JavaBean是特殊的Java类,是用Java语言写成的可重用组件,并且遵守JavaBeans API规范:
一个例子:
public class StudentsBean implements java.io.Serializable
{
private String firstName = null;
private String lastName = null;
private int age = 0;
public StudentsBean() {
}
public String getFirstName(){
return firstName;
}
public String getLastName(){
return lastName;
}
public int getAge(){
return age;
}
public void setFirstName(String firstName){
this.firstName = firstName;
}
public void setLastName(String lastName){
this.lastName = lastName;
}
public void setAge(Integer age){
this.age = age;
}
}
jsp:useBean标签可以在JSP中声明一个JavaBean,然后使用。声明后,JavaBean对象就成了脚本变量,可以通过脚本元素或其他自定义标签来访问。jsp:useBean标签的语法格式如下:
<jsp:useBean id=“bean’s name” scope=“bean’s scope” typeSpec/>
其中,根据具体情况,scope的值可以是page,request,session或application。id值可任意只要不和同一JSP文件中其它jsp:useBean中id值一样就行了。
<html>
<head>
<title>get and set properties Example</title>
</head>
<body>
<jsp:useBean id="students" class="action.Students">
<jsp:setProperty name="students" property="firstName" value="Zara"/>
<jsp:setProperty name="students" property="lastName" value="Ali"/>
<jsp:setProperty name="students" property="age" value="10"/>
</jsp:useBean>
<p>Student First Name:
<jsp:getProperty name="students" property="firstName"/>
</p>
<p>Student Last Name:
<jsp:getProperty name="students" property="lastName"/>
</p>
<p>Student Age:
<jsp:getProperty name="students" property="age"/>
</p>
</body>
</html>
注意这里有一个错误:undefined type:action.Students
我把Students类的implements java.io.Serializable语句删除,错误就消失了:
但是运行时又遇到新的错误:
org.apache.jasper.JasperException: Cannot find a method to write property [age] of type [int] in a bean of type [action.Students]
org.apache.jasper.runtime.JspRuntimeLibrary.introspecthelper(JspRuntimeLibrary.java:367)
org.apache.jsp.main_jsp._jspService(main_jsp.java:135)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:477)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
Note The full stack trace of the root cause is available in the server logs.
把此处的Integer改成int,错误消失: