Advanced Web Systems 3- Portlet and JSP-JSTL. A. Venturini

Transcription

1 Advanced Web Systems 3- Portlet and JSP-JSTL A. Venturini

2 Contents Portlet: doview flow Handling Render phase Portlet: processaction flow Handling the action phase Portlet URL Generation JSP and JSTL

3 Sample: WeatherPortlet Download from: It is a JSR 168 Portlet compliant Runs virtually on any portal server It fully exploits JSR 168 APIs We use it in this lecture as example, to explain the typical flows

4 Weather Portlet Class diagram

5 Weather Portlet We assume to have the weather portlet on one page The page can contain more portlets

6 Scenario: show the page The page should be rendered The page hosts several portlets The render method of each portlet is called: portletmode=view windowstate=normal ALL THE PORTLETS ARE ASKED TO PRODUCE THEIR HTML FRAGMENT NO PROCESS ACTION IS INVOKED, only the render()

7 Portal and Portlet Interaction User Portal Portlet container Portlets A B C B A C Action on B Do action on B processaction Render A render These requests may be done in parallel Render B Render C render render A B C Outside of the scope of the Portlet specification Scope of the Portlet specification

8 Weather Portlet Render Sequence Diagram

9 1. User accesses the page The get request is managed directly by the portal server not by your application The Portal Server, through the Portlet Container, invoke the render() method The render() method, superclass of WeatherPortlet class, invokes the doview method (portletmode=view and windowstate=normal)

10 2. Render Method The portlet has been previously initilized by the portlet container (at the startup) The parent class of the portlet (PortletMVC) dispatch the execution to the jsp configured in the portlet.xml file, parameter view-jsp

11 VIEW.JSP Render the HTML JSP 1.0: <% for (String zip : zips) { Weather weather = WeatherUtil.getWeather(zip); if (weather!= null) { %>..

12 How to generate URL for the portlet Show data is only one of the things a JSP has to do Within the HTML generated by the JSP you need to create links to the application You cannot use simply (for example): <a href=?p1=x&p2=y&p3=z /> You need to use the Portlet API Portlet has two type of URL actionurl: typically for form submission, or url that changes the application state renderurl: display one view (also with parameters) Choosing one or the other is not always obvious

13 .you can use the portlet taglib in the jsp taglib uri=" prefix="portlet"%> <portlet:renderurl var="showcitydetailurl"> <portlet:param name="cityname" value= bolzano, Italy"/> <portlet:param name=" desiredview" value= showcitydetail"/> </portlet:renderurl> <a href="${showcitydetailurl}"> show info of Bolzano</a>

14 What is a JSP taglib? Is a way to define custom tags Custom tags are mapped to java classes implementing a specific interface These classes can dynamically produce the html code which will replace the tag itself Or can set attributes in the request, to be read in the jsp

15 When user will click on the link The doview method is called: public void doview(renderrequest request,renderresponse response) throws PortletException,IOException { } String cityname = request.getparameter("cityname"); String desiredview = request.getparameter("desiredview "); } if(desiredview.equals( showcitydetail ) { // do the required business logic // dispatch to a specific jsp (for instance)

16 Second scenario We want to add a link allowing to change the city to be displayed

17 Or using the taglib taglib uri=" prefix="portlet"%> <portlet:actionurl var="setcitynameurl"> <portlet:param name="cityname" value= bolzano, Italy"/> <portlet:param name=" desiredview" value= setcityname"/> </portlet:actionurl> <a href="${setcitynameurl}"> switch to the weather in Bolzano</a>

18 ProcessAction flow

19 When user will click on the link The processaction method is called: public void processaction(actionrequest request, ActionResponse response) { } PortletPreferences pref = request.getpreferences(); String cityname = request.getparameter("cityname"); pref.setvalue("cityname", cityname); pref.store();

20 Remarks The ProcessAction reads parameters and sets the new parameters in the configuration The render method has dispatched to the JSP The JSP has just to format and build the html The JSP does not do any business logic, does not change the application state This is an example of Model View Controller pattern

21 Remarks The JSP is invoked by the portlet class (via include()) MODEL 2 approach

22 Models of JSP development Origin of the terms model 1 and model 2. JSP 0.92 spec: You can apply the JavaServer Pages technology in two ways... Model 1: A request sent to a JavaServer Pages file.... Model 2: A request sent to a Java Servlet.

23 Simple model 2 example public void doget(httpservletrequest request HttpServletResponse response) { // business logic that results in object data request.setattribute( d, data); sc.getrequestdispatcher( /view.jsp ); } view.jsp We have some data to display: <b>${d.property1}</b> In this case, the data passed is a simple bean-style object. It could also be an XML document; we d then use JSTL s XML-manipulation tags.

