Servlet request and Servlet Collaboration

An HTTP request is every kind of information that could be of interest and is requested by your computer from a web server. <!--more--> A servletRequest object can forward client information from the request, such as content type, names, and values of parameters, header information, attributes, etc.

Introduction #

The RequestDispatcher interface allows the request to be forwarded or included to another resource. This can be from servlet to another servlet or servlet to HTML file, or servlet to JSP file.

This can also be used to add other resource content. It's one approach to work with Servlet Collaboration.

Prerequisites #

To follow this article along the reader will need the following:

• Some basic knowledge of core Java.
• An introductory path of the servlet and its life cycle.
• Some basic knowledge of HTML is also required.

You will need to install the following tools:

• An open-source editor, such as Eclipse, or any other related Java editor. In my case, I will be using Eclipse IDE for Java EE Developers 2021‑06 windows version
• Java JDK current version or any. In my case, I will be using Java SE Development Kit 17 for Windows 64 bit system.
• You need a web browser installed on your computer.
• Server. In my case, I will be using TomCat version 9.0.54 for Windows. You can download it here.

Table of contents #

• ServletRequest
• Methods of ServletRequest
• ServletRequest interface example
• RequestDispatcher
• RequestDispatcher Methods
• RequestDispatcher example
• Conclusion

ServletRequest #

When we interact with websites, we keep asking web pages to do something for us, for example, client updating their profiles, etc. Whenever a client or user tries to update their profile. In this case, Java provides us with an object of the ServletRequest interface, which forwards requested information to a servlet.   The service container creates objects for ServletRequest and ServletResponse when a customer sends requests to a web server that passes through the service method as an argument. The request object provides access to query information, such as the header and information from the requested database.

Methods of ServletRequest #

The ServletRequest interface provides us with many methods to work with client request information.

Some are explained below:

• getParameter(String parameterName): This method returns a client's requested parameter value of the String type.
• String[] getParameterValues(type parameterName): Majorly used to obtain all values of a given multi-valued parameter name. In this case, it would be useful to work with a list box that contains multiple values in a single parameter.
• getContentLength(): The actual size of the type of data requested is returned.
• Public String getContentType(): Returns the media type or null if unknown.
• Enumeration getParameterNames(): The name of the target parameter is used to return an enumeration.
• String getCharacterEncoding(): If the encoded character is specified, this method will return the name. It returns null in the request body if not specified.
• public int getServerPort(): The port number received by this method is returned.
• public abstract String getServerName(): It returns the server name which receives the request.
• ServletInputStream getInputStream(): Returns the binary data input stream in the query body.
• String getCharacterQueryString(): Returns the URL path of the request from the protocol name of a type String.
• getInputStream(): This method returns information stream from the standard output stream of a type ServletInputStream.
• String getLocalAddr(): It returns the IP address of the interface from which the request has taken.
• getAttribute(String name): It returns the attribute of the requested object set by its name, and the return type is Object.
• Enumeration getAttributeName(): It returns the Attribute name of the type Enumeration available in the current request.
• ServletContext getServletContext(): It returns the content of the current Servlet request and the return type is ServletContext.
• removeAttribute(String name): Used when removing the attribute from the current request of a type void.

ServletRequest interface example #

We will create a user login project with a servlet in this example. In this context, we will be using getParameter() to return the value of the specified query parameter name.

Steps to create this project #

Step 1: Download the Eclipse IDE for Java EE developers and install, as shown.

Step 2: Install TomCat current version. In my case, I will be using TomCat version 9.0.10 for Windows. You can download it here.

Extract it to a new folder of your choice.

Step 3: Open Eclipse IDE for Java EE developers. Create a Dynamic web project by selecting files, new then Dynamic web projects, and press enter as shown.

Step 4: We will name our project LogInDemo, and leave the other fields with default values then select Finish.

Step 5: Right-click on the LogInDemo on the Project Explorer, select new -> HTML file option and name it Login.html. In the HTML page, you created, replace the default code with the following code.

<!DOCTYPE html>
<html>

<head>
    <meta charset="ISO-8859-1">
    <title>login demo</title>
</head>

<body>
    <form action="LoginAction1" method="post">
        <input type="text" name="name" placeholder="Enter username" required>
        <input type="password" name="password" placeholder="Enter password" required>
        <input type="submit" value="submit">
    </form>
</body>

</html>

Step 6: Create a new servlet file as follows:

• Right-click on LogInDemo on the Project Explorer, select new -> servlet as shown.

• Finish by giving your servlet class a name. LoginAction1 is the name I'll be using.

• Substitute the code below for the code in the servlet page you just created.

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet({ "/LogInDemo", "/LoginAction1" })
public class LoginAction1 extends HttpServlet 
{
		
	private static final long serialVersionUID = 1L;

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
	{
		String userName=request.getParameter("name");
        String password=request.getParameter("password");
        if(userName.equals("India") && password.equals("1234"))
        {
        response.sendRedirect("welcomePage1.jsp");
        }
        else
        {
        	response.sendRedirect("Login.html");
        }
		
	}

}

Step 5: Create a new JSP file as follows:

• Right-click on the LogInDemo on the Project Explorer, select new -> JSP file as shown.

• Finish by giving your jsp page a class name. We'll call it welcomePage1.jsp in this case.

• Replace the code in the JSP page you just created with the code below.

