JspWriter类型中的print（boolean）方法不适用于参数（void） [英] The method print(boolean) in the type JspWriter is not applicable for the arguments (void)

问题描述

您好，我正面临一个错误，名为JspWriter类型中的方法print（boolean）不适用于GAE中我的JSP代码的参数（void）。

行：<％= request.getSession（true）.setAttribute（state，firstNumber）％>

以下是代码：

`

 < c：when test ='$ {param.event ==NewCall}> 
 <％
响应resp1 = new Response（）; 
 CollectDtmf cd = new CollectDtmf（）; 
 cd.addPlayText（Welcome。请输入第一个数字，终止于＃）; 
 resp1.addCollectDtmf（cd）; 
％> 
<％= request.getSession（true）.setAttribute（state，firstNumber）％> 
 <％out.println（resp1.getXML（））; ％GT; 
< / c：当> 
  

`

请告诉我是什么在这里做错了。感谢

解决方案

<％=％> 其值被打印到JSP的作者。以下

 <％= foo％> 
  

因此相当于

 的out.print（FOO）; 
 
 request.getSession（true）.setAttribute（state，firstNumber）
  

是一个表达式，其类型为void。而且你不能打印空白。

你想要的只是简单的

 <％request.getSession （true）.setAttribute（state，firstNumber）％> 
  

但是，当然，因为它已被无数次地重新编译，所以scriptlet不应该用在JSP中。 JSP是视图组件，只能使用JSP EL，JSTL和其他自定义标记生成HTML。更不用说，设置会话属性通常是一个坏主意，在视图组件中更糟糕的是，除了打印到JSP书写器之外，它不应该有任何副作用。

Hi I am facing a error named "The method print(boolean) in the type JspWriter is not applicable for the arguments (void) " with my JSP code in GAE.

In line :<%= request.getSession(true).setAttribute("state","firstNumber") %>

Here is the code:

`

  <c:when test='${param.event == "NewCall"}'>
      <% 
         Response resp1=new Response();
         CollectDtmf cd= new CollectDtmf(); 
         cd.addPlayText("Welcome. Please enter the first number. Terminate with #");           
         resp1.addCollectDtmf(cd);
      %>
      <%= request.getSession(true).setAttribute("state","firstNumber") %> 
      <% out.println(resp1.getXML()); %>
  </c:when>

`

Please tell what am I doing wrong here. Thanks

解决方案

<%= %>expects an expression, whose value is printed to the JSP's writer. The following

<%= foo %>

is thus equivalent to

out.print(foo);

request.getSession(true).setAttribute("state","firstNumber")

is an expression whose type is void. And you can't print a void.

What you want is simply

<% request.getSession(true).setAttribute("state","firstNumber") %>

But of course, as it has been rehashed countless times, scriptlets should not be used in a JSP. JSPs are view components which should only generate HTML using the JSP EL, the JSTL and other custom tags. Not to mention that setting session attributes is, in general, a bad idea, and is even more a bad idea in a view component, which shouldn't have any side effect other than printing to the JSP writer.

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