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BASIC SERVLET CODE


REFERENCE SERVLETS IN HTML CODE
A) server side include:
	
	<servlet code=MyServlet codebase=http://remoteserver:8080/directory>
		<param name=city value="Maastricht">
	</servlet>
	

B) form:
	
	<form method=POST action="/servlet/MyServlet">
		Place of birth:
		<input type=text name="city"><p>
		<input type=submit value="click">
	</form>
	



BASIC SERVLET STATEMENTS

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public clas MyServlet extends HttpServlet{



	public void doGet( HttpServletRequest request, HttpServletResponse res) {

		PrintWriter 		writer_out	= res.getWriter();	 	// for TEXT output
		ServletOutputStream	bin_out		= res.getOutputStream();	// for BINARY output (eg images)



		// get a parameter value
		String name = request.getParameter("name_par");

		// get all parameter names
		java.util.Enumeration enum = request.getParameterNames();

		// get username client
		String user = request.getRemoteUser();

		// get raw query string
		String q = request.getQueryString();

		// write text to client
		writer_out.println( "Hello world");


		// get content type
		String contenttype = getServletContext().getMimeType( file_string );

		// set content type out-file
		res.setContentType( contenttype );

	}
}





GENERATE IMAGES (using acme package)

import java.awt.*;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import Acme.JPM.Encoders.GifEncoder;

public clas MyServlet extends HttpServlet{

	ServletOutputStream	bin_out	= res.getOutputStream();	// for BINARY output


	Frame frame = null;
	Graphics g = null;


	public void doGet( HttpServletRequest request, HttpServletResponse res) {


		frame = new Frame();
		// make Frame component displayable by connecting it to a native screen resource
		frame.addNotify();

		try{
			// create image and get its Graphics object
			Image image = frame.createImage( 400, 300 );
			g = image.getGraphics();

			g.setFont("verdana", Font.BOLD, 50 );
			g.drawString( "Image text" );

			res.setContentType( "image/gif" );

			GifEncoder encoder = new GifEncoder( image, bin_out );
			encoder.encode();
		} finally {
			// clean up resources
			if (null!=g!) g.dispose();
			if (null!=frame) frame.removeNotify();
		}
	}
}




HEADER INFORMATION

	// retrieve some common header values
	String s;
	s = request.getMethod();		// e.g. GET
	s = request.getRequestURI();	// e.g. /servlets/public/apage.txt
	s = request.getProtocol();		// e.g. HTTP/1.0

	// get a header value
	String headerValue = request.getHeader(headerName);

	// retrieve all header names
	Enumeration headerNames = request.getHeaderNames();




SESSION TRACKING


	// Get session. Par. true: automatically create a new session if there isn't one already
	HttpSession session = request.getSession(true);

	// set a value
	session.putValue( aString, anObject );
	session.setAttribute( aString, anObject );		// version 2.2 


	// get a value
	Object object = session.getValue( aString );
	Object object = session.getAttribute( aString );		// version 2.2 




RETRIEVE COMMON CGI VARIABLES

	AUTH_TYPE					request.getAuthType()
	CONTENT_LENGTH					String.valueOf(request.getContentLength())
	CONTENT_TYPE					request.getContentType()
	DOCUMENT_ROOT					getServletContext().getRealPath("/")
	PATH_INFO					request.getPathInfo()
	PATH_TRANSLATED				request.getPathTranslated()
	QUERY_STRING					request.getQueryString()
	REMOTE_ADDR					request.getRemoteAddr()
	REMOTE_HOST					request.getRemoteHost()
	REMOTE_USER					request.getRemoteUser()
	REQUEST_METHOD					request.getMethod()
	SCRIPT_NAME					request.getServletPath()
	SERVER_NAME					request.getServerName()
	SERVER_PORT					String.valueOf(request.getServerPort())
	SERVER_PROTOCOL				request.getProtocol()
	SERVER_SOFTWARE				getServletContext().getServerInfo()




<== misc. ==>



GET SERVLET PATH INFORMATION
	public String request.getPathInfo()		 
	public String request.getPathTranslated()		 
	public String request.getRealPath()