java 大文件上传提速

为了提高Java大文件上传的速度，我们可以使用多线程上传。以下是实现多线程上传的步骤：

1.将大文件分割成多个小文件，每个小文件的大小可以根据实际情况进行设置。

2.使用多线程同时上传这些小文件，可以使用Java的CompletableFuture来实现。

3.在服务器端，将这些小文件合并成一个大文件。

下面是一个Java多线程上传大文件的示例代码：

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CompletableFuture;

public class MultiThreadUpload {
    private static final int THREAD_NUM = 5; // 线程数
    private static final int BUFFER_SIZE = 1024 * 1024; // 缓冲区大小
    private static final String UPLOAD_URL = "http://example.com/upload"; // 上传地址
    private static final String FILE_PATH = "/path/to/large/file"; // 大文件路径

    public static void main(String[] args) throws IOException {
        File file = new File(FILE_PATH);
        long fileSize = file.length();
        long blockSize = fileSize / THREAD_NUM + 1; // 每个线程上传的块大小

        List<CompletableFuture<Void>> futures = new ArrayList<>();        for (int i = 0; i < THREAD_NUM; i++) {
            long start = i * blockSize;
            long end = Math.min(start + blockSize, fileSize);
            CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
                try {
                    uploadBlock(file, start, end);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            });
            futures.add(future);
        }

        CompletableFuture.allOf(futures.toArray(new CompletableFuture[0])).join();
        System.out.println("Upload finished.");
    }

    private static void uploadBlock(File file, long start, long end) throws IOException {
        URL url = new URL(UPLOAD_URL);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("POST");
        conn.setDoOutput(true);
        conn.setRequestProperty("Content-Type", "application/octet-stream");
        conn.setRequestProperty("Content-Range", "bytes " + start + "-" + (end - 1) + "/" + file.length());

        try (InputStream in = new FileInputStream(file);
             OutputStream out = conn.getOutputStream()) {
            byte[] buffer = new byte[BUFFER_SIZE];
            long pos = 0;
            while (pos < start) {
                long n = in.skip(start - pos);
                if (n <= 0) {
                    throw new IOException("Unexpected EOF");
                }
                pos += n;
            }

            while (pos < end) {
                int n = in.read(buffer, 0, (int) Math.min(buffer.length, end - pos));
                if (n < 0) {
                    throw new IOException("Unexpected EOF");
                }
                out.write(buffer, 0, n);
                pos += n;
            }
        }

        if (conn.getResponseCode() != HttpURLConnection.HTTP_CREATED) {
            throw new IOException("Failed to upload block: " + conn.getResponseCode() + " " + conn.getResponseMessage());
        }
    }
}