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Java Server Pages (JSP) - Sharad Ballepu

Java Server Pages (JSP) - Sharad Ballepu. Java Server Pages (JSP). Servlets & JSPs. Agenda Introduction JSP Elements Implicit Objects Tag Libraries JSP Actions Error Handling Demo. Introduction – What is JSP.

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Java Server Pages (JSP) - Sharad Ballepu

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  1. Java Server Pages (JSP) - Sharad Ballepu

  2. Java Server Pages (JSP) Servlets & JSPs Agenda • Introduction • JSP Elements • Implicit Objects • Tag Libraries • JSP Actions • Error Handling • Demo

  3. Introduction – What is JSP • JSP Stands for Java Server Pages • Presents dynamic content to users • Handles the presentation logic in an MVC architecture (business logic) servlet request Container Business Tier Helper Objects JSP (presentation logic) response

  4. Introduction – JSP v/s Servlet How is JSP different / similar to Servlet?

  5. Introduction – JSP is a Servlet • In the end, a JSP is just a Servlet Is loaded and Initialized as Is translated to Compiles to writes JSP Import javax. servlet. HttpServlet.* 0010 0001 1100 1001 0001 0011 Servlet MyJsp_jsp Servlet MyJsp.jsp MyJsp_jsp.java MyJsp_jsp.class

  6. Introduction – Comments • JSP Comments • <%-- {CODE HERE} --%> • Does not show the comments on the page • Does not show the comments in page source • Can only be used outside JSP Elements • HTML Comments • <!– {CODE HERE} --> • Does not show the comments on the page • Shows the comments in page source • Can only be used outside JSP Elements • Single line Comments • // {CODE HERE} • When put outside JSP Elements, shows comments on the page & source • When put inside Scriptlets/Declarations, does not show on page & source • Can be used inside scriptlets/declarations and outside JSP Elements

  7. JSP Elements – Intro • Need to write some Java in your HTML? • Want to make your HTML more dynamic? • JSP Declarations :: Code that goes outside the service method • JSP Scriptlets :: Code that goes within the service method • JSP Expressions :: Code inside expressions is evaluated • JSP Directives :: Commands given to the JSP engine

  8. JSP Elements - Declarations • What are declarations? • Whatever goes inside the “<%!{JAVA_HERE}%>” tags is called a declaration • Everything you write in a declarations goes outside the service method • Treat them as instance methods and instance variables • What do you declare in declarations? • You can declare methods and variables in declarations • Why do you need declarations? • You have any variable that needs to be shared across different requests. • You have repeated common code in you jsp, declare it in a method. • Example <%! int instanceVar = 10; %>

  9. JSP Elements - Declarations Request 1 Service1 Service2 Service3 Request 2 Declarations Request 3

  10. JSP Elements - Scriptlets • What are declarations? • Whatever goes inside the “<%{JAVA_HERE}%>” tags is called a scriptlet • Everything you write in a scriptlets goes in the service method • Treat variables in scriptlets as method/local variables • What do you put in scriptlets? • Business logic in JSPs are put in scriptlets. Set of java statements • Why do you need scriptlets? • Need to perform some small business logic (if logic is complex, do in java) • Need to perform some basic validations • Example • <% int localVar = 10; %>

  11. JSP Elements - Expressions • What are expressions? • Whatever goes inside the “<%={JAVA_HERE}%>” tags is called an expression • Code inside expressions is evaluated, and output is displayed • Whatever is put inside expressions should evaluate to a value • What do you put in scriptlets? • Variables or methods that return some values • Why do you need scriptlets? • Need to print some text onto the page • Example • <%= localVar %>

  12. JSP Elements - Example • <html><head><title>JSP Elements Example</title> • </head> • <body> • <%! int userCnt = 0; %> • <% • String name = "Sharad"; • userCnt++; • %> • <table> • <tr><td> • Welcome <%=name%>. You are user number <%=userCnt%> • </td></tr> • </table> • </body> • </html> Declarations Scriptlets Expressions

