簡述
一些知名的視頻app客戶端（優(yōu)酷，愛奇藝）播放視頻的時候都有一些緩存進度(二級進度緩存)，還有一些短視頻app，都有邊播邊緩的處理。還有就是當文件緩存完畢了再次播放的話就不再請求網絡了直接播放本地文件了。既節(jié)省了流程又提高了加載速度。
今天我們就是來研究討論實現(xiàn)這個邊播邊緩存的框架，因為它不和任何的業(yè)務邏輯耦合。
開源的項目
目前比較好的開源項目是：https://github.com/danikula/AndroidVideoCache
代碼的架構寫的也很不錯，網絡用的httpurlconnect，文件緩存處理，文件最大限度策略，回調監(jiān)聽處理，斷點續(xù)傳,代理服務等。很值得研究閱讀.
個人覺得項目中有幾個需要優(yōu)化的點，今天就來處理這幾個并簡要分析下原理
優(yōu)化點比如：
該開源項目的原理分析-本地代理
優(yōu)化點
1. 文件的緩存超過限制后沒有按照lru算法刪除.
Files類。
由于在移動設備上file.setLastModified（） 方法不支持毫秒級的時間處理，導致超出限制大小后本應該刪除老的，卻沒有刪除拋出了異常。注釋掉主動拋出的異常即可。因為文件的修改時間就是對的。
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. 處理返回給播放器的http響應頭消息，響應頭消息的獲取處理改為head請求(需要服務器支持)
HttpUrlSource類。fetchContentInfo方法是獲取視頻文件的Content-Type，Content-Length信息，是為了播放器播放的時候給播放器組裝http響應頭信息用的。所以這一塊需要用數據庫保存，這樣播放器每次播放的時候不要在此獲取了，減少了請求的次數，節(jié)省了流量。既然是只需要頭信息，不需要響應體，所以我們在獲取的時候可以直接采用HEAD方法。所以代碼增加了一個方法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); } //只返回頭部，不需要BODY，既可以提高響應速度也可以減少網絡流量 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.替換網絡庫為okhttp（因為大部分的項目都是以okhttp為網絡請求庫的）
為什么我們要換呢？！一是OKHttp是一款高效的HTTP客戶端，支持連接同一地址的鏈接共享同一個socket，通過連接池來減小響應延遲，還有透明的GZIP壓縮，請求緩存等優(yōu)勢，其核心主要有路由、連接協(xié)議、攔截器、代理、安全性認證、連接池以及網絡適配，攔截器主要是指添加，移除或者轉換請求或者回應的頭部信息。得到了android/222730.html">android開發(fā)的認可。二是大部分的app都是采用OKHttp，而且google會將其納入android 源碼中。三是該作者代碼中用的httpurlconnet在HttpUrlSource有這么一段：
@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); } } }在沒有像okhttp這些優(yōu)秀的網絡開源項目之前，android開發(fā)都是采用httpurlconnet或者httpclient，部分手機可能會遇到這個問題哈。
這里采用的 compile 'com.squareup.okhttp:okhttp:2.7.5' 版本的來實現(xiàn)該類的功能。在原作者的架構思路上我們只需要增加實現(xiàn)Source接口的類OkHttpUrlSource即可，可見作者的代碼架構還是不錯的，當然我們同樣需要處理上文中提高的優(yōu)化點2中的問題。將項目中所有用到HttpUrlSource的地方改為OkHttpUrlSource即可。
源碼如下：
/** * ================================================ * 作 者：顧修忠 * 版 本： * 創(chuàng)建日期：2017/4/13-上午12:03 * 描 述：在一些Android手機上HttpURLConnection.disconnect()方法仍然耗時太久， * 進行導致MediaPlayer要等待很久才會開始播放，因此決定使用okhttp替換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 { //只返回頭部，不需要BODY，既可以提高響應速度也可以減少網絡流量 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 + "}"; }}以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持VEVB武林網。
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