Java Web Programming [2/9] : Servlet Basic

Module 2: Servlet Basics Thanisa Kruawaisayawan Thanachart Numnonda www.imcinstitute.com

Objectives What is Servlet? Request and Response Model Method GET and POST Servlet API Specifications The Servlet Life Cycle Examples of Servlet Programs 2

What is a Servlet? 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

Servlet vs. CGIServlet 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

Servlet vs. CGI (cont.)Request CGI1 Child for CGI1Request CGI2 CGI Based Child for CGI2 WebserverRequest CGI1 Child for CGI1Request Servlet1 Servlet Based WebserverRequest Servlet2 Servlet1 JVMRequest Servlet1 Servlet2 5

Single Instance of Servlet 6

Servlet Request and Response Model Servlet Container Request Browser HTTP Request Servlet Response Web Response Server 7

What does Servlet Do? 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

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

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

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

HttpRequestInfo.javapublic class HttpRequestInfo extends 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

Reading Request Header General  getHeader  getHeaders  getHeaderNames Specialized  getCookies  getAuthType and getRemoteUser  getContentLength  getContentType  getDateHeader  getIntHeader 13

Frequently Used Request Methods HttpServletRequest methods  getParameter() returns value of named parameter  getParameterValues() if more than one value  getParameterNames() for names of parameters 14

Example: hello.html<HTML> : <BODY> <form action="HelloNameServlet"> Name: <input type="text" name="username" /> <input type="submit" value="submit" /> </form> </BODY></HTML> 15

HelloNameServlet.javapublic class HelloNameServlet extends 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

Result 17

HTTP GET and POST 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

TestServlet.javaimport javax.servlet.*;import javax.servlet.http.*;import java.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

Steps of Populating HTTP Response Fill Response headers Get an output stream object from the response Write body content to the output stream 20

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

Servlet API Specificationshttp://tomcat.apache.org/tomcat-7.0-doc/servletapi/index.html 22

Servlet Interfaces & Classes Servlet GenericServlet HttpSession HttpServletServletRequest ServletResponseHttpServletRequest HttpServletResponse 23

CounterServlet.java::public class CounterServlet extends 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

Servlet Life-Cycle Is Servlet Loaded? Http request Load Invoke No Http response Yes Run Servlet Servlet ContainerClient Server 25

Servlet Life Cycle Methods service( ) init( ) destroy( ) ReadyInit parameters doGet( ) doPost( ) Request parameters 26

The Servlet Life Cycle 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

doGet() and doPost() Methods Server HttpServlet subclass doGet( )Request Service( )Response doPost( ) Key: Implemented by subclass 28

Servlet Life Cycle Methods 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

Implementation in method service()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 }

Username and Password Example 31

AcknowledgementSome contents are borrowed from thepresentation slides of Sang Shin, Java™Technology Evangelist, Sun Microsystems,Inc. 32

Thank you [email protected]/imcinstitute www.imcinstitute.com 33

Java Web Programming [2/9] : Servlet Basic

by IMC Institute on Jan 06, 2013

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Java Web Programming [2/9] : Servlet Basic Presentation Transcript