关于 WebView 缓存的重写

在现在的 app 中，越来越多的公司开始使用 webview 来进行一些活动页面的展示，甚至一些公司开始使用 webview 做为主要显示组件，把所有的内容都使用 H5 来呈现，这样一来，就对 WebView 的加载速度开始有越来越高的要求，我们要讨论的是 webview 的原本缓存机制所存在的弊端和如何复写 WebView 的缓存机制。

首先说一下 webview 的自带缓存机制的弊端：
webview 的自带缓存机制是无差别缓存，也就是说，不管是页面，样式还是图片，都会缓存到本地，刷新 webview 的缓存一般分为以下几种：

LOAD_CACHE_ONLY: 不使用网络，只读取本地缓存数据
LOAD_DEFAULT: 根据 cache-control 决定是否从网络上取数据。
LOAD_CACHE_NORMAL: API level 17 中已经废弃, 从 API level 11 开始作用同 LOAD_DEFAULT 模式
LOAD_NO_CACHE: 不使用缓存，只从网络获取数据.
LOAD_CACHE_ELSE_NETWORK，只要本地有，无论是否过期，或者 no-cache，都使用缓存中的数据。

反正不管以上几种具体情况如何，都肯定不是我们想要的。

我们想要的机制是：
1.缓存自己想要缓存的内容。
2.指定一个缓存策略，在需要的时候重新去服务器获取最新数据

于是我想到了以下方法
重写

Java 代码

1. WebViewClient.shouldInterceptRequest(WebView view,WebResourceRequest request)

方法
首先需要新建一个类，继承 WebViewClient：

Java 代码

1. public class DVDWebViewClient extends WebViewClient

然后实现

Java 代码

1. public WebResourceResponse shouldInterceptRequest(WebView view,WebResourceRequest request)

方法
shouldInterceptRequest 方法会将所有页面的资源 URL 都一一列举出来，这样一来就好办了，我们似乎只需要缓存自己想要缓存的 url 就可以了。
然后事实是不是这样的呢？

Java 代码

1. @Override

2.  public WebResourceResponse shouldInterceptRequest(WebView view,  
   ​

3.                                                    WebResourceRequest request) {  
   ​

4.      //获取本地的URL主域名  
   ​

5.      String curDomain = request.getUrl().getHost();  
   ​

6.      //这行LOG可以不看  
   ​

7.      if (BuildConfig.DEBUG) {  
   ​

8.          Log.d(LOG_TAG, "curDomain " + curDomain + " request headers " + request.getRequestHeaders());  
   ​

9.          for (Map.Entry entry : request.getRequestHeaders().entrySet()) {  
   ​

10.              Log.d(LOG_TAG, "key=" + entry.getKey() + " #####value=" + entry.getValue() + "\n");  
    ​

11.          }  
    ​

12.      }  
    ​

13.      //取不到domain就直接返回，把接下俩的动作交给webview自己处理  
    ​

14.      if (curDomain == null || !isPicUrl(curDomain)) {  
    ​

15.          return null;  
    ​

16.      }  
    ​

17.      if (BuildConfig.DEBUG) {  
    ​

18.          Log.d(LOG_TAG, "shouldInterceptRequest url " + request.getUrl().toString());  
    ​

19.      }  
    ​

20.      //读取当前webview正准备加载URL资源  
    ​

21.      String url = request.getUrl().toString();  
    ​

22.      try {  
    ​

23.         //根据资源url获取一个你要缓存到本地的文件名，一般是URL的MD5  
    ​

24.          String resFileName = getResourcesFileName(url);  
    ​

25.          if (resFileName == null || "".equals(resFileName)) {  
    ​

26.              return null;  
    ​

27.          }  
    ​

28.         //这里是处理本地缓存的URL，缓存到本地，或者已经缓存过的就直接返回而不去网络进行加载  
    ​

29.          this.dvdUrlCache.register(url, getResourcesFileName(url),  
    ​

30.                  request.getRequestHeaders().get("Accept"), "UTF-8", DVDUrlCache.ONE_MONTH);  
    ​

