java https 无效证书

产生原因

Java程序在访问https资源时，出现报错
sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
这本质上，是java在访问https资源时的证书信任问题。如何解决这个问题呢？

为何有这个问题？
解决这个问题前，要了解
1）https通信过程
客户端在使用HTTPS方式与Web服务器通信时有以下几个步骤，如图所示。
（1）客户使用https的URL访问Web服务器，要求与Web服务器建立SSL连接。
（2）Web服务器收到客户端请求后，会将网站的证书信息（证书中包含公钥）传送一份给客户端。
（3）客户端的浏览器与Web服务器开始协商SSL连接的安全等级，也就是信息加密的等级。
（4）客户端的浏览器根据双方同意的安全等级，建立会话密钥，然后利用网站的公钥将会话密钥加密，并传送给网站。
（5）Web服务器利用自己的私钥解密出会话密钥。
（6）Web服务器利用会话密钥加密与客户端之间的通信。

2)java程序的证书信任规则
如上文所述，客户端会从服务端拿到证书信息。调用端（客户端）会有一个证书信任列表，拿到证书信息后，会判断该证书是否可信任。
如果是用浏览器访问https资源，发现证书不可信任，一般会弹框告诉用户，对方的证书不可信任，是否继续之类。
Java虚拟机并不直接使用操作系统的keyring，而是有自己的security manager。与操作系统类似，jdk的security manager默认有一堆的根证书信任。如果你的https站点证书是花钱申请的，被这些根证书所信任，那使用java来访问此https站点会非常方便。因此，如果用java访问https资源，发现证书不可信任，则会报文章开头说到的错误。
参考链接

解决方法

环境：Linux

Linux执行方法如上，或者是常规方法（已记不清楚）

/* 
 * 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. 
 */  
  
import java.io.*;  
import java.net.URL;  
  
import java.security.*;  
import java.security.cert.*;  
  
import javax.net.ssl.*;  
  
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 [: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);  
    }  
    }  
  
} 

执行方式

java InstallCert my.hoolai.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

Linux运行java程序报错：Could not find or load main class …

参考链接