Can't use : “Bean cannot be resolved to a type”

问题

I'm just playing around with JSP. I just wanted to test some <jsp:useBean> stuff, but I can't. Every time if I'm using <jsp:useBean>, I get an error. Even if I just have this, I get an error:

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>Test</title>
  </head>
  <body>
    <jsp:useBean id="mybean" class="Users" scope="session" >
      <jsp:setProperty name="mybean" property="name" value="Hello world" />
    </jsp:useBean>
  </body>
</html>

Without the <jsp:useBean> it runs fine. With the <jsp:useBean> I get an error like:

Servlet.service() for servlet [jsp] in context with path [/JSPTest] threw exception [Unable to compile class for JSP: 

An error occurred at line: 10 in the jsp file: /index.jsp
Users cannot be resolved to a type
7:     <title>Insert title here</title>
8:   </head>
9:   <body>
10:     <jsp:useBean id="mybean" class="Users" scope="session" >
11:       <jsp:setProperty name="mybean" property="name" value="Hello world" />
12:     </jsp:useBean>
13:   </body>

I am using Eclipse, Tomcat 7.0.23 and Java 1.7.0_01.

Any ideas?

PS: I had to change the port 8xxx to 9xxx because the oracle DB is using the standard 8xxx. But that's likely not the cause of the problem.

回答1:

You need to put classes in a package in order to be able to use them in another classes. Classes in the default package are invisible to classes which are by itself in a package (like as the JSP would end up).

So, give the Users class a package like so:

package com.example;

public class Users {
    // ...
}

Recompile and put it in /WEB-INF/classes/com/example/Users.class.

Then you can reference it as follows:

<jsp:useBean id="myBean" class="com.example.Users" />

Unrelated to the concrete problem, having a plural as class name of an entity is usually a smell. Does a single instance of that class really represent multiple users? Why would you not have a List<User> for example? Or does it actually represent a single user? It should then be named User instead.

来源：https://stackoverflow.com/questions/8329451/cant-use-jspusebean-bean-cannot-be-resolved-to-a-type

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Can't use <jsp:useBean>: “Bean cannot be resolved to a type”

问题

回答1: