JavaServer Pages (JSP) The Context The Presentation Layer of a Web - - PowerPoint PPT Presentation
JavaServer Pages (JSP) The Context The Presentation Layer of a Web App the graphical (web) user interface frequent design changes usually, dynamically generated HTML pages Should we use servlets? No (not directly)
– the graphical (web) user interface – frequent design changes – usually, dynamically generated HTML pages
– difficult to develop and maintain (the view) – lack of flexibility – lack of role separation: design → designer
import javax.servlet.*; import javax.servlet.http.*; import java.io.*; public class Hello extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException { response.setContentType("text/html"); PrintWriter out = new PrintWriter(response.getWriter());
"<head><title>Welcome!</title></head>" + "<body>" + "<h1><font color=\"red\"> Welcome! </font></h1>" + "<h2>Current date and time:" + new java.util.Date() + " </h2>" + "</body>" + "</html>");
} }
<html> <head> <title>Welcome!</title> </head> <body> <h1><font color="red"> Welcome! </font></h1> <h2>Current date and time: <%= new java.util.Date() %> </h2> </body> </html>
– static data (template) (HTML, SVG, WML, etc.) – JSP elements, which construct the content
– JSP tags – scriptles (code sequences written in Java...)
//Example taken from Apache Tomcat application server //This is the source file of the servlet generated for hello.jsp package org.apache.jsp; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.jsp.*; public final class hello_jsp extends org.apache.jasper.runtime.HttpJspBase implements org.apache.jasper.runtime.JspSourceDependent { ... public void _jspService(HttpServletRequest request, HttpServletResponse response) throws java.io.IOException, ServletException { ...
...
} } implements javax.servlet.Servlet
<%-- Hello World example, not again ... --%> <%@ page language="java" contentType="text/html; pageEncoding="UTF-8"%> <html> <head> <title>First JSP</title> </head> <%@ page import="java.util.Date" %> <%@ include file="header.html" %> <%! String message = "Hello World"; %> <body> <% for(int i=1; i<=4; i++) {
} %> <!-- Page generated at: <%= new Date() %> --> </body> </html> JSP Directives JSP Expression JSP Comment JSP Declaration JSP Scriptlet
Element Standard Syntax XML Syntax Comment
<%--.. --%> <!-- .. -->
Declarations
<%! ..%> <jsp:declaration> .. </jsp:declaration>
Directives
<%@ include .. %> <%@ page .. %> <%@ taglib .. %> <jsp:directive.include .. /> <jsp:directive.page .. /> xmlns:prefix="tag library URL"
Expressions
<%= ..%> <jsp:expression> .. </jsp:expression>
Scriptles
<% ..%> <jsp:scriptlet> .. </jsp:scriptlet>
Standard actions
<jsp:action> .. </jsp:action> <jsp:useBean> .. </jsp:useBean> <jsp:forward> .. </jsp:forward> <jsp:include> .. </jsp:include> ..
Everything else besides the JSP elements is considered static content and it appears unaltered in the output.
<html> <!-- this is static content --> Hello world! </html>
request HttpServletRequest REQUEST response HttpServletResponse PAGE application ServletContext APPLICATION pageContext PageContext PAGE
JSPWriter PAGE config ServletConfig PAGE page (this) HttpJspPage PAGE session HttpSession SESSION exception Throwable PAGE
Get a parameter from the request <%= request.getParameter("nume") %> Get the IP address of the client and the type of his browser <%= request.getRemoteAddr() %> <%= request.getHeader("user-agent") %> <% session.setAttribute("user", "Duke"); synchronized (application) { application.setAttribute("sharedObject", new Object()); }
response.sendRedirect("http://www.google.ro"); response.sendError(404); %>
<%@ page errorPage="ShowError.jsp" %> <html> <head> <title>Error Handling Example</title> </head> <body> <% // Throw an exception to invoke the error page int x = 1; if (x == 1) { throw new RuntimeException("Boom!"); } %> </body> </html> <%@ page isErrorPage="true" %> <html> <head> <title>Show Error Page</title> </head> <body> <h1>Opps...</h1> <p>Sorry, an error occurred.</p> <p>Here is the exception stack trace: </p> <pre> <% exception.printStackTrace(response.getWriter()); %> </pre> </body> </html>
Error Handler Some JSP Page
– to eliminate scriptlets from a page – to promote reusability
– standard, of the form <jsp:action …/> – custom
– <jsp:useBean> – <jsp:setProperty> – <jsp:getProperty>
– <jsp:forward> – <jsp:include>
package test; public class Person { private String name; private BigDecimal salary; ... public String getName() { return name; } public void setName(String name) { this.nume = nume; } ... }
(too ugly, don’t use it)
Creating/Accessing an instance of the bean
<jsp:useBean id="pers" class="test.Person" scope="session" > pers.setName("Duke"); ... </jsp:useBean>
Accessing the properties of the bean
<jsp:setProperty name="pers" property="name" value="Joe" /> Person, your name is: <jsp:getProperty name="pers" property="name"/>
A (small) step towards accesing the data layer without writing Java code...
Person, your name is: ${pers.name}
<html> <jsp:useBean id="pers" scope="request" class="test.Person" /> <%-- We use introspection to populate the bean --%> <jsp:setProperty name="pers" property="*" /> <% if ( request.getParameter("name") == null ) { %> <form method="get"> Nume: <input type="text" name="name" size="25" /> <br/> <input type="submit" value="OK"/> </form> <% } else { <!-- If we decide not to use introspection: <jsp:setProperty name="pers" property="name" value="<%= request.getParameter("name") %>" />
Salut, <jsp:getProperty name="pers" property="name" />! <% } %> </html>
public void doGet (HttpServletRequest request, HttpServletResponse response) { //Get the JavaBean from its scope Person person = (Person) request.getAttribute("pers"); // Use the JavaBean person.setName("Joe"); //Eventually, forward the request getServletContext().getRequestDispatcher("result.jsp") .forward(request, response); }
<%@ include … %> directive ≠ <jsp: include …/> action
The first JSP of the chain maps the input elements of the form to the properties of the bean.
<jsp:setProperty name="pers" property="name" value="*" />