java - 如何从android中的URL下载文件的一部分？

Question

我正在尝试使用 setRequestProperty("Range","bytes="+ startbytes + "-"+ endbytes); 给定下载 URL 下载文件的一部分；以下代码 fragment 显示了我正在尝试做的事情。

protected String doInBackground(String... aurl) {
    int count;
    Log.d(TAG,"Entered");
    try {

        URL url = new URL(aurl[0]);
        HttpURLConnection connection =(HttpURLConnection) url.openConnection();

        int lengthOfFile = connection.getContentLength();

        Log.d(TAG,"Length of file: "+ lengthOfFile);

        connection.setRequestProperty("Range", "bytes=" + 0 + "-" + 1000);

问题是，引发了一个异常，显示“建立连接后无法设置请求属性”。请帮我解决这个问题。

Answer 1

选项 1

如果不需要知道内容长度:

[注意，不要调用 connection.getContentLength()。如果你调用它，你会得到异常。如果需要调用，则勾选第二个]

URL url = new URL(aurl[0]);
HttpURLConnection connection =(HttpURLConnection) url.openConnection();
connection.setRequestProperty("Range", "bytes=" + 0 + "-" + 1000);
//Note that, response code will be 206 (Partial Content) instead of usual 200 (OK)
if(connection.getResponseCode() == HttpURLConnection.HTTP_PARTIAL){
    //Your code here to read response data
}

选项 2

如果需要知道内容长度:

URL url = new URL(aurl[0]);
//First make a HEAD call to get the content length  
HttpURLConnection connection =(HttpURLConnection) url.openConnection();
connection.setRequestMethod("HEAD");
if(connection.getResponseCode() == HttpURLConnection.HTTP_OK){
    int lengthOfFile = connection.getContentLength();
    Log.d("ERF","Length of file: "+ lengthOfFile);
    connection.disconnect();

    //Now that we know the content lenght, make the GET call
    connection =(HttpURLConnection) url.openConnection();
    connection.setRequestMethod("GET");
    connection.setRequestProperty("Range", "bytes=" + 0 + "-" + 1000);
    //Note that, response code will be 206 (Partial Content) instead of usual 200 (OK)
    if(connection.getResponseCode() == HttpURLConnection.HTTP_PARTIAL){
        //Your code here to read response data

    }
}