HttpURLConnection方式下载文件之实现断点续传

public class DownloadTest {
public static void main(String[] args) {
try {
File file = new File("test.apk");
HttpURLConnection connection = (HttpURLConnection) new URL("http://skycnxz2.wy119.com/4/wandoujia.apk").openConnection();
connection.setRequestMethod("GET");
long sum = 0;
if (file.exists()) {
sum = file.length();
/*
*
* GET /down.zip HTTP/1.0
* User-Agent: NetFox
* RANGE: bytes=2000070-
*/
// 设置断点续传的开始位置
connection.setRequestProperty("Range", "bytes=" + file.length() + "-");
}
int code = connection.getResponseCode();
System.out.println("code = " + code);
if (code == 200 || code == 206) {
//                Map<String, List<String>> fields = connection.getHeaderFields();
//                for (Map.Entry<String, List<String>> entry : fields.entrySet()) {
//                    System.out.println(entry.getKey());
//                    System.out.println(entry.getValue());
//                    System.out.println("===================");
//                }
int contentLength = connection.getContentLength();
System.out.println("contentLength = " + contentLength);
contentLength += sum;
InputStream is = connection.getInputStream();
/*
*
* 创建一个向具有指定 name 的文件中写入数据的输出文件流。
* true表示当文件在下载过程中出现中断，
* 当再次链接网络时，将会从断点处追加。
*
* */
FileOutputStream fos = new FileOutputStream(file, true);

byte[] buffer = new byte[102400];
int length;
long startTime = System.currentTimeMillis();
while ((length = is.read(buffer)) != -1) {
fos.write(buffer, 0, length);
sum += length;
float percent = sum * 100.0f / contentLength;
System.out.print("\r[");
int p = (int) percent / 2;
/*
* 实现进度条
* */
for (int i = 0; i < 50; i++) {
if (i < p) {
System.out.print('=');
} else if (i == p){
System.out.print('>');
} else {
System.out.print(' ');
}
}
System.out.print(']');
System.out.printf("\t%.2f%%", percent);
long speed = sum * 1000 / (System.currentTimeMillis() - startTime);
if (speed > (1 << 20)) {
System.out.printf("\t%d MB/s", speed >> 20);
} else if (speed > (1 << 10)) {
System.out.printf("\t%d KB/s", speed >> 10);
} else {
System.out.printf("\t%d B/s", speed);
}
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
}