  13. JSP Elements - Directives • What are directives? • Whatever goes inside the “<%@{DIRECTIVES}%>” tags is called a directive • Directives gives pre-processing commands to the JSP Engine. • Everything in directives are processed before JSP is translated to Servlet • What do you put in directives? • Processing commands to the JSP Engine. • Why do you need directives? • To incorporate certain additional features into the JSP • Modifying the Servlet behaviour generated from the JSP • Include other html/jsp files in the JSP. • Provide tag libraries • Example • <%@ page import=“java.util.ArrayList” %>

  14. Directives – page directive • Any number of the pre-defined attributes can be added to the page directive • <%@ page import = “{IMPORTED_CLASSES}” • contentType = “{CONTENT_TYPE}” • isThreadSafe = “{true/false} • session = “{true/false}” • buffer = “{BUFFER_SIZE}” • autoflush = “{true/false}” • extends = “{EXTENDS_FROM_PAGE}” • info = “{PAGE_INFO”} • errorPage = “{ERROR_PAGE_NAME}” • isErrorPage = “{true/false}” • language = “{LANGUAGE}”

  15. Directives – include directive • Including other page content into your JSP • <%@ include file = {PAGE_URL_TO_INCLUDE} %> • Includes files at translation time • If included file is modified, the main jsp needs to be recompiled Main page Hello <%=userName%> <%@ include file =“header.jsp"/> header.jsp <table><tr> <td>Contact Details</td> <tr></table> <%@ include file =“footer.jsp"/> main.jsp footer.jsp

  16. Directives – taglib directive • Providing output based on common custom logic • <%@ taglib uri=“{TLD_FILE}" prefix=“{PREFIX}" %> • Components involved in tag libraries • Tag handler class • Common custom logic and HTML generation • Descriptor configuration file • Directive’s properties mapping information • taglib directive • Used in JSPs to use the tag handler functionality

  17. taglib directive – high-level overview <tag> <name>txtBox</name> <tagclass>TxtBoxTag</tagclass> <bodycontent>EMPTY</bodycontent> <attribute> <name>name</name> <required>true</required> …. </attribute> … </tag> <%@ taglib uri=“sharmanjTags” prefix=“sharmanj” %> ….. < sharmanj:txtBox length=“10“ name=“userName”/> ….. test.jsp sharmanj-taglib.tld • <web-app> • <taglib> • <taglib-uri>sharmanjTags</taglib-uri> • <taglib-location> • sharmanj-taglib.tld • </taglib-location> • </taglib> • </web-app> public class TxtBoxTag extends TagSupport { public int doStartTag() { …. } } TxtBoxTag.java web.xml

  18. Implicit Objects - Introduction • Set of predefined objects readily available for use. • out: JspWriter • request: HttpRequest • response: HttpResponse • session: HttpSession • config: ServletConfig • application: ServletContex • page: JSP page • pageContext: Special object

  19. Implicit Objects - Example • <html> • <head> • <title>JSP Implicit objects Example</title> • </head> • <body> • <% • if (“YES”.equals(request.getAttribute(“SCOPE”))) { • out.println(“REQUEST”); • } else { • if (“YES”.equals(session.getAttribute(“SCOPE”))) { • out.println(“SESSION”); • } else { • out.println(“NONE”); • } • } • %> • </body> • </html>

  20. Implicit Objects – out • An instance of JspWriter • Writes statements to the page • The java way to display text on the webpage • Displaying dynamic data

  21. Implicit Objects – request • Instance of HttpServletRequest • Use the attributes stored in request object for display /basic validations in JSP Forwards request to JSP JSP JSP Servlet Servlet request.setAttribute(“a”, “10”) a = 10 Helper Object (a = 10) Uses helper object

  22. Implicit Objects – response • Instance of HttpServletResponse • Send the response back to the client (HTML in most of the cases) JSP1 Send response to client response.sendRedirect(“url”); JSP1 JSP2 Redirect to JSP2 Send response to client

  23. Implicit Objects – session • Instance of HttpSession • Retrieve and set the session attributes in JSP • Remember the client across multiple requests Request 1 Web App Response1 CLIENT Request 1 Response2 SESSION

