SERVLETS TUTORIAL PDF BEGINNERS
SERVLET BASICS. Topics in This Chapter. • The basic structure of servlets. • A simple servlet that generates plain text. • A servlet that generates HTML. Java, JSF 2, PrimeFaces, Servlets, JSP, Ajax, jQuery, Spring, Hibernate, RESTful Web Servlets and JSP, and this tutorial. The basic structure of servlets. What are Servlets? Designed to provide dynamic functionality to any internet server service. HTTP servers. SMTP servers. FTP servers. Opposite of Applets.
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This tutorial will teach you how to use Java Servlets to develop your web great if you have a basic understanding of web application and how internet works. Servlets Tutorial for Beginners - Learning Java Servlets in simple and easy steps Servlets Tutorial. Previous Page · Next Page. Servlets Tutorial. PDF Version. Check out our Java Servlet Tutorial where we explain the concepts Besides studying them online you may download the eBook in PDF format! .. This is the initial and basic interface which all filter class should implement.
Servlet technology is used to create a web application resides at server side and generates a dynamic web page. Servlet technology is robust and scalable because of java language. However, there were many disadvantages to this technology. We have discussed these disadvantages below. A web application is an application accessible from the web.
The RequestDispatcher can be obtained via ServletContext:. Once the servlet obtained a RequestDispatcher of another servlet within the same web application, it could include or forward the request to that servlet, e. A filter is a reusable piece of code that can transform the content of HTTP requests, responses, and header information. Examples of filtering components are:. The " web. Tomcat's has a system-wide global " web. Each web application has its own " web.
Tomcat monitors web. The resultant URL is http: You can pass initialization parameters in the form of name-value pairs into a particular servlet from " web. Inside the servlet, you can retrieve the init parameters via the ServletConfig object:. You can use the getInitParameter method of ServletContext object to retrieve the init parameters.
Use the getInitParameter method of ServletContext object to retrieve the init parameters. Servlet API 3. The above is equivalent to the following configuration in " web. The web application deployment descriptor " web. WebServlet defines a servlet component and its metadata, with the following attributes:. WebInitParam is Used to declare init params in servlet, with the following attributes:.
WebFilter defines a filter which implements javax. Filter interface. Read " Uploading Files in Servlet 3. Introduction In the early days, web servers deliver static contents that are indifferent to users' requests. Server-Side Technologies There are many competing server-side technologies available: Java Servlet Versions Java Servlet has these versions: First "Hello-world" Servlet Let us begin by writing a servlet that says hello in response to a client's request.
Create a new Webapp " helloservlet " We shall begin by defining a new webapp web application called " helloservlet " in Tomcat.
The resources must be kept in the respective directories: This directory is known as context root for the web context " helloservlet ". These resources will be delivered to the clients as it is. You could create sub-directories such as images , css and scripts , to further categories the resources.
This directory is NOT accessible by the clients directly. This is where you keep your application-specific configuration files such as " web. Keep the Java program source files.
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It is a good practice to separate the source files and classes to facilitate deployment. Keep the Java classes compiled from the source codes.
Classes defined in packages must be kept according to the package directory structure. This directory is also NOT accessible by the clients.
It keeps resources and configurations e. We define a Java class called HelloServlet in Line 8. Line 2 places this class in a package called mypkg.
We need the Servlet API library to compile this program. Tomcat provides a copy of servlet API called "servlet-api. You could copy "servlet-api. The compiler creates the package directory " mypkg " automatically.
We don't write a servlet from scratch. Instead, we create a servlet by sub-classing javax. HttpServlet in Line 8. As mentioned, a servlet is invoked in response to a request URL issued by a client.
Specifically, a client issues an HTTP request, the server routes the request message to the servlet for processing. The servlet returns a response message to the client. In the HelloServlet , we override the doGet method as denoted by the annotation Override. 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.
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We then use the out. This servlet also echoes some of the clients's request information, and prints a random number for each request. 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 Try selecting "View Source" in your browser, which produces these output: Text field for single line only.
Each of the input elements has an attribute " name ", and an optional attribute " value ". Observe that: The URL http: 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. We can retrieve the query parameters from the request message captured in doGet 's argument HttpServletRequest request via one of the following methods: 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. 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. Form-Data Submission Methods: Since they often perform identical operations, we re-direct doPost to doGet or vice versa , as follows: HttpServletRequest provides many methods for you to retrieve the headers: General methods: Specific methods: URL related: 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: 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. URL Rewriting: 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. 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.
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. The Servlet interface declares these abstract methods: 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.
The methods available are: 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. The RequestDispatcher can be obtained via ServletContext: Examples of filtering components are: 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.
Define a servlet component WebInitParam: Define initialization parameters for a servlet WebListener: Define a listener WebFilter: Define a filter MultipartConfig: String urlPatterns: An array of String declaring the url-pattern for servlet-mapping.
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