ServletContext Attributes

In this article, we are going to understand how to associate attributes with a ServletContext object. An attribute is an object and when such objects are associated with a ServletContext object, they are called context attributes and are available to the whole application i.e. all the Servlets in the application can access these attributes through the ServletContext object. These context attributes are stored in the context scope on the server side used for the request processing.

We can set and get the value of context attributes associated with the ServletContext object by using the methods of ServletContext interface. After setting some attributes with the ServletContext object, we can even access these attributes from one to another Servlet in order to have a shared request processing by multiple Servlets.

Methods of ServletContext to set,get and remove context attributes

Method	Description
Object *getAttribute(String str)*	This method gets an individual context attributes.
Enumeration getAttributesNames()	This method gets all the named of context attributes.
void *setAttribute(String name, Object value)*	This method sets the context attributes.
void *removeAttribute(String name)*	This method sets the context attributes.

A Request Attribute Example

We are creating a webpage which asks the user to submit asking the user to enter the name and percentage at high school to know if he/she is eligible to get a scholarship at an university or not, based on a condition -

A user must have a percentage of more than 90

after filling the details when submit button is clicked, the request is are dispatched or forwarded to the Servlet named FirstServlet (mentioned in the deployment descriptor file(web.xml).

Webpage1.jsp

<html>

<head>
<title>  Context Attributes Demo </title>
</head>


<body>
<b>Please enter your details to know if you are eligible to apply for scholarship at our university.</b>
<br/>
<br/>
<br/>

<form action = "FirstServlet">
Name :<input type = "text"  name = "username"/>


Percentage :<input type = "text"  name = "percentile"/>


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

</body>
</html>

Creating a Servlet to set request attributes

We are creating a Servlet extending GenericServlet abstract class. GenericServlet class implements Servlet and ServletConfig interface, hence we can directly call the methods of ServletConfig within this Servlet.

In this Servlet class named MyServlet1.java, we have implemented the service(ServletRequest req, ServletResponse res) of GenericServlet. Within the service() method, we have created to context attributes named Name and Percent and have set them with the ServletContext object using the method setAttribute() method of ServletContext.

Next, by using the ServletContext object we have called its method getRequestDispatcher(String path) method to create an an object of RequestDispatcher.

If the pencentage of the user is less than 90, then by using the object of RequestDispatcher, we are going to call its method forward(ServletRequest req, ServletResponse res) to forward the current request and the context attributes from the current Servlet named FirstServlet to another Servlet named SecondServlet, as mentioned in the deployment descriptor file(web.xml)

If the Salary of the user is greater than 5000, then by using the object of RequestDispatcher, we are going to call its method forward(ServletRequest req, ServletResponse res) to forward the current request and context attributes from the current Servlet named FirstServlet to another Servlet named ThirdServlet, as mentioned in the deployment descriptor file(web.xml)

MyServlet1.java

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


public class MyServlet1 extends GenericServlet
{

public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException
{

//Creating ServletContext object
ServletContext servCon = getServletContext();

response.setContentType("text/html");
PrintWriter out = response.getWriter();

out.println("Using ServletContext object to set and read context attributes");


//Setting Request Attributes to be shared between multiple servlets
servCon.setAttribute("Name", request.getParameter("username"));
servCon.setAttribute("Percent", request.getParameter("percentile"));

if(new Integer(servCon.getAttribute("Percent")) <90)
{
RequestDispatcher reqDispatch = servCon.getRequestDispatcher("/SecondServlet");
reqDispatch.forward(request,response);
}
else
{
RequestDispatcher reqDispatch = servCon.getRequestDispatcher("/ThirdServlet");
reqDispatch.forward(request,response);
}

}
}

MyServlet2.java

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

public class MyServlet2 extends GenericServlet
{

public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException
{
ServletContext servCon = getServletContext();
response.setContentType("text/html");
PrintWriter out = response.getWriter();

out.println("<b>" + "Hello " + servCon.getAttribute("Name") + "," + "</b>");
out.println("<br/>");

out.println("<br/>");
out.println("<br/>");
out.println("<br/>");
out.println("<b>Sorry, you are not eligible to get a scholarship at our university </b>");
out.println("<b>, because your percentage of " + servCon.getAttribute("Salary") + " does not meet our criteria.<b>");

