servlets sessions and cookies, jdbc connectivity
- 2. Introduction to Servlets • Servlet is a java program that runs inside JVM on the web server. It is used for developing dynamic web applications. • Dynamic web application?
- 3. • Servlet technology is robust and scalable because of java language. • Before Servlet, CGI (Common Gateway Interface) scripting language was common as a server-side programming language. However, there were many disadvantages to this technology.
- 4. What is a Servlet? • Servlet can be described in many ways, depending on the context. • Servlet is a technology which is used to create a web application. • Servlet is an API that provides many interfaces and classes including documentation. • Servlet is an interface that must be implemented for creating any Servlet. • Servlet is a class that extends the capabilities of the servers and responds to the incoming requests. It can respond to any requests. • Servlet is a web component that is deployed on the server to create a dynamic web page.
- 5. • Difference between static and dynamic web page ? • static page as name suggests remains same for all users however a dynamic web page changes based on the request from client (user’s browser). • What is a web application? • A web application is an application accessible from the web. A web application is composed of web components like Servlet, JSP, Filter, etc. and other elements such as HTML, CSS, and JavaScript. The web components typically execute in Web Server and respond to the HTTP request.
- 6. Common Gateway Interface (CGI) • The common gateway interface (CGI) is a standard way for a Web server to pass a Web user's request to an application program and to receive data back to forward to the user. • CGI technology enables the web server to call an external program and pass HTTP request information to the external program to process the request. For each request, it starts a new process.
- 7. • How Servlet is better than CGI • CGI has several limitations such as performance, scalability, reusability. • If number of clients increases, it takes more time for sending response. • For each request, it starts a process and Web server is limited to start processes. • It uses platform dependent language e.g. C, C++, perl.
- 8. Advantage of Servlet • The web container creates threads for handling the multiple requests to the servlet. • they share a common memory area and lightweight, cost of communication between the threads are low . • better performance: because it creates a thread for each request not process. • Portability: because it uses java language. • Robust: Servlets are managed by JVM so we don't need to worry about memory leak, garbage collection etc. • Secure: because it uses java language..
- 10. Life Cycle of a Servlet • 1. Servlet class is loaded. • 2. Servlet instance is created. • 3. init method is invoked. • 4. service method is invoked. • 5. destroy method is invoked.
- 11. • The init() method : •The init() method is called when the servlet is first requested by a browser. •It is not called again for each request. •Used for one-time initialization. •There are two versions of the init() method: • Version 1: takes no arguments • Version 2: takes a servletConfig object as an argument. •We will focus only on the first option. • public void init() throws ServletException { // Initialization code...
- 12. • The init() method is a good place to put any initialization variables. • For example, the following servlet records its Birth Date/time… import java.io.*; import java.util.*; import javax.servlet.*; import javax.servlet.http.*; public class Birth extends HttpServlet { Date birthDate; // Init() is called first public void init() throws ServletException { birthDate = new Date(); }
- 13. • The service() method : • The service() method checks the HTTP request type (GET, POST, PUT, DELETE, etc.) and calls doGet, doPost, doPut, doDelete, • Here is the signature of this method: • public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException { }
- 14. the signature of these two methods. • The doGet() Method public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // Servlet code The doPost() Method public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // Servlet code
- 15. Handle an HTTP GET Request public void doGet(HttpServletRequest request,HttpServletResponse response) throws IOException, ServletException { response.setContentType("text/plain"); PrintWriter out = response.getWriter(); out.println ("I was born on: "+birthDate); out.close();
- 16. • The destroy() method : • only once at the end of the life cycle of a servlet • close database connections, halt background threads, write cookie lists are cleanup . • After the destroy() method is called, the servlet object is marked for garbage collection public void destroy() { // Finalization code...
- 17. Architecture Diagram: • First the HTTP requests coming to the server are delegated to the servlet container. • The servlet container loads the servlet before invoking the service() method. • Then the servlet container handles multiple requests by spawning multiple threads, each thread executing the service() method of a single instance of the servlet.
