Java Servlets

Java Servlets

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  AN OVERVIEW OFSERVLET TECHNOLOGY SERVER SETUP AND CONFIGURATION WEB APPLICATION STRUCTURE BASIC SERVLET EXAMPLE Java Servlets Java Servlets - Compiled By Nitin Pai
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  Servlet basics Servletsare the Java technology for serving HTTP requests. They are particularly used for serving HTTP requests, but they can be used as a basis for serving other requests, too. Basic servlet functionalities implemented by the basic HTTP servlet classes have the features for accessing HTTP request data and managing cookies and sessions. Typically some other technology is used for user interface or representation part. Basic servlets are not that handy for representation matters. Java Servlets - Compiled By Nitin Pai
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  Servlet info Servletsare intialized (at this moment you may want to initialize some data common etc.) Servlets serve the Service requests Finally, servlets are either destroyed by the container or are terminated due to exceptions. Java Servlets - Compiled By Nitin Pai
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  Important To Knowjavax.servlet.Servlet Interface defining methods that all servlets implement javax.servlet.GenericServlet An abstract class for all Servlets javax.servlet.HttpServlet An abstract class for servlets serving HTTP requests. Most importantly, a Http servlet needs to implement the doPost() and doGet() methods, which are called when a post or get request is received. This is the basis for getting started with the implementation http servlets. Java Servlets - Compiled By Nitin Pai
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  Apache Tomcat Servletspecification is a standard. To execute servlets, one needs software to implement a standard. Jakarta tomcat of the Apache project is one implementation. For us, it is much easier and much more practical to study servlets using some environment to execute them. For running Tomcat you need to have: JDK installed and the JAVA_HOME environment variable set CATALINA_HOME set to the tomcat installation directory Java Servlets - Compiled By Nitin Pai
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  Servers and IDE’sTomcat is a servlet container used for hosting JSP/Servlets Basic installation is easy Tomcat port (the port that tomcat listens) can be configured, by default it is 8080 Once tomcat is up and running, you may build and install applications. Eclipse and NetBeans are the most commonly used IDE’s used today. Eclipse is available as a zip archive and has a pluggable architecture Java Servlets - Compiled By Nitin Pai
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  Development & DeploymentStructures Deployment is configured in build.xml and built through Ant Application root: build.xml Configures the application properties and how to build/install/remove it. src subdirectory: application sources web subdirectory: web contents (web documentroot) html files, jsp files (more on these later), WEB-INF subdirectory contains web configuration (see examples) build subdirectory: This is where deployment will build the application (the contents are not supplied by the developer, the installation will normally create these files). Again, see examples. Java Servlets - Compiled By Nitin Pai
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  Tomcat application installation(deployment) There are many ways for web application deployment Using the Tomcat manager For this, use a war file (a jar file with a name ending in .war). Using the tomcat web manager, upload the war file. There is password authentication here and you need a Tomcat username/password with rights to install applications. Upload the file with managers html interface. Tomcat will unpack the war file and install the application as it is configured in the configuration files. ant installation using the xml file that specifies the installation build.xml specifies the ant operations Ant is in a sense similar to the Make facility on Linux. Java Servlets - Compiled By Nitin Pai
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  Java Servlet WebApplication Servlet development (learning) life cycle Development Defining servlet classes, methods and properties Deployment Servlet mapping to web environment (Deployment on Tomcat) Execution Understand its execution life cycle Java Servlets - Compiled By Nitin Pai
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  Basic Servlet Structurepublic class HelloWorld extends javax.servlet.http. HttpServlet { public void doGet ( javax.servlet.http. HttpServletRequest request, javax.servlet.http. HttpServletResponse response ) throws javax.servlet. ServletException , java.io.IOException { … } public void doPost ( javax.servlet.http. HttpServletRequest request, javax.servlet.http. HttpServletResponse response ) throws javax.servlet. ServletException , java.io.IOException { … } } Java Servlets - Compiled By Nitin Pai
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  Constructor and “Main”Method Servlet instances are created (invoked) by servlet container automatically when requested – not by user classes or methods No need to define constructor The entry point is NOT the “main” method, but the two methods Use “doGet” or “doPost” to perform tasks Java Servlets - Compiled By Nitin Pai
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  Servlet Deployment SampleWeb content root folder (public_html) The starting point of the whole web application All files and sub-directories goes here: html, images, documents … /public_html/WEB-INF/ This folder contains configuration files and compiled class Not directly accessible through the web /public_html/WEB-INF/classes/ All compiled classes (servlet classes and other classes) are in this folder Java Servlets - Compiled By Nitin Pai
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  Servlet Mapping Servletclass needs to be mapped to an accessible URI (mainly through HTTP) For convenience, a servlet can be accessed in a general pattern ( invoker servlet ) http://[domain]/[context]/servlet/[ServletClassName] http://localhost:8080/servletintro/servlet/SimpleServlet Specific mapping: using the configuration file “web.xml” A servlet is specifically mapped to a user defined URL Java Servlets - Compiled By Nitin Pai
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  “ web.xml” ConfigurationUsing the file “web.xml” for more specific mapping The file is in the “WEB-INF” folder Example Servlet class HelloWorld.class Application context: http://localhost:8988/servletintro/ Invoker class mapping http://localhost:8988/servletintro/servlet/HelloWorld Specific mapping http://localhost:8988/servletintro/hello For more mapping examples, see example “web.xml” Java Servlets - Compiled By Nitin Pai <servlet> <servlet-name>HelloW</servlet-name> <servlet-class>HelloWorld</servlet-class> </servlet> <servlet-mapping> <servlet-name>HelloW</servlet-name> <url-pattern>hello</url-pattern> </servlet-mapping>
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  Tomorrow: Request &Response Java Servlets - Compiled By Nitin Pai Assignment Install Tomcat and run it at localhost:8080 Create a new Web Project “Training Project” in Eclipse Make a new Servlet com.training.web.LoginFormServlet Map the servlet to http://localhost:8080/training/Login.do Create a war file and upload it to Tomcat using Eclipse and Tomcat Manager