package main.week03.download.impl;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Arrays;
import main.week03.download.FileDownloader;
import main.week03.download.api.Connection;
import main.week03.download.api.ConnectionException;
//包级可见,是保护措施
class ConnectionImpl implements Connection {
URL url;
static final int BUFFER_SIZE = 1024;
public ConnectionImpl(String _url) throws ConnectionException {
try {
//传入的字符串必须是url格式
url = new URL(_url);
} catch (MalformedURLException e) {
throw new ConnectionException(e);
}
}
@Override
public byte[] read(int startPos, int endPos) throws IOException {
int totalLen = endPos - startPos + 1;
//是URLConnection的子类,负责http协议的链接
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
InputStream inputStream = conn.getInputStream();
//客户端可以在请求里放置参数,设置接收数据区间
//代替了is.skip(),但是is.skip里有read,所以是边读边移动下标的,和本程序意图相违背。
conn.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);
byte[] buffer = new byte[BUFFER_SIZE];
//输出流
ByteArrayOutputStream baos = new ByteArrayOutputStream();
while (baos.size() < totalLen) {
//一次读取1024字节
int len = inputStream.read(buffer);
if (len < 0) {
break;
}
baos.write(buffer, 0, len);
}
//防止这个线程过度读取
if (baos.size() > totalLen) {
byte[] data = baos.toByteArray();
return Arrays.copyOf(data, totalLen);
}
return baos.toByteArray();
}
@Override
public int getContentLength() throws ConnectionException {
int res = -1;
try {
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
res = conn.getContentLength();
conn.disconnect();
return res;
} catch (IOException e) {
throw new ConnectionException(e);
}
}
@Override
public void close() {
}
}