Outline. Servlets. JSPs. Basic Taglibs. SOEN 387 Web-based Enterprise Application Design. Stuart Thiel. Servlets. JSPs. Expression Language (EL)

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1 /22 Concordia University Department of Computer & Software Engineering Fall, 2015

2 2/22 Outline

3 3/22 What Does A Servlet Look Like File-wise? appdev/deployment.html *.html, *.jsp, etc. /WEB-INF/web.xml /WEB-INF/classes/ /WEB-INF/lib/

4 4/22 Some Suggestions for le-size? appdev/source.html web/ webapp document root under which you nd WEB-INF, etc src/ keeps the source for your webapp nearby docs/ keep any documentation nearby Put src/docs in SVN (repo)! Put document root, save classes in SVN!

5 5/22 How to access I put where they cannot be directly accessed inside WEB-INF/JSP We'll talk about why this can be useful

6 6/22 A Look at Servlet API servletapi/ GenericServlet destroy() : void getinitparameter(string:name) : String getinitparameternames() : Enumeration <String> getservletcong() : ServletCong getservletcontext() : ServletContext getservletinfo() : String getservletname() : String init() : void init(servletcong:cong) : void log(string:message) : void log(string:message, Throwable:t) : void service(req:servletrequest, resp:servletresponse) : void interface Servlet destroy() : void getservletcong() : ServletCong getservletinfo() : String init(servletcong:cong) : void service(req:servletrequest, resp:servletresponse) : void HttpServlet HttpServlet(): # dodelete(req:httpservletrequest, resp:httpservletresponse) : void # doget(req:httpservletrequest, resp:httpservletresponse) : void # dohead(req:httpservletrequest, resp:httpservletresponse) : void # dooptions(req:httpservletrequest, resp:httpservletresponse) : void # dopost(req:httpservletrequest, resp:httpservletresponse) : void # doput(req:httpservletrequest, resp:httpservletresponse) : void # dotrace(req:httpservletrequest, resp:httpservletresponse) : void # getlastmodied(req:httpservletrequest) : long # service(req:httpservletrequest, resp:httpservletresponse) : void service(req:servletrequest, resp:servletresponse) : void

7 7/22 Presentation in Code is BAD! package org.cu.soen387; import java.io.ioexception; import java.io.printwriter; import javax.servlet.servletexception; import javax.servlet.http.httpservlet; import javax.servlet.http.httpservletrequest; import javax.servlet.http.httpservletresponse; public class HelloServlet extends HttpServlet { protected void doget(httpservletrequest request, HttpServletResponse response) throws ServletException, IOException { response.setcontenttype("text/html"); PrintWriter out = response.getwriter(); out.println("<html>"); out.println("<body>"); out.println("hello " + request.getparameter("name")) out.println("</body>"); out.println("</html>"); out.close(); } }

8 8/22 What are? A template language to separate out presentation An xml-based servlet language?

9 9/22 How do we get to them? Access them directly through servlet container Forward from an explicit servlet

10 0/22 Servlet Forwarding package org.cu.soen387; import java.io.ioexception; import java.io.printwriter; import javax.servlet.servletexception; import javax.servlet.http.httpservlet; import javax.servlet.http.httpservletrequest; import javax.servlet.http.httpservletresponse; public class HelloServlet extends HttpServlet { protected void doget(httpservletrequest request, HttpServletResponse response) throws ServletException, IOException { } } getservletcontext().getrequestdispatcher("/hello.jsp").forward(request,response);

11 1/22 Forwarding I told you it was messy!

12 12/22 Forward vs. Include Forwarding entity is done outputting Forwarded entity closes output Can keep including stu

13 13/22 HttpRequest/Response interface ServletRequest getattribute(name:string) : Object getattributenames() : Enumeration<String> getcontenttype() : String getparameter(name:string): String getparameternames() : Enumeration<String> removeattribute(name:string) : void setattribute(name:string, o:object)() : void interface HttpServletRequest BASIC_AUTH : String CLIENT_CERT_AUTH : String DIGEST_AUTH : String FORM_AUTH : String getcontextpath() : String getcookies() : Cookie[] getheader(name:string) : String getheadernames(): Enumeration <String> getmethod() : String getservletpath() : String getsession() : Session getsession(create:boolean) : Session Headers have convenience methods for casting results.

14 4/22 Basic Hello World JSP page contenttype="text/html; charset=utf-8" language="java" %> <html> <body> Hello <%= request.getparameter("name") %> </body> </html>

15 15/22 Basic That's inline code in a JSP Avoid code in JSP Code confuses non-programmers Messy, multiple languages to parse Error-prone Same reason we don't want presentation in code

16 6/22 Hello World JSP with EL page contenttype="text/html; charset=utf-8" language="java" %> <html> <body> Hello ${param[name]} </body> </html>

17 17/22 EL s identied by ${} resolves many expressions knows a few useful operators empty not empty basic arithmetic

18 18/22 EL And Attributes Some preset attributes available param Always read-only Square brackets treat attributes like a map Looks up context chain for attribute page request session application Prints nothing if it can't nd or is null

19 9/22 EL and Attributes The act like beans can use. notation to dig in ${greeting.name} looks for greeting attribute calls getname() on it

20 0/22 Simple Taglibs page language="java" contenttype="text/html; charset=utf-8" pageencoding="utf-8" %> taglib prefix="c" uri=" %> <html> <body> <c:if test="${empty param[name]}"> Hello unnamed person </c:if> <c:if test="${not empty param[name]}"> Hello ${param[name]} </c:if> </body> </html>

21 21/22 Taglibs and Namespace That junk at the top says where taglibs are dened It also says what letter to use to namespace things prex Can dene this in web.xml JSTL should live somewhere in tomcat, just have to say you're using it Other taglibs you need to stick stu in WEB-INF/lib or /classes

22 22/22 Taglibs Brief Mention Can do conditionals, switches, loops Note that you can pass labeled parameters You can write your own... Start with the JSTL Core

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