JavaServer Pages

Chapter 5
Generating Dynamic Content

By Hans Bergsten

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Accessing JavaBean Properties

The bean's data is represented by its properties. If you're a page author charged with developing a JSP page to display the content represented by a bean, you first need to know the names of all the bean's properties. This information should be available from the Java programmers on the team or from a third-party source. In this example, we use a standard Java class named java.util.Date as a bean with properties representing date and time information. Table 5-1 describes the properties used in this example. (If you're not a programmer, don't worry about the Java Type and Access columns at this point.)

Table 5-1:Properties for java.util.Date

Property Name	Java Type	Access	Description
date	int	read	The day of the month as a number between 1 and 31
hours	int	read	The hour as a number between 0 (midnight) and 23
minutes	int	read	The number of minutes past the hour as a number between 0 and 59
month	int	read	The month as a number from 0 to 11
year	int	read	The current year minus 1900

Once you have created a bean and given it a name, you can retrieve the values of the bean's properties in the response page with another JSP standard action, <jsp:getProperty>. This action obtains the current value of a bean property and inserts it directly into the response body.

To include the current date property value in the page, use the following tag:

<jsp:getProperty name="clock" property="date" />

The name attribute, set to clock, refers to the specific bean instance we defined with the <jsp:useBean> action previously. This action locates the bean and asks it for the value of the property specified by the property attribute. As documented in Table 5-1, the date property contains the day of the month as a number between 1 and 31. In Example 5-1, multiple <jsp:getProperty> actions are used to generate a list of all the clock bean's property values. The result is the page shown in Figure 5-2.

Input and Output

User input is a necessity in modern web pages. Most dynamic web sites generate pages based on user input. Unfortunately, users seldom enter information in exactly the format you need, so before you can use such input, you probably want to validate it.

And it's not only the input format that's important. Web browsers are also picky about the format of the HTML you send them. For instance, when you generate an HTML form with values taken from a database, a name such as O'Reilly can cause problems. The single quote character after the O can fool the browser into believing that it's at the end of the string, so you end up with just an O in your form.