24 JSP and JST 2.0 Some tutorial: Author of next slides is: Shawn Bayern, Research Programmer, Yale University

25 J2EE presentation tier Servlets Java classes that handle requests by producing responses (e.g., HTTP requests and responses) (Portlets are invoked by Portal server servlets!) JavaServer Pages (JSP) HTML-like pages with some dynamic content. They turn into servlets automatically. JSP Standard Tag Library (JSTL) Set of standard components for JSP. It is used inside JSP pages.

26 Organization of the platform Your web pages JSTL Your application JavaServer Pages (JSP) Java Servlet API Java language

27 What kinds of things go in JSP pages? Scriptlets <% getfoo(request); printfoo(out); String a = italy ; %> <% if (a.equals( italy ) {%> <img src= italy.png/> <% } %> Java (and more?) embedded within template text Access to implicit objects: request, response, etc. Conditional blocks, loops manually constructed

28 What kinds of things go in JSP pages? Tag libraries <foo:bar/> <c:if test= ${c} > c is true </c:if> <c:foreach var= i items= ${items} > loop </c:foreach> XML tags Invoke Java logic behind the scenes. May access body, e.g., for iteration, conditional inclusion or just as arbitrary parameter May access PageContext Libraries and prefixes

29 Extension introduced with JSP 2.0 Expression language Tag files Simplified Tag API (SimpleTag versus Tag) Also, though it s not really part of JSP, JSTL improves things too. The end result: JSP pages become easier to write and maintain.

30 The JSP Expression Language (EL): Key syntax Expressions appear between ${ and }. Note that ${ and } may contain whole expressions, not just variable names, as in the Bourne shell (and its dozen derivatives.) E.g., ${myexpression + 2} Expressions default targets are scoped attributes (page, request, session, application) ${city} pagecontext.findattribute( city )

31 The JSP Expression Language (EL): Key syntax The. and [] operators refer to JavaBeanstyle properties and Map elements: ${city.cityname} can resolve to ((City) pagecontext.getattribute( city )).getcityname() Note the automatic type-cast. This is one of the great features of the EL: users do not need to concern themselves with types in most cases (even though the underlying types of data objects are preserved.)

32 The JSP Expression Language (EL): advanced data access Expressions may also refer to cookies, request parameters, and other data: ${cookie.crumb} ${param.password} ${header[ User-Agent ]} ${pagecontext.request.remoteuser}

33 The JSP Expression Language (EL): more syntax The EL supports Arithmetic ${age + 3} Comparisons ${age > 21} Equality checks ${age = 55} Logical operations Emptiness detection ${empty a} ${city= bolzano or city= trento } a is empty String ( ), empty List, null, etc. Useful for ${empty param.x}

34 The JSP Expression Language: Uses JSTL 1.0 introduced the EL, but it could be used only within tags. In JSP 2.0, it can be used almost anywhere <font color= ${color} > Hi, ${user}. You are <user:age style= ${style} /> years old. </font>

35 Tag Files: nature and purpose Solve difficulty of reusing text/html within a tag. And makes it much easier to write simple tags, since you can do so in JSP instead of Java. Stand-alone file with <%@ tag %> directive instead of traditional <%@ page %> directive.

36 JSP 2.0 tag files tag name= tabletag %> attribute name= items %> <table width= bgcolor= > <th> <td>name</td> <td>age</td> </th> <c:foreach var= i items= ${items} > <tr> <td>${i.fullname}</td> <td>${i.age}</td> </tr> </c:foreach> </table>

37 Using the new tag Your shopping cart: <my:tabletag items= ${cart} /> Your wish list: <my:tabletag items= ${wishlist} /> Things we want you to buy: <my:tabletag items= ${pressuredsales} />

38 Old tag handler Tag attributes dostarttag() doendtag() doinitbody() doafterbody() docatch() release() dofinally() Tag handler Tag body

39 SimpleTag handler Tag attributes dotag() Tag body (no scriptlets) Tag handler

40 USER GENERATED TAG FUNCTION (1) package mytaglib; public class MyFunctions { public static boolean contains(java.util.set<string> set, String target) } { return set.contains(target); }

41 USER GENERATED TAG FUNCTION (2) WEB-INF/MyTags.tld <?xml version="1.0" encoding="utf-8"?> <taglib version="2.0" xmlns=" xmlns:xsi=" xsi:schemalocation= " webjsptaglibrary_2_0.xsd"> <tlib-version>1.1</tlib-version> <uri>/web-inf/mytags</uri> <function> <name>contains</name> <function-class>mytaglib.myfunctions</function-class> <function-signature> boolean contains(java.util.set,java.lang.string) </function-signature> </function> </taglib>

