类声明：
package test;
public class Student {
private int age;
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
jsp代码：
<jsp:useBean id="student" scope="session" class="test.Student"></jsp:useBean>
<jsp:setProperty property="age" name="student" value="12"/>
<jsp:setProperty property="age" name="student" param="12"/> 此处12只是一个参数名字
<jsp:getProperty property="age" name="student"/>
=》12
源码如下：
test.Student student = null;
synchronized (session) {
student = (test.Student) _jspx_page_context.getAttribute("student", PageContext.SESSION_SCOPE);
if (student == null){
student = new test.Student();
_jspx_page_context.setAttribute("student", student, PageContext.SESSION_SCOPE);
}
}
out.write("\r\n");
out.write(" \t");
org.apache.jasper.runtime.JspRuntimeLibrary.introspecthelper(_jspx_page_context.findAttribute("student"), "age", "12", null, null, false);
out.write("\r\n");
out.write(" \t");
org.apache.jasper.runtime.JspRuntimeLibrary.introspecthelper(_jspx_page_context.findAttribute("student"), "age", request.getParameter("12"), request, "12", false);
out.write("\r\n");
out.write(" \t");
out.write(org.apache.jasper.runtime.JspRuntimeLibrary.toString((((test.Student)_jspx_page_context.findAttribute("student")).getAge())));
解释：
1.
<jsp:useBean id="student" scope="request" class="test.Student"></jsp:useBean>
<jsp:setProperty property="age" name="student" value="12"/>必须和<jsp:useBean配套使用
2.在useBean中声明要放在哪个useBean范围内：page，request，session，application，然后指定id也就是属性名和class也就是属性类型。
3.利用setProperty往useBean声明的变量中放置值，property为属性的变量名，name为useBean中声明的id名这两者必须相同，因为是将值设置到id指定的属性中去，value直接设置属性值，param则是接受传递过来的参数值设置到属性中，如request.getParameter。
param例子：
test2.jsp:
<jsp:forward page="test3.jsp">
<jsp:param value="10" name="age"/>
</jsp:forward>
test3.jsp:
<jsp:useBean id="student" scope="request" class="test.Student"></jsp:useBean>
<jsp:setProperty property="age" name="student" param="age"/>
<jsp:getProperty property="age" name="student"/>
结果为：10
4.通过getProperty从id中取直，property指定属性名，那么指定从哪个id中取值。
注意：修改scope范围生成的servlet中的源代码只有以下部分发生改变
synchronized (session) {
student = (test.Student) _jspx_page_context.getAttribute("student", PageContext.SESSION_SCOPE);
if (student == null){
student = new test.Student();
_jspx_page_context.setAttribute("student", student, PageContext.SESSION_SCOPE);
}
}
此代码先判断在session中是否存在student对象不存在创建一个放入session中，如果存在则不创建。之后设置值时就是往该对象中放置。
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