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
- WebViewClient.shouldInterceptRequest(WebView view,WebResourceRequest request)
方法
首先需要新建一个类,继承 WebViewClient:
Java 代码
- public class DVDWebViewClient extends WebViewClient
然后实现
Java 代码
- 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
- @Override
-
public WebResourceResponse shouldInterceptRequest(WebView view,
-
WebResourceRequest request) {
-
//获取本地的URL主域名
-
String curDomain = request.getUrl().getHost();
-
//这行LOG可以不看
-
if (BuildConfig.DEBUG) {
-
Log.d(LOG_TAG, "curDomain " + curDomain + " request headers " + request.getRequestHeaders());
-
for (Map.Entry entry : request.getRequestHeaders().entrySet()) {
-
Log.d(LOG_TAG, "key=" + entry.getKey() + " #####value=" + entry.getValue() + "\n");
-
}
-
}
-
//取不到domain就直接返回,把接下俩的动作交给webview自己处理
-
if (curDomain == null || !isPicUrl(curDomain)) {
-
return null;
-
}
-
if (BuildConfig.DEBUG) {
-
Log.d(LOG_TAG, "shouldInterceptRequest url " + request.getUrl().toString());
-
}
-
//读取当前webview正准备加载URL资源
-
String url = request.getUrl().toString();
-
try {
-
//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
-
String resFileName = getResourcesFileName(url);
-
if (resFileName == null || "".equals(resFileName)) {
-
return null;
-
}
-
//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
-
this.dvdUrlCache.register(url, getResourcesFileName(url),
-
request.getRequestHeaders().get("Accept"), "UTF-8", DVDUrlCache.ONE_MONTH);
-
return this.dvdUrlCache.load(url);
-
} catch (Exception e) {
-
Log.e(LOG_TAG, "", e);
-
}
-
return null;
-
}
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
- private static class CacheEntry {
-
//用作存储的URL
-
public String url;
-
//本地保存的文件名称
-
public String fileName;
-
//标记资源的头部,通过request参数取回
-
String mimeType;
-
//需要缓存的资源文件的编码
-
public String encoding;
-
//缓存最大有效时间
-
long maxAgeMillis;
-
private CacheEntry(String url, String fileName,
-
String mimeType, String encoding, long maxAgeMillis) {
-
this.url = url;
-
this.fileName = fileName;
-
this.mimeType = mimeType;
-
this.encoding = encoding;
-
this.maxAgeMillis = maxAgeMillis;
-
}
-
}
接下来是类的构造放方法以及需要映射的 map
Java 代码
- //Key 为 URL
- private Map cacheEntries = new HashMap<>();
- //缓存路径的根目录
-
private File rootDir = null;
-
DVDUrlCache() {
- //获取本地缓存路径,这个请在调试中自行修改
-
this.rootDir = DiskUtil.getDiskCacheDir(DVDApplicationContext.getInstance().getApplicationContext());
-
}
- //资源注册,参考 DVDWebViewClient 的调用
- public void register(String url, String cacheFileName,
-
String mimeType, String encoding,
-
long maxAgeMillis) {
-
CacheEntry entry = new CacheEntry(url, cacheFileName, mimeType, encoding, maxAgeMillis);
-
this.cacheEntries.put(url, entry);
-
}
然后是核心内容
Java 代码
- public WebResourceResponse load(final String url) {
-
try {
-
final CacheEntry cacheEntry = this.cacheEntries.get(url);
-
if (cacheEntry == null) {
-
return null;
-
}
-
final File cachedFile = new File(this.rootDir.getPath() + File.separator + cacheEntry.fileName);
-
if (BuildConfig.DEBUG) {
-
Log.d(LOG_TAG, "cachedFile is " + cachedFile);
-
}
-
if (cachedFile.exists() && isReadFromCache(url)) {
-
//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
-
if (queueMap.containsKey(url)) {
-
return null;
-
}
- //过期后直接删除本地缓存内容
-
long cacheEntryAge = System.currentTimeMillis() - cachedFile.lastModified();
-
if (cacheEntryAge > cacheEntry.maxAgeMillis) {
-
cachedFile.delete();
-
if (BuildConfig.DEBUG) {
-
Log.d(LOG_TAG, "Deleting from cache: " + url);
-
}
-
return null;
-
}
-
//cached file exists and is not too old. Return file.