31.          return this.dvdUrlCache.load(url);  
    ​

32.      } catch (Exception e) {  
    ​

33.          Log.e(LOG_TAG, "", e);  
    ​

34.      }  
    ​

35.      return null;  
    ​

36.  }  
    ​

接下来我们看下 DVDUrlCache 的实现：
DVDUrlCache 主要做了这么几件事：
1.封装一个内部类 CacheEntry，做一些基本信息存储

Java 代码

1. private static class CacheEntry {

2.     //用作存储的URL  
   ​

3.      public String url;  
   ​

4.      //本地保存的文件名称  
   ​

5.      public String fileName;  
   ​

6.      //标记资源的头部，通过request参数取回  
   ​

7.      String mimeType;  
   ​

8.      //需要缓存的资源文件的编码  
   ​

9.      public String encoding;  
   ​

10.      //缓存最大有效时间  
    ​

11.      long maxAgeMillis;  
    ​

13.      private CacheEntry(String url, String fileName,  
    ​

14.                         String mimeType, String encoding, long maxAgeMillis) {  
    ​

15.          this.url = url;  
    ​

16.          this.fileName = fileName;  
    ​

17.          this.mimeType = mimeType;  
    ​

18.          this.encoding = encoding;  
    ​

19.          this.maxAgeMillis = maxAgeMillis;  
    ​

20.      }  
    ​

21.  }  
    ​

接下来是类的构造放方法以及需要映射的 map

Java 代码

1. //Key 为 URL
2. private Map cacheEntries = new HashMap<>();
3. //缓存路径的根目录

4.  private File rootDir = null;  
   ​

5.  DVDUrlCache() {  
   ​

6. //获取本地缓存路径，这个请在调试中自行修改

7.      this.rootDir = DiskUtil.getDiskCacheDir(DVDApplicationContext.getInstance().getApplicationContext());  
   ​

8.  }  
   ​

9. //资源注册，参考 DVDWebViewClient 的调用
10. public void register(String url, String cacheFileName,

11.                       String mimeType, String encoding,  
    ​

12.                       long maxAgeMillis) {  
    ​

13.      CacheEntry entry = new CacheEntry(url, cacheFileName, mimeType, encoding, maxAgeMillis);  
    ​

14.      this.cacheEntries.put(url, entry);  
    ​

15.  }  
    ​

然后是核心内容

Java 代码

1. public WebResourceResponse load(final String url) {

2.      try {  
   ​

3.          final CacheEntry cacheEntry = this.cacheEntries.get(url);  
   ​

4.          if (cacheEntry == null) {  
   ​

5.              return null;  
   ​

6.          }  
   ​

8.          final File cachedFile = new File(this.rootDir.getPath() + File.separator + cacheEntry.fileName);  
   ​

9.          if (BuildConfig.DEBUG) {  
   ​

10.              Log.d(LOG_TAG, "cachedFile is " + cachedFile);  
    ​

11.          }  
    ​

12.          if (cachedFile.exists() && isReadFromCache(url)) {  
    ​

13.              //还没有下载完,在快速切换URL的时候，可能会有很多task并没有及时完成，所以这里需要一个map用于存储正在下载的URL，下载完成后需要移除相应的task  
    ​

14.              if (queueMap.containsKey(url)) {                 
    ​

15.                  return null;  
    ​

16.              }  
    ​

17. //过期后直接删除本地缓存内容

18.              long cacheEntryAge = System.currentTimeMillis() - cachedFile.lastModified();  
    ​

19.              if (cacheEntryAge > cacheEntry.maxAgeMillis) {  
    ​

20.                  cachedFile.delete();  
    ​

21.                  if (BuildConfig.DEBUG) {  
    ​

22.                      Log.d(LOG_TAG, "Deleting from cache: " + url);  
    ​

23.                  }  
    ​

24.                  return null;  
    ​

25.              }  
    ​

26.              //cached file exists and is not too old. Return file.  
    ​

27.              if (BuildConfig.DEBUG) {  
    ​

28.                  Log.d(LOG_TAG, url + " ### cache file : " + cachedFile.getAbsolutePath());  
    ​

29.              }  
    ​

30.              return new WebResourceResponse(  
    ​

31.                      cacheEntry.mimeType, cacheEntry.encoding, new FileInputStream(cachedFile));  
    ​

32.          } else {  
    ​

33.              if (!queueMap.containsKey(url)) {  
    ​

34.                  queueMap.put(url, new Callable() {  
    ​

35.                      @Override  
    ​

36.                      public Boolean call() throws Exception {  
    ​

37.                          return downloadAndStore(url, cacheEntry);  
    ​

38.                      }  
    ​

39.                  });  
    ​

40.                  final FutureTask futureTask = ThreadPoolManager.getInstance().addTaskCallback(queueMap.get(url));  
    ​

41.                  ThreadPoolManager.getInstance().addTask(new Runnable() {  
    ​

42.                      @Override  
    ​

43.                      public void run() {  
    ​

44.                          try {  
    ​

45.                              if (futureTask.get()) {  
    ​

46.                                  if (BuildConfig.DEBUG) {  
    ​

47.                                      Log.d(LOG_TAG, "remove " + url);  
    ​

48.                                  }  
    ​

49.                                  queueMap.remove(url);  
    ​

50.                              }  
    ​

51.                          } catch (InterruptedException | ExecutionException e) {  
    ​

