JavaBean

JavaBean.

JavaBean ：软件组件，主要用于事务处理

       规范要求（反射）：是一个公共（public）类

                                   不带参数的构造方法

                                   通过setXXX方法设置属性，getXXX方法获取属性

    1.   JSP访问javaBean 的语法             

                     导入JavaBean 类

                     声明JavaBean对象

                     访问JavaBean属性

              例：<%@ import = “mypack.CounterBean”%>

                     <jsp:useBeanid=”myBean” class=”mypack.CounterBean” scope=”session”/>

                     <jsp:getPropertyname=”myBean” property=”count”/>

                     <jsp:setPropertyname=”myBean” property=”count” value=”0”/>

     2.  可以在<jsp:setProperty>中通过param参数来为bean的属性动态赋值

              <jsp；setProperty property=”age” name=”person”value=”helloworld”/>

              对应的Servlet代码是：

   org.apache.jasper.runtime.JspRuntimeLibrary.introspecthelper(_jspx_page_context.findAttribute（"person"),"age", request.getParameter("helloworld"), request,"helloworld", false);

   3.   JavaBean 的存活范围
              ---page  (默认值)

              ---request

              ---session

              ---application

 

   4 . 当javaBean放在session范围内时，放在application也不一样

       <jsp:useBeanid=”student” scope=”session” class=”javaBean.Stdent”/>

       生成的servlet源代码是：

                 javaBean.Student student = null;

                 synchronized (session) {

                           student = (javaBean.Student)_jspx_page_context.getAttribute("student",javax.servlet.jsp.PageContext.SESSION_SCOPE);

                         if (student == null){

                                       student = new javaBean.Student();

                                      _jspx_page_context.setAttribute("student", student, javax.servlet.jsp.PageContext.SESSION_SCOPE);

                               }

                         }