-
if (BuildConfig.DEBUG) {
-
Log.d(LOG_TAG, url + " ### cache file : " + cachedFile.getAbsolutePath());
-
}
-
return new WebResourceResponse(
-
cacheEntry.mimeType, cacheEntry.encoding, new FileInputStream(cachedFile));
-
} else {
-
if (!queueMap.containsKey(url)) {
-
queueMap.put(url, new Callable() {
-
@Override
-
public Boolean call() throws Exception {
-
return downloadAndStore(url, cacheEntry);
-
}
-
});
-
final FutureTask futureTask = ThreadPoolManager.getInstance().addTaskCallback(queueMap.get(url));
-
ThreadPoolManager.getInstance().addTask(new Runnable() {
-
@Override
-
public void run() {
-
try {
-
if (futureTask.get()) {
-
if (BuildConfig.DEBUG) {
-
Log.d(LOG_TAG, "remove " + url);
-
}
-
queueMap.remove(url);
-
}
-
} catch (InterruptedException | ExecutionException e) {
-
Log.d(LOG_TAG, "", e);
-
}
-
}
-
});
-
}
-
}
-
} catch (Exception e) {
-
Log.d(LOG_TAG, "Error reading file over network: ", e);
-
}
-
return null;
-
}
- //这个方法是资源下载
-
private boolean downloadAndStore(final String url, final CacheEntry cacheEntry)
-
throws IOException {
-
FileOutputStream fileOutputStream = null;
-
InputStream urlInput = null;
-
try {
-
URL urlObj = new URL(url);
-
URLConnection urlConnection = urlObj.openConnection();
-
urlInput = urlConnection.getInputStream();
-
String tempFilePath = DVDUrlCache.this.rootDir.getPath() + File.separator + cacheEntry.fileName + ".temp";
-
File tempFile = new File(tempFilePath);
-
fileOutputStream = new FileOutputStream(tempFile);
-
byte[] buffer = new byte[1024];
-
int length;
-
while ((length = urlInput.read(buffer)) > 0) {
-
fileOutputStream.write(buffer, 0, length);
-
}
-
fileOutputStream.flush();
-
File lastFile = new File(tempFilePath.replace(".temp", ""));
-
boolean renameResult = tempFile.renameTo(lastFile);
-
if (!renameResult) {
-
Log.w(LOG_TAG, "rename file failed, " + tempFilePath);
-
}
- // Log.d(LOG_TAG, "Cache file: " + cacheEntry.fileName + " stored. ");
-
return true;
-
} catch (Exception e) {
-
Log.e(LOG_TAG, "", e);
-
} finally {
-
if (urlInput != null) {
-
urlInput.close();
-
}
-
if (fileOutputStream != null) {
-
fileOutputStream.close();
-
}
-
}
-
return false;
-
}
-
private boolean isReadFromCache(String url) {
-
return true;
-
}
完整的 DVDURLCache 代码,方便大家直接 copy
Java 代码
- package com.davdian.seller.util.WebUtil;
- import android.util.Log;
- import android.webkit.WebResourceResponse;
- import com.davdian.seller.BuildConfig;
- import com.davdian.seller.global.DVDApplicationContext;
- import com.davdian.seller.util.DiskUtil;
- import com.davdian.seller.util.ThreadPoolManager;
- import java.io.*;
- import java.net.URL;
- import java.net.URLConnection;
- import java.util.HashMap;
- import java.util.LinkedHashMap;
- import java.util.Map;
- import java.util.concurrent.Callable;
- import java.util.concurrent.ExecutionException;
- import java.util.concurrent.FutureTask;
- /**
-
- 只缓存图片的自定义接口
-
-
- Created by hongminghuangfu on 16/9/3.
