JavaSercer Pages 5.1.4 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, . 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: The name attribute, set to clock, refers to the specific bean instance we defined with the 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 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. 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. 5.2.1 Using JavaBeans to Process Input As we saw earlier, a bean is often used as a container for data, created by some server process, and used in a JSP page that displays the data. But a bean can also be used to capture user input. The captured data can then be processed by the bean itself or used as input to some other server component (e.g., a component that stores the data in a database or picks an appropriate banner ad to display). The nice thing about using a bean this way is that all information is in one bundle. Say you have a bean that can contain information about a person, and it captures the name, birth date, and email address as entered by the person on a web form. You can then pass this bean to another component, providing all the information about the user in one shot. Now, if you want to add more information about the user, you just add properties to the bean, instead of having to add parameters all over the place in your code. Another benefit of using a bean to capture user input is that the bean can encapsulate all the rules about its properties. Thus, a bean representing a person can make sure the birthDate property is set to a valid date. page 46
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