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Introduction to Java Server Pages (JSPs) Robert Thornton
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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).– Installed App Server (such as Tomcat).
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?
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.
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.
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.
JSP Example 1
<%-- JSP Training: Example 1 --%><%@ page contentType="text/html" pageEncoding="UTF-8" %><%@ page import="java.util.logging.Logger,java.util.Date" %>
<%-- define a logger for the current page --%><%! private static final 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()); %>
Lab 1: JSP Servlet Compilation
Lab 1https://tech.lds.org/wiki/
Introduction_to_JSP#Lab_1:_JSP_Servlet_Compilation
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).
JSP Elements: Page Directive
• Example syntax: <%@ page contentType="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.
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
JSP Elements: Page Directive Examples
<%@ page contentType="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.*" %>
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 will not included in the generated servlet.
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.
JSP Elements: Example Declarations
<%!private final int FOO = 1024;private String[] options = { "green", "red", "blue", "yellow" };%>
<%!private String doSomething(HttpServletRequest req) {
// do something}%>
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.
JSP Elements: Example Scriptlets
<% String[] options = { "green", "red", "blue", "yellow" };%><select name="options"> <% for (int i = 0; i < options.length; i++) { %> <option><% out.write(options[i]); %><option> <% } %></select>
Lab 2: Hello World in JSP
Lab 2https://tech.lds.org/wiki/
Introduction_to_JSP#Lab_2:_Hello_World_in_JSP
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.
JSP Elements: Example Scriptlets
<% String[] options = { "green", "red", "blue", "yellow" };%><select name="options"> <% for (int i = 0; i < options.length; i++) { %> <option value="<%= i %>"><%= options[i] %><option> <% } %></select>
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.
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
Lab 3: A JSP Calendar
Lab 3https://tech.lds.org/wiki/
Introduction_to_JSP#Lab_3:_A_JSP_Calendar
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.
Lab 4: Pre-compiling JSPs with Maven
Lab 4https://tech.lds.org/wiki/
Introduction_to_JSP#Lab_4:_Pre-compiling_JSPs_with_Maven
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
