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

注：网上搜来的快照，暂未验证

在java代码中请求https链接的时候，可能会报下面这个错误

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

原因是没有证书。在浏览器中直接使用url访问是可以的，应该是浏览器之前就保存过对应的.cer证书。

解决方法有两种，从目标机器获得有效证书或者忽略证书信任问题。

一、获得目标机器有效证书

1、编译安装证书程序 javac InstallCert.java（代码如下）

/*

 * Copyright 2006 Sun Microsystems, Inc. All Rights Reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 *  - Redistributions of source code must retain the above copyright

 *   notice, this list of conditions and the following disclaimer.

 *

 *  - Redistributions in binary form must reproduce the above copyright

 *   notice, this list of conditions and the following disclaimer in the

 *   documentation and/or other materials provided with the distribution.

 *

 *  - Neither the name of Sun Microsystems nor the names of its

 *   contributors may be used to endorse or promote products derived

 *   from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS

 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,

 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR

 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,

 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,

 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR

 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF

 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING

 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS

 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

/**

 * http://blogs.sun.com/andreas/resource/InstallCert.java

 * Use:

 * java InstallCert hostname

 * Example:

 *% java InstallCert ecc.fedora.redhat.com

 */

import javax.net.ssl.*;

import java.io.*;

import java.security.KeyStore;

import java.security.MessageDigest;

import java.security.cert.CertificateException;

import java.security.cert.X509Certificate;

/**

 * Class used to add the server's certificate to the KeyStore

 * with your trusted certificates.

 */

public class InstallCert {

    public static void main(String[] args) throws Exception {

        String host;

        int port;

        char[] passphrase;

        if ((args.length == 1) || (args.length == 2)) {

            String[] c = args[0].split(":");

            host = c[0];

            port = (c.length == 1) ? 443 : Integer.parseint(c[1]);

            String p = (args.length == 1) ? "changeit" : args[1];

            passphrase = p.toCharArray();

        } else {

            System.out.println("Usage: java InstallCert <host>[:port] [passphrase]");

            return;

        }

        File file = new File("jssecacerts");

        if (file.isFile() == false) {

            char SEP = File.separatorchar;

            File dir = new File(System.getProperty("java.home") + SEP

                      + "lib" + SEP + "security");

            file = new File(dir, "jssecacerts");

            if (file.isFile() == false) {

                file = new File(dir, "cacerts");

            }

        }

        System.out.println("Loading KeyStore " + file + "...");

        InputStream in = new FileInputStream(file);

        KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());

        ks.load(in, passphrase);

        in.close();

        SSLContext context = SSLContext.getInstance("TLS");

        TrustManagerFactory tmf =

                TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());

        tmf.init(ks);

        X509TrustManager defaultTrustManager = (X509TrustManager) tmf.getTrustManagers()[0];

        SavingTrustManager tm = new SavingTrustManager(defaultTrustManager);

        context.init(null, new TrustManager[]{

            tm

        }

        , null);

        SSLSocketFactory factory = context.getSocketFactory();

        System.out.println("Opening connection to " + host + ":" + port + "...");

        SSLSocket socket = (SSLSocket) factory.createSocket(host, port);

        socket.setSoTimeout(10000);

        try {

            System.out.println("Starting SSL handshake...");

            socket.startHandshake();

            socket.close();

            System.out.println();

            System.out.println("No errors, certificate is already trusted");

        }

        catch (SSLException e) {

            System.out.println();

            e.printStackTrace(System.out);

        }

        X509Certificate[] chain = tm.chain;

        if (chain == null) {

            System.out.println("Could not obtain server certificate chain");

            return;

        }

        BufferedReader reader =

                new BufferedReader(new InputStreamReader(System.in));

        System.out.println();

        System.out.println("Server sent " + chain.length + " certificate(s):");

        System.out.println();

        MessageDigest sha1 = MessageDigest.getInstance("SHA1");

        MessageDigest md5 = MessageDigest.getInstance("MD5");

        for (int i = 0; i < chain.length; i++) {

            X509Certificate cert = chain[i];

            System.out.println

                      (" " + (i + 1) + " Subject " + cert.getSubjectDN());

