Introduction to Java Server Pages (JSPs) Robert Thornton

Notes This is a training NOT a presentation Please ask questions 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 Hello World! The current date is

Lab 1: JSP Servlet Compilation Lab 1 _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 import="java.util.Date" import="java.text.SimpleDateFormat" import="java.io.*,java.net.*" import="static org.lds.stack.Constants.*" %>

JSP Elements: Comments Syntax: 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: 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: 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" }; %>

Lab 2: Hello World in JSP Lab 2 _2:_Hello_World_in_JSP

JSP Elements: Expressions Syntax: 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" }; %> ">

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 3 _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 4 _4:_Pre-compiling_JSPs_with_Maven

Credit where credit is due Core Servlets and JavaServer Pages, Marty Hall and Larry Brown, Sun Microsystems & Prentice Hall, 2000 – ISBN-13: