如何处理httpclient的ssl错误

今天使用httpclient 4.5，爬取https网站时报错：

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:1627)        at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:204)        at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:198)        at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:994)        at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:142)        at sun.security.ssl.Handshaker.processLoop(Handshaker.java:533)        at sun.security.ssl.Handshaker.process_record(Handshaker.java:471)        at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:904)        at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1132)        at sun.security.ssl.SSLSocketImpl.writeRecord(SSLSocketImpl.java:643)        at sun.security.ssl.AppOutputStream.write(AppOutputStream.java:78)        at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:82)        at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:140)        at org.apache.commons.httpclient.HttpConnection.flushRequestOutputStream(HttpConnection.java:828)        at org.apache.commons.httpclient.HttpMethodBase.writeRequest(HttpMethodBase.java:2116)        at org.apache.commons.httpclient.HttpMethodBase.execute(HttpMethodBase.java:1096)        at org.apache.commons.httpclient.HttpMethodDirector.executeWithRetry(HttpMethodDirector.java:398)        at org.apache.commons.httpclient.HttpMethodDirector.executeMethod(HttpMethodDirector.java:171)        at org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:397)        at org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:323)        at simpleapachehttp.Main.main(Main.java:41)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:302)        at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:205)        at sun.security.validator.Validator.validate(Validator.java:235)        at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:147)        at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:230)        at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:270)        at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:973)        ... 17 moreCaused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target        at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:191)        at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:255)        at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:297)        ... 23 more

网上搜索时，各种答案，最后采用下列方法解决：

org.apache.http.ssl.SSLContextBuilder context_b = SSLContextBuilder.create();        context_b.loadTrustMaterial(new org.apache.http.conn.ssl.TrustSelfSignedStrategy());        SSLContext ssl_context = context_b.build();        org.apache.http.conn.ssl.SSLConnectionSocketFactory sslSocketFactory = new SSLConnectionSocketFactory(ssl_context,                new org.apache.http.conn.ssl.DefaultHostnameVerifier());        HttpClientBuilder builder = HttpClients.custom()            .setSSLSocketFactory(sslSocketFactory);        httpclient = builder.build();