我們網站要進行https改造，配置上購買的SSL證書後，瀏覽器訪問正常，但是寫了個java代碼用httpcomponents調用https rest接口時報錯：
Exception in thread "main" 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:192)
at sun.security.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:1904)
at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:279)
at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:273)
at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1446)
at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:209)
at sun.security.ssl.Handshaker.processLoop(Handshaker.java:901)
at sun.security.ssl.Handshaker.process_record(Handshaker.java:837)
at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:1023)
at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1332)
at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1359)
at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1343)
at org.apache.http.conn.ssl.SSLConnectionSocketFactory.createLayeredSocket(SSLConnectionSocketFactory.java:394)
at org.apache.http.conn.ssl.SSLConnectionSocketFactory.connectSocket(SSLConnectionSocketFactory.java:353)
at org.apache.http.impl.conn.DefaultHttpClientConnectionOperator.connect(DefaultHttpClientConnectionOperator.java:141)
at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.connect(PoolingHttpClientConnectionManager.java:353)
at org.apache.http.impl.execchain.MainClientExec.establishRoute(MainClientExec.java:380)
at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:236)
at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:184)
at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:88)
at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:184)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:82)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:107)
at com.duiba.activity.cmsweb.controller.DappConfigCtrl.main(DappConfigCtrl.java:1248)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)
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:385)
at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:292)
at sun.security.validator.Validator.validate(Validator.java:260)
at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:326)
at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:231)
at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:126)
at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1428)
... 25 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:196)
at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:268)
at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:380)
... 31 more
網上查了一堆資料，要麼說要把網站證書放到某個目錄下，要麼要改代碼，沒有我想要的，因爲不可能讓其他開發者去做這些事情。
後來瞭解到證書鏈這回事，才知道如何解決這個問題。有關證書鏈可以讀這裏：http://blog.sina.com.cn/s/blog_53ed87c10102vn8b.html
此問題產生的原因是因爲我們運維配置證書時只使用了簽發的證書，java客戶端無法找到可信任的上級證書，所以報錯。解決方法也很簡單，把中級證書、根證書附加到簽發證書後面就可以了，具體方法參考這裏：https://yq.aliyun.com/articles/26569