Servlet & JSP: A Tutorial, Second Edition [Book]
Date Snoop Error Page Session Carts 9. JSP Custom Tag JavaServer Pages (JSP) is a complimentary technology to Java Servlet which. JSP Tutorial for Beginners - Learn JSP (Java Server Pages) in simple and easy File Uploading, Handling Date, Page Redirect, Hits Counter, Auto Refresh. Writing the Date JSP What are the best books to learn JSP and Servlets and Hibernate as well as Online tutorials are available in stirim.info
The service methods takes two arguments: A PrintWriter object called out is used for writing out the response message to the client over the network. The generated servlet for "first. The relevant part of the generated servlet is extracted below: A JspWriter called out, corresponding to servlet's PrintWriter, is allocated to write the response message over the network to the client.
The Java codes in the JSP script are translated according to their respective types: Scriptlets form the program logic.
The Java expression is placed inside a out. In other words, the Java expression will be evaluated, and the result of the evaluation written out as part of the response message.
Subsequent accesses to the this JSP page will be much faster, because they will be re-directed to the translated and compiled servlet directly no JSP-to-servlet translation and servlet compilation needed againunless the JSP page has been modified.
It is often used to retrieve the query parameters in the request message. A Writer JspWriter object used to write response message to the client over the network socket, via methods print or println.
- Servlet and JSP: A Tutorial
- JSP Tutorial for Beginners: Learn in 7 Days
- Java Server-Side Programming
You can use session's attributes to pass information between pages within this session, via methods getAttribute "name" and setAttribute "name", object. A ServletContext object retrieved via getServletContextwhich maintains information about this web context web application.
You can use the application's attributes to pass information between JSP pages and servlets, via methods getAttribute "name" and setAttribute "name", object. A ServletConfig object, obtained via getServletConfig.
Servlet & JSP: A Tutorial, Second Edition
Can be used to access the elements of this page. Behind the Scene The translated servlet shows these seven variables are allocated and initialized as follows with re-arrangements: In a servlet, you need to use out.
Pieces of Java codes written by programmer are embedded into the HTML file to perform the business logic. The presentation and business logic can be cleanly separated. This example displays a form with checkboxes, and echos your selections. The default "action" is the current page i. The JSP scriptlet checks if the query parameter "author" exists. For the first request, "author" parameter is absent. Once the user fills in and submits the form, "author" will be present in the HTTP request.
The values are echoed back to the client in an unordered list. The Java expression will be placed inside a out. Hence, the expression will be evaluated and resultant value printed out as part of the response message. Any valid Java expression can be used. There is no semi-colon at the end of the expression. The Java codes must be syntactically correct, with Java statements terminated by a semi-colon.
That is, scriptlets are safe and secure! The syntax of the JSP directive is: These information will be written to the response message's header.
The default is "true". Setting to "false" could reduce the server's load, if session tracking is not needed in your application. You can use include directive to include navigation bar, copyright statement, logo, etc. You can use the taglib directive to tell Tomcat what libraries to load and where they are. A JSP action may contain sub-action. The client need to know the message type in order to correctly display the data received.
In Line 15, we retrieve a Writer object called out for writing the response message to the client over the network. We then use the out. This servlet also echoes some of the clients's request information, and prints a random number for each request.JSP and Servlets Tutorial : First Java Web Application In 25 Steps
Configure the Application Deployment Descriptor - "web. 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. In other words, the absolute URL for this servlet is http: 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: Deploying web application directory helloservlet Assume that Tomcat is running in port number Try selecting "View Source" in your browser, which produces these output: User does not receive the servlet's program codes, which are kept under a hidden directory "WEB-INF" and not directly accessible by web users.
Everything that can possibly go wrong will go wrong Read " Common Error Messages ". This allows web users to interact with the web server by submit data. Text field for single line only. Each of the input elements has an attribute "name", and an optional attribute "value". For example, suppose that we enter "Alan Smith" in the text field, select "male", and click the "SEND" button, we will get a " page not found" error because we have yet to write the processing script.
Relative URL is used in this example. Hence, the relative URL "echo" resolves into http: Some input elements such as checkboxes may trigger multiple parameter values, e.
HTTP provides two request methods: 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. Let us write a servlet called EchoServlet, which shall be mapped to the URL "echo", to process the incoming form data.
The servlet simply echoes the data back to the client. We can retrieve the query parameters from the request message captured in doGet 's argument HttpServletRequest request via one of the following methods: Take note that the parameter name is case sensitive.
If the parameter is present not nullwe 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. Any text string taken from the client and echoing back via out. 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. Fill up the form, click the submit button to trigger the servlet. Alternatively, you could issue a URL with query string. That is, gather the name-value pairs of the selected input elements, URL-encode, and pack them into a query string.
I recommend POST request for production, as it does not show the strange looking query string in the URL, even if the amount of data is limited. Since they often perform identical operations, we re-direct doPost to doGet or vice versaas follows: The request and response messages consists of two parts: HttpServletRequest provides many methods for you to retrieve the headers: Read " Request Header Example ".
HttpServletResponse The response message is encapsulated in the HttpServletResponse, which is passed into doGet by reference for receiving the servlet output. In other words, the current request does not know what has been done in the previous requests. This creates a problem for applications that runs over many requests, such as online shopping or shopping cart. You need to maintain a so-called session to pass data among the multiple requests.
You can maintain a session via one of these three approaches: 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.
JSP Tutorial for Beginners: Learn in 7 Days
Passes data by appending a short text string at the end of every URL, e. You need to rewrite all the URLs e. Hidden field in an HTML form: Again, you need to include the hidden field in all the pages. For detailed information, read " HTTP state and session management ". 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. To ensure robust session tracking, all the URLs emitted from the server-side programs should pass thru the method response.
If cookie is used for session tracking, encodeURL url returns the url unchanged. The session object maintains data in the form of key-value pairs. Any page within the session can retrieve the shopping cart: 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. Try refreshing the page. Try also closing and restart the browser, and issue the URL. Under Firefox, a cookie named jsessionid is created for this session.
The value of the cookie is the same as the return value of session. The session data are kept in the server, only a session ID is passed to the client. Try disabling the cookie, and use a the refresh button F5b refresh and clear cache Ctrl-F5c the refresh link, and d the refresh with URL re-writing, to refresh the page. It is passed as the argument in the init method. The init parameters are declared in the application-specific deployment descriptor "web. You can retrieve the init parameters via ServletConfig.
For example, suppose the application's "web. In Servlet API, this context is defined in javax. ServletContext interface a better name is probably WebappContext. A webapp may use many servlets. Servlets deployed in the same webapp can share information between them using the shared ServletContext object.