更简单的非阻塞I/O用法:

URL website = new URL("http://www.website.com/information.asp");
try (InputStream in = website.openStream()) {
    Files.copy(in, target, StandardCopyOption.REPLACE_EXISTING);
}

如果你使用代理，你可以在Java程序中设置代理，如下所示:

Properties systemSettings = System.getProperties();
systemSettings.put("proxySet", "true");
systemSettings.put("https.proxyHost", "HTTPS proxy of your org");
systemSettings.put("https.proxyPort", "8080");

如果您没有使用代理，请不要在代码中包含上述代码行。完整的工作代码下载文件时，你是一个代理。

public static void main(String[] args) throws IOException {
    String url = "https://raw.githubusercontent.com/bpjoshi/fxservice/master/src/test/java/com/bpjoshi/fxservice/api/TradeControllerTest.java";
    OutputStream outStream = null;
    URLConnection connection = null;
    InputStream is = null;
    File targetFile = null;
    URL server = null;

    // Setting up proxies
    Properties systemSettings = System.getProperties();
        systemSettings.put("proxySet", "true");
        systemSettings.put("https.proxyHost", "HTTPS proxy of my organisation");
        systemSettings.put("https.proxyPort", "8080");
        // The same way we could also set proxy for HTTP
        System.setProperty("java.net.useSystemProxies", "true");
        // Code to fetch file
    try {
        server = new URL(url);
        connection = server.openConnection();
        is = connection.getInputStream();
        byte[] buffer = new byte[is.available()];
        is.read(buffer);

        targetFile = new File("src/main/resources/targetFile.java");
        outStream = new FileOutputStream(targetFile);
        outStream.write(buffer);
    } catch (MalformedURLException e) {
        System.out.println("THE URL IS NOT CORRECT ");
        e.printStackTrace();
    } catch (IOException e) {
        System.out.println("I/O exception");
        e.printStackTrace();
    }
    finally{
        if(outStream != null)
            outStream.close();
    }
}

import java.io.*;
import java.net.*;

public class filedown {
    public static void download(String address, String localFileName) {
        OutputStream out = null;
        URLConnection conn = null;
        InputStream in = null;

        try {
            URL url = new URL(address);
            out = new BufferedOutputStream(new FileOutputStream(localFileName));
            conn = url.openConnection();
            in = conn.getInputStream();
            byte[] buffer = new byte[1024];

            int numRead;
            long numWritten = 0;

            while ((numRead = in.read(buffer)) != -1) {
                out.write(buffer, 0, numRead);
                numWritten += numRead;
            }

            System.out.println(localFileName + "\t" + numWritten);
        } 
        catch (Exception exception) { 
            exception.printStackTrace();
        } 
        finally {
            try {
                if (in != null) {
                    in.close();
                }
                if (out != null) {
                    out.close();
                }
            } 
            catch (IOException ioe) {
            }
        }
    }

    public static void download(String address) {
        int lastSlashIndex = address.lastIndexOf('/');
        if (lastSlashIndex >= 0 &&
        lastSlashIndex < address.length() - 1) {
            download(address, (new URL(address)).getFile());
        } 
        else {
            System.err.println("Could not figure out local file name for "+address);
        }
    }

    public static void main(String[] args) {
        for (int i = 0; i < args.length; i++) {
            download(args[i]);
        }
    }
}

使用Apache Commons IO。它只是一行代码:

FileUtils.copyURLToFile(URL, File)

这是另一个基于Brian Risk的答案的Java 7变体，使用了try-with语句:

public static void downloadFileFromURL(String urlString, File destination) throws Throwable {

    URL website = new URL(urlString);
    try(
        ReadableByteChannel rbc = Channels.newChannel(website.openStream());
        FileOutputStream fos = new FileOutputStream(destination);
       ) {

        fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
    }
}

就我个人而言，我发现Apache的HttpClient在这方面比我需要做的任何事情都有能力。这里有一个关于使用HttpClient的很棒的教程