Writing small servlet program

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Data Science. Angular 7. Machine Learning. Data Structures. Operating System. Computer Network. Compiler Design. Computer Organization. Discrete Mathematics. Ethical Hacking. Therefore, you must hide your JSP files in a place where the user can not access. When the user requests to a Servlet, it will dispose user's requirements, such insert, update and query the data, eventually forward to the JSP page to display the data.

Thus, each servlet has 0 or multiple corresponding JSP pages Usually only need 1. JSP is only considered as the place to display data, which means that you should not handle the application logic on the JSP, such as update, insert, delete,.. You need to run scripts to create some tables and necessary data for this example. The application needs to run on a WebServer, such as Tomcat Server , you can refer to download and declaration instructions of Server Tomcat in Eclipse at:.

Install Tomcat Server for Eclipse. Right-click the SimpleWebApp select Properties. OK, here everything is fine. It provides the configuration options for that particular web application, such as defining the the mapping between URL and servlet class. The above configuration defines a servlet named " HelloWroldServlet ", implemented in " mypkg. Run the Hello-world Servlet To run the servlet, first start the Tomcat server. Verify that the web context " helloservlet " has been deployed by observing the following messages in the Tomcat's console: xxx x, xxxx xx:xx:xx xx org.

Text field for single line only. Each of the input elements has an attribute " name ", and an optional attribute " value ". Relative URL is used in this example. Some input elements such as checkboxes may trigger multiple parameter values, e. For POST request, the query string are sent in the request message's body.

POST request is often preferred, as users will not see the strange string in the URL and it can send an unlimited amount of data. In this tutorial, we use the GET request, so that you can inspect the query string. We can retrieve the query parameters from the request message captured in doGet 's argument HttpServletRequest request via one of the following methods: request. Enumeration, possibly empty. Take note that the parameter name is case sensitive. We use request. If the parameter is present not null , we trim the returned string to remove the leading and trailing white spaces.

This step is necessary to prevent the so-called command-injection attack , where user enters a script into the text field. The replacement is done via a static helper method htmlFilter. If the parameter could possess multiple values e. One of the nice features of Java servlet is that all the form data decoding i. Configure the Servlet URL mapping in " web. HttpServletRequest provides many methods for you to retrieve the headers: General methods: getHeader name , getHeaders name , getHeaderNames.

HttpServletResponse The response message is encapsulated in the HttpServletResponse , which is passed into doGet by reference for receiving the servlet output.

You can maintain a session via one of these three approaches: Cookie: A cookie is a small text file that is stored in the client's machine, which will be send to the server on each request.

You can put your session data inside the cookie. The biggest problem in using cookie is clients may disable the cookie. You need to rewrite all the URLs e. Again, you need to include the hidden field in all the pages. HttpSession Programming your own session tracking using the above approaches is tedious and cumbersome. It allows servlets to: View and manipulate information about a session, such as the session identifier, creation time, and last accessed time.

Bind objects to sessions, allowing user information to persist across multiple user requests. The procedure is as follows: Check if a session already exists.

If so, use the existing session object; otherwise, create a new session object. Each session is identified via a session ID. You can use session. HttpSession , by default, uses cookie to pass the session ID in all the client's requests within a session. The session object maintains data in the form of key-value pairs. You can use set setMaxInactiveInterval and getMaxInactiveInterval to set and get the inactive interval from the last client request, before the server invalidate the session.

Example The following servlet demonstrates the use of session, by counting the number of accesses within this session from a particular client. Create a new session otherwise. Loading and Initialization Servlet container e. String getInitParameter String name java.

In Service Once a servlet is initialized, the servlet container invokes its service method to handle client requests. End of Service When the servlet container decides that a servlet should be removed from the container e. Interface ServletContext The ServletContext interface defines a servlet's view of the webapp or web context in which it is running a better name is actually ApplicationContext.

Enumeration getInitParameterNames A servlet can bind an attribute of name-value pair into the ServletContext , which will then be available to other servlet in the same web application.

URL getResource String path java. InputStream getResourceAsStream String path Dispatch Request - RequestDispatcher When building a web application, it is often useful to forward a request to another servlet, or to include the output of another servlet in the response.

A Sample " web. Servlet Initialization Parameters You can pass initialization parameters in the form of name-value pairs into a particular servlet from " web. Welcome Page Specifies the page to be displayed for request to web context root. String[] value : urlPatterns. String name : servlet-name , default is empty string "". String smallIcon , String largeIcon , String description : icon and description of the servlet. Last Updated : 13 Jan, Attention reader!

Get hold of all the important Java Foundation and Collections concepts with the Fundamentals of Java and Java Collections Course at a student-friendly price and become industry ready. Recommended Articles. Article Contributed By :. Kartik Thakral.