52.                              Log.d(LOG_TAG, "", e);  
    ​

53.                          }  
    ​

54.                      }  
    ​

55.                  });  
    ​

56.              }  
    ​

57.          }  
    ​

58.      } catch (Exception e) {  
    ​

59.          Log.d(LOG_TAG, "Error reading file over network: ", e);  
    ​

60.      }  
    ​

61.      return null;  
    ​

62.  }  
    ​

64. //这个方法是资源下载

65.  private boolean downloadAndStore(final String url, final CacheEntry cacheEntry)  
    ​

66.          throws IOException {  
    ​

67.      FileOutputStream fileOutputStream = null;  
    ​

68.      InputStream urlInput = null;  
    ​

69.      try {  
    ​

70.          URL urlObj = new URL(url);  
    ​

71.          URLConnection urlConnection = urlObj.openConnection();  
    ​

72.          urlInput = urlConnection.getInputStream();  
    ​

73.          String tempFilePath = DVDUrlCache.this.rootDir.getPath() + File.separator + cacheEntry.fileName + ".temp";  
    ​

74.          File tempFile = new File(tempFilePath);  
    ​

75.          fileOutputStream = new FileOutputStream(tempFile);  
    ​

76.          byte[] buffer = new byte[1024];  
    ​

77.          int length;  
    ​

78.          while ((length = urlInput.read(buffer)) > 0) {  
    ​

79.              fileOutputStream.write(buffer, 0, length);  
    ​

80.          }  
    ​

81.          fileOutputStream.flush();  
    ​

82.          File lastFile = new File(tempFilePath.replace(".temp", ""));  
    ​

83.          boolean renameResult = tempFile.renameTo(lastFile);  
    ​

84.          if (!renameResult) {  
    ​

85.              Log.w(LOG_TAG, "rename file failed, " + tempFilePath);  
    ​

86.          }  
    ​

87. // Log.d(LOG_TAG, "Cache file: " + cacheEntry.fileName + " stored. ");

88.          return true;  
    ​

89.      } catch (Exception e) {  
    ​

90.          Log.e(LOG_TAG, "", e);  
    ​

91.      } finally {  
    ​

92.          if (urlInput != null) {  
    ​

93.              urlInput.close();  
    ​

94.          }  
    ​

95.          if (fileOutputStream != null) {  
    ​

96.              fileOutputStream.close();  
    ​

97.          }  
    ​

98.      }  
    ​

99.      return false;  
    ​

100.  }  
     ​

102.  private boolean isReadFromCache(String url) {  
     ​

103.      return true;  
     ​

104.  }  
     ​

完整的 DVDURLCache 代码，方便大家直接 copy

Java 代码

1. package com.davdian.seller.util.WebUtil;
3. import android.util.Log;
4. import android.webkit.WebResourceResponse;
5. import com.davdian.seller.BuildConfig;
6. import com.davdian.seller.global.DVDApplicationContext;
7. import com.davdian.seller.util.DiskUtil;
8. import com.davdian.seller.util.ThreadPoolManager;
10. import java.io.*;
11. import java.net.URL;
12. import java.net.URLConnection;
13. import java.util.HashMap;
14. import java.util.LinkedHashMap;
15. import java.util.Map;
16. import java.util.concurrent.Callable;
17. import java.util.concurrent.ExecutionException;
18. import java.util.concurrent.FutureTask;
20. /**
21. • 只缓存图片的自定义接口
23. • Created by hongminghuangfu on 16/9/3.
24. */
25. public class DVDUrlCache {

27.  private static final String LOG_TAG = "DVDUrlCache";  
    ​

29.  private static final long ONE_SECOND = 1000L;  
    ​

30.  private static final long ONE_MINUTE = 60L * ONE_SECOND;  
    ​

31.  static final long ONE_HOUR = 60 * ONE_MINUTE;  
    ​

32.  static final long ONE_DAY = 24 * ONE_HOUR;  
    ​

33.  static final long ONE_MONTH = 30 * ONE_DAY;  
    ​

36.  private static final LinkedHashMap> queueMap = new LinkedHashMap<>();  
    ​

