SIZE = 1024;

 public void handle(HttpExchange exchange) throws IOException
 {
  String method = exchange.getRequestMethod();

  if(method.equalsIgnoreCase("get"))
  {
   String request = "";
   ByteArrayOutputStream baos = new ByteArrayOutputStream(BUFFER_SIZE);
   InputStream is = exchange.getRequestBody();

   byte[] buff = new byte[BUFFER_SIZE];
   while (true) 
   {
    int out = is.read(buff);
    if(out == -1)
     break;
    baos.write(buff, 0, out);
   }

   is.close();

   if (baos.size() > 0) {
    request = URLDecoder.decode(baos.toByteArray().toString(), "UTF-8");
   } else {
    request = null;
   }

   StringBuilder buf = new StringBuilder();
   buf.append("<html><head><title>Simple HTTP Server !!</title></head><body>");
   buf.append("<p><pre>");
   buf.append(exchange.getRequestMethod() + " " + exchange.getRequestURI() + " " + exchange.getProtocol() + JavaServer.nl);

   Headers headers = exchange.getRequestHeaders();

   for (String name : headers.keySet()) {
    List<String> values = headers.get(name);
    for (String value : values) {
     buf.append(name + " --> " + value + JavaServer.nl);
    }
   }
   if (request != null) {
    buf.append(JavaServer.nl);
    buf.append(request);
   }

   buf.append("</pre></p>");
   buf.append("</body></html>\n");

   String response = buf.toString();

   Headers responseHeaders = exchange.getResponseHeaders();
   responseHeaders.set("Content-Type", "text/html");
   exchange.sendResponseHeaders(HttpURLConnection.HTTP_OK, response.length());

   OutputStream res = exchange.getResponseBody();
   res.write(response.getBytes());
   res.close();
  }else
  {
   String response = "Bad request method !!";
   exchange.sendResponseHeaders(HttpURLConnection.HTTP_BAD_METHOD, response.length());
   OutputStream res = exchange.getResponseBody();
   res.write(response.getBytes());

   res.close();
  }
  exchange.close();
 }
}

Steps to run the above code

1. Compile it using Oracle JDK 1.6
2. Then execute this command on console (without quotes) 'Java JavaServer -p<port number> -a<ipaddress or localhost>' . For example, java JavaServer  -p5463 -a127.0.0.1
3. Open your browser and type the URL. For example, http://127.0.0.1:5463/

You should see something like this (depends on the browser):

How to open a Java file in read-only mode?

In one of my eclipse plugin based application I wanted to open Java files in read only mode. One option was to use org.eclipse.jface.text.source.SourceViewer , where I could have used JavaSourceViewerConfiguration
for providing Java highlighting and all. But there were two problems:

1. Source viewer won't inherit the Java editor settings (and if you have modified eclipse Java editor theme), which means your background and foreground in the SourceViewer gets completely messed up.
2. Secondly you would lose all the markup and bookmarking facilities available with editors

So, I decided to extend the existing Java editor. The steps are extremely simple,

1. Create an editor extension
2. Extend the extension class with org.eclipse.jdt.internal.ui.javaeditor.CompilationUnitEditor
3. Override some of the methods
4. Open your file with this editor

Code

Editor Code

import org.eclipse.jdt.internal.ui.javaeditor.CompilationUnitEditor;

@SuppressWarnings("restriction")
public class ReadonlyEd extends CompilationUnitEditor 
{
 public static final String ID = "read.only";
 public ReadonlyEd() {
 }
 @Override
 public boolean isEditable() {
     return false;
 }
 @Override
 public boolean isEditorInputModifiable() {
     return false;
 }
 @Override
 public boolean isEditorInputReadOnly() {
     return true;
 }
 @Override
 public boolean isDirty() {
     return false;
 }
}

Code for Invoking the Editor

IFile file = ...; // Get the Java file instance
IWorkbenchPage page = ...; // Get the workbench page
  
FileEditorInput input = new FileEditorInput(file);
try {
 IDE.openEditor(window.getActivePage(), input, ReadonlyEd.ID);
} catch (PartInitException e) {
 e.printStackTrace();
}

How to hide a window from Win32 Taskbar?

Argh !!! I don't know why but I keep forgetting the ex-style bit for this... 

To prevent the window button from being placed on the taskbar, create the unowned window with the WS_EX_TOOLWINDOW extended style. As an alternative, you can create a hidden window and make this hidden window the owner of your visible window.

The Shell will remove a window's button from the taskbar only if the window's style supports visible taskbar buttons. If you want to dynamically change a window's style to one that doesn't support visible taskbar buttons, you must hide the window first (by calling ShowWindow with SW_HIDE), change the window style, and then show the window.

Taken from here: The Taskbar

3 easy steps to self-sign a Applet Jar file

Found this link that explains how to self-sign an applet in 3 easy steps:

1. keytool -genkey -keystore myKeyStore -alias me
2. keytool -selfcert -keystore myKeyStore -alias me
3. jarsigner -keystore myKeyStore jarfile.jar me