unable to find valid certification path to requested target'解决办法

这个java类会打开一个连接到你指定的host，开始握手过程。如果出现异常会打印到控制台并且会显示服务端所使用的证书，此时它会问你是否要把证书加入到你的keystore。如果你不想加，输入"q",否则输入"1". 

当你输入"1"后，InstallCert.java 会显示证书的有关信息，然后把证书导入到一个名为"jssecacerts"的keystore中(当前目录），只需要把这个文件拷贝到％JAVA_HOME/jre/lib/security目录中，重命名为"cacerts". 

类内容：

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 <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);
 }
    }

}