如何处理httpclient的ssl错误

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 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:191)
at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:255)
at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:297)
... 23 more

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();