ConnectionImpl.java

package com.johnChnia.coderising2017.download.impl;

import com.johnChnia.coderising2017.download.api.Connection;
import com.johnChnia.coderising2017.download.api.ConnectionException;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.util.Arrays;

public class ConnectionImpl implements Connection {
    URL url;
    static final int BUFFER_SIZE = 1024;

    ConnectionImpl(String _url) throws ConnectionException {
        try {
            url = new URL(_url);
        } catch (Exception e) {
            throw new ConnectionException();
        }
    }
    @Override
    public byte[] read(int startPos, int endPos) throws IOException {
        //开始
        System.out.println("开始");
        HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
        // 设置读取的位置
        httpConn.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);
        // 从URL连接获得输入流
        InputStream is = httpConn.getInputStream();

        //is.skip(startPos);
        byte[] buff = new byte[BUFFER_SIZE];
        int totalLen = endPos - startPos + 1;
        ByteArrayOutputStream baos = new ByteArrayOutputStream();

        while(baos.size() < totalLen){
            int len = is.read(buff);
            if(len<0){
                break;
            }
            baos.write(buff,0,len);
        }

        if(baos.size() > totalLen){
            byte[] data = baos.toByteArray();
            return Arrays.copyOf(data, totalLen);
        }
        return baos.toByteArray();
    }

    @Override
    public int getContentLength() {
        URLConnection con;
        try {
            con = url.openConnection();
            return con.getContentLength();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return -1;
    }

    @Override
    public void close() {

    }
}