Android应用中怎么实现一个视频点播功能

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采用了本地代理服务的方式，通过原始url给播放器返回一个本地代理的一个url ，代理URL类似：http://127.0.0.1:57430/xxxx；然后播放器播放的时候请求到了你本地的代理上了。

本地代理采用ServerSocket监听127.0.0.1的有效端口，这个时候手机就是一个服务器了，客户端就是socket，也就是播放器。
读取客户端就是socket来读取数据（http协议请求）解析http协议。
根据url检查视频文件是否存在，读取文件数据给播放器，也就是往socket里写入数据。同时如果没有下载完成会进行断点下载,当然弱网的话数据需要生产消费同步处理。

优化点

1. 文件的缓存超过限制后没有按照lru算法删除.

Files类。

由于在移动设备上file.setLastModified（）方法不支持毫秒级的时间处理，导致超出限制大小后本应该删除老的，却没有删除抛出了异常。注释掉主动抛出的异常即可。因为文件的修改时间就是对的。

  static void setLastModifiedNow(File file) throws IOException {
    if (file.exists()) {
      long now = System.currentTimeMillis();
      boolean modified = file.setLastModified(now/1000*1000); // on some devices (e.g. Nexus 5) doesn't work
      if (!modified) {
        modify(file);
//        if (file.lastModified() < now) {
//          VideoCacheLog.debug("LruDiskUsage", "modified not ok ");
//          throw new IOException("Error set last modified date to " + file);
//        }else{
//          VideoCacheLog.debug("LruDiskUsage", "modified ok ");
//        }
      }
    }
  }

2. 处理返回给播放器的http响应头消息，响应头消息的获取处理改为head请求(需要服务器支持)

HttpUrlSource类。fetchContentInfo方法是获取视频文件的Content-Type，Content-Length信息，是为了播放器播放的时候给播放器组装http响应头信息用的。所以这一块需要用数据库保存，这样播放器每次播放的时候不要在此获取了，减少了请求的次数，节省了流量。既然是只需要头信息，不需要响应体，所以我们在获取的时候可以直接采用HEAD方法。所以代码增加了一个方法openConnectionForHeader如下：

 private void fetchContentInfo() throws ProxyCacheException {
    VideoCacheLog.debug(TAG,"Read content info from " + sourceInfo.url);
    HttpURLConnection urlConnection = null;
    InputStream inputStream = null;
    try {
      urlConnection = openConnectionForHeader(20000);
      long length = getContentLength(urlConnection);
      String mime = urlConnection.getContentType();
      inputStream = urlConnection.getInputStream();
      this.sourceInfo = new SourceInfo(sourceInfo.url, length, mime);
      this.sourceInfoStorage.put(sourceInfo.url, sourceInfo);
      VideoCacheLog.debug(TAG,"Source info fetched: " + sourceInfo);
    } catch (IOException e) {
      VideoCacheLog.error(TAG,"Error fetching info from " + sourceInfo.url ,e);
    } finally {
      ProxyCacheUtils.close(inputStream);
      if (urlConnection != null) {
        urlConnection.disconnect();
      }
    }
  }

  // for HEAD
  private HttpURLConnection openConnectionForHeader(int timeout) throws IOException, ProxyCacheException {
    HttpURLConnection connection;
    boolean redirected;
    int redirectCount = 0;
    String url = this.sourceInfo.url;
    do {
      VideoCacheLog.debug(TAG, "Open connection for header to " + url);
      connection = (HttpURLConnection) new URL(url).openConnection();
      if (timeout > 0) {
        connection.setConnectTimeout(timeout);
        connection.setReadTimeout(timeout);
      }
      //只返回头部，不需要BODY，既可以提高响应速度也可以减少网络流量
      connection.setRequestMethod("HEAD");
      int code = connection.getResponseCode();
      redirected = code == HTTP_MOVED_PERM || code == HTTP_MOVED_TEMP || code == HTTP_SEE_OTHER;
      if (redirected) {
        url = connection.getHeaderField("Location");
        VideoCacheLog.debug(TAG,"Redirect to:" + url);
        redirectCount++;
        connection.disconnect();
        VideoCacheLog.debug(TAG,"Redirect closed:" + url);
      }
      if (redirectCount > MAX_REDIRECTS) {
        throw new ProxyCacheException("Too many redirects: " + redirectCount);
      }
    } while (redirected);
    return connection;
  }

3.替换网络库为okhttp（因为大部分的项目都是以okhttp为网络请求库的）

为什么我们要换呢？！一是OKHttp是一款高效的HTTP客户端，支持连接同一地址的链接共享同一个socket，通过连接池来减小响应延迟，还有透明的GZIP压缩，请求缓存等优势，其核心主要有路由、连接协议、拦截器、代理、安全性认证、连接池以及网络适配，拦截器主要是指添加，移除或者转换请求或者回应的头部信息。得到了android开发的认可。二是大部分的app都是采用OKHttp，而且google会将其纳入android 源码中。三是该作者代码中用的httpurlconnet在HttpUrlSource有这么一段：

