javax.servlet.ServletException：在作用域内找不到bean [name] [英] javax.servlet.ServletException: bean [name] not found within scope

问题描述

我收到此错误：

  javax.servlet.ServletException：在范围内找不到bean 
  

在页面顶部。

 < jsp：useBean id =beantype =com.example.Beanscope =request/> 
  

该类存在于类路径中，它今天早上起作用了，我找不到未找到的内容在范围内意味着。

这是如何引起的，我该如何解决？

解决方案

您需要类属性而不是类型属性。

以下内容：

 < ; jsp：useBean id =beantype =com.example.Beanscope =request/> 
  

基本以下幕后操作：

  Bean bean =（Bean）pageContext.getAttribute（bean，PageContext.REQUEST_SCOPE）; 
 
 if（bean == null）{
抛出新的ServletException（bean未在范围内找到）; 
} 
 
 //使用bean ... 
  

虽然以下内容：

 < jsp：useBean id =beanclass =com.example .Beanscope =request/> 
  

在幕后基本上完成以下工作：

< pre class =lang-java prettyprint-override> Bean bean =（Bean）pageContext.getAttribute（bean，PageContext.REQUEST_SCOPE）;

if（bean == null）{
bean = new Bean（）;
pageContext.setAttribute（bean，bean，PageContext.REQUEST_SCOPE）;
}

//使用bean ...


如果它以前工作过，而且突然没有工作，那么这意味着负责将bean放入范围的某事已停止工作。例如，一个servlet在 doGet（）中执行以下操作：

  request.setAttribute（bean，new Bean（））; 
 request.getRequestDispatcher（page.jsp）。forward（request，response）; 
  

也许你是通过URL直接调用JSP页面而不是通过URL调用Servlet。如果您想禁用对JSP页面的直接访问，请将它们放在 / WEB-INF 中，然后转发给它。

I'm getting this error:

javax.servlet.ServletException: bean not found within scope

on a page with this at the top.

<jsp:useBean id="bean" type="com.example.Bean" scope="request" />

The class exists in the classpath, it worked this morning, and I don't get what not found within scope means.

How is this caused and how can I solve it?

解决方案

You need the class attribute instead of the type attribute.

The following:

<jsp:useBean id="bean" type="com.example.Bean" scope="request" />

does basically the following behind the scenes:

Bean bean = (Bean) pageContext.getAttribute("bean", PageContext.REQUEST_SCOPE);

if (bean == null) {
    throw new ServletException("bean not found within scope");
}

// Use bean ...

While the following:

<jsp:useBean id="bean" class="com.example.Bean" scope="request" />

does basically the following behind the scenes:

Bean bean = (Bean) pageContext.getAttribute("bean", PageContext.REQUEST_SCOPE);

if (bean == null) {
    bean = new Bean();
    pageContext.setAttribute("bean", bean, PageContext.REQUEST_SCOPE);
}

// Use bean ...

If it has worked before and it didn't work "in a sudden", then it means that something which is responsible for putting the bean in the scope has stopped working. For example a servlet which does the following in the doGet():

request.setAttribute("bean", new Bean());
request.getRequestDispatcher("page.jsp").forward(request, response);

Maybe you've invoked the JSP page directly by URL instead of invoking the Servlet by URL. If you'd like to disable direct access to JSP pages, then put them in /WEB-INF and forward to it instead.

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