}
}

MyServlet3.java

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


public class MyServlet3 extends GenericServlet
{


public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException
{
ServletContext servCon = getServletContext();
response.setContentType("text/html");
PrintWriter out = response.getWriter();

out.println("<b>" + "Hello " + servCon.getAttribute("Name") + "," + "</b>");
out.println("<br/>");

out.println("<br/>");
out.println("<br/>");
out.println("<br/>");
out.println("<b>Congratulations, you are eligible to get a scholarship at our university, <b>");
out.println("<b> because your percentage of " + servCon.getAttribute("Salary") + " meets our criteria.</b>");

}
}

Directory Structure of Servlet files

Project Folder - We have created a project folder named ServletContextAttributesEx within the webapps folder of Tomcat installation folder. This folder contains the Servlet class(.java) file and WEB-INF folder.

WEB-INF - Within your project folder, you create another folder named WEB-INF and this folder should contain the deployment descriptor file(web.xml) of your Java Servlet program.

classes - Within the WEB-INF folder you should create a folder named classes. This folder should contain the compiled(.class) form of your Java Servlet class.

Creating the Deployment Descriptor file

XML

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
  version="4.0"
  metadata-complete="true">

  <display-name>Welcome tomcat</display-name>
  <description>
     Welcome tomcat
  </description>

<servlet>
 	<servlet-name>Servlet1</servlet-name>
	<servlet-class>MyServlet1</servlet-class>
</servlet>

<servlet>
 	<servlet-name>Servlet2</servlet-name>
	<servlet-class>MyServlet2</servlet-class>
</servlet>

<servlet>
 	<servlet-name>Servlet2</servlet-name>
	<servlet-class>MyServlet3</servlet-class>
</servlet>



<servlet-mapping>
	<servlet-name>Servlet1</servlet-name>
	<url-pattern>/FirstServlet</url-pattern>
</servlet-mapping>

<servlet-mapping>
	<servlet-name>Servlet2</servlet-name>
	<url-pattern>/SecondServlet</url-pattern>
</servlet-mapping>

<servlet-mapping>
	<servlet-name>Servlet2</servlet-name>
	<url-pattern>/ThirdServlet</url-pattern>
</servlet-mapping>


</web-app>

deployment descriptor

<servlet>

<servlet-name>

<servlet-class>

<servlet-name> tag is used to specify a unique name for our Servlet class.

<servlet-class> tag is used to specify the full qualified name of the Servlet class .

Note

<servlet-name>

<servlet>

<servlet-name>

<servlet-mapping>

<url-pattern>

URL

We have named this URL FirstServlet. to access the first servlet, MyServlet1.java
We have named this URL SecondServlet to access the second servlet, MyServlet2.java.
We have named this URL ThirdServlet to access the third servlet, MyServlet3.java.

Setting the classpath

classpath

servlet-api.jar

lib

Tomcat installation folder

C: Drive

lib

servlet-api.jar

C:\apache-tomcat-9.0.2\lib

You could set the classpath by entering this command at the Command Prompt, but this only temporarily sets the classpath to the path of servlet-api.jar file. If you restart your system, you will have to set the classpath again.
```
set classpath=C:\apache-tomcat-9.0.2\lib\servlet-api.jar
```
In order to set the classpath permanently, you need to set your classpath system variables. A simple tutorial on how to permanently set the classpath system variables, you may read How to permanently set the classpath system variable

Compiling the Servlet class

javac -d WEB-INF/classes MyServlet1.java

javac -d WEB-INF/classes MyServlet2.java

javac -d WEB-INF/classes MyServlet3.java

Executing the Servlet

name

percentage

FirstServlet

current request

context attribute

forward()

SecondServlet

context attributes

ThirdServlet

context attributes

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