 @Override
  public void close() throws ProxyCacheException {
    if (connection != null) {
      try {
        connection.disconnect();
      } catch (NullPointerException | IllegalArgumentException e) {
        String message = "Wait... but why? WTF!? " +
            "Really shouldn't happen any more after fixing https://github.com/danikula/AndroidVideoCache/issues/43. " +
            "If you read it on your device log, please, notify me danikula@gmail.com or create issue here " +
            "https://github.com/danikula/AndroidVideoCache/issues.";
        throw new RuntimeException(message, e);
      } catch (ArrayIndexOutOfBoundsException e) {
        VideoCacheLog.error(TAG,"Error closing connection correctly. Should happen only on Android L. " +
            "If anybody know how to fix it, please visit https://github.com/danikula/AndroidVideoCache/issues/88. " +
            "Until good solution is not know, just ignore this issue :(", e);
      }
    }
  }

在没有像okhttp这些优秀的网络开源项目之前，android开发都是采用httpurlconnet或者httpclient，部分手机可能会遇到这个问题哈。

这里采用的 compile 'com.squareup.okhttp:okhttp:2.7.5' 版本的来实现该类的功能。在原作者的架构思路上我们只需要增加实现Source接口的类OkHttpUrlSource即可，可见作者的代码架构还是不错的，当然我们同样需要处理上文中提高的优化点2中的问题。将项目中所有用到HttpUrlSource的地方改为OkHttpUrlSource即可。
源码如下：

/**
 * ================================================
 * 作  者：顾修忠

 * 版  本：
 * 创建日期：2017/4/13-上午12:03
 * 描  述：在一些Android手机上HttpURLConnection.disconnect()方法仍然耗时太久，
 * 进行导致MediaPlayer要等待很久才会开始播放，因此决定使用okhttp替换HttpURLConnection
 */

public class OkHttpUrlSource implements Source {

  private static final String TAG = OkHttpUrlSource.class.getSimpleName();
  private static final int MAX_REDIRECTS = 5;
  private final SourceInfoStorage sourceInfoStorage;
  private SourceInfo sourceInfo;
  private OkHttpClient okHttpClient = new OkHttpClient();
  private Call requestCall = null;
  private InputStream inputStream;

  public OkHttpUrlSource(String url) {
    this(url, SourceInfoStorageFactory.newEmptySourceInfoStorage());
  }

  public OkHttpUrlSource(String url, SourceInfoStorage sourceInfoStorage) {
    this.sourceInfoStorage = checkNotNull(sourceInfoStorage);
    SourceInfo sourceInfo = sourceInfoStorage.get(url);
    this.sourceInfo = sourceInfo != null ? sourceInfo :
        new SourceInfo(url, Integer.MIN_VALUE, ProxyCacheUtils.getSupposablyMime(url));
  }

  public OkHttpUrlSource(OkHttpUrlSource source) {
    this.sourceInfo = source.sourceInfo;
    this.sourceInfoStorage = source.sourceInfoStorage;
  }

  @Override
  public synchronized long length() throws ProxyCacheException {
    if (sourceInfo.length == Integer.MIN_VALUE) {
      fetchContentInfo();
    }
    return sourceInfo.length;
  }

  @Override
  public void open(long offset) throws ProxyCacheException {
    try {
      Response response = openConnection(offset, -1);
      String mime = response.header("Content-Type");
      this.inputStream = new BufferedInputStream(response.body().byteStream(), DEFAULT_BUFFER_SIZE);
      long length = readSourceAvailableBytes(response, offset, response.code());
      this.sourceInfo = new SourceInfo(sourceInfo.url, length, mime);
      this.sourceInfoStorage.put(sourceInfo.url, sourceInfo);
    } catch (IOException e) {
      throw new ProxyCacheException("Error opening okHttpClient for " + sourceInfo.url + " with offset " + offset, e);
    }
  }

  private long readSourceAvailableBytes(Response response, long offset, int responseCode) throws IOException {
    long contentLength = getContentLength(response);
    return responseCode == HTTP_OK ? contentLength
        : responseCode == HTTP_PARTIAL ? contentLength + offset : sourceInfo.length;
  }

  private long getContentLength(Response response) {
    String contentLengthValue = response.header("Content-Length");
    return contentLengthValue == null ? -1 : Long.parseLong(contentLengthValue);
  }

  @Override
  public void close() throws ProxyCacheException {
    if (okHttpClient != null && inputStream != null && requestCall != null) {
      try {
        inputStream.close();
        requestCall.cancel();
      } catch (IOException e) {
        e.printStackTrace();
        throw new RuntimeException(e.getMessage(), e);
      }
    }
  }

