A
Simple Servlet
To become familiar with the
key servlet concepts, we will begin by building and testing a simple servlet.
The basic steps are the following:
Create and compile the
servlet source code. Then, copy the servlet’s class file to the proper
directory, and add the servlet’s name and mappings to the proper web.xml file.
Start Tomcat.
Start a web browser and request the servlet.
Let us examine each of these
steps in detail.
Create
and Compile the Servlet Source Code
To begin, create a file named
HelloServlet.java that contains the
following program:
import java.io.*; import javax.servlet.*;
public class HelloServlet extends
GenericServlet {
public void service(ServletRequest request,
ServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html"); PrintWriter pw =
response.getWriter(); pw.println("<B>Hello!");
pw.close();
}
}
Let’s look closely at this
program. First, note that it imports the javax.servlet
package. This package contains the classes and interfaces required to build
servlets. You will learn more about these later in this chapter. Next, the
program defines HelloServlet as a
subclass of GenericServlet. The GenericServlet class provides
functionality that simplifies the creation of a servlet. For example, it provides
versions of init( ) and destroy( ), which may be used as is.
You need supply only the service( )
method.
Inside HelloServlet, the service( )
method (which is inherited from GenericServlet)
is overridden. This method handles requests from a client. Notice that the
first argument is a ServletRequest object.
This enables the servlet to read data that is provided via the client request. The second argument is a ServletResponse object. This enables
the servlet to formulate a response for the client.
The call to setContentType( ) establishes the MIME
type of the HTTP response. In this program, the MIME type is text/html. This
indicates that the browser should interpret the content as HTML source code.
Next, the getWriter( ) method obtains a PrintWriter. Anything written to this
stream is sent to the client as part of the HTTP response. Then println( ) is used to write some simple
HTML source code as the HTTP response.
Compile this source code and
place the HelloServlet.class file in
the proper Tomcat directory as described in the previous section. Also, add HelloServlet to the web.xml file, as described earlier.
Start
Tomcat
Start Tomcat as explained
earlier. Tomcat must be running before you try to execute a servlet.
Start
a Web Browser and Request the Servlet
Start a web browser and enter
the URL shown here:
http://localhost:8080/examples/servlets/servlet/HelloServlet
Alternatively, you may enter
the URL shown here:
http://127.0.0.1:8080/examples/servlets/servlet/HelloServlet
This can be done because 127.0.0.1
is defined as the IP address of the local machine.
You will observe the output
of the servlet in the browser display area. It will contain the string Hello! in bold type.
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