Android HttpClient和多线程下载

[迁移]

0x80 HttpClient

虽然HttpClient类已被抛弃，Google官方推荐使用HttpUrlConnection代替，但是它的用法依然对于网络操作的使用有所帮助。
HttpClient是Apache封装的一个网页客户端模拟类，其中封装了一些方法用于简化Http操作。

0x81 GET用法

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HttpGet httpGet = new HttpGet("http://host:port/index.php?username=" + URLEncoder.encode(username,"UTF-8") + "&password=" + URLEncoder.encode(password,"UTF-8"));

0x82 POST用法

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HttpPost httpPost = new HttpPost(url);
    List parameters = new ArryList();
    parameters.add(new BasicNameValuePair("username",username));
    parameters.add(new BasicNameValuePair("password",password));
    httpPost.setEntity(new URLEncoderFormEntity(parameters,"UTF-8"));

0x83 HttpResponse

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HttpResponse httpResponse = client.execute(httpGet/Post);
    int code = httpResponse.getStatusLine().getStatusCode();
    if(200 == code){
        InputStream is = response.getEntity().getContent();
    }

0x84 多线程下载思路

  1. 本地创建一个相同大小的临时文件
  2. 分配线程下载并计算各线程下载位置（(tid - 1) * block -- tid * block - 1）
  3. 各线程分别下载各自内容

0x85 简单实例

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Url url = new Url("http://host:port/test");
HttpUrlConnection conn = (HttpUrlConnection)url.openConnection(); //打开链接
conn.setConnectionTimeout(5000); // 设置超时
conn.setRequestMethod("GET"); // 设置访问方式为GET

int length = conn.getContentLength(); // 获取文件长度
RandomAccessFile raf = new RandomAccessFile("/sdcard/test","rwd");
raf.setLength(length); // 创建同大小临时空文件
raf.close();

int blockSize = length / 3; // 计算块大小
for (int threadId = 0; threadId < 3; threadId ++){
    int startIndex = (i - 1) * blockSize;
    int endIndex = (i) * blockSize - 1;
    if(2 == i){
        endIndex = length; // 若是最后一个线程，负责下载完所有剩余内容
    }
    new DownloadThread(path,threadId,startIndex,endIndex).run(); // 启动线程下载
}

// 下载线程类
public class DownloadThread extends Thread{
    private int threadId;
    private int startIndex;
    private int endIndex;
    private String path;

    public void run(){
        conn.setRequestProperty("Range","bytes=" + startIndex + "-" + "endIndex");
        if (206 == conn.getResponseCode()){ // 此处部分下载返回状态码206
            InputStream is = conn.getInputStream(); // 获取下载文件流
            RandomAccessFile raf = new RandomAccessFile("/sdcard/test","rwd"); // "rwd"是数据内容变化立即写入而不等待缓存
            raf.seek(startIndex); // 将文件指针挪到指定位置

            int len = 0;
            byte[] buffer =new byte[1024];
            while((len = is.read(buffer)) != -1){
                raf.write(buffer,0,len);
            }
        }
    }
}

上方即是简单的多线程下载，可以用SharedPreference或文件保存当前下载进度以便下载异常恢复下载。