- 18. Sample Code how a compiled servlet would be deployed in production. // Import required java libraries import java.io.*; import javax.servlet.*; import javax.servlet.http.*; // Extend HttpServlet class public class HelloWorld extends HttpServlet { private String message; public void init() throws ServletException { // Do required initialization message = "Hello World"; } public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // Set response content type response.setContentType("text/html"); // Actual logic goes here. PrintWriter out = response.getWriter(); out.println("<h1>" + message + "</h1>"); } public void destroy() { // do nothing. }}
- 19. Servlet Deployment By default, a servlet application is located at the path <Tomcat-installationdirectory>/webapps/ROOT and the class file would reside in <Tomcat-installationdirectory>/webapps/ROOT/WEB-INF/classes. If you have a fully qualified class name of com.myorg.MyServlet, then this servlet class must be located in WEB-INF/classes/com/myorg/MyServlet.class. For now, let us copy HelloWorld.class into <Tomcat-installationdirectory>/webapps/ROOT/WEB-INF/classes and create following entries in web.xml file located in <Tomcat-installation-directory>/webapps/ROOT/WEB-INF/
- 21. The Servlet API javax.servlet The javax.servlet package contains a number of classes and interfaces that describe and define the contracts between a servlet class and the runtime environment provided for an instance of such a class by a conforming servlet container. javax.servlet.http The javax.servlet.http package contains a number of classes and interfaces that describe and define the contracts between a servlet class running under the HTTP protocol and the runtime environment provided for an instance of such a class by a conforming servlet container.
- 22. Reading and Initialization Servlet parameters Interfaces in javax.servlet package Classes in javax.servlet package Interfaces in javax.servlet.http package Classes in javax.servlet.http package Servlet ServletRequest ServletResponse ServletConfig ServletContext GenericServlet ServletInputStream ServletOutputStream ServletException HttpServletRequest HttpServletResponse HttpSession HttpSessionListener HttpSessionBindingLis tener HttpServlet Cookie HttpSessionEvent HttpSessionBindingEv ent
- 23. Handling Http Request & Responses • The Client make the request to the web server using HTTP protocol. • There HttpServlet class in which there are some methods which can be used to handle HTTP requests. • doGet() • doPost()
- 24. Session Tracking using Servlets • In servlets,for creating the sessions getSession() method can be used. • This method returns the object which stores the bindings with the names that use this object. • These bindings can be managed using getAttribute(),setAttribute(),removieAttribute() methods.
- 25. • The Session tracking two things are playing an important roles. • One is HttpServletRequest interface which supports getSession() Method. • The another class is HttpSession class which supports the binding managing functions such as getAttribute(),setAttribute(),removieAttribute() and getAttributeNames().
- 26. Cookies in Servlet • A cookie is a small piece of information that is persisted between the multiple client requests. • A cookie has a name, a single value, and optional attributes such as a comment, path and domain qualifiers, a maximum age, and a version number.
- 27. How Cookie works • By default, each request is considered as a new request. • In cookies technique, we add cookie with response from the servlet. • So cookie is stored in the cache of the browser. • After that if request is sent by the user, cookie is added with request by default. Thus, we recognize the user as the old user.
- 28. Introduction to JDBC • Java Database Connectivity(JDBC) is an Application Programming Interface(API) used to connect Java application with Database. • JDBC is used to interact with various type of Database such as Oracle, MS Access, My SQL and SQL Server. • JDBC can also be defined as the platform-independent interface between a relational database and Java programming. It allows java program to execute SQL statement and retrieve result from database. • The JDBC API consists of classes and methods that are used to perform various operations like: connect, read, write and store data in the database.
- 29. How JDBC Works? • First of all java application establishes connection with the data source. • Then java application invokes classes and interfaces from jdbc drivers for sending queries to the data source. • The jdbc driver connects to corresponding database and retrives the result. • These results are based on SQL statements which are then returned to java application. • Java application then uses the retrieved information for further processing.
- 30. JDBC Driver • JDBC-ODBC bridge • Type-1 Driver act as a bridge between JDBC and other database connectivity mechanism(ODBC). This driver converts JDBC calls into ODBC calls and redirects the request to the ODBC driver. • Native API Driver • This type of driver make use of Java Native Interface(JNI) call on database specific native client API. These native client API are usually written in C and C++.
- 31. • Network Protocol Driver • This driver translate the JDBC calls into a database server independent and Middleware server-specific calls. Middleware server further translate JDBC calls into database specific calls. • Thin Driver • This is Driver called Pure Java Driver because. This driver interact directly with database. It does not require any native database library, that is why it is also known as Thin Driver.