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IBM Labs in Haifa JSP – Dynamic Content Generation Made Simple Gal Shachor
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IBM Labs in Haifa
JSP – Dynamic Content Generation Made Simple
Gal Shachor
IBM Labs in Haifa
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Agenda
JSP – What and Why? My first JSP JSP Fundamentals JSP Directives and APIs JSP and Tags MVC (Model 2) Application We did not talk about…
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JSP
What is it? Why do we need it?
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What is JSP?
JSP == Java Server Pages
A simplified way to generate dynamic web content Simpler then Servlets (Java is not mandatory) Editing tool friendly Can be used to separate the coding of presentation and business
logic
JSP is based on Java and Servlet technologies An HTML page with imbedded tags and Java Code. At runtime the JSP page is translated into a Java Servlet The runtime is usually encapsulated in a special JSP-Runtime
Servlet.
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JSP – A standard
JSP is a Java Standard: Defined by a group of companies led by JavaSoft. Current version is 1.2, but previous versions are also in use (mainly
1.1). Ongoing effort to improve JSP.
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Why JSP?
Because it is needed! In fact, there are several JSP like technologies both in the Java (as
well as non-Java) world
Servlets that generate HTML output hide the HTML inside Java. Makes it hard for an HTML expert (!= Java expert) to fix stuff. Lock the content in Java. Makes look and feel changes to the site problematic.
The ability to script with Java and JavaBeans makes generating dynamic content simpler. The competitors (ASP/SSJS) provide an extremely !!! simple (and
appealing) method for generating dynamic content.
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The JSP Syntax
Inline Java code delimited by <% and %>. Also printing of expressions as text by using <%= %>.
Special tags to declare class wide variables and methods. Special tags to use with JavaBeans. Special tags to expose JSP services. JSP directives to specify.
Interfaces implemented by the Servlet, classes it extends, packages to import etc.
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My first JSP
Hello World
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Helloworld.jsp – The code
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML>
<HEAD>
<%@ page language="java"
contentType="text/html; charset=US-ASCII"
pageEncoding="US-ASCII" %>
<META name="GENERATOR" content="IBM WebSphere Studio">
<TITLE>helloworld.jsp</TITLE>
</HEAD>
<BODY>
<P> <% out.print("This is a sample JSP file"); %> </P>
</BODY>
</HTML>
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Helloworld.jsp – Output
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Helloworld.jsp – Observations
At first, the JSP file looks like a regular HTML page HTML tags, doctype, etc.
There is a new <%@ page … %> “Tag” that has nothing to do with HTML This is a JSP directive
We have some Java code enclosed between <% and %> This is a JSP scriptlet
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JSP Fundamentals
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JSP Fundementals
Adding Java to a plain HTML page. Scriptlets
Use JSP implicit variables. To obtain information. To write data back to the user.
Defining class wide variables and methods. For initialization.
Commenting your scripts.
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JSP Scriptlets
Scriptlets let the developer place inline Java code inside the HTML General syntax: <% Java code %>
<% i++; %>
Expression placement lets the developer place a Java expression (converted to a String) inline with the HTML General syntax <%= expression %>
<%= new Date() %>
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Scriptlets and Conditional HTML
Scriptlets can be used to implement conditional HTML
<% if(variable ) { %>
<h1> variable is true </h1>
<% } else { %>
<h1> variable is false </h1>
<% } %>
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Scriptlets and Looping
Scriptlets can be used to implement loops inside the HTML.
<% for(int k = 0 ; k < 10 ; k++ ) { %>
<h1> variable’s value is <%= k %> </h1>
<% } %>
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JSP Implicit Variables
JSP has several implicit variables that can be used freely within the JSP page. Available without prior declaration and definition. Provides all the services and APIs that are available for the
servlet developer. Some of the implicit variables are:
request – The HttpServletRequest object as arrived to the service method.
response – The HttpServletResponse object as arrived to the service method.
out – A JspWriter connected to the ServletOutputStream of response.
session – The HttpSession object associated with the current user-session.
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Class Wide Declarations
Class wide can be used to define instance methods and variables in the page. These methods and variables end up defined in the class created
from the JSP file. Class wide declarations are enclosed within a <%! %> pair. Example usage can be creating initialization code.
<%!
int varname = 1;
void jspInit()
{
System.out.println("inside init");
}
%>
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Comments in JSP
There are two types of comments in JSP. HTML comments that should arrive to the client's browser.
These comments can contain JSP code and Scriptlets that are executed.
<!-- <% out.print("My comment"); %> --> Comments to the JSP page itself.
These comments and their content are not interpreted and will not arrive to the client.
<%-- anything but a closing --%> ... --%>
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Including Content – The include Directive
A tool for inclusion of content inside the JSP page at translation time. General syntax:
<%@ Include file="relativeURLspec" %> File points to a URI that identifies the resource to be included into the
JSP page. Very useful for sites with specific headers footers etc.
