我想用
java下载HTTP查询,但我下载的文件在下载时的长度不确定.
我认为这是非常标准的,所以我搜索并找到了它的代码片段：http://snipplr.com/view/33805/
但是它有一个contentLength变量的问题.由于长度未知,我得到-1回.这会产生错误.当我省略关于contentLength的整个检查时,这意味着我总是必须使用最大缓冲区.
但问题是该文件还没有准备好.因此,flush只会被部分填充,部分文件会丢失.
如果您尝试使用该片段下载类似http://overpass-api.de/api/interpreter?data=area%5Bname%3D%22Hoogstade%22%5D%3B%0A%28%0A++node%28area%29%3B%0A++%3C%3B%0A%29+%3B%0Aout+meta+qt%3B的链接,您会注意到该错误,并且当您总是下载最大缓冲区以省略错误时,您最终会得到一个损坏的XML文件.
解决方法
这应该工作,我测试它,它适用于我：
void downloadFromUrl(URL url,String localFilename) throws IOException {
InputStream is = null;
FileOutputStream fos = null;
try {
URLConnection urlConn = url.openConnection();//connect
is = urlConn.getInputStream(); //get connection inputstream
fos = new FileOutputStream(localFilename); //open outputstream to local file
byte[] buffer = new byte[4096]; //declare 4KB buffer
int len;
//while we have availble data,continue downloading and storing to local file
while ((len = is.read(buffer)) > 0) {
fos.write(buffer,len);
}
} finally {
try {
if (is != null) {
is.close();
}
} finally {
if (fos != null) {
fos.close();
}
}
}
}
Thread download = new Thread(){
public void run(){
URL url= new URL("http://overpass-api.de/api/interpreter?data=area%5Bname%3D%22Hoogstade%22%5D%3B%0A%28%0A++node%28area%29%3B%0A++%3C%3B%0A%29+%3B%0Aout+Meta+qt%3B");
String localFilename="mylocalfile"; //needs to be replaced with local file path
downloadFromUrl(url,localFilename);
}
};
download.start();//start the thread
