Declaring a Bean in a JSP Page

Example 6-1 shows a JSP page that uses the bean described in Table 6-1 to display a cartoon strip.

Example 6-1. A page using a bean (cartoon.jsp)

    <title>A dose of Dilbert</title>
  <body bgcolor="white">
    <h1>A dose of Dilbert</h1>
    <jsp:useBean id="cartoon" 
      class="com.ora.jsp.beans.motd.CartoonBean" />
    <img src="images/<jsp:getProperty name="cartoon" 
                  property="fileName" />">

Before you use a bean in a page, you must tell the JSP container which type of bean it is and associate it with a name: in other words, you must declare the bean. The first JSP action in Example 6-1, <jsp:useBean>, is used for this purpose:

<jsp:useBean id="cartoon" class="com.ora.jsp.beans.motd.CartoonBean" />

The <jsp:useBean> action is one of the JSP standard actions (identified by the jsp prefix). The action creates an instance of the bean class specified by the class attribute and associates it with the name specified by the id attribute. The name must be unique in the page and be a valid Java variable name: it must start with a letter and can’t contain special characters such as dots, plus signs, etc.

Other attributes you can specify for the <jsp:useBean> action are scope, type, and beanName. Chapter 10 explores how the scope attribute is used. The others are rarely used, but Appendix A contains descriptions of how you can use them if you wish.

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