HomeJava & J2EE Page 4 - The JSP Files (part 1): Purple Pigs In A Fruitbasket
Enter John Doe - Java
Get to grips with Java Server Pages with this introductorytutorial and find out how to use one of the more powerful server-sidelanguages around. This first part explains the history and basics of JSPdocuments, and also illustrates variables, includes and the String object.
Variables are the bread and butter of every programming language...and JSP has them too. A variable can be thought of as a programming construct used to store both numeric and non-numeric data; this data can then be used in different places in your JSP scriptlets.
JSP supports a number of different variable types: integers, floating point numbers, strings and arrays. Unlike PHP, which can automagically determine variable type based on the data it holds, JSP requires you to explicitly define the type of each variable before using it.
Every variable has a name - in JSP, a variable name is preceded by a keyword indicating the variable type, and must begin with a letter, optionally followed by more letters and numbers. Variable names are case-sensitive, and reserved keywords cannot be used as variable names.
For example, "popeye", "one_two_three" and "bigPirateShip" are all valid variable names, while "byte" and "123" are invalid variable names.
The following example demonstrates how variables can be used in a JSP document.
<html>
<head>
</head>
<body>
<%!
// define variables here
String name = "John Doe";
%>
<%
// code comes here
out.println("My name is " + name );
%>
</body>
</html>
As you can see, we've first defined a variable named
"name", set things up so that it will hold string, or character, data, and assigned a value ("John Doe") to it. This value is then used by the println() function to display a message in the HTML page.
My name is John Doe
If you're sharp-eyed, you'll have noticed a slight
difference between the two JSP blocks in the example above - the first looks like this
<%!
...
%>
while the second looks like this
<%
...
%>
The first block, within which the variables are defined,
is referred to as the "declaration block"; variables declared within this block are available globally, to each and every scriptlet within that JSP document.
You can also define a variable without assigning a value to it, or assign a value to it at a later stage - for example, the following code snippets are equivalent.
<%
String name;
name = "John Doe";
%>
<%
String name = "John Doe";
%>
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