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Middleware Technology JavaServer Pages (JSP)

Middleware Technology JavaServer Pages (JSP). Agenda. Developing JSP-based Web Application JSP 2.0 (in J2EE 1.4) EL JSTL Custom tags in JSP pages. Web Application & Components. Web Application is a deployable package Web components (Servlets and JSP's)

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Middleware Technology JavaServer Pages (JSP)

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  1. Middleware TechnologyJavaServer Pages (JSP)

  2. Agenda • Developing JSP-based Web Application • JSP 2.0 (in J2EE 1.4) • EL • JSTL • Custom tags in JSP pages

  3. Web Application & Components • Web Application is a deployable package • Web components (Servlets and JSP's) • Static resource files such as images • Helper classes • Libraries • Deployment descriptor (web.xml file) • Web Application can be represented as • A hierarchy of directories and files (unpacked form) or • *.WAR file reflecting the same hierarchy (packed form)

  4. Web Application Development and Deployment Steps • 1.Write (and compile) the Web component code (Servlet or JSP) and helper classes referenced by the web component code • 2.Create any static resources (for example, images or HTML pages) • 3.Create deployment descriptor (web.xml) • 4.Build the Web application (*.war file or deployment-ready directory) • 5.Deploy the web application into a Web container • Web clients are now ready to access them via URL

  5. Example Tomcat将JSTL默认放在了jsp-examples目录中, greeting.jsp应该放在那里

  6. Example.

  7. Write and compile the Web component code • Create development tree structure • Write either servlet code or JSP pages along with related helper code • IDE (i.e. NetBeans, Eclipse with Plugin) handles all these chores

  8. Create any static resources • HTML pages • Custom pages • Login pages • Error pages • Image files that are used by HTML pages or JSP pages • Example: duke.waving.gif

  9. Development Tree Structure • JSP file can be placed under the deployment directory together with the main HTML files. • JSP files can also be mapped to specific URLs in the web.xml file.

  10. Deployment Descriptor (web.xml) • Every web application has to have web.xml • The configuration information for JSP pages is described in the web.xml file rooted on the <jsp-config> element. • Configuration elements may include: • <taglib> - element in mapping of tag libraries • <jsp-property-group> - properties of collections of JSP files, such as page encoding or automatic includes before and after pages, etc

  11. Example: Deployment Descriptor • Common header and footer for JSP file can be defined in the web.xml file as follows: • <?xml version="1.0" encoding="UTF-8"?> • <web-app> • <jsp-config> • <jsp-property-group> • <url-pattern>*.jsp</url-pattern> • <include-prelude>/header.jsp</include-prelude> • <include-coda>/footer.jsp</include-coda> • </jsp-property-group> • </jsp-config> • </web-app>

  12. Mapping JSP to a URL • A JSP page can be mapped to a specific URL by modifying the web.xml file. • <?xml version="1.0" encoding="UTF-8"?> • <web-app> • <servlet> • <servlet-name>greeting</servlet-name> • <jsp-file>/greeting.jsp</jsp-file> • </servlet> • <servlet-mapping> • <servlet-name>greeting</servlet-name> • <url-pattern>/greeting</url-pattern> • </servlet-mapping> • </web-app>

  13. Example: Mapping JSP • Investigate the mapping mechanism for JSP file. • Create a JSP • Put it under the directory <your_web_context>/WEB-INF/classes/ • Browse it with a web browser

  14. Build the Web application • Either *.WAR file or unpacked form of *.WAR file • Build the “.war” file • Use IDE (Eclipse with Lomboz) • Use ant tool after putting proper build instruction in build.xml file • Use “jar cvf <filename>.war .” command under build directory

  15. Directory Structure of *.WAR file

  16. Install or Deploy Web application • There are 2 different ways to install/deploy Web application • By manually copying files to Tomcat's webapps directory and then restarting Tomcat • By asking Tomcat Manager via sending a command to it (Tomcat Manager is just another Servlet app that is always running) • ant install • ant deploy

  17. Perform Client Access to Web Application • From a browser, go to URL of the Web application • http://localhost:8080/hello/greeting

  18. Document Root & Context • Document Root of the Web application • Top-level directory of WAR • Contains JSP pages, client-side classes and archives, and static Web resources are stored • Also contains WEB-INF directory • A context is a name that gets mapped to the document root of a Web application • /hello is context for hello example • Distinguishes a Web application in a single Web container • Has to be specified as part of client URL

  19. JSP 2.0 (in J2EE 1.4)

  20. JSP 2.0 Expression Language • JSP-specific expression language(JSP EL), is defined in JSP 2.0 specification. • JSP EL provides a cleaner syntax and is designed specially for JSP.

