the basic use of simple syntax (i.e, elements) involved with JSP development.
Elements of JSP
The elements of JSP have been described below −
The Scriptlet
A scriptlet can contain any number of JAVA language statements, variable or method declarations, or expressions that are valid in the page scripting language.
Following is the syntax of Scriptlet −
<% code fragment %>
You can write the XML equivalent of the above syntax as follows −
<jsp:scriptlet>
code fragment
</jsp:scriptlet>
Any text, HTML tags, or JSP elements you write must be outside the scriptlet. Following is the simple and first example for JSP −
<html>
<head><title>Hello World</title></head>
<body>
Hello World!<br/>
<%
out.println("Your IP address is " + request.getRemoteAddr());
%>
</body>
</html>NOTE − Assuming that Apache Tomcat is installed in C:\apache-tomcat-7.0.2 and your environment is setup as per environment setup tutorial.
Let us keep the above code in JSP file hello.jsp and put this file in C:\apache-tomcat7.0.2\webapps\ROOT directory. Browse through the same using URL http://localhost:8080/hello.jsp. The above code will generate the following result −
JSP Declarations
A declaration declares one or more variables or methods that you can use in Java code later in the JSP file. You must declare the variable or method before you use it in the JSP file.
Following is the syntax for JSP Declarations −
<%! declaration; [ declaration; ]+ ... %>
You can write the XML equivalent of the above syntax as follows −
<jsp:declaration>
code fragment
</jsp:declaration>
Following is an example for JSP Declarations −
<%! int i = 0; %>
<%! int a, b, c; %>
<%! Circle a = new Circle(2.0); %>
JSP Expression
A JSP expression element contains a scripting language expression that is evaluated, converted to a String, and inserted where the expression appears in the JSP file.
Because the value of an expression is converted to a String, you can use an expression within a line of text, whether or not it is tagged with HTML, in a JSP file.
The expression element can contain any expression that is valid according to the Java Language Specification but you cannot use a semicolon to end an expression.
Following is the syntax of JSP Expression −
<%= expression %>
You can write the XML equivalent of the above syntax as follows −
<jsp:expression>
expression
</jsp:expression>Following example shows a JSP Expression −
<html>
<head><title>A Comment Test</title></head>
<body>
<p>Today's date: <%= (new java.util.Date()).toLocaleString()%></p>
</body>
</html> The above code will generate the following result −
Today's date: 11-Sep-2010 21:24:25
JSP Comments
JSP comment marks text or statements that the JSP container should ignore. A JSP comment is useful when you want to hide or "comment out", a part of your JSP page.
Following is the syntax of the JSP comments −
<%-- This is JSP comment --%>
Following example shows the JSP Comments −
<html>
<head><title>A Comment Test</title></head>
<body>
<h2>A Test of Comments</h2>
<%-- This comment will not be visible in the page source --%>
</body>
</html> The above code will generate the following result −
A Test of Comments
There are a small number of special constructs you can use in various cases to insert comments or characters that would otherwise be treated specially. Here's a summary −
| S.No. | Syntax & Purpose |
|---|---|
| 1 | <%-- comment --%> A JSP comment. Ignored by the JSP engine. |
| 2 | <!-- comment --> An HTML comment. Ignored by the browser. |
| 3 | <\% Represents static <% literal. |
| 4 | %\> Represents static %> literal. |
| 5 | \' A single quote in an attribute that uses single quotes. |
| 6 | \" A double quote in an attribute that uses double quotes. |
JSP Directives
A JSP directive affects the overall structure of the servlet class. It usually has the following form −
<%@ directive attribute="value" %>
There are three types of directive tag −
| S.No. | Directive & Description |
|---|---|
| 1 | <%@ page ... %> Defines page-dependent attributes, such as scripting language, error page, and buffering requirements. |
| 2 | <%@ include ... %> Includes a file during the translation phase. |
| 3 | <%@ taglib ... %> Declares a tag library, containing custom actions, used in the page |
We would explain the JSP directive in a separate chapter JSP - Directives
JSP Actions
JSP actions use constructs in XML syntax to control the behavior of the servlet engine. You can dynamically insert a file, reuse JavaBeans components, forward the user to another page, or generate HTML for the Java plugin.
