Atualmente, estou trabalhando em um pequeno cliente rápido e tive alguns problemas de desempenho difícil ao baixar arquivos.

Após milhares de verificações, localizei o problema baixando arquivos através do ssl.

Os downloads normais (http) funcionam bem sem problemas (ou problemas de desempenho). Mas os downloads SSL explodem minha CPU ... um único núcleo sobe para 100% de carga (para um único thread)

Eu escrevi uma pequena classe de teste sem todo o meu programa e posso confirmar minhas observações anteriores.

package testDownload;

import java.io.File;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import java.net.URL;
import java.net.URLConnection;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.WritableByteChannel;
import java.security.KeyManagementException;
import java.security.NoSuchAlgorithmException;
import java.security.cert.X509Certificate;

import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSession;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;

public class Downloader {

    public Downloader(boolean sslTrigger) throws IOException {

        try {
            this.allowSelfSignCerts();
        } catch (KeyManagementException | NoSuchAlgorithmException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        URL url;
        // Http Download
        if (sslTrigger) {
            System.out.println("HTTPS-Mode");
            url                 = new URL("HTTPS LINK");
        } else {
            System.out.println("HTTP-Mode");
            url                 = new URL("HTTP LINK");
        }

        URLConnection conn      = url.openConnection();
        InputStream     input   = conn.getInputStream();
        OutputStream    output  = new FileOutputStream(new File(System.getProperty("user.home")+System.getProperty("file.separator")+"test.dat"));

        ReadableByteChannel inputChannel    = Channels.newChannel(input);
        WritableByteChannel outputChannel   = Channels.newChannel(output);
        System.out.println("start download");
        this.fastChannelCopy(inputChannel, outputChannel);
        inputChannel.close();
        outputChannel.close();
        System.out.println("finish");


    }

    private void fastChannelCopy(ReadableByteChannel src, WritableByteChannel dest) throws IOException {
          ByteBuffer buffer = ByteBuffer.allocateDirect(16 * 1024);
            while (src.read(buffer) != -1) {
              buffer.flip();
              dest.write(buffer);
              buffer.compact();
            }
            buffer.flip();
            while (buffer.hasRemaining()) {
              dest.write(buffer);
            }
    }

    private void allowSelfSignCerts() throws NoSuchAlgorithmException, KeyManagementException {
     TrustManager[] trustAllCerts = new TrustManager[] {new X509TrustManager() {
             public java.security.cert.X509Certificate[] getAcceptedIssuers() {
                 return null;
             }
             public void checkClientTrusted(X509Certificate[] certs, String authType) {
             }
             public void checkServerTrusted(X509Certificate[] certs, String authType) {
             }
         }
     };

     SSLContext sc = SSLContext.getInstance("SSL");
     sc.init(null, trustAllCerts, new java.security.SecureRandom());
     HttpsURLConnection.setDefaultSSLSocketFactory(sc.getSocketFactory());

     HostnameVerifier allHostsValid = new HostnameVerifier() {
         public boolean verify(String hostname, SSLSession session) {
             return true;
         }
     };
     HttpsURLConnection.setDefaultHostnameVerifier(allHostsValid);
    }

}

versão java usada

java -version
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)

Alguém tem uma idéia para resolver esse problema?