Java , J2EE,SQL Notes: February 2014

Tuesday, February 25, 2014

Nested if else in Apache Ant

Often we may have requirement to implement nested if in Apache Ant without using ant-contrib.

My requirement was to set a xml property by the following condition

1) If the property xml file is passed using -D parameter it should take the precedence
2) If I set an environment variable for property xml path it will take the 2nd preference
3) Above two conditions are not met it will take the property from a default location.

if( -Dparameter Set)
else
{
   if(Env variable set)
   {
} else
{
   //take from default
}
}

This is how I accomplish the task above :

<target name="init-pls-config-xml"
         depends="init-pls-config-dparam,int-pls-config-osset"></target>
<target name="init-pls-config-dparam" if="pls-config">
<echo>*********** Using pls-config file as -D param : ${pls-config} *********** </echo>
<xmlproperty file="${pls-config}" collapseattributes="true" keeproot="false"/>
</target>
<target name="int-pls-config-osset" unless="pls-config"
         depends="init-pls-config-osenvxml,init-pls-config-default"></target>
<target name="init-pls-config-osenvxml" if="OS_ENV.PLS_ANT_CONFIG">
<echo>*********** Using pls-config file from the environment variable : ${OS_ENV.PLS_ANT_CONFIG} *********** </echo>
<xmlproperty file="${OS_ENV.PLS_ANT_CONFIG}" collapseattributes="true"
               keeproot="false"/>
</target>
<target name="init-pls-config-default" unless="OS_ENV.PLS_ANT_CONFIG">
<echo>*********** Using pls-config file from the default location: ${OS_ENV.HOME}/pls-config.xml *********** </echo>
<xmlproperty file="${OS_ENV.HOME}/pls-config.xml" collapseattributes="true"
               keeproot="false"/>
</target>

Thursday, February 20, 2014

Servlets: Getting the form parameters

Form parameters methods are defined in the interface ServletRequest .These are the main methods :

getParameter(String ) - Getting the parameter from the request object for the parameter name
getParameterMap() - Getting the name value map of the parameters
getParameterNames() - Returning enumeration of parameter names
getParameterValues(String) - Returns array of values for the parameter name

parameters.html :

<!DOCTYPE html>

<html>

<head>

<title>reqparameters</title>

</head>

<body>

<tr>

<td>First Name</td>

<td>

</td>

</tr>

<tr>

<td>

</td>

</tr>

<tr>

<td>Login Name</td>

<td>

</td>

</tr>

<tr>

<td>

</td>

</tr>

</table>

</form>

</body>

</html>

The servlet :

package view;

import java.io.IOException;
import java.io.PrintWriter;

import java.util.Enumeration;

import javax.servlet.*;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;

@WebServlet(name = "GetParameters", urlPatterns = { "/getparameters" })
public class GetParameters extends HttpServlet {
    private static final String CONTENT_TYPE = "text/html; charset=windows-1252";

    public void init(ServletConfig config) throws ServletException {
        super.init(config);
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType(CONTENT_TYPE);
        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<head><title>GetParameters</title></head>");
        out.println("<body>");
        out.println("<p>The servlet has received a GET. This is the reply.</p>");
        Enumeration params = request.getParameterNames();
        while(params.hasMoreElements()) {
            String name =(String)params.nextElement();
            String value = request.getParameter(name);
            out.println(" Name = "+name+" : Value "+value);
        }
        System.out.println(" Request hash Map = "+request.getParameterMap());
        out.println("</body></html>");
        out.close();
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}

Wednesday, February 19, 2014

Upload Servlet

upload.html :

<html>
<body>
<form enctype="multipart/form-data" method="POST" action="uploadservlet">
<input type="file" size="20" name="FileToUpload" value="Select a File" >
<input type="submit" name="UploadFile" value="Upload">

</form>
</body>
</html>

Servlet :

package view;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;

import java.util.Enumeration;

import javax.servlet.*;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;

@WebServlet(name = "UploadServlet", urlPatterns = { "/uploadservlet" })
public class UploadServlet extends HttpServlet {
    static final String dir = "D:/tmp";
    private static final String CONTENT_TYPE = "text/html; charset=windows-1252";

    public void init(ServletConfig config) throws ServletException {
        super.init(config);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {



        PrintWriter outHTML = response.getWriter();
        outHTML.println("Done ");

        ServletInputStream is = request.getInputStream();
        BufferedInputStream bis = new BufferedInputStream(is);
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));

        File file = new File("D:\\Projects\\tmp\\out.txt");
        FileWriter out = new FileWriter(file);
        int i;
        while ((i = reader.read()) != -1) {
            out.write(i);
        }
        out.close();
        bis.close();
    }

