Java Web Programming [2/9] : Servlet Basic

Java Web Programming [2/9] : Servlet Basic

• 1.
  Module 2: ServletBasics Thanisa Kruawaisayawan Thanachart Numnonda www.imcinstitute.com
• 2.
  Objectives  What isServlet?  Request and Response Model  Method GET and POST  Servlet API Specifications  The Servlet Life Cycle  Examples of Servlet Programs 2
• 3.
  What is aServlet?  Java™ objects which extend the functionality of a HTTP server  Dynamic contents generation  Better alternative to CGI  Efficient  Platform and server independent  Session management  Java-based 3
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  Servlet vs. CGI Servlet CGI  Requests are handled by  New process is created threads. for each request  Only a single instance (overhead & low will answer all requests scalability) for the same servlet  No built-in support for concurrently (persistent sessions data) 4
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  Servlet vs. CGI(cont.) Request CGI1 Child for CGI1 Request CGI2 CGI Based Child for CGI2 Webserver Request CGI1 Child for CGI1 Request Servlet1 Servlet Based Webserver Request Servlet2 Servlet1 JVM Request Servlet1 Servlet2 5
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  Single Instance ofServlet 6
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  Servlet Request andResponse Model Servlet Container Request Browser HTTP Request Servlet Response Web Response Server 7
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  What does ServletDo?  Receives client request (mostly in the form of HTTP request)  Extract some information from the request  Do content generation or business logic process (possibly by accessing database, invoking EJBs, etc)  Create and send response to client (mostly in the form of HTTP response) or forward the request to another servlet or JSP page 8
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  Requests and Responses  What is a request?  Informationthat is sent from client to a server  Who made the request  Which HTTP headers are sent  What user-entered data is sent  What is a response?  Information that is sent to client from a server  Text(html, plain) or binary(image) data  HTTP headers, cookies, etc 9
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  HTTP  HTTP request contains  Header  Method  Get: Input form data is passed as part of URL  Post: Input form data is passed within message body  Put  Header  request data 10
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  Request Methods  getRemoteAddr()  IP address of the client machine sending this request  getRemotePort()  Returns the port number used to sent this request  getProtocol()  Returns the protocol and version for the request as a string of the form <protocol>/<major version>.<minor version>  getServerName()  Name of the host server that received this request  getServerPort()  Returns the port number used to receive this request 11
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  HttpRequestInfo.java public class HttpRequestInfoextends HttpServlet {{ public class HttpRequestInfo extends HttpServlet :: protected void doGet(HttpServletRequest request, protected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {{ HttpServletResponse response)throws ServletException, IOException response.setContentType("text/html"); response.setContentType("text/html"); PrintWriter out == response.getWriter(); PrintWriter out response.getWriter(); out.println("ClientAddress: "" ++ request.getRemoteAddr() ++ out.println("ClientAddress: request.getRemoteAddr() "<BR>"); "<BR>"); out.println("ClientPort: "" ++ request.getRemotePort() ++ "<BR>"); out.println("ClientPort: request.getRemotePort() "<BR>"); out.println("Protocol: "" ++ request.getProtocol() ++ "<BR>"); out.println("Protocol: request.getProtocol() "<BR>"); out.println("ServerName: "" ++ request.getServerName() ++ "<BR>"); out.println("ServerName: request.getServerName() "<BR>"); out.println("ServerPort: "" ++ request.getServerPort() ++ "<BR>"); out.println("ServerPort: request.getServerPort() "<BR>"); out.close(); out.close(); }} :: }} 12
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  Reading Request Header  General  getHeader  getHeaders  getHeaderNames  Specialized  getCookies  getAuthType and getRemoteUser  getContentLength  getContentType  getDateHeader  getIntHeader 13
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  Frequently Used RequestMethods  HttpServletRequest methods  getParameter() returns value of named parameter  getParameterValues() if more than one value  getParameterNames() for names of parameters 14
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  Example: hello.html <HTML> : <BODY> <form action="HelloNameServlet"> Name: <input type="text" name="username" /> <input type="submit" value="submit" /> </form> </BODY> </HTML> 15
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  HelloNameServlet.java public class HelloNameServletextends HttpServlet {{ public class HelloNameServlet extends HttpServlet :: protected void doGet(HttpServletRequest request, protected void doGet(HttpServletRequest request, HttpServletResponse response) HttpServletResponse response) throws ServletException, IOException {{ throws ServletException, IOException response.setContentType("text/html"); response.setContentType("text/html"); PrintWriter out == response.getWriter(); PrintWriter out response.getWriter(); out.println("Hello "" ++ request.getParameter("username")); out.println("Hello request.getParameter("username")); out.close(); out.close(); }} :: }} 16
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  Result 17
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  HTTP GET andPOST  The most common client requests  HTTP GET & HTTP POST  GET requests:  User entered information is appended to the URL in a query string  Can only send limited amount of data  .../chap2/HelloNameServlet?username=Thanisa  POST requests:  User entered information is sent as data (not appended to URL)  Can send any amount of data 18
• 19.
