如何将自签名证书添加到HttpsURLConnection中的默认证书

import javax.net.ssl.*;
import java.io.FileInputStream;
import java.security.KeyStore;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;

public class CustomTrustManager implements X509TrustManager {
    private X509TrustManager defaultTrustManager;

    public CustomTrustManager() throws Exception {
        // 获取默认的TrustManager
        TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
        trustManagerFactory.init((KeyStore) null);
        TrustManager[] trustManagers = trustManagerFactory.getTrustManagers();
        if (trustManagers.length == 0) {
            throw new Exception("No default trust managers found");
        }
        defaultTrustManager = (X509TrustManager) trustManagers[0];
    }

    @Override
    public void checkClientTrusted(X509Certificate[] x509Certificates, String s) throws CertificateException {
        defaultTrustManager.checkClientTrusted(x509Certificates, s);
    }

    @Override
    public void checkServerTrusted(X509Certificate[] x509Certificates, String s) throws CertificateException {
        try {
            // 加载自签名证书
            FileInputStream fis = new FileInputStream("path/to/your/certificate.crt");
            CertificateFactory cf = CertificateFactory.getInstance("X.509");
            X509Certificate certificate = (X509Certificate) cf.generateCertificate(fis);

            // 创建一个新的KeyStore，并将自签名证书添加到信任链中
            KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
            keyStore.load(null, null);
            keyStore.setCertificateEntry("custom", certificate);

            // 创建一个新的TrustManager，并将默认的TrustManager和自定义TrustManager组合起来
            TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
            trustManagerFactory.init(keyStore);
            TrustManager[] trustManagers = trustManagerFactory.getTrustManagers();
            for (int i = 0; i < trustManagers.length; i++) {
                if (trustManagers[i] instanceof X509TrustManager) {
                    trustManagers[i] = new CustomTrustManager((X509TrustManager) trustManagers[i]);
                }
            }

            // 创建一个新的SSLContext，并使用自定义的TrustManager初始化
            SSLContext sslContext = SSLContext.getInstance("TLS");
            sslContext.init(null, trustManagers, null);

            // 设置默认的SSL上下文
            HttpsURLConnection.setDefaultSSLSocketFactory(sslContext.getSocketFactory());
        } catch (Exception e) {
            throw new CertificateException(e);
        }
    }

    @Override
    public X509Certificate[] getAcceptedIssuers() {
        return defaultTrustManager.getAcceptedIssuers();
    }
}

public class Main {
    public static void main(String[] args) {
        try {
            // 创建一个自定义的TrustManager
            CustomTrustManager customTrustManager = new CustomTrustManager();

            // 创建一个SSLContext，并使用自定义的TrustManager初始化
            SSLContext sslContext = SSLContext.getInstance("TLS");
            sslContext.init(null, new TrustManager[]{customTrustManager}, null);

            // 设置默认的SSL上下文
            HttpsURLConnection.setDefaultSSLSocketFactory(sslContext.getSocketFactory());

            // 建立与服务器的连接
            URL url = new URL("https://example.com");
            HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
            connection.setRequestMethod("GET");

            // 发送请求并处理响应
            // ...
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}