  24. Implicit Objects – config and application • config - Instance of ServletConfig • Application – instance of ServletContext Servlet Context JSP 1 JSP 1 JSP 1 JSP 1 Servlet Config Servlet Config Servlet Config Servlet Config

  25. Implicit Objects – page Main page Hello <%=userName%> <jsp:include page=“/header.jsp"/> header.jsp <table><tr> <td>Contact Details</td> <tr></table> <jsp:include page=“/footer.jsp"/> footer.jsp main.jsp

  26. Implicit Objects – pageContext application session pageContext Least visible to most visible request page

  27. JSP Actions • Special tags which provides special features • The container handles these tags in a special way • Addresses certain common functionalities • Achieve functionality with less code, and more standard way <jsp:include> <jsp:forward> <jsp:param> <jsp:useBean> <jsp:getProperty> <jsp:setProperty>

  28. JSP Actions - <jsp:include> • Definition: • Includes a page at the given location in the main page Syntax: • <jsp:include page="{PAGE_TO_INCLUDE}" flush="true" />

  29. JSP Actions – Include Action v/s Include Directive

  30. JSP Actions - <jsp:forward> Definition: Forwards the request to the given page Syntax: <jsp:forward page=“{PAGE_TO_FORWARD}" />

  31. JSP Actions - <jsp:param> Definition: Pass parameters to the included/forwarded page Syntax: <jsp:include page="{PAGE_TO_INCLUDE}" flush="true" > <jsp:param name=“{parameterName}” value="{paramValue}" /> </jsp:include> <jsp:forward page="{PAGE_TO_FORWARD}" flush="true" > <jsp:param name=“{parameterName}” value="{paramValue}" /> </jsp:forward>

  32. JSP Actions - <jsp:useBean> getId(); setId(..) getName() setName(…) How can I use that bean? bean JSP Servlet request.setAttribute(“userBean”, userBean”) <jsp:useBean …./>

  33. JSP Actions - <jsp:useBean> Definition: Instantiate a bean class, use bean properties, and set property values Syntax: <jsp:useBean id=“{beanInstanceName}" scope="page|request|session|application" class=“{package.class}" type=“{package.class}" beanName=" {package.beanName}”> </ jsp:useBean> UserBean ub = new UserBean();

  34. JSP Actions - <jsp:getProperty> Definition: Gets property values of a Bean Syntax: <jsp:getProperty name=“{beanInstanceName}" property= “{propertyName}">

  35. JSP Actions - <jsp:setProperty> Definition: Sets property values in a Bean Syntax: <jsp:setProperty name=“{beanInstanceName}" property= "*" | property="propertyName" param=“{parameterName}" value="{paramValue}" } />

  36. JSP Actions – useBean <jsp:useBean id=“userBean" scope="session“ class=“com.sharmanj.UserBean" > <jsp:setProperty name=“userBean” property=“userName” value=“Sharad”/> </ jsp:useBean> <jsp:getProperty name=“userBean" property=“userName" />

  37. Error Handling – Types of errors • Errors in java code in scriptlets • handle errors in try/catch block • may occur at runtime • Errors in HTML • adhere to the HTML rules • can be caught during testing

  38. Error Handling Why is error handling important in JSPs?

  39. Error Handling – Error page • Error pages come to the rescue <%@page isErrorPage="true" %> <html> <head> <title>My Error Page</title> </head> <body> We are sorry, the page you are trying to access is currently not available. Please try after some time </body> </html>

  40. Error Handling • Specify error page in your main page • Specify error page in web.xml <%@page errorPage=“errPage.jsp" %> <html> <head> <title>This is the main page</title> </head> <body> ………………….. ………………….. …………………… …………………… // ERROR CODE GOES HERE …………………. …………………. </body> </html> <web-app> ……………. …………… <error-page> <exception-type>com.a.myExp</exception-type> <location>/error.jsp</location> </error-page> <error-page> <error-code>404</error-code> <location>/errorServlet</location> </error-page> ……………….. ………………. </web-app>

  41. Thanks

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