jsp 读取 证书

我用的是apache ssl 实现的 https
我们用的是 apache + tomcat 组合
现在的问题是我怎么用jsp 读取 apahce ssl 证书的内容

<%
    String certSubject = null;
    java.security.cert.X509Certificate[] certChain=
        (java.security.cert.X509Certificate[])
            request.getAttribute("javax.servlet.request.X509Certificate");
    if (null!=certChain){
        int len=certChain.length;
        if (len>0){
            java.security.cert.X509Certificate cert =
                (java.security.cert.X509Certificate)certChain[0];
            java.security.Principal pSubject = cert.getSubjectDN();
            certSubject = pSubject.getName();
        }
    }
%>
Subject = <%=certSubject%>

这种是jsp 读取 tomcat ssl 证书的内容
但是apache 的不行