There is only one syntax for the Action element, as it conforms to the XML standard −
<jsp:action_name attribute="value" />
Action elements are basically predefined functions. Following table lists out the available JSP Actions −
| S.No. | Syntax & Purpose |
|---|---|
| 1 | jsp:include Includes a file at the time the page is requested. |
| 2 | jsp:useBean Finds or instantiates a JavaBean. |
| 3 | jsp:setProperty Sets the property of a JavaBean. |
| 4 | jsp:getProperty Inserts the property of a JavaBean into the output. |
| 5 | jsp:forward Forwards the requester to a new page. |
| 6 | jsp:plugin Generates browser-specific code that makes an OBJECT or EMBED tag for the Java plugin. |
| 7 | jsp:element Defines XML elements dynamically. |
| 8 | jsp:attribute Defines dynamically-defined XML element's attribute. |
| 9 | jsp:body Defines dynamically-defined XML element's body. |
| 10 | jsp:text Used to write template text in JSP pages and documents. |
We would explain JSP actions in a separate chapter JSP - Actions
JSP Implicit Objects
JSP supports nine automatically defined variables, which are also called implicit objects. These variables are −
| S.No. | Object & Description |
|---|---|
| 1 | request This is the HttpServletRequest object associated with the request. |
| 2 | response This is the HttpServletResponse object associated with the response to the client. |
| 3 | out This is the PrintWriter object used to send output to the client. |
| 4 | session This is the HttpSession object associated with the request. |
| 5 | application This is the ServletContext object associated with the application context. |
| 6 | config This is the ServletConfig object associated with the page. |
| 7 | pageContext This encapsulates use of server-specific features like higher performance JspWriters. |
| 8 | page This is simply a synonym for this, and is used to call the methods defined by the translated servlet class. |
| 9 | Exception The Exception object allows the exception data to be accessed by designated JSP. |
We would explain JSP Implicit Objects in a separate chapter JSP - Implicit Objects.
Control-Flow Statements
You can use all the APIs and building blocks of Java in your JSP programming including decision-making statements, loops, etc.
Decision-Making Statements
The if...else block starts out like an ordinary Scriptlet, but the Scriptlet is closed at each line with HTML text included between the Scriptlet tags.
<%! int day = 3; %>
<html>
<head><title>IF...ELSE Example</title></head>
<body>
<% if (day == 1 || day == 7) { %>
<p> Today is weekend</p>
<% } else { %>
<p> Today is not weekend</p>
<% } %>
</body>
</html> The above code will generate the following result −
Today is not weekend
Now look at the following switch...case block which has been written a bit differentlty using out.println() and inside Scriptletas −
<%! int day = 3; %>
<html>
<head><title>SWITCH...CASE Example</title></head>
<body>
<%
switch(day) {
case 0:
out.println("It\'s Sunday.");
break;
case 1:
out.println("It\'s Monday.");
break;
case 2:
out.println("It\'s Tuesday.");
break;
case 3:
out.println("It\'s Wednesday.");
break;
case 4:
out.println("It\'s Thursday.");
break;
case 5:
out.println("It\'s Friday.");
break;
default:
out.println("It's Saturday.");
}
%>
</body>
</html> The above code will generate the following result −
It's Wednesday.
Loop Statements
You can also use three basic types of looping blocks in Java: for, while, and do…while blocks in your JSP programming.
Let us look at the following for loop example −
<%! int fontSize; %>
<html>
<head><title>FOR LOOP Example</title></head>
<body>
<%for ( fontSize = 1; fontSize <= 3; fontSize++){ %>
<font color = "green" size = "<%= fontSize %>">
JSP Tutorial
</font><br />
<%}%>
</body>
</html> The above code will generate the following result −
JSP Tutorial
JSP Tutorial
JSP Tutorial
Above example can be written using the while loop as follows −
<%! int fontSize; %>
<html>
<head><title>WHILE LOOP Example</title></head>
<body>
<%while ( fontSize <= 3){ %>
<font color = "green" size = "<%= fontSize %>">
JSP Tutorial
</font><br />
<%fontSize++;%>
<%}%>
</body>
</html> The above code will generate the following result −
JSP Tutorial
JSP Tutorial
JSP Tutorial
JSP Operators
JSP supports all the logical and arithmetic operators supported by Java. Following table lists out all the operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom.