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Snoop.jsp
Uses scriptlets to present the request headers and form parameters sent to the page Employs scriptlets, implicit variables and comments
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Snoop.jsp – The code
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><HTML><HEAD><%@ page language="java"contentType="text/html; charset=WINDOWS-1255"pageEncoding="WINDOWS-1255"import="java.util.*" %>
<META name="GENERATOR" content="IBM WebSphere Studio"><TITLE>JSP snoop page</TITLE></HEAD><BODY>
<H1>JSP Snoop page</H1>
…
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Snoop.jsp – The code
<% Enumeration e = request.getHeaderNames();
if(e != null && e.hasMoreElements()) { %>
<H2>Request headers</H2>
<TABLE>
<TR>
<TH align=left>Header:</TH>
<TH align=left>Value:</TH>
</TR>
<% while(e.hasMoreElements()) {
String k = (String) e.nextElement(); %>
<TR>
<TD><%= k %></TD>
<TD><%= request.getHeader(k) %></TD>
</TR>
<% } %>
</TABLE>
<% } %>
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Snoop.jsp – The code<% e = request.getParameterNames();
if(e != null && e.hasMoreElements()) { %>
<H2>Request parameters</H2>
<TABLE>
<TR valign=top>
<TH align=left>Parameter:</TH>
<TH align=left>Value:</TH>
</TR>
<% while(e.hasMoreElements()) {
String k = (String) e.nextElement();
String val = request.getParameter(k); %>
<TR valign=top>
<TD><%= k %></TD>
<TD><%= val %></TD>
</TR>
<% } %>
</TABLE>
<% } %>
</BODY>
</HTML>
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Snoop.jsp – Output
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Directives and APIs
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JSP Directives and APIs
JSP 1.0 provides directives and APIs to allow enhanced control over the page.
Directives provides: Declarative page control (caching for example). Defining Java related page attributes.
The APIs provides: Programmatic page control. Access to information that was supplied by using directives
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JSP Directives
Directives begin with <%@ and ends with %> Directives have a type, attributes and values
<%@ type attribute="value" %> For now the types are
page include taglib
<%@ page attribute="value">
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JSP Page Directives
Page directives provides fine-grained control over the JSP Page Buffering. Session Usage. Importing a Java class Programming language used in the page Required locale …<%@ page language="java"
contentType="text/html; charset=WINDOWS-1255"
pageEncoding="WINDOWS-1255"
import="java.util.*" %>
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The taglib Directive
A syntax extension tool for JSP General syntax
<%@ taglib uri="uriToTagLibrary" prefix="tagprefix" %> uri - A URI that uniquely names the tag library prefix - Defines the prefix for the tags in the tag library. The prefix
distinguishes the custom tag. For example myPrefix is the prefix in the following tag <myPrefix:myTag/>
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JSP APIs
Extends the servlet APIs to sign a better contract between the JSP runtime and the JSP Developer.
Expose JSP related information and services to the developer. JspWriter
Somewhat separate the JSP implementation internals from the page generated Servlet. Example PageContext, JspFactory
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JspWriter
Provides many methods to write data to the user and to manipulate the page buffer. For example: clear() flush() getBufferSize() isAutoFlush()
The JspWriter is useful when: You are writing output from a scriptlet. You want to control the page buffering.
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Servlet Instantiation
The container instantiates a new Servlet in two occasions: A user request service from a Servlet that was not
instantiated yet. The Servlet is in the list of startup Servlets and the container
is starting.
A Servlet is instantiated in the following manner: The container loads the Servlet’s class. Using Class.newInstance() the container instantiates a new
instance of the Servlet.
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JSP, Java Beans and Tags
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JSP and JavaBeans
JavaBeans is the component model used for the Java language: Portable. Platform independent. Written in Java.
Beans are: Java classes. Reusable software components. You can combine several beans to create a bigger whole.
One of the main ideas in JSP is that developers can use JavaBeans to separate the HTML view from the Java implementation code.
Developers integrate the JavaBeans into the JSP page using special tags and Scriptlets.
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Bean Tags in JSP
JSP introduces new tags to handle beans: Attaching to a certain bean.
jsp:useBean Initializing a bean. Setting a bean attribute
jsp:setProperty Getting a bean attribue.
jsp:getProperty
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Beanmyname.jsp
Print a name as submitted by the user
Uses JavaBeans and JSP JavaBeans tags: To parse the parameters sent Print the parameters
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Beanmyname.jsp – The code<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML>
<HEAD>
<%@ page language="java"
contentType="text/html; charset=WINDOWS-1255"
pageEncoding="WINDOWS-1255"
import="NameBean"
%>
<META http-equiv="Content-Type"
content="text/html; charset=WINDOWS-1255">
<TITLE>beanmyname.jsp</TITLE>
</HEAD>
<jsp:useBean id="myusername" scope="page" class="NameBean">
<jsp:setProperty name="myusername" property="*" />
</jsp:useBean>
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Beanmyname.jsp – The code<BODY>
<H1>Print my name using JavaBeans</H1>
Your full name Is:
<jsp:getProperty name="myusername" property="name" />
<jsp:getProperty name="myusername" property="family" />
<H1>Send Your Name</H1>
<FORM method="GET" action="beanmyname.jsp">
<P>Your Name: <INPUT type="text" name="name" size="20"></P>
<P>Your Family: <INPUT type="text" name="family" size="20"></P>
<P><INPUT type="submit" value="Submit"> <INPUT type="reset"value="Reset"></P>
</FORM>
</BODY>
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NameBean – The codeimport java.io.Serializable;
public class NameBean implements Serializable {
String nameProperty = null;
String fnameProperty = null;
public void setName(String name) {
nameProperty = name;
}
public String getName() {
return nameProperty;
}
public void setFamily(String name) {
fnameProperty = name;
}
public String getFamily() {
return fnameProperty;
}
}
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Beanmyname.jsp – Output
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MVC (Model 2) Application
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General Web Application Design Rules
Separate presentation and business logic. JSP is only about presenting data. The JSP file does not need to know where the data came from.