  TestServlet.java import javax.servlet.*; import javax.servlet.http.*; importjava.io.*; public class TestServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); out.println("<h2>Get Method</h2>"); } } 19
• 20.
  Steps of PopulatingHTTP Response  Fill Response headers  Get an output stream object from the response  Write body content to the output stream 20
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  Example: Simple Response Public class HelloServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // Fill response headers response.setContentType("text/html"); // Get an output stream object from the response PrintWriter out = response.getWriter(); // Write body content to output stream out.println("<h2>Get Method</h2>"); } } 21
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  Servlet API Specifications http://tomcat.apache.org/tomcat-7.0-doc/servletapi/index.html 22
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  Servlet Interfaces &Classes Servlet GenericServlet HttpSession HttpServlet ServletRequest ServletResponse HttpServletRequest HttpServletResponse 23
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  CounterServlet.java :: public class CounterServletextends HttpServlet {{ public class CounterServlet extends HttpServlet private int count; private int count; :: protected void doGet(HttpServletRequest request, protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {{ HttpServletResponse response) throws ServletException, IOException response.setContentType("text/html"); response.setContentType("text/html"); PrintWriter out == response.getWriter(); PrintWriter out response.getWriter(); count++; count++; out.println("Count == "" ++ count); out.println("Count count); out.close(); out.close(); }} :: }} 24
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  Servlet Life-Cycle Is Servlet Loaded? Http request Load Invoke No Http response Yes Run Servlet Servlet Container Client Server 25
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  Servlet Life CycleMethods service( ) init( ) destroy( ) Ready Init parameters doGet( ) doPost( ) Request parameters 26
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  The Servlet LifeCycle  init  executed once when the servlet is first loaded  Not call for each request  Perform any set-up in this method  Setting up a database connection  destroy  calledwhen server delete servlet instance  Not call after each request  Perform any clean-up  Closing a previously created database connection 27
• 28.
  doGet() and doPost()Methods Server HttpServlet subclass doGet( ) Request Service( ) Response doPost( ) Key: Implemented by subclass 28
• 29.
  Servlet Life CycleMethods  Invoked by container  Container controls life cycle of a servlet  Defined in  javax.servlet.GenericServlet class or  init()  destroy()  service() - this is an abstract method  javax.servlet.http.HttpServlet class  doGet(), doPost(), doXxx()  service() - implementation 29
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  Implementation in methodservice() protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String method = req.getMethod(); if (method.equals(METHOD_GET)) { ... doGet(req, resp); ... } else if (method.equals(METHOD_HEAD)) { ... doHead(req, resp); // will be forwarded to doGet(req, resp) } else if (method.equals(METHOD_POST)) { doPost(req, resp); } else if (method.equals(METHOD_PUT)) { doPut(req, resp); } else if (method.equals(METHOD_DELETE)) { doDelete(req, resp); } else if (method.equals(METHOD_OPTIONS)) { doOptions(req,resp); } else if (method.equals(METHOD_TRACE)) { doTrace(req,resp); } else { ... } 30 }
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  Username and PasswordExample 31
• 32.
  Acknowledgement Some contents areborrowed from the presentation slides of Sang Shin, Java™ Technology Evangelist, Sun Microsystems, Inc. 32
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  Thank you [email protected] www.facebook.com/imcinstitute www.imcinstitute.com 33