- */
- public class DVDUrlCache {
-
private static final String LOG_TAG = "DVDUrlCache";
-
private static final long ONE_SECOND = 1000L;
-
private static final long ONE_MINUTE = 60L * ONE_SECOND;
-
static final long ONE_HOUR = 60 * ONE_MINUTE;
-
static final long ONE_DAY = 24 * ONE_HOUR;
-
static final long ONE_MONTH = 30 * ONE_DAY;
-
private static final LinkedHashMap> queueMap = new LinkedHashMap<>();
-
private static class CacheEntry {
-
public String url;
-
public String fileName;
-
String mimeType;
-
public String encoding;
-
long maxAgeMillis;
-
private CacheEntry(String url, String fileName,
-
String mimeType, String encoding, long maxAgeMillis) {
-
this.url = url;
-
this.fileName = fileName;
-
this.mimeType = mimeType;
-
this.encoding = encoding;
-
this.maxAgeMillis = maxAgeMillis;
-
}
-
}
-
private Map cacheEntries = new HashMap<>();
-
private File rootDir = null;
-
DVDUrlCache() {
- //本地缓存路径,请在调试中自行修改
-
this.rootDir = DiskUtil.getDiskCacheDir(DVDApplicationContext.getInstance().getApplicationContext());
-
}
-
public void register(String url, String cacheFileName,
-
String mimeType, String encoding,
-
long maxAgeMillis) {
-
CacheEntry entry = new CacheEntry(url, cacheFileName, mimeType, encoding, maxAgeMillis);
-
this.cacheEntries.put(url, entry);
-
}
-
public WebResourceResponse load(final String url) {
-
try {
-
final CacheEntry cacheEntry = this.cacheEntries.get(url);
-
if (cacheEntry == null) {
-
return null;
-
}
-
final File cachedFile = new File(this.rootDir.getPath() + File.separator + cacheEntry.fileName);
-
if (BuildConfig.DEBUG) {
-
Log.d(LOG_TAG, "cachedFile is " + cachedFile);
-
}
-
if (cachedFile.exists() && isReadFromCache(url)) {
-
//还没有下载完
-
if (queueMap.containsKey(url)) {
-
return null;
-
}
-
long cacheEntryAge = System.currentTimeMillis() - cachedFile.lastModified();
-
if (cacheEntryAge > cacheEntry.maxAgeMillis) {
-
cachedFile.delete();
-
if (BuildConfig.DEBUG) {
-
Log.d(LOG_TAG, "Deleting from cache: " + url);
-
}
-
return null;
-
}
-
//cached file exists and is not too old. Return file.
-
if (BuildConfig.DEBUG) {
-
Log.d(LOG_TAG, url + " ### cache file : " + cachedFile.getAbsolutePath());
-
}
-
return new WebResourceResponse(
-
cacheEntry.mimeType, cacheEntry.encoding, new FileInputStream(cachedFile));
-
} else {
-
if (!queueMap.containsKey(url)) {
-
queueMap.put(url, new Callable() {
-
@Override
-
public Boolean call() throws Exception {
-
return downloadAndStore(url, cacheEntry);
-
}
-
});
-
final FutureTask futureTask = ThreadPoolManager.getInstance().addTaskCallback(queueMap.get(url));
-
ThreadPoolManager.getInstance().addTask(new Runnable() {
-
@Override
-
public void run() {
-
try {
-
if (futureTask.get()) {
-
if (BuildConfig.DEBUG) {
-
Log.d(LOG_TAG, "remove " + url);
-
}
-
queueMap.remove(url);
-
}
-
} catch (InterruptedException | ExecutionException e) {
-
Log.d(LOG_TAG, "", e);
-
}
-
}
-
});
-
}
-
}
-
} catch (Exception e) {
-
Log.d(LOG_TAG, "Error reading file over network: ", e);
-
}
-
return null;
-
}
-
private boolean downloadAndStore(final String url, final CacheEntry cacheEntry)
-
throws IOException {
-
FileOutputStream fileOutputStream = null;
-
InputStream urlInput = null;
-
try {
-
URL urlObj = new URL(url);
-
URLConnection urlConnection = urlObj.openConnection();
-
urlInput = urlConnection.getInputStream();
-
String tempFilePath = DVDUrlCache.this.rootDir.getPath() + File.separator + cacheEntry.fileName + ".temp";
-
File tempFile = new File(tempFilePath);
-
fileOutputStream = new FileOutputStream(tempFile);
-
byte[] buffer = new byte[1024];
-
int length;
-
while ((length = urlInput.read(buffer)) > 0) {
-
fileOutputStream.write(buffer, 0, length);
-
}
-
fileOutputStream.flush();
-
File lastFile = new File(tempFilePath.replace(".temp", ""));
-
boolean renameResult = tempFile.renameTo(lastFile