  21. JSP EL Examples • A variable can be accessed as: ${variable_name} • The property can be accessed as: <c:if test="${aBean.age < 20}"> … </c:if>

  22. JSP EL: Syntax • In JSP EL, expressions are always enclosed by ${} characters. • Any values not begin with ${ is literal. • Literal value containers the ${ has to be escaped with “\” character.

  23. JSP EL: Attributes • Attributes are accessed by name, with an optional scope. • Members, getter methods, and array items are all accessed with a “.” • Examples: • A member b in object a ${a.b} • A member in an array a[b] ${a.b} or ${a["b"]}

  24. Example 1 • Using scriptlets: • Equivalent, using an EL expression: <center> <jsp:useBean id="foo" class="FooBean" /> <%= foo.getBar() %> </center> <center> ${foo.bar} </center>

  25. Example 2 • Using scriptlets: • Equivalent, using an EL expression: <% Map m = (Map)pageContext.getAttribute("state" ); State s = ((State)m.get( "NY" )); if( s != null ) { %> <%= s.getCapitol() %> <% } %> ${state["NY"].capitol}

  26. Data structures: arrays, maps, sets • Arrays and maps permit access to their collection via indices • arrays via integer indices • maps via key indices. • EL regards both of these accesses as syntactically similar using the [ ] operator. <% Map<String,String> theMap = new HashMap<String,String>(); theMap.put("John", "5"); theMap.put("Jim", "7"); String theArray[] = { "aaa", "bbb", "ccc" }; session.setAttribute( "theMap", theMap ); session.setAttribute( "theArray", theArray ); %> ${theMap["Jim"]} <!-- same as theMap.get("Jim"), outputs 7 --> ${theArray[1]} <!-- outputs bbb -->

  27. Data structures: arrays, maps, sets • The EL expressions for maps, sets and lists can all print directly. • Arrays, as in Java, don't print directly, but must use an auxiliary function. • In this case the fn:join function serves the purpose: ${fn:join(theArray,",")}

  28. JSP EL: Operators • [] . • () - Used to change the precedence of operators. • - (unary) not ! empty • * / div % mod • + - (binary) • < > <= >= lt gt le ge • == != eq ne • && and • || or • ? : • Note: order of preference from top to bottom, left to right

  29. Notes for EL • The == operator for strings functions like the Java .equals operator. • An EL expression with an undefined value, which (normally represented by null in Java) is also represented by null in EL, but is equivalent to the empty string. • EL has a unary operator empty: empty(x) acts like the expression x==null but also means "x equals the empty string". • The operators or, and are synonyms for ||, &&, respectively.

  30. Reserved Words • The following words are reserved for the JSP expression language and should not be used as identifiers. • and   eq   gt   true   instanceof or    ne   le   false  empty not   lt   ge   null   div   mod • Note that many of these words are not in the language now, but they may be in the future, so you should avoid using them.

  31. Query parameters • The value of the parameter “xx” is expressed by the EL expression param.xx. (param是一个内置对象) • Using an EL expression • Equivalent, using scriptlets: ${param.xx} <%= (request.getParameter("xx") != null) ? (request.getParameter("xx") : "" %>

  32. JSP EL: Implicit Objects 1 • A set of implicit objects is defined to match the JSP equivalents: • 1) pageContext: the context for the JSP page • Through pageContext, the following implict objects can be accessed: • servletContext • session • sequest/response • For example, the context path can be accessed as: • ${pageContext.request.contextPath}

  33. JSP EL: Implicit Objects 2 • 2) param • Maps name of parameter to a single string value • Same as ServletRequest.getParameter(String name) • E.g. ${param.name} • 3) paramValues • Map name of parameter to an array of string objects • Same as ServletRequest.getParameterValues(String name) • E.g. ${paramValues.name}

  34. JSP EL: Implicit Objects 3 • 4) header • Maps a request header name to a single string header value • Same as HttpServletRequest.getHeader(String name) • E.g. ${header.name} • 5) headerValues • Map request header names to an array of string objects • Same as HttpServletRequest.getHeaders(String name) • E.g. ${headerValues.name} • 6) cookie • Maps the single cookie objects that are available by invoking HttpServletRequest.getCookies() • If there are multiple cookies with the same name, only the first one encountered is placed in the map