Separate the work done by the HTML and Java coders to eliminate contention. These are two different developers. The tools used by the HTML/Java coders are not that good when it
comes to handle Java/HTML code. Data access and business logic is done in Java. JSP get to see the results of this business logic via JavaBeans/special
tags. Servlets and JSP can interact in two access models known as Model-1
and Model-2
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Java Server Pages Access Models
You can apply the JSP technology in two ways: Model-1 – A user working in a client web browser makes a request
that is sent to a JSP (.jsp) file. The JSP file accesses server components that generate dynamic content and displays the dynamic content in the browser.
Model-2 – A user working in a client web browser makes a request that is sent to a java Servlet that generates a result and stores the result in component. The Servlet then calls a JSP file, which accesses the component and displays the dynamic content in the browser.
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Model - 1
Model-1 is very simple to understand and itMakes generation of simple pages simple.
But it also messy when a complex page is needed and tends to require lots of Java code in the JSP file (a real no no from a design point of view).
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Model - 2
Model-2 is very clean, Makes generation of complex pages simpler as it removes most of the Java code from the JSP file and places most of the logic work in Java (where it belongs).
But its not as simple as Model-1 and is makes creation of simple JSP files a bit complex.
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Implementing Model-2
Advanced staff
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Model 2 Implementation – RequestDispatcher
RequestDispatcher Allows a Servlet to forward a request to another servlet (or JSP file)
or to include this servlet output in the response Exposes the methods:
forward(ServletRequest, ServletResponse) – Forwards a request from a servlet to another resource on the server.
include(ServletRequest, ServletResponse) – Includes the content of a resource in the response.
Can be obtained using: ServletContext.getRequestDispatcher(uri),
ServletContext.getNamedDispatcher(servletName), ServletRequest.getRequestDispatcher(uri)
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Model 2 Implementation – Passing Parameters
A servlet that uses a RequestDispatcher can pass parameters to the resource using the ServletRequest object attributes setAttribute(name, o) – Stores an attribute in this request. removeAttribute(name) – Removes an attribute from this request. getAttribute(name) – Returns the value of the named attribute as an
Object, or null if no attribute of the given name exists. getAttributeNames() – Returns an Enumeration containing the
names of the attributes available to this request. A dispatching servlet can then use the input parameters to perform
some business logic, obtain data and save it in beans and submit it to a JSP file Inside the JSP file tags can be used to extract the bean’s contents
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Model2myname – Presenting name using Model 2
Same as beanmyname but: A servlet constructs the
bean with parameters Uses
RequestDispatcher to include a View JSP in the output
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Model2Dispatcher Servlet – The code
package com.hrl.sample;
import NameBean;
import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.*;
public class Model2Dispatcher extends HttpServlet {
public void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
doGet(req, resp);
}
...
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Model2Dispatcher Servlet – The code
...
public void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
final NameBean name = new NameBean();
name.setName(req.getParameter("name"));
name.setFamily(req.getParameter("family"));
req.setAttribute("myusername", name);
final RequestDispatcher disp =
req.getRequestDispatcher("model2myname.jsp");
disp.forward(req, resp);
}
}
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Model2myname.jsp – The code
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML>
<HEAD>
<%@ page language="java"
contentType="text/html; charset=WINDOWS-1255"
pageEncoding="WINDOWS-1255"
import="NameBean"
%>
<META http-equiv="Content-Type"
content="text/html; charset=WINDOWS-1255">
<TITLE>model2myname.jsp</TITLE>
</HEAD>
<jsp:useBean id="myusername" scope="request" class="NameBean"/>
...
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Model2myname.jsp – The code
...
<BODY>
<H1>Print my name using MVC</H1>
Your full name Is:
<jsp:getProperty name="myusername" property="name" />
<jsp:getProperty name="myusername" property="family" />
<H1>Send Your Name</H1>
<FORM method="GET" action="Model2Dispatcher">
<P>Your Name: <INPUT type="text" name="name" size="20"></P>
<P>Your Family: <INPUT type="text" name="family" size="20"></P>
<P><INPUT type="submit" value="Submit"> <INPUT type="reset"value="Reset"></P>
</FORM>
</BODY>
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We did not talk about…
Advanced staff
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Lots of interesting staff (20/80 principle kicked in)
70% of the APIs and directives Custom tags Struts, WebWorks …
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End
