Introduction | Mobile Engine Structure | Developing with Eclipse

Basics of Java Server Pages (JSP)

JSP can have following elements:

Expressions – formats expression as a string for output .
Scriptlets – Java code embedded in the page.
Declaratives – page-wide variable and method declarations.
Directives – gives JSP engine information for the page.

JSP Syntax Overview

Expressions

Syntax:

<%= Expression Here %>

Behavior:

Evaluated at run time.
Converted to strings.
Inserted as text directly into HTML page.
Full access to information about the request
Access to predefined variables listed above

Example:

<%= request.getRemoteHost() %>

Scriptlets

Syntax:

<% Java Code Here %>

Behavior:

Pieces of Java code embedded in the HTML page.
Access to predefined variables listed above.
Provides mechanism for more complex coding than expressions.
Can set properties for response object.
Can test parameters for null values.

Example 1:

<%
   String queryData = request.getQueryString();
   out.println("Attached GET data: "+ queryData);
%>

Example 2:

<%
     String bgColor = request.getParameter("bgColor");
     boolean hasExplicitColor;
     if (bgColor != null) {
       hasExplicitColor = true;
     } else {
       hasExplicitColor = false;
       bgColor = "WHITE";
     }
%>
<BODY BGCOOLOR ="<%= bgColor %>">

Declarations

Syntax:

<%! declaration code %>

Behavior:

Defines methods or variables to be inserted in the main body of the servlet class – become class level variables or methods.
Do not generate output on page.
Can be used in expressions and scriptlets.
Does not have to be declared static because only one instance of the servlet is created.

Example:

...
<BODY>
  <%! private int accessCounter = 0; %>
  <H2>This page has had
     <%= ++accessCounter %>
     Hits
  </H2>
</BODY>

Directives

Syntax:

<%@ attribute="value" %>

Behavior:

Affects the overall structure of the servlet that results from the Java Server Page.
Can list multiple NVPs in one set of tags
<%@ attribute1=“value1”
attribute2=“value2”
attribute3=“value3” %>

Type of Directives

page

Controls servlet class.
Can be located anywhere on the page.
Attributes include: import, contentType, isThreadSafe, session, buffer, autoflush, extends, info, errorPage, isErrorPage, language
<%@ page import=“java.util.*,coreservlets.*” %>

include

Includes a file.
File is inserted where the tag is located
<%@ include file=“subfile.jsp” %>

taglib – to define custom tags

you can define your own JSP tags

Other JSP Tags

JSP comment

<%-- This is a JSP Comment --%>

XML type tag for expressions

<jsp:expression>

Java Expression

</jsp:expression>

XML type tag for declarations

<jsp:declaration>

Code

</jsp:declaration>

XML type tag for directives

<jsp:directive.directiveType attribute="value"/>
<jsp:directive.page language="java"/>

Examples

Using Expressions

<BODY>
   <%@ page language="java" %>
   <%! String title = "My First Java Server Page"; %>
   <H2>JSP Expressions</H2>
   <UL>
    <LI>Page Title: <%= title %>
    <LI>Current time: <%= new java.util.Date() %>
    <LI>Your hostname: <%= request.getRemoteHost() %>
    <LI>Your session ID: <%= session.getId() %>
    <LI>Your First Name : <%= request.getParameter("firstName")    %>
    <LI>Your Last Name : <%= request.getParameter("lastName")    %>
   </UL>
</BODY>

Using Declarations - import

Compare:

<%
  java.util.Calendar rightNow = java.util.Calendar.getInstance();
  int hour = rightNow.get(java.util.Calendar.HOUR_OF_DAY);
%>

With:
<%@ page import="java.util.*" %>
<%
  Calendar rightNow = Calendar.getInstance();
  int hour = rightNow.get(Calendar.HOUR_OF_DAY);
%>

You do not have to type the full package name all the time, when you use the import declaration

Conditional Content Type

<%
   String format = request.getParameter("format");
   if ((format != null) && (format.equals("excel"))) {
//  Content type based on parameter.
       response.setContentType("application/vnd.ms-excel");
   }
%>

<TABLE BORDER=1>
   <TR><TH></TH><TH>Apples<TH>Oranges
   <TR><TH>First Quarter<TD>2307<TD>4706
   <TR><TH>Second Quarter<TD>2982<TD>5104
   <TR><TH>Third Quarter<TD>3011<TD>5220
   <TR><TH>Fourth Quarter<TD>3055<TD>5287
</TABLE>

JSP Programming Examples in the MDK

The JSP in the Example 2 of the "Getting Started" section demonstrates the usage of a gridlayout for better positioning of the graphical user interface elements and places an input field and a button in the grid layout

Example 2: welcome.jsp

The tableView.jsp of Example 2 demonstrates a layout to represent data in a tabular form. It uses variables supplied by a bean to keep the rows and columns of the table flexible.

Example 2: tableView.jsp

The menu.jsp in the persistence example uses a table structure similar to tableView.jsp but has additional checkboxes in the first row.

Persistence example: menu.jsp