Within an expression, higher precedence operators will be evaluated first.
| Category | Operator | Associativity |
|---|---|---|
| Postfix | () [] . (dot operator) | Left to right |
| Unary | ++ - - ! ~ | Right to left |
| Multiplicative | * / % | Left to right |
| Additive | + - | Left to right |
| Shift | >> >>> << | Left to right |
| Relational | > >= < <= | Left to right |
| Equality | == != | Left to right |
| Bitwise AND | & | Left to right |
| Bitwise XOR | ^ | Left to right |
| Bitwise OR | | | Left to right |
| Logical AND | && | Left to right |
| Logical OR | || | Left to right |
| Conditional | ?: | Right to left |
| Assignment | = += -= *= /= %= >>= <<= &= ^= |= | Right to left |
| Comma | , | Left to right |
JSP Literals
The JSP expression language defines the following literals −
Boolean − true and false
Integer − as in Java
Floating point − as in Java
String − with single and double quotes; " is escaped as \", ' is escaped as \', and \ is escaped as \\.
Null − null
JSP - Directives
These directives provide directions and instructions to the container, telling it how to handle certain aspects of the JSP processing.
A JSP directive affects the overall structure of the servlet class. It usually has the following form −
<%@ directive attribute = "value" %>
Directives can have a number of attributes which you can list down as key-value pairs and separated by commas.
The blanks between the @ symbol and the directive name, and between the last attribute and the closing %>, are optional.
There are three types of directive tag −
| S.No. | Directive & Description |
|---|---|
| 1 | <%@ page ... %> Defines page-dependent attributes, such as scripting language, error page, and buffering requirements. |
| 2 | <%@ include ... %> Includes a file during the translation phase. |
| 3 | <%@ taglib ... %> Declares a tag library, containing custom actions, used in the page |
JSP - The page Directive
The page directive is used to provide instructions to the container. These instructions pertain to the current JSP page. You may code page directives anywhere in your JSP page. By convention, page directives are coded at the top of the JSP page.
Following is the basic syntax of the page directive −
<%@ page attribute = "value" %>
You can write the XML equivalent of the above syntax as follows −
<jsp:directive.page attribute = "value" />
Attributes
Following table lists out the attributes associated with the page directive −
| S.No. | Attribute & Purpose |
|---|---|
| 1 | buffer Specifies a buffering model for the output stream. |
| 2 | autoFlush Controls the behavior of the servlet output buffer. |
| 3 | contentType Defines the character encoding scheme. |
| 4 | errorPage Defines the URL of another JSP that reports on Java unchecked runtime exceptions. |
| 5 | isErrorPage Indicates if this JSP page is a URL specified by another JSP page's errorPage attribute. |
| 6 | extends Specifies a superclass that the generated servlet must extend. |
| 7 | import Specifies a list of packages or classes for use in the JSP as the Java import statement does for Java classes. |
| 8 | info Defines a string that can be accessed with the servlet's getServletInfo() method. |
| 9 | isThreadSafe Defines the threading model for the generated servlet. |
| 10 | language Defines the programming language used in the JSP page. |
| 11 | session Specifies whether or not the JSP page participates in HTTP sessions |
| 12 | isELIgnored Specifies whether or not the EL expression within the JSP page will be ignored. |
| 13 | isScriptingEnabled Determines if the scripting elements are allowed for use. |
Check for more details related to all the above attributes at Page Directive.
The include Directive
The include directive is used to include a file during the translation phase. This directive tells the container to merge the content of other external files with the current JSP during the translation phase. You may code the include directives anywhere in your JSP page.
The general usage form of this directive is as follows −
<%@ include file = "relative url" >
The filename in the include directive is actually a relative URL. If you just specify a filename with no associated path, the JSP compiler assumes that the file is in the same directory as your JSP.
You can write the XML equivalent of the above syntax as follows −
<jsp:directive.include file = "relative url" />
For more details related to include directive, check the Include Directive.
The taglib Directive
The JavaServer Pages API allow you to define custom JSP tags that look like HTML or XML tags and a tag library is a set of user-defined tags that implement custom behavior.
The taglib directive declares that your JSP page uses a set of custom tags, identifies the location of the library, and provides means for identifying the custom tags in your JSP page.
The taglib directive follows the syntax given below −
<%@ taglib uri="uri" prefix = "prefixOfTag" >
Here, the uri attribute value resolves to a location the container understands and the prefix attribute informs a container what bits of markup are custom actions.
You can write the XML equivalent of the above syntax as follows −
<jsp:directive.taglib uri = "uri" prefix = "prefixOfTag" />
Comments
Post a Comment