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>

<head>
    <meta charset="ISO-8859-1">
    <title>Insert title here</title>
</head>

<body>
    <h1>Hello World !</h1>
</body>

</html>

Setup Apache Tomcat server in the Eclipse IDE and run the project #

• Select "No servers are available" from the Servers Tab as shown.

• Next, select Tomcat v9.0 Server or any of your choice, but I recommend the current version.

• Add Apache installation directory

Click Finish after adding the Apache installation directory.

• Right-click on the Login.html page, select Run As then Run on Server.

• When TomCat server is selected as shown below. Select Finish and restart the server when the screen pops up.

• In the internal browser, the following page will appear. Try logging in with the credentials we specified in LoginAction1.java (user name India, password 1234)

Explanation #

From the example above, the LoginAction1.java servlet, in the Post Request form, is called if a user enters the correct credentials on the login page.

A doPost () will set the user parameters, and store them in variables userName and password, as shown:

      String userName=request.getParameter("name");
      String password=request.getParameter("password");

If the user provided the correct details, with the help of the equals() method, the welcomePage1.jsp will be executed, otherwise, the client browser will remain on the login.html page.

• Get project source code here

RequestDispatcher #

RequestDispatcher interface allows us to send a client query to another resource. Servlet, Html, JSP. It also defines an object that receives the request and includes the content of the target resource.

RequestDispatcher methods #

Here are two methods provided by the RequestDispatcher interface, mainly forward() and include() method explained below.

• public void forward(ServletRequest request, ServletResponse response): This method offers an efficient way to forward customer requests. It can be to HTML file, Servlet, or JSP file from servlet resource.

• public void include(ServletRequest request, ServletResponse response): From its name include(), it helps to include in the response the content of another resource.

NOTE: Both of these two methods throw IOExceptions.

RequestDispatcher example #

How it works #

This example shows how RequestDispatcher can forward a resource response or include it on a server. Here we use index.jsp to get a user response. In this case, Controller Servlet checks the entered response if a user is more than 18 years old or below.

If the user selects Above18, the Above18 servlet page will be executed with the help of the forward() method. Otherwise, the client browser will remain on the index.jsp page and a denial message will appear, indicating that the user is under the age of 18.

Construct the ServletDispatcherDemo project as follows, assuming you know how to create and run a web project using the Eclipse IDE and TomCat server as explained in the ServletRequest interface example above.

Steps to create this project #

Step 1: Open Eclipse IDE for Java EE developers. Create a web project by selecting Files -> New -> Dynamic Web Project.

Step 2: Provide a project name. We will name ours ServletDispatcherDemo, then select Finish.

Step 3: Right-click on the ServletDispatcherDemo on the Project Explorer, select new -> JSP file option.

Give the page you just created a name. We'll call it index.jsp in this example. Replace the code in the HTML file with the code below:

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>page verification</title>
</head>
<body>
<body>
<form action="Controller" method="post">
 <select name="selectOption" required>
  <option value="Select you option">Select you option</option>
  <option value="Above18">Above18</option>
  <option value="below18">below18</option>
 </select>
 <input type="submit" value="Submit">				    
</form>

  <%
  String msg=request.getParameter("msg");
  if("below18".equals(msg))
  {
  %>
 <h1> Access denied! You are below 18 years!<h1>
  <%} %>
</body>
</html>

Step 4: Create a new servlet file as follows:

• Right-click on the ServletDispatcherDemo on the Project Explorer, select new -> servlet and finish by giving your servlet class a name. We'll call it Controller in this case.

• Replace the code in the servlet page you just created with the code below:

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
@WebServlet({ "/ServletDispatcherDemo", "/Controller" })
public class Controller extends HttpServlet 
{
	
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
	{
		response.setContentType("Text/html");
		String select=request.getParameter("selectOption");
		HttpSession session=request.getSession();
		session.setAttribute("userName", select);
		
		response.getWriter().append("<html><body'></body></html>");
		if(select.equals("Above18"))
		{
			RequestDispatcher rd=request.getRequestDispatcher("Above18");  
	        rd.forward(request, response); 
	    }	 
		else
		{
			RequestDispatcher rd=request.getRequestDispatcher("index.jsp?msg=below18");
			rd.include(request,response);
		}
		
	}


	

}

Step 5: Create a new servlet file as follows:

• Right-click on the ServletDispatcherDemo on the Project Explorer, select new -> servlet and finish by giving your servlet class a name. We'll call it Above18 in this case.

• Replace the code in the servlet page you just created with the code below.

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet({ "/Above18" })
public class Above18 extends HttpServlet 
{
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
	{
		PrintWriter out = response.getWriter();  
       
	    out.print("Welcome to the adult page."); 
	}
}

Right-click on the index.jsp page and choose run As-> Run on Server -> Save all changes and restart the server to run the project. In the internal browser, a menu will appear, prompting you to select your age category.

This example will give you a solid foundation for working with the ServletDispatcher interface in your project. To improve your understanding and enhance your coding skills, I recommend that you start exploring more examples.

We assumed the reader knew how to use the Eclipse IDE and configure the Tomcat server in this example.

If not, take a look at the resources below:

• ServletRequest example above
• Get project source code here

Conclusion #

In conclusion, we learned some of the ServletRequest methods and ServletDispatcher methods and how to implement them with the help of examples. We discussed both these interfaces (ServletRequest and ServletDispatcher) and what they are comprised of.

This article will help you get started with servlet and understand how users send requests to a server. From here, you should be able to use servlet and JSP technology to build your own dynamic website.

Happy coding!!

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Peer Review Contributions by: Samuel Mwangi