  @Override
  public int read(byte[] buffer) throws ProxyCacheException {
    if (inputStream == null) {
      throw new ProxyCacheException("Error reading data from " + sourceInfo.url + ": okHttpClient is absent!");
    }
    try {
      return inputStream.read(buffer, 0, buffer.length);
    } catch (InterruptedIOException e) {
      throw new InterruptedProxyCacheException("Reading source " + sourceInfo.url + " is interrupted", e);
    } catch (IOException e) {
      throw new ProxyCacheException("Error reading data from " + sourceInfo.url, e);
    }
  }

  private void fetchContentInfo() throws ProxyCacheException {
    VideoCacheLog.debug(TAG, "Read content info from " + sourceInfo.url);
    Response response = null;
    InputStream inputStream = null;
    try {
      response = openConnectionForHeader(20000);
      if (response == null || !response.isSuccessful()) {
        throw new ProxyCacheException("Fail to fetchContentInfo: " + sourceInfo.url);
      }
      long length = getContentLength(response);
      String mime = response.header("Content-Type", "application/mp4");
      inputStream = response.body().byteStream();
      this.sourceInfo = new SourceInfo(sourceInfo.url, length, mime);
      this.sourceInfoStorage.put(sourceInfo.url, sourceInfo);
      VideoCacheLog.info(TAG, "Content info for `" + sourceInfo.url + "`: mime: " + mime + ", content-length: " + length);
    } catch (IOException e) {
      VideoCacheLog.error(TAG, "Error fetching info from " + sourceInfo.url, e);
    } finally {
      ProxyCacheUtils.close(inputStream);
      if (response != null && requestCall != null) {
        requestCall.cancel();
      }
    }
  }

  // for HEAD
  private Response openConnectionForHeader(int timeout) throws IOException, ProxyCacheException {
    if (timeout > 0) {
//      okHttpClient.setConnectTimeout(timeout, TimeUnit.MILLISECONDS);
//      okHttpClient.setReadTimeout(timeout, TimeUnit.MILLISECONDS);
//      okHttpClient.setWriteTimeout(timeout, TimeUnit.MILLISECONDS);
    }
    Response response;
    boolean isRedirect = false;
    String newUrl = this.sourceInfo.url;
    int redirectCount = 0;
    do {
      //只返回头部，不需要BODY，既可以提高响应速度也可以减少网络流量
      Request request = new Request.Builder()
          .head()
          .url(newUrl)
          .build();
      requestCall = okHttpClient.newCall(request);
      response = requestCall.execute();
      if (response.isRedirect()) {
        newUrl = response.header("Location");
        VideoCacheLog.debug(TAG, "Redirect to:" + newUrl);
        isRedirect = response.isRedirect();
        redirectCount++;
        requestCall.cancel();
        VideoCacheLog.debug(TAG, "Redirect closed:" + newUrl);
      }
      if (redirectCount > MAX_REDIRECTS) {
        throw new ProxyCacheException("Too many redirects: " + redirectCount);
      }
    } while (isRedirect);

    return response;
  }

  private Response openConnection(long offset, int timeout) throws IOException, ProxyCacheException {
    if (timeout > 0) {
//      okHttpClient.setConnectTimeout(timeout, TimeUnit.MILLISECONDS);
//      okHttpClient.setReadTimeout(timeout, TimeUnit.MILLISECONDS);
//      okHttpClient.setWriteTimeout(timeout, TimeUnit.MILLISECONDS);
    }
    Response response;
    boolean isRedirect = false;
    String newUrl = this.sourceInfo.url;
    int redirectCount = 0;
    do {
      VideoCacheLog.debug(TAG, "Open connection" + (offset > 0 ? " with offset " + offset : "") + " to " + sourceInfo.url);
      Request.Builder requestBuilder = new Request.Builder()
          .get()
          .url(newUrl);
      if (offset > 0) {
        requestBuilder.addHeader("Range", "bytes=" + offset + "-");
      }
      requestCall = okHttpClient.newCall(requestBuilder.build());
      response = requestCall.execute();
      if (response.isRedirect()) {
        newUrl = response.header("Location");
        isRedirect = response.isRedirect();
        redirectCount++;
      }
      if (redirectCount > MAX_REDIRECTS) {
        throw new ProxyCacheException("Too many redirects: " + redirectCount);
      }
    } while (isRedirect);

    return response;
  }

  public synchronized String getMime() throws ProxyCacheException {
    if (TextUtils.isEmpty(sourceInfo.mime)) {
      fetchContentInfo();
    }
    return sourceInfo.mime;
  }

  public String getUrl() {
    return sourceInfo.url;
  }

  @Override
  public String toString() {
    return "OkHttpUrlSource{sourceInfo='" + sourceInfo + "}";
  }
}

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