错误信息：

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

问题原因：

在Java8及高版本以上的版本在源应用程序不信任目标应用程序的证书，因为在源应用程序的JVM信任库中找不到该证书或证书链。也就是目标站点启用了HTTPS 而缺少安全证书时出现的异常

常见的解决方法有三种：

1. 手动生成证书;

2. 忽略证书验证。(建议使用)

3. 在JDK安装目录中删除

三种方式的实现：

1、手动导入安全证书

手动生成证书方法参考大佬博客：手动生成证书方法

2、忽略证书验证（建议使用）

public class Base64Util {

    public static String getBase64FromUrl(String fileUrl) {
        InputStream inputStream = null;
        byte[] data = null;
        ByteArrayOutputStream swapStream = null;
        HttpsURLConnection conn = null;
        try {
            URL url = new URL(fileUrl);
            //判断当前文件url是否是https
            if (fileUrl.contains("https:")){
                //是https
                //绕过证书
                SSLContext context = createIgnoreVerifySSL();
                createIgnoreVerifySSL();
                conn = (HttpsURLConnection) url.openConnection();
                conn.setSSLSocketFactory(context.getSocketFactory());
                inputStream = conn.getInputStream();
            }else {
                //当前链接是http
                inputStream =  url.openConnection().getInputStream();
            }

            swapStream = new ByteArrayOutputStream();
            byte[] buff = new byte[100];
            int rc = 0;
            while ((rc = inputStream.read(buff, 0, 100)) > 0) {
                swapStream.write(buff, 0, rc);
            }
            data = swapStream.toByteArray();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            IOUtils.closeQuietly(inputStream);
            IOUtils.closeQuietly(swapStream);
        }
        return new String(Base64.encodeBase64(data));
    }

    //绕过SSL、TLS证书
    public static SSLContext createIgnoreVerifySSL() throws NoSuchAlgorithmException, KeyManagementException {
        SSLContext sc = SSLContext.getInstance("TLS");
        // 实现一个X509TrustManager接口，用于绕过验证，不用修改里面的方法
        X509TrustManager trustManager = new X509TrustManager() {
            @Override
            public void checkClientTrusted(
                    java.security.cert.X509Certificate[] paramArrayOfX509Certificate,
                    String paramString) throws CertificateException {
            }

            @Override
            public void checkServerTrusted(
                    java.security.cert.X509Certificate[] paramArrayOfX509Certificate,
                    String paramString) throws CertificateException {
            }

            @Override
            public java.security.cert.X509Certificate[] getAcceptedIssuers() {
                return null;
            }
        };

        sc.init(null, new TrustManager[]{trustManager}, null);
        return sc;
    }
}

3、删除JDK安装目录下jre/lib/security的java.security文件的SSLv3, TLSv1, TLSv1.1，（不建议使用，本地环境和生产环境不一样）