39.  private static class CacheEntry {  
    ​

40.      public String url;  
    ​

41.      public String fileName;  
    ​

42.      String mimeType;  
    ​

43.      public String encoding;  
    ​

44.      long maxAgeMillis;  
    ​

46.      private CacheEntry(String url, String fileName,  
    ​

47.                         String mimeType, String encoding, long maxAgeMillis) {  
    ​

48.          this.url = url;  
    ​

49.          this.fileName = fileName;  
    ​

50.          this.mimeType = mimeType;  
    ​

51.          this.encoding = encoding;  
    ​

52.          this.maxAgeMillis = maxAgeMillis;  
    ​

53.      }  
    ​

54.  }  
    ​

56.  private Map cacheEntries = new HashMap<>();  
    ​

57.  private File rootDir = null;  
    ​

59.  DVDUrlCache() {  
    ​

60. //本地缓存路径，请在调试中自行修改

61.      this.rootDir = DiskUtil.getDiskCacheDir(DVDApplicationContext.getInstance().getApplicationContext());  
    ​

62.  }  
    ​

64.  public void register(String url, String cacheFileName,  
    ​

65.                       String mimeType, String encoding,  
    ​

66.                       long maxAgeMillis) {  
    ​

67.      CacheEntry entry = new CacheEntry(url, cacheFileName, mimeType, encoding, maxAgeMillis);  
    ​

68.      this.cacheEntries.put(url, entry);  
    ​

69.  }  
    ​

71.  public WebResourceResponse load(final String url) {  
    ​

72.      try {  
    ​

73.          final CacheEntry cacheEntry = this.cacheEntries.get(url);  
    ​

74.          if (cacheEntry == null) {  
    ​

75.              return null;  
    ​

76.          }  
    ​

78.          final File cachedFile = new File(this.rootDir.getPath() + File.separator + cacheEntry.fileName);  
    ​

79.          if (BuildConfig.DEBUG) {  
    ​

80.              Log.d(LOG_TAG, "cachedFile is " + cachedFile);  
    ​

81.          }  
    ​

82.          if (cachedFile.exists() && isReadFromCache(url)) {  
    ​

83.              //还没有下载完  
    ​

84.              if (queueMap.containsKey(url)) {                  
    ​

85.                  return null;  
    ​

86.              }  
    ​

87.              long cacheEntryAge = System.currentTimeMillis() - cachedFile.lastModified();  
    ​

88.              if (cacheEntryAge > cacheEntry.maxAgeMillis) {  
    ​

89.                  cachedFile.delete();  
    ​

90.                  if (BuildConfig.DEBUG) {  
    ​

91.                      Log.d(LOG_TAG, "Deleting from cache: " + url);  
    ​

92.                  }  
    ​

93.                  return null;  
    ​

94.              }  
    ​

95.              //cached file exists and is not too old. Return file.  
    ​

96.              if (BuildConfig.DEBUG) {  
    ​

97.                  Log.d(LOG_TAG, url + " ### cache file : " + cachedFile.getAbsolutePath());  
    ​

98.              }  
    ​

99.              return new WebResourceResponse(  
    ​

100.                      cacheEntry.mimeType, cacheEntry.encoding, new FileInputStream(cachedFile));  
     ​

101.          } else {  
     ​

102.              if (!queueMap.containsKey(url)) {  
     ​

103.                  queueMap.put(url, new Callable() {  
     ​

104.                      @Override  
     ​

105.                      public Boolean call() throws Exception {  
     ​

106.                          return downloadAndStore(url, cacheEntry);  
     ​

107.                      }  
     ​

108.                  });  
     ​

109.                  final FutureTask futureTask = ThreadPoolManager.getInstance().addTaskCallback(queueMap.get(url));  
     ​

110.                  ThreadPoolManager.getInstance().addTask(new Runnable() {  
     ​

111.                      @Override  
     ​

112.                      public void run() {  
     ​

113.                          try {  
     ​

114.                              if (futureTask.get()) {  
     ​

115.                                  if (BuildConfig.DEBUG) {  
     ​

116.                                      Log.d(LOG_TAG, "remove " + url);  
     ​

117.                                  }  
     ​

118.                                  queueMap.remove(url);  
     ​

119.                              }  
     ​

120.                          } catch (InterruptedException | ExecutionException e) {  
     ​

121.                              Log.d(LOG_TAG, "", e);  
     ​

122.                          }  
     ​

123.                      }  
     ​

124.                  });  
     ​

125.              }  
     ​

126.          }  
     ​

127.      } catch (Exception e) {  
     ​

128.          Log.d(LOG_TAG, "Error reading file over network: ", e);  
     ​

129.      }  
     ​

130.      return null;  
     ​

131.  }  
     ​

133.  private boolean downloadAndStore(final String url, final CacheEntry cacheEntry)  
     ​

