struts2里的struts.xml中 当result的type="stream"

<action name="cert_*" method="{1}"
            class="cn.com.***.pki.ra.web.action.CertAction">
            <result type="json" />
            <result name="view_input">WEB-INF/pages/cert/cert_view.jsp</result>
            <result name="update_input">WEB-INF/pages/cert/cert_update_request_input.jsp</result>
            <result name="p7bdown" type="stream">
                <param name="contentType">application/octet-stream</param>
                <param name="inputName">inputStream</param>
                <param name="contentDisposition">attachment;filename="user.cer"</param>
                <param name="bufferSize">1024</param>
            </result>
        </action>