Sending Values From Servlet to Html and Again From Second Servlet to Second Html

Servlet Collaboration In Java Using RequestDispatcher and HttpServletResponse

What is Servlet Collaboration?

The commutation of information among servlets of a particular Java spider web application is known as Servlet Collaboration. This enables passing/sharing information from one servlet to the other through method invocations.

What are the principle ways provided by Java to achieve Servlet Collaboration?
The servlet api provides two interfaces namely:

1. javax.servlet.RequestDispatcher
2. javax.servlet.http.HttpServletResponse

These two interfaces include the methods responsible for achieving the objective of sharing information between servlets.

Using RequestDispatcher Interface

The RequestDispatcher interface provides the option of dispatching the client's request to another web resource, which could be an HTML page, another servlet, JSP etc. It provides the following two methods:

• public void forward(ServletRequest request, ServletResponse response)throws ServletException, java.io.IOException:
  The forward() method is used to transfer the client request to some other resource (HTML file, servlet, jsp etc). When this method is called, the command is transferred to the next resource called. On the other hand, the include() method is used to include the content of the calling file into the called file. Subsequently calling this method, the control remains with the calling resource, but the processed output is included into the chosen resource.
  The following diagram explains the way it works:
  

• public void include(ServletRequest request, ServletResponse response)throws ServletException, java.io.IOException:
  The include() method is used to include the contents of the calling resource into the called one. When this method is called, the command still remains with the calling resources. It only includes the processed output of the calling resource into the chosen ane.
  The following diagram explains how it works:
  

• Example of using RequestDispatcher for Servlet Collaboration
  The following example explains how to use RequestDispatcher interface to achieve Servlet Collaboration:
  alphabetize.html
  

html

< html >

< head >

< body >

< form action = "login" method = "post" >

Name:< input type = "text" name = "userName" />< br />

Countersign:< input blazon = "password" name = "userPass" />< br />

< input type = "submit" value = "login" />

</ form >

</ torso >

</ html >

• Login.java

Java

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

public class Login extends HttpServlet {

public void doPost(HttpServletRequest req,

HttpServletResponse res)

throws ServletException, IOException

{

res.setContentType( "text/html" );

PrintWriter out = response.getWriter();

String due north = request.getParameter( "userName" );

Cord p = request.getParameter( "userPass" );

if (p.equals( "Thanos" ){

RequestDispatcher rd = request.getRequestDispatcher( "servlet2" );

rd.forrard(request, response);

}

else {

out.print( "Password mismatch" );

RequestDispatcher rd = request.getRequestDispatcher( "/index.html" );

rd.include(asking, response);

}

}

}

• Welcome.java

Java

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

public class Welcome extends HttpServlet {

public void doPost(HttpServletRequest request,

HttpServletResponse response)

throws ServletException, IOException

{

response.setContentType( "text/html" );

PrintWriter out = response.getWriter();

String n = request.getParameter( "userName" );

out.print( "Welcome " + n);

}

}

• web.xml

html

< web-app >

< servlet >

< servlet-name >Login</ servlet-name >

< servlet-class >Login</ servlet-grade >

</ servlet >

< servlet >

< servlet-name >WelcomeServlet</ servlet-name >

< servlet-class >Welcome</ servlet-grade >

</ servlet >

< servlet-mapping >

< servlet-proper noun >Login</ servlet-name >

< url-design >/servlet1</ url-pattern >

</ servlet-mapping >

< servlet-mapping >

< servlet-name >WelcomeServlet</ servlet-proper noun >

< url-pattern >/servlet2</ url-blueprint >

</ servlet-mapping >

< welcome-file-listing >

< welcome-file >index.html</ welcome-file >

</ welcome-file-list >

</ web-app >

Output:

• alphabetize.html

• If password matches:

• If password doesn't lucifer:

Using HttpServletResponse Interface

• The HttpServletResponse interface is entrusted with managing Http responses. To achieve servlet collaboration, information technology uses the post-obit method:

public void sendRedirect(String URL)throws IOException;          

• This method is used redirect response to another resource, which may be a servlet, jsp or an html file. The statement accepted by it, is a URL which tin can exist both, absolute and relative. Information technology works on the client side and uses the browser'southward URL bar to make a asking.
  

Example of using sendRedirect() for redirection

• The following example of a web application created using servlet takes the text written in the text field in the webpage, and directs information technology to the servlet. The servlet and so redirects information technology to google, which so produces search results based on the text written.
  index.html

html

< html >

< head >

< trunk >

< course action = "search" method = "GET" >

< input type = "text" name = "name" >

< input type = "submit" value = "search" >

</ class >

</ body >

</ html >

Java

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class MySearcher extends HttpServlet {

protected void doGet(HttpServletRequest

request,

HttpServletResponse response)

throws ServletException, IOException

{

String proper name = request.getParameter( "proper name" );

}

}

• web.xml

html

< web-app >

< servlet >

< servlet-name >MySearcher</ servlet-name >

< servlet-course >MySearcher</ servlet-class >

</ servlet >

< servlet-mapping >

< servlet-name >MySearcher</ servlet-name >

< url-pattern >/search</ url-pattern >

</ servlet-mapping >

< welcome-file-list >

< welcome-file >alphabetize.html</ welcome-file >

</ welcome-file-list >

</ web-app >

Output:

• index.html

• Search upshot

What is the departure between forward() method of RequestDiispatcher and sendRedirect() of HttpServletResponse?

• Although the ii methods appear to exercise the aforementioned matter, there are still differences between the 2, which are as follows:

forward()	sendRedirect()
It works on the server side	It works on the client side
It sends the same request and response objects to another resource.	Information technology always send a new request
It works but within the server.	It can be used inside and outside the server.

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Source: https://www.geeksforgeeks.org/servlet-collaboration-java-using-requestdispatcher-httpservletresponse/

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