Presentation on java servlets
- 1. Department of Computer Science Govt Post Graduate College Dargai Malakand Presenting By: Aamir SohailPresenting By: Aamir Sohail Subject: Advance OOP(Java)Subject: Advance OOP(Java) Java ServletsJava Servlets
- 2. Page 2 What are the java servlets? OR Servlets are java-based server side programs Java Servlets are programs that run on a Web server and act as a middle layer between a requests coming from a Web browser or other HTTP client and databases or applications on the HTTP server. ??
- 3. Page 3 Server…Server… A server is a computer that responds to requests from a client. Typical requests: provide a web page, upload or download a file, send email. A client could be the browser or other software making these requests Typically, My little computer is the client, and someone else’s big computer is the server
- 4. Page 4 Servlets… Servlets are java-based server side programs Servlets are Java technology’s answer to Common Gateway Interface (CGI) programming. They are programs that run on a Web server, acting as a middle layer between a request coming from a Web browser or other HTTP client and databases or applications on the HTTP server.
- 5. Page 5 Servlets…Servlets… Using Servlets, you can collect input from users through web page forms, present records from a database or another source, and create web pages dynamically. Java Servlets often serve the same purpose as programs implemented using the Common Gateway Interface (CGI). If we have this Why we need Servlets????
- 6. Page 6 let me explain
- 7. Page 7 CGI… CGI stands for “Common Gateway Interface” Client sends a request to server Server starts a CGI script Script computes a result for server Another client sends a request CGI Creates a new procces Server returns response to client
- 8. Page 8 Servlets…Servlets… Client sends a request to server Server starts a servlet Servlet computes a result for server and does not quit Another client sends a request Server calls the servlet again Etc. Server returns response to client
- 9. Page 9 Servlets vs. CGI scripts Advantages: Running a servlet doesn’t require creating a separate process each time A servlet stays in memory, so it doesn’t have to be reloaded each time There is only one instance handling multiple requests, not a separate instance for every request
- 10. Page 10 The Advantages of Servlets Over “Traditional” CGI Java servlets are more efficient, easier to use, more powerful, more portable, safer, and cheaper than traditional CGI and many alternative CGI-like technologies
- 11. Page 11 With traditional CGI, a new process is started for each HTTP request. If the CGI program itself is relatively short, the overhead of starting the process can dominate the execution time. With servlets, the Java virtual machine stays running and handles each request with a lightweight Java thread, not a heavyweight operating system process
- 12. Page 12 Similarly, in traditional CGI, if there are N requests to the same CGI program, the code for the CGI program is loaded into memory N times. With servlets, however, there would be N threads, but only a single copy of the servlet class would be loaded. This approach reduces server memory requirements and saves time by instantiating fewer objects
- 13. Page 13 The Servlet Life Cycle In Slide 10 and 11 (The Advantages of Servlets Over “Traditional” CGI), I referred to the fact that only a single instance of a servlet gets created, with each user request resulting in a new thread that is handed off to doGet or doPost as appropriate. I’ll now explain how servlets are created and destroyed, and how and when the various methods are invoked. I give a quick summary here, then elaborate in the following subsections.
- 14. Page 14 After this, each user request results in a thread that calls the service method of the previously created instance. Multiple concurrent requests normally result in multiple threads calling service The service method then calls doGet, doPost, or another method, depending on the type of HTTP request it received. When the servlet is first created, its init method is invoked, so init is where you put one-time setup code.
- 15. Page 15 Finally, when the server decides to unload a servlet, it first calls the servlet’s destroy method.
- 16. Page 16 The init Method… The init method is called when the servlet is first created; it is not called again for each user request. So, it is used for one-time initializations. The servlet is normally created when a user first invokes a URL corresponding to the servlet, but you can also specify that the servlet be loaded when the server is first started
- 17. Page 17 The service Method Each time the server receives a request for a servlet, the server spawns a new thread and calls service. The service method checks the HTTP request type (GET, POST, PUT, DELETE, etc.) and calls doGet, doPost, doPut, doDelete, etc
- 18. Page 18 Destroy Method Called when server deletes servletinstance. Not called after each request
- 19. Page 19 how to create servletshow to create servlets (Basic Structure)(Basic Structure)
- 20. Page 20 In the above program a basic servlet that handles GET requests. GET requests, for those unfamiliar with HTTP, are the usual type of browser requests for Web pages. A browser generates this request when the user enters a URL on the address line, follows a link from a Web page, or submits an HTML form that either does not specify a METHOD or specifies METHOD="GET".
- 21. Page 21 Servlets can also easily handle POST requests, which are generated when someone submits an HTML form that specifies METHOD="POST".
- 22. Page 22 Advantages of Servlets over other server side technologies (ASP, CGI etc) A servlet can be imagined to be as an applet running on the server side. Some of the other server side technologies available are Common Gateway Interface (CGI), server side JavaScript and Active Server Pages (ASP). Advantages of servlets over these server side technologies are as follows:
- 23. Page 23 Persistent Servlets remain in memory until explicitly destroyed. This helps in serving several incoming requests. Servlets establishes connection only once with the database and can handle several requests on the same database. This reduces the time and resources required to establish connection again and again with the same database. Whereas, CGI programs are removed from the memory once the request is processed and each time a new process is initiated whenever new request arrives.
- 24. Page 24 Portable Since servlets are written in Java, they are portable. That is, servlets are compatible with almost all operating systems. The programs written on one operating system can be executed on other operating system
- 25. Page 25 Server-independent Servlets are compatible with any web server available today. Most of the software vendors today support servlets within their web server products. On the other hand, some of the server side technologies like server side JavaSricpt and ASP can run on only selected web servers. The CGI is compatible with the web server that has features to supports it.
- 26. Page 26 Fast Since servlets are compiled into bytecodes, they can execute more quickly as compared to other scripting languages. The bytecode compilation feature helps servlets to give much better performance. In addition, it also provides advantage of strong error and type checking.
- 27. Page 27 How to run servlet? There are Six Steps to Running Your First Servlet Create a directory structure under Tomcat for your application. Write the servlet source code. You need to import the javax.servlet package and the javax.servlet.http package in your source file. Compile your source code. Create a deployment descriptor. Run Tomcat. Call your servlet from a web browser.
- 28. Page 28 Create a Directory Structure under Tomcat When you install Tomcat, several subdirectories are automatically created under the Tomcat home directory (%TOMCAT_HOME%). One of the subdirectories is webapps. The webapps directory is where you store your web applications. A web application is a collection of servlets and other contents installed under a specific subset of the server's URL namespace. A separate directory is dedicated for each servlet application. Therefore, the first thing to do when you build a servlet application is create an application directory
- 29. Page 29 Compile Your Source Code For your servlet source code to compile, you need to include in your CLASSPATH environment variable the path to the servlet.jar file. The servlet. jar is located in the commonlib subdirectory under %CATALINA_HOME%.
- 30. 30 Thank You !!! References: Wikipedi.org Videos on youtube Askme.com And some PDF files about Java Servlets.