为什么页面不能跳转？

Question

提示错误：
java.lang.IllegalStateException: Cannot forward after response has been committed
org.apache.jasper.runtime.PageContextImpl.doForward(PageContextImpl.java:670)
org.apache.jasper.runtime.PageContextImpl.forward(PageContextImpl.java:637)
org.apache.jsp.coremail.maillist_jsp._jspService(maillist_jsp.java:77)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
好像之前没有输出任何内容啊?

Answer 1

doStartTag() 方法所在的类要继承TagSupport类

Answer 2

也许是配置有误，给你参照下我的吧？public class ValidSession extends TagSupport {
    public int doStartTag() throws JspException {
       HttpSession session = pageContext.getSession();
        if ((session != null)
                && (session.getAttribute(Constants.SESSION_KEY) != null)) { 
            System.out.println("已通过验证");
            return EVAL_PAGE;
        } else {
            try {
                pageContext.forward("/login.jsp");
                System.out.println("没通过验证");            } catch (Exception ex) {
                ex.printStackTrace();
            }
            return SKIP_PAGE;
        }    }
}

Answer 3

toi sghys(冥府左使) ( ) :你的我试了，打印出了“没通过验证”
但就是没有跳转，和我的结果一样
什么原因？你是怎么配置的?

Answer 4

1.
  <tag>
    <name>check</name>
    <tagclass>com.xxx.mailuser.tag.Check</tagclass>
    <bodycontent>jsp</bodycontent>
    <attribute>
<name>p1</name>
<required>false</required>
    </attribute>
    <info>
      hello
    </info>
  </tag>
2.
  <tag>
    <name>check</name>
    <tagclass>com.xxx.mailuser.tag.Check</tagclass>
    <bodycontent>empty</bodycontent>
    <attribute>
<name>p1</name>
<required>false</required>
    </attribute>
    <info>
      hello
    </info>
  </tag>
不报错就是不跳转

Answer 5

<attribute>
<name>p1</name>
<required>false</required>
         <rtexprvalue>true</rtexprvalue>
    </attribute>