134.          throws IOException {  
     ​

135.      FileOutputStream fileOutputStream = null;  
     ​

136.      InputStream urlInput = null;  
     ​

137.      try {  
     ​

138.          URL urlObj = new URL(url);  
     ​

139.          URLConnection urlConnection = urlObj.openConnection();  
     ​

140.          urlInput = urlConnection.getInputStream();  
     ​

141.          String tempFilePath = DVDUrlCache.this.rootDir.getPath() + File.separator + cacheEntry.fileName + ".temp";  
     ​

142.          File tempFile = new File(tempFilePath);  
     ​

143.          fileOutputStream = new FileOutputStream(tempFile);  
     ​

144.          byte[] buffer = new byte[1024];  
     ​

145.          int length;  
     ​

146.          while ((length = urlInput.read(buffer)) > 0) {  
     ​

147.              fileOutputStream.write(buffer, 0, length);  
     ​

148.          }  
     ​

149.          fileOutputStream.flush();  
     ​

150.          File lastFile = new File(tempFilePath.replace(".temp", ""));  
     ​

151.          boolean renameResult = tempFile.renameTo(lastFile);  
     ​

152.          if (!renameResult) {  
     ​

153.              Log.w(LOG_TAG, "rename file failed, " + tempFilePath);  
     ​

154.          }  
     ​

155. // Log.d(LOG_TAG, "Cache file: " + cacheEntry.fileName + " stored. ");

156.          return true;  
     ​

157.      } catch (Exception e) {  
     ​

158.          Log.e(LOG_TAG, "", e);  
     ​

159.      } finally {  
     ​

160.          if (urlInput != null) {  
     ​

161.              urlInput.close();  
     ​

162.          }  
     ​

163.          if (fileOutputStream != null) {  
     ​

164.              fileOutputStream.close();  
     ​

165.          }  
     ​

166.      }  
     ​

167.      return false;  
     ​

168.  }  
     ​

170.  private boolean isReadFromCache(String url) {  
     ​

171.      return true;  
     ​

172.  }  
     ​

174. }

ThreadPoolManager 很简单：

Java 代码

1. package com.davdian.seller.util;
3. import android.util.Log;
5. import java.util.concurrent.Callable;
6. import java.util.concurrent.ExecutorService;
7. import java.util.concurrent.Executors;
8. import java.util.concurrent.FutureTask;
10. /**
11. • 线程池
13. • Created by hongminghuangfu on 16/9/9.
14. */
15. public class ThreadPoolManager {

17.  private static final String LOG_TAG = "ThreadPoolManager";  
    ​

18.  private static final ThreadPoolManager instance = new ThreadPoolManager();  
    ​

20.  private ExecutorService threadPool = Executors.newFixedThreadPool(100);  
    ​

22.  public static ThreadPoolManager getInstance() {  
    ​

23.      return instance;  
    ​

24.  }  
    ​

26.  /** 
    ​

27.   * @param runnable 不返回执行结果的异步任务 
    ​

28.   */  
    ​

29.  public void addTask(Runnable runnable) {  
    ​

30.      try {  
    ​

31.          if (runnable != null) {  
    ​

32.              threadPool.execute(runnable);  
    ​

33.          }  
    ​

34.      } catch (Exception e) {  
    ​

35.          Log.e(LOG_TAG, "", e);  
    ​

36.      }  
    ​

37.  }  
    ​

39.  /** 
    ​

40.   * @param callback 异步任务 
    ​

41.   * @return 你可以获取相应的执行结果 
    ​

42.   */  
    ​

43.  public FutureTask addTaskCallback(Callable callback) {  
    ​

44.      if (callback == null) {  
    ​

45.          return null;  
    ​

46.      } else {  
    ​

47.          FutureTask futureTask = new FutureTask<>(callback);  
    ​

48.          threadPool.submit(futureTask);  
    ​

49.          return futureTask;  
    ​

50.      }  
    ​

52.  }  
    ​

53. // 这是一个 demo，如果你看不懂，可以打开跑一下
54. // public static void main(String args[]) {
55. // FutureTask ft = ThreadPoolManager.getInstance().addTaskCallback(new Callable() {
56. // @Override
57. // public Object call() throws Exception {
58. // int sum = 0;
59. // for (int i = 0; i < 1000; i++) {
60. // sum++;
61. // }
62. // return sum;
63. // }
64. // });
65. // try {
66. // System.out.println("执行结果是:" + ft.get());
67. // } catch (InterruptedException | ExecutionException e) {
68. // e.printStackTrace();
69. // }
70. //
71. // }
72. }