            System.out.println("  Issuer " + cert.getIssuerDN());

            sha1.update(cert.getEncoded());

            System.out.println("  sha1  " + toHexString(sha1.digest()));

            md5.update(cert.getEncoded());

            System.out.println("  md5   " + toHexString(md5.digest()));

            System.out.println();

        }

        System.out.println("Enter certificate to add to trusted keystore or 'q' to quit: [1]");

        String line = reader.readLine().trim();

        int k;

        try {

            k = (line.length() == 0) ? 0 : Integer.parseint(line) - 1;

        }

        catch (NumberFormatException e) {

            System.out.println("KeyStore not changed");

            return;

        }

        X509Certificate cert = chain[k];

        String alias = host + "-" + (k + 1);

        ks.setCertificateEntry(alias, cert);

        OutputStream out = new FileOutputStream("jssecacerts");

        ks.store(out, passphrase);

        out.close();

        System.out.println();

        System.out.println(cert);

        System.out.println();

        System.out.println

                ("Added certificate to keystore 'jssecacerts' using alias '"

                    + alias + "'");

    }

    private static final char[] HEXDIGITS = "0123456789abcdef".toCharArray();

    private static String toHexString(byte[] bytes) {

        StringBuilder sb = new StringBuilder(bytes.length * 3);

        for (int b : bytes) {

            b &= 0xff;

            sb.append(HEXDIGITS[b >> 4]);

            sb.append(HEXDIGITS[b & 15]);

            sb.append(' ');

        }

        return sb.toString();

    }

    private static class SavingTrustManager implements X509TrustManager {

        private final X509TrustManager tm;

        private X509Certificate[] chain;

        SavingTrustManager(X509TrustManager tm) {

            this.tm = tm;

        }

        public X509Certificate[] getAcceptedIssuers() {

            throw new UnsupportedOperationException();

        }

        public void checkClientTrusted(X509Certificate[] chain, String authType)

                throws CertificateException {

            throw new UnsupportedOperationException();

        }

        public void checkServerTrusted(X509Certificate[] chain, String authType)

                throws CertificateException {

            this.chain = chain;

            tm.checkServerTrusted(chain, authType);

        }

    }

}

2、运行安装证书程序生成证书

java InstallCert www.xxx.com

例如：java InstalCert smtp.zhangsan.com:465 admin
如果不加参数password和host的端口号，上面的获取证书程序中默认给的端口号是：443，密码是:changeit

3、根据运行提示信息，输入1，回车，在当前目录下生成名为： jssecacerts 的证书

将证书放置到$JAVA_HOME/jre/lib/security目录下， 切记该JDK的jre是工程所用的环境！！！

或者：

System.setProperty("javax.net.ssl.trustStore", "你的jssecacerts证书路径");

可以更改密码，在security目录下运行命令

keytool -storepasswd -new xxxcom -keystore cacerts

就可以修改密码，修改后使用命令

keytool -list -v -keystore cacerts

查看文件的信息，会提示需要密码才能查看，如果输入密码与修改后的密码匹配，说明修改成功了。

PS：至此这种方式可以成功使用ssl了，另外再补充一下，根据刚才生成的文件jssecacerts，可以生成cer文件，

命令如下

keytool -export -alias xxx.com-1 -keystore jssecacerts -rfc -file xxx.cer

如上，之前的工具类中默认命名别名是加上"-1"。使用InstallCert设置的密码需要跟cacerts文件中的密码一致，

如果修改过密码，就需要修改InstallCert类中对应的密码字符串，否则会有下面这个异常：

java.security.UnrecoverableKeyException: Password verification failed

二、忽略证书信任问题

源码：http://mengyang.iteye.com/blog/575671

一定要注意需要在connection创建之前调用文章里所述的方法，像这个样子：

trustAllHttpsCertificates();

HostnameVerifier hv = new HostnameVerifier() {

    public boolean verify(String urlHostName, SSLSession session) {

      return true;

    }

  };
    

trustAllHttpsCertificates();

HostnameVerifier hv = new HostnameVerifier() {

    public boolean verify(String urlHostName, SSLSession session) {

      return true;

    }

  };

HttpsURLConnection.setDefaultHostnameVerifier(hv);

connection = (HttpURLConnection) url.openConnection();