  35. JSP EL: Implicit Objects 4 • Additional implicit objects are available for accessing scope attributes: • pageScope • requestScope • sessionScope • applicationScope • For example: • ${sessionScope.user.userid}

  36. Session variables are EL variables • A session variable x automatically becomes available as an EL variable • Example: <% session.setAttribute( "x", "hello" ); // or pageContext.setAttribute( "x", "hello" ); %> x = ${x} <!-- prints: x = hello -- >

  37. JSP EL: Defining EL Functions 1 • To define a function you program it as a public static method in a public class. package mypkg; public class MyLocales {    ...    public static boolean equals( String l1, String l2 ) {      return l1.equals(l2);    } }

  38. JSP EL: Defining EL Functions 2 • Map the function name as used in the EL expression to the defining class and function signature in a TLD (Tag Library Descriptor). • <?xml version="1.0" encoding="UTF-8"?> • <web-app>No two functions within a tag library can have the same name. • <jsp-config> • <taglib> • <function>    • <name>equals</name> • <function-class>mypkg.MyLocales</function-class>   • <function-signature> • boolean equals( java.lang.String,  java.lang.String ) • </function-signature> • </function> • </taglib> • </jsp-config> • </web-app> No two functions within a tag library can have the same name.

  39. JSP EL: Using EL Functions • The previous EL functions can be used as following: • ${equals('string1', 'string2')}

  40. JSP EL Compatibility • Using JSP EL may cause compatibility problems with JSP1.2 and earlier code. • JSP EL is disabled by default for a web application with a deployment descriptor that is not Servlet 2.4 conformant and it's enabled by default for a web application with a Servlet 2.4 deployment descriptor. • JSP EL is enabled by default for a web applications with Servlet 2.4 deployment descriptor.

  41. Enabling / Disabling JSP EL • For a single page with the el-Ignored page attribute • <%@ page isELIgnored＝"true|false"%> • For a set of JSP pages with an <el-ignored> element in a JSP group: <web-app ...> ... <jsp-config> <jsp-property-group> <url-pattern>*.jsp</url-pattern> <el-ignored>true</el-ignored> </jsp-property-group> </jsp-config> ... </web-app>

  42. Standard Tag Library • JavaServer Pages Standard Tag Library (JSTL) is an extended set of JSP standard action includes the following tags: • Iteration and conditional • Expression language • Url manipulation • Internationalization-capable text formatting • Xml manipulation • Database access

  43. Problems with JSP Scriptlet Tags • Java code is embedded within scriptlet tags • Non-Java developer cannot understand the embedded java code • Java code within JSP scriptlets cannot be reused by other JSP pages • Casting to the object’s class is required when retrieving objects out of HTTP request and session.

  44. Advantage of JSTL • JSTL tags are in xml format and can be cleanly and uniformly blended into a page’s html mark up tags. • JSTL tag libraries are organized into four libraries which include most functionality required for a JSP page and are easier for non-programmers to use • JSTL tags encapsulate reusable logic and allow to be reused. • No casting is requiring while using JSTL referencing objects in the request and session • JSP’s EL allows using dot notation to access the attributes of java objects.

  45. Example: JSTL 1 • Without JSTL, some scriplets may look as follows • <% • List addresses = (List)request.getAttribute("addresses"); • Iterator addressIter = addresses.iterator(); • while(addressIter.hasNext()) { • AddressVo address = (AddressVo)addressIter.next(); • if(address != null) {%> • <%=address.getLastName() %><br /> • <% } else { %> N/A<br /> • <% } • } • %>

  46. Example: JSTL 2 • With JSTL, the previous may looks as follows • <% taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> • <c:forEach item=${addresses} var="address" > • <c:choose> • <c:when test="${address != null}"> • <c:out value="${address.lastName}"/><br/> • <c:otherwise> • N/A<br/> • </c:otherwise> • </c:choose> • </c:forEach>

  47. Using JSTL • JSTL is standardized, but not a standard part of JSP 1.2 or 2.0 • JSTL must be downloaded and installed separately before being used.

  48. Installing the JSTL • The JSTL will be installed and setup for used. • Download the library from this URL: • http://www.apache.org/dist/jakarta/taglibs/standard/ • Unpack the file and two jar files are inside the /lib dirctory: • jstl.jar • standard.jar

  49. Installing the JSTL • Copy the jar file to the following directory • <Tomcat_Home>/common/lib • The jar file can also be copied to the /WEB-INF/lib directory under your application context. • In the JSP page, the following tags can be used to refer to the installed JSTL: <%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>

  50. Organization of JSTL • The JSTL tags are organized into five libraries

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