42 USER GENERATED TAG FUNCTION (3) In the JSP you can use: prefix="mtg" uri="/web-inf/mytags"%> <c:if test="${mtg:contains(someset,somevalue)}" >... </c:if>

43 JSTL 1.0 features Control flow Iteration, conditions URL management Retrieve data, add session IDs Text formatting and internationalization Dates and numbers Localized messages XML manipulation XPath, XSLT Database access Queries, updates

44 JSTL 1.0 libraries Library features Core (control flow, URLs, variable access) Text formatting XML manipulation Database access Recommended prefix c fmt x sql

45 JSTL TAGS c: prefix="c" uri=" fn: prefix="fn" uri=" %> fmt: prefix="fmt" uri=" %> xml: prefix="x" uri=" %>

46 JSTL features: managing variables Outputting values with EL <c:out value= ${user.age} /> Storing data <c:set var= user scope= session > // arbitrary text </c:set> Note the use of var and scope : a JSTL convention

47 JSTL features: iteration Iteration <c:foreach items= ${list} begin= 5 end= 20 step= 4 var= item > <c:out value= ${item} /> </c:foreach> paging

48 Iteration (2) Iterating over a list: <!-- L represents either an array, list or set --> <c:foreach var="x" items="${l}" > ${x} </c:foreach> Iterating over a map: <!-- M is a map --> <c:foreach var="x" items="${m}" > ${x.key}: ${x.value} </c:foreach>

49 JSTL features: conditional logic Conditional evaluation <c:if test= ${a == b} > a equals b </c:if> Mutually exclusive conditionals <c:choose> <c:when test= ${a == b} > a equals b </c:when> <c:when test= ${a == c} > a equals c </c:when> <c:otherwise> I don t know what a equals. </c:otherwise> </c:choose>

50 JSTL features: URL management Retrieving data <c:import var= cnn url= /> Data exposed as String or Reader All core URLs supported (HTTP, FTP, HTTPS with JSSE) Local, cross-context imports supported Printing URLs <c:url value= /foo.jsp > Redirection <c:redirect url= /foo.jsp >

51 JSTL features: text formatting Locale-sensitive formatting and parsing Numbers Dates Internationalization Message bundles Message argument substitution Hi {0}. Your cart is {1}. <fmt:formatnumber type= currency value= ${salary} /> <fmt:message key= welcome />

52 JSTL features: XML manipulation Use of XPath to access, display pieces of XML documents <c:import url= var= cnn /> <x:parse xml= ${cnn} var= dom > <x:out value= $dom//item[1]/title /> Chaining XSLT transformations <x:transform xslt= ${xsl2} /> <x:transform xml= ${xml} xslt= ${xsl} /> </x:transform>

53 JSTL features: database manipulation (BUT DO NOT USE THEM!) Queries (and ResultSet caching) Updates / inserts Transactions (<sql:transaction>) <sql:query sql= SELECT * FROM USERS var= result /> substitution (<sql:param>) <c:foreach items= ${result.rows} > </c:foreach> Parametric (PreparedStatement) argument DataSource-based connection management

54 SQL tags: the debate Tag library Database Back-end Java code Tag library JSP page

55 SQL Tags: The expert group s conclusion SQL tags are needed because many nonstandard offerings exist it is not JSTL s role to dictate a choice of framework As popular as MVC is, it s not universal. Even in an MVC application, not all data is worth handling carefully. prototyping is important users ask for it! The JSTL specification recommends avoidance of SQL tags in large applications.

56 Examples: a select allowing to choose a date among a set of dates In the doview method: List<String> datescoll = new ArrayList(); datescoll.add("12/02/2009"); datescoll.add("13/02/2009"); renderrequest.setattribute("datescoll", datescoll); renderrequest.setattribute("selecteddate", "13/12/2009"); In the included jsp: <select name= dates"> <c:foreach items="${datescoll}" var= dateoption'> <option value="${dateoption}" ${dateoption ==selecteddate? 'selected' : ''}>${dateoption}</option> </c:foreach> </select>

57 Examples: a list of maps In the doview method: List<Map<String, Item>> weeklylist =getweeklydata(); renderrequest.setattribute("weeklylist", weeklylist); In the included jsp: <c:foreach items="${weeklylist}" var="mapitems" varstatus="liststatus"> <c:out value="day "/><c:out value="${liststatus.count}"/><br> <c:foreach items="${mapitems}" var="mapiter"> <div class="list_item"> <a href> ${mapiter.value.itemname} </a><br> </div> </c:foreach> </c:foreach>

58 Questions?