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:1884)
    at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:276)
    at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:270)
    at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1341)
    at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:153)
    at sun.security.ssl.Handshaker.processLoop(Handshaker.java:868)
    at sun.security.ssl.Handshaker.process_record(Handshaker.java:804)
    at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:1016)
    at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1312)
    at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1339)
    at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1323)
    at sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:563)
    at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:185)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1300)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:254)
    at SslTest.getRequest(SslTest.java:16)
    at SslTest.main(SslTest.java:40)
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:230)
    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:1323)
    ... 13 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)
    ... 19 more

解决办法：

1、导入证书到本地证书库

2、信任所有SSL证书

最好的解决办法或许是信任所有SSL证书，因为某些时候不能每次都手动的导入证书非常麻烦。现在封装了个方法，在连接openConnection的时候忽略掉证书就行了。

SslUtils.ignoreSsl();

import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSession;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;
public class SslUtils {
    private static void trustAllHttpsCertificates() throws Exception {
        TrustManager[] trustAllCerts = new TrustManager[1];
        TrustManager tm = new miTM();
        trustAllCerts[0] = tm;
        SSLContext sc = SSLContext.getInstance("SSL");
        sc.init(null, trustAllCerts, null);
        HttpsURLConnection.setDefaultSSLSocketFactory(sc.getSocketFactory());
    }
    static class miTM implements TrustManager,X509TrustManager {
        public X509Certificate[] getAcceptedIssuers() {
            return null;
        }
        public boolean isServerTrusted(X509Certificate[] certs) {
            return true;
        }
        public boolean isClientTrusted(X509Certificate[] certs) {
            return true;
        }
        public void checkServerTrusted(X509Certificate[] certs, String authType)
                throws CertificateException {
            return;
        }
        public void checkClientTrusted(X509Certificate[] certs, String authType)
                throws CertificateException {
            return;
        }
    }
    /**
     * 忽略HTTPS请求的SSL证书，必须在openConnection之前调用
     * @throws Exception
     */
    public static void ignoreSsl() throws Exception{
        HostnameVerifier hv = new HostnameVerifier() {
            public boolean verify(String urlHostName, SSLSession session) {
                System.out.println("Warning: URL Host: " + urlHostName + " vs. " + session.getPeerHost());
                return true;
            }
        };
        trustAllHttpsCertificates();
        HttpsURLConnection.setDefaultHostnameVerifier(hv);
    }
}

import java.io.OutputStreamWriter;
import java.net.URL;
import java.net.URLConnection;
import org.apache.commons.io.IOUtils;
public class SslTest {
    public String getRequest(String url,int timeOut) throws Exception{
        URL u = new URL(url);
        if("https".equalsIgnoreCase(u.getProtocol())){
            SslUtils.ignoreSsl();
        }
        URLConnection conn = u.openConnection();
        conn.setConnectTimeout(timeOut);
        conn.setReadTimeout(timeOut);
        return IOUtils.toString(conn.getInputStream());
    }
    public String postRequest(String urlAddress,String args,int timeOut) throws Exception{
        URL url = new URL(urlAddress);
        if("https".equalsIgnoreCase(url.getProtocol())){
            SslUtils.ignoreSsl();
        }
        URLConnection u = url.openConnection();
        u.setDoInput(true);
        u.setDoOutput(true);
        u.setConnectTimeout(timeOut);
        u.setReadTimeout(timeOut);
        OutputStreamWriter osw = new OutputStreamWriter(u.getOutputStream(), "UTF-8");
        osw.write(args);
        osw.flush();
        osw.close();
        u.getOutputStream();
        return IOUtils.toString(u.getInputStream());
    }
    public static void main(String[] args) {
        try {
            SslTest st = new SslTest();
            String a = st.getRequest("https://xxx.com/login.action", 3000);
            System.out.println(a);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

原文连接