jsp 的 javabean的方法 无法访问

package bean;
public class UserBean
{
private String username;
private String userpass;
public String getUsername()
{
return username;
}
public void setUsername(String username)
{
this.username = username;
}
public String getUserpass()
{
return userpass;
}
public void setUserpass(String userpass)
{
this.userpass = userpass;
}
public int check()
{
if(username.equals("zhangsan")&&userpass.equals("wangwu"))
return 0;
else if(username.equals("wangwu")&&userpass.equals("zhangsan"))
return 1;
else
return -1;
}
public int getResult()
{
return check();
}
}

tomcat错误代码如下java.lang.NullPointerException
bean.UserBean.check(UserBean.java:26)
bean.UserBean.getResult(UserBean.java:33)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:597)
javax.el.BeanELResolver.getValue(BeanELResolver.java:87)
javax.el.CompositeELResolver.getValue(CompositeELResolver.java:67)
org.apache.el.parser.AstValue.getValue(AstValue.java:169)
org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)
org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:985)
org.apache.jsp.login_005fprocess_jsp._jspx_meth_c_005fset_005f0(login_005fprocess_jsp.java:125)
org.apache.jsp.login_005fprocess_jsp._jspService(login_005fprocess_jsp.java:86)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:419)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:391)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

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