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原理解析：利用RandomAccessFile在本地創建一個隨機訪問文件，文件大小和服務器要下載的文件大小相同。根據線程的數量（假設有三個線程），服務器的文件三等分，并把我們在本地創建的文件同樣三等分，每個線程下載自己負責的部分，到相應的位置即可。
示例圖：
示例demo
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
public class MutilDownload {
private static String path = "http://192.168.80.85:8080/test.doc";
private static final int threadCount = 3;
public static void main(String[] args) {
try {
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
int responseCode = conn.getResponseCode();
if (responseCode == 200) {
int contentLength = conn.getContentLength();
System.out.println("length" + contentLength);
RandomAccessFile rafAccessFile = new RandomAccessFile("test.doc", "rw");
rafAccessFile.setLength(contentLength);
int blockSize = contentLength / threadCount;
for (int i = 0; i < threadCount; i++) {
int startIndex = i * blockSize; //每個現成下載的開始位置
int endIndex = (i + 1) * blockSize - 1;// 每個線程的結束位置
if (i == threadCount - 1) {
//最后一個線程
endIndex = contentLength - 1;
}
new DownloadThread(startIndex, endIndex, i).start();
}
}
} catch (Exception e) {
}
}
private static class DownloadThread extends Thread {
private int startIndex;
private int endIndex;
private int threadId;
public DownloadThread(int startIndex, int endIndex, int threadId) {
this.startIndex = startIndex;
this.endIndex = endIndex;
this.threadId = threadId;
}
@Override
public void run() {
try {
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex); //固定寫法，請求部分資源
int responseCode = conn.getResponseCode(); // 206表示請求部分資源
if (responseCode == 206) {
RandomAccessFile rafAccessFile = new RandomAccessFile("test.doc", "rw");
rafAccessFile.seek(startIndex);
InputStream is = conn.getInputStream();
int len = -1;
byte[] buffer = new byte[1024];
while ((len = is.read(buffer)) != -1) {
rafAccessFile.write(buffer, 0, len);
}
rafAccessFile.close();
System.out.println("線程" + threadId + "下載完成");
}
} catch (Exception e) {
}
}
}
}
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