解决CAS单点登录出现PKIX path building failed的问题

在一次调试中，出现了这个错误：

PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target

详细报错信息如下:

严重: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.ssl.Alerts.getSSLException(Alerts.java:)
    at sun.security.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:)
    at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:)
    at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:)
    at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:)
    at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:)
    at sun.security.ssl.Handshaker.processLoop(Handshaker.java:)
    at sun.security.ssl.Handshaker.process_record(Handshaker.java:)
    at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:)
    at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:)
    at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:)
    at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:)
    at sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:)
    at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:)
    at org.jasig.cas.client.util.CommonUtils.getResponseFromServer(CommonUtils.java:)
    at org.jasig.cas.client.util.CommonUtils.getResponseFromServer(CommonUtils.java:)
    at org.jasig.cas.client.validation.AbstractCasProtocolUrlBasedTicketValidator.retrieveResponseFromServer(AbstractCasProtocolUrlBasedTicketValidator.java:)
    at org.jasig.cas.client.validation.AbstractUrlBasedTicketValidator.validate(AbstractUrlBasedTicketValidator.java:)
    at org.jasig.cas.client.validation.AbstractTicketValidationFilter.doFilter(AbstractTicketValidationFilter.java:)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:)
    at org.jasig.cas.client.authentication.AuthenticationFilter.doFilter(AuthenticationFilter.java:)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:)
    at org.jasig.cas.client.session.SingleSignOutFilter.doFilter(SingleSignOutFilter.java:)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:)
    at java.lang.Thread.run(Thread.java:)
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:)
    at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:)
    at sun.security.validator.Validator.validate(Validator.java:)
    at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:)
    at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:)
    at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:)
    at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:)
    ...  more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:)
    at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:)
    at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:)
    ...  more

十二月 ,  :: 下午 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet [jsp] in context with path [] threw exception
java.lang.RuntimeException: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at org.jasig.cas.client.util.CommonUtils.getResponseFromServer(CommonUtils.java:)
    at org.jasig.cas.client.util.CommonUtils.getResponseFromServer(CommonUtils.java:)
    at org.jasig.cas.client.validation.AbstractCasProtocolUrlBasedTicketValidator.retrieveResponseFromServer(AbstractCasProtocolUrlBasedTicketValidator.java:)
    at org.jasig.cas.client.validation.AbstractUrlBasedTicketValidator.validate(AbstractUrlBasedTicketValidator.java:)
    at org.jasig.cas.client.validation.AbstractTicketValidationFilter.doFilter(AbstractTicketValidationFilter.java:)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:)
    at org.jasig.cas.client.authentication.AuthenticationFilter.doFilter(AuthenticationFilter.java:)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:)
    at org.jasig.cas.client.session.SingleSignOutFilter.doFilter(SingleSignOutFilter.java:)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:)
    at java.lang.Thread.run(Thread.java:)
Caused by: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.ssl.Alerts.getSSLException(Alerts.java:)
    at sun.security.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:)
    at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:)
    at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:)
    at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:)
    at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:)
    at sun.security.ssl.Handshaker.processLoop(Handshaker.java:)
    at sun.security.ssl.Handshaker.process_record(Handshaker.java:)
    at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:)
    at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:)
    at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:)
    at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:)
    at sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:)
    at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:)
    at org.jasig.cas.client.util.CommonUtils.getResponseFromServer(CommonUtils.java:)
    ...  more
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:)
    at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:)
    at sun.security.validator.Validator.validate(Validator.java:)
    at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:)
    at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:)
    at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:)
    at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:)
    ...  more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:)
    at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:)
    at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:)
    ...  more

这个错误最终定位在这个方法：

protected final String retrieveResponseFromServer(final URL validationUrl,
            final String ticket) {
        HttpURLConnection connection = null;
        try {
            connection = (HttpURLConnection) validationUrl.openConnection();
            final BufferedReader in = new BufferedReader(new InputStreamReader(
                    connection.getInputStream()));

            String line;
            final StringBuffer stringBuffer = new StringBuffer(255);

            synchronized (stringBuffer) {
                while ((line = in.readLine()) != null) {
                    stringBuffer.append(line);
                    stringBuffer.append("\n");
                }
                return stringBuffer.toString();
            }

        } catch (final IOException e) {
            log.error(e, e);
            return null;
        } catch (final Exception e1){
            log.error(e1, e1);
            return null;
        }finally {
            if (connection != null) {
                connection.disconnect();
            }
        }
    }

后来上网查了很久，说是证书出问题了，服务器不信任我们自己创建的证书，所以在代码中必须要忽略证书信任问题。只要在创建connection之前调用两个方法：

trustAllHttpsCertificates();
HttpsURLConnection.setDefaultHostnameVerifier(hv);

具体的实现是：

HostnameVerifier hv = new HostnameVerifier() {
        public boolean verify(String urlHostName, SSLSession session) {
            System.out.println("Warning: URL Host: " + urlHostName + " vs. "
                               + session.getPeerHost());
            return true;
        }
    };

    private static void trustAllHttpsCertificates() throws Exception {
        javax.net.ssl.TrustManager[] trustAllCerts = new javax.net.ssl.TrustManager[1];
        javax.net.ssl.TrustManager tm = new miTM();
        trustAllCerts[0] = tm;
        javax.net.ssl.SSLContext sc = javax.net.ssl.SSLContext
                .getInstance("SSL");
        sc.init(null, trustAllCerts, null);
        javax.net.ssl.HttpsURLConnection.setDefaultSSLSocketFactory(sc
                .getSocketFactory());
    }

    static class miTM implements javax.net.ssl.TrustManager,
            javax.net.ssl.X509TrustManager {
        public java.security.cert.X509Certificate[] getAcceptedIssuers() {
            return null;
        }

        public boolean isServerTrusted(
                java.security.cert.X509Certificate[] certs) {
            return true;
        }

        public boolean isClientTrusted(
                java.security.cert.X509Certificate[] certs) {
            return true;
        }

        public void checkServerTrusted(
                java.security.cert.X509Certificate[] certs, String authType)
                throws java.security.cert.CertificateException {
            return;
        }

        public void checkClientTrusted(
                java.security.cert.X509Certificate[] certs, String authType)
                throws java.security.cert.CertificateException {
            return;
        }
    }

附件:AbstractCasProtocolUrlBasedTicketValidator