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Robert Thornton

Introduction to Java Server Pages (JSPs). Robert Thornton. Notes. This is a training NOT a presentation Please ask questions https://tech.lds.org/wiki/Java_Stack_Training Prerequisites Basic Java and HTML skills. Installed LDSTech IDE (or other equivalent).

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Robert Thornton

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  1. Introduction to Java Server Pages (JSPs) Robert Thornton

  2. Notes • This is a training NOT a presentation • Please ask questions • https://tech.lds.org/wiki/Java_Stack_Training • Prerequisites • Basic Java and HTML skills. • Installed LDSTech IDE (or other equivalent). • Installed App Server (such as Tomcat).

  3. Overview • Java Server Pages • What are they? • What is their role? • JSP Programming Fundamentals: • Directives • Declarations • Expressions, Scriptlets, and implicit objects. • Error handling • Maven JSP Compiler • What does a compiled JSP look like?

  4. What is a JSP really? • A text document containing: • Static data (usually HTML) • JSP elements that construct dynamic content • Typically ends with a .jsp extension • Translated into a Java class • Extends HttpServlet • May be compiled as part of a build or compiled at runtime in response to a detected change.

  5. What is the role of a JSP? • Provides the view of MVC. • Allows generation of static HTML using familiar web tools and syntax. • Allows generation of dynamic HTML using familiar Java syntax and language features. • Allows rapid prototyping of web pages.

  6. JSPs versus Java Servlets • Java Servlets: • Strictly written in Java • HTML must be embedded and escaped within Java strings literals. • Must be defined and mapped within web.xml • Java Server Pages (JSPs) • Mostly static HTML with JSP elements. • No servlet definitions or mappings necessary.

  7. JSP Example 1 <%-- JSP Training: Example 1 --%> <%@ pagecontentType="text/html"pageEncoding="UTF-8" %> <%@ pageimport="java.util.logging.Logger,java.util.Date" %> <%-- define a logger for the current page --%> <%! privatestaticfinal Logger logger = Logger.getLogger("/example1.jsp");%> <!DOCTYPE html> <html> <head> <title>JSP Training: Example 1</title> </head> <body> <h1>Hello World!</h1> <%-- write something dynamic --%> <p>The current date is <% out.write(new Date().toString()); %></p> </body> </html> <%-- log something --%> <% logger.info("Finished rendering " + request.getRequestURL());%>

  8. Lab 1: JSP Servlet Compilation Lab 1 https://tech.lds.org/wiki/Introduction_to_JSP#Lab_1:_JSP_Servlet_Compilation

  9. JSP Elements: Directives • Directives allow control over how the JSP is translated into a servlet. • Three types of directives: • Page: defines attributes that affect the structure and definition of the generated servlet. • Include: statically includes the contents of other files in the JSP (covered in a later training). • Taglib: imports a JSP tag library for use by the page (also covered in a later training).

  10. JSP Elements: Page Directive • Example syntax: <%@pagecontentType="text/html" pageEncoding="UTF-8" errorPage="error.jsp" import="java.util.*"%> • A page directive may appear anywhere in the JSP. • A page directive may appear multiple times.

  11. JSP Elements: Page Directive Attributes • contentType • The value passed to ServletResponse.setContentType • pageEncoding • The value passed to ServletResponse.setCharacterEncoding • import • Import statements to include in the generated servlet • errorPage • Relative path to an error page if an exception is thrown • isErrorPage • Whether this page is to handle exceptions from other pages

  12. JSP Elements: Page Directive Examples <%@ pagecontentType="text/html" pageEncoding="UTF-8" %> <%@ page errorPage="internalError.jsp" %> <%@ page import="java.util.Date" import="java.text.SimpleDateFormat" import="java.io.*,java.net.*" import="static org.lds.stack.Constants.*" %>

  13. JSP Elements: Comments • Syntax: <%-- one or more lines --%> • Can be used to comment out both JSP and HTML elements. • JSP comments will be ignored by the JSP parser and willnot included in the generated servlet.

  14. JSP Elements: Declarations • Syntax: <%! Java declarations%> • May contain one or more Java declarations to be inserted into the class body of the generated servlet. • May be used multiple times to declare both member variables and helper functions on the generated servlet.

  15. JSP Elements: Example Declarations <%! privatefinalint FOO = 1024; private String[] options = { "green","red", "blue", "yellow" }; %> <%! private String doSomething(HttpServletRequest req) { // do something } %>

  16. JSP Elements: Scriptlets • Syntax: <% java code%> • Consists of one or more Java statements to be inserted into the generated servlet’s _jspService method (called by service). • Each scriptlet will be inserted after streaming any preceding static content and before streaming any subsequent static content.

  17. JSP Elements: Example Scriptlets <% String[] options = { "green", "red", "blue", "yellow"}; %> <selectname="options"> <% for (int i = 0; i < options.length; i++) { %> <option><% out.write(options[i]); %><option> <% } %> </select>

  18. Lab 2: Hello World in JSP Lab 2 https://tech.lds.org/wiki/Introduction_to_JSP#Lab_2:_Hello_World_in_JSP

  19. JSP Elements: Expressions • Syntax: <%= java expression%> • Consists of Java code to be evaluated and written to the response output stream during the evaluation of the _jspService method. • Expression return type must not be void. • Each expression’s output will be inserted into the output stream after any preceding static content and before any subsequent static content.

  20. JSP Elements: Example Scriptlets <% String[] options = { "green", "red", "blue", "yellow"}; %> <selectname="options"> <% for (int i = 0; i < options.length; i++) { %> <option value="<%= i%>"><%= options[i] %><option> <% } %> </select>

  21. JSP Elements: Implicit Objects • Implicit objects are variables available to both expressions and scriptlets. • They are not available within declarations. • They are, in fact, local variables of the _jspService method.

  22. JSP Elements: Implicit Objects • request – javax.servlet.http.HttpServletRequest • response – javax.servlet.http.HttpServletResponse • session – javax.servlet.http.HttpSession • application – javax.servlet.ServletContext • config – javax.servlet.ServletConfig • out – javax.servlet.jsp.JspWriter • pageContext – javax.servlet.jsp.PageContext • exception – java.lang.Throwable

  23. Lab 3: A JSP Calendar Lab 3 https://tech.lds.org/wiki/Introduction_to_JSP#Lab_3:_A_JSP_Calendar

  24. Using Maven to Compile JSPs Maven can be used to validate and pre-compile JSPs before deploying them to a server. • This protects against inadvertently sending broken pages to the server. • This can also be used to analyze bugs how changes in the JSP affect the compiled servlet • JSP Servlets generated by the maven build will not necessarily match JSP servlets generated by the application server.

  25. Lab 4: Pre-compiling JSPs with Maven Lab 4 https://tech.lds.org/wiki/Introduction_to_JSP#Lab_4:_Pre-compiling_JSPs_with_Maven

  26. Credit where credit is due • http://download.oracle.com/javaee/5/tutorial/doc/bnagx.html • http://java.sun.com/products/jsp/tags/11/syntaxref11.fm7.html • Core Servlets and JavaServer Pages, Marty Hall and Larry Brown, Sun Microsystems & Prentice Hall, 2000 • ISBN-13: 978-0130092298

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