高手们帮忙给看看是什么问题

<html:form action="admin_message.do" method="GET">
<html:text property="adminmessage.admin_name" />
</html:form>
页面和配置没问题我就不贴了
我的这个表单运行后报
javax.servlet.ServletException: No getter method for property adminmessage.admin_name of bean org.apache.struts.taglib.html.BEAN
org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:673)
org.apache.jsp.index_jsp._jspService(index_jsp.java:82)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:133)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:311)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)错误。
我是按照书上的例子写的
我的值对象类和FORM类都是按照例子写的请问这个错误怎样改？值对象类是public class admin_message
{

public String admin_name;        public void setAdmin_Name(String name)
{
this.admin_name=name;
}
        
public String getAdmin_Name()
{
return this.admin_name;
}
}FORM是
public class Admin_messageForm extends ActionForm {
       private admin_message adminmessage=new admin_message();
       public void setAdmin_Name(String name)
       {
         this.adminmessage.setAdmin_Name(name);
       }
       public String getAdmin_Name()
       {
         return this.adminmessage.getAdmin_Name();
       }
       public void setAdmin_message(admin_message adminmessage)
       {
         this.adminmessage=adminmessage;
       } 
       public admin_message getAdmin_message(){
         return this.adminmessage;
       }
各位大侠们帮帮我吧！