    @Override
    protected void doGet(HttpServletRequest httpServletRequest,
                         HttpServletResponse httpServletResponse) throws ServletException, IOException {
        // TODO Implement this method
        doPost(httpServletRequest, httpServletResponse);
    }
}

doGet(),doPost() , doPut(),doHead()

Get append the data to the URL as name value pair.
Post sends the data separately in the body of the request
Get is for small amount of data
Get requests can be bookmarked
Get is used for simple html requests
In Post request the query limit is unlimited
User seen the data in the URL in Get request, can be a security issue. Post requests the data is hidden.
Get request is always ascii. Post can be both ascii and binary.
Post is used for posting long messages
Put() is uploading the file to the server. But many container it wont work and Post is used instead.
Get request can be triggered by clicking on a link ,Typing address ,location.href and submitting a page with method ="get" in the form element.
Post is triggered when submitting an html form.
head() returns same header that Get return .But nobody or content
Receives and return small amount of message faster and light weight.

How the servlets works

While start up the servlet container pre-load servlets in the memory if the servlet is defined in the web.xml.If not there in the web.xml the servlet is getting loaded on first time access.First time the servlet loads it will call the init() method. Init method is getting used to initialize the objects like db connection file connection etc.Each time the user make a request to the servlet the service method is getting called which is overridden in doGet() and doPost() methods.The response from these method back to container and to the browser.Web application is a collection of jsp,sevlets,images ,css etc , packaged to a .war file.Servlet container normally have one instance of servlet.If the servlet implements single threaded model multiple instance of servlets are possible.In order to convert your servlet into distributable the servlet should implement single threaded model and in the deployment descriptor make the servlet as distributable.

Tuesday, February 4, 2014

Servlet container model

Servlets are pure java code
JSP contains HTML and small amount of java code
Browser sends the request to the webserver
Webserver hands the request to the servlet container
Webserver checks the type of request
If the request is coming from jsp it will be translated to servlet in the container
Container loads the servlets if not already loaded
Container hands the request object to init() ,the service() and last the destroy()
service() calles the appropriate doXXX()
Container creates the HTTP response
If Http response is fine it will send the http response or error response.

JSP introduction

JSPs are converted into servlets before contatiner run
JSPs reduce the skill level of developers
Translation is completed servlet is compiled and loaded into memory

<!DOCTYPE html>

<%@ page contentType="text/html;charset=windows-1252"%>

<html>

<head>

</head>

<body>

out.println("Hellow World");

</body>

</html>

Servlets Introduction

Servlets run on a single process using threads
Overhead of additional requests are small as it run on single process
Servlets requires java programming skills
JSP and servlets enables to develop modular ,maintainable ,scalable and portable applications
Servlets run on a web containter or servlet egine
Servlets can generate HTML response object
Servlets are compiled into byte code.Servlets are java class file.On requests this byte codes are loaded into the memory
Serlets talk to the client using web server
Client request first go to the web server and webserver re-direct the requests to the container . Containter calls the generic servlet interface which calls HTTPServlet class and My Servlet class
The response from Servlet again go back to the container and from there to web server and finally to the browser
Most of the containter implementations are in java
Servlet container instatiate the objects that encapsulate request or response .
Servlet containter do initialization,processing of the request and response,unloading and finalization of servlets
Container creates ServletContext object through which the servlet can log events ,set and store attributes at application or session level and grab file paths.

package view;

import java.io.IOException;

import java.io.PrintWriter;

import javax.servlet.*;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.*;

@WebServlet(name = "Servlet1", urlPatterns = { "/servlet1" })

public class Servlet1 extends HttpServlet {

private static final String CONTENT_TYPE = "text/html; charset=windows-1252";

public void init(ServletConfig config) throws ServletException {

// Initialize resources

super.init(config);

}

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

response.setContentType(CONTENT_TYPE);

PrintWriter out = response.getWriter();

out.println("<html>");

out.println("<head><title>Servlet1</title></head>");

out.println("<body>");

out.println("<p>The servlet has received a GET. This is the reply.</p>");

out.println("</body></html>");

out.close();

}

public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

doGet(request, response);

}

public void destroy() {

//Clean up resources

}

Java , J2EE,SQL Notes

Tuesday, February 25, 2014

Nested if else in Apache Ant

Thursday, February 20, 2014

Servlets: Getting the form parameters

Wednesday, February 19, 2014

Upload Servlet

doGet(),doPost() , doPut(),doHead()

How the servlets works

Tuesday, February 4, 2014

Servlet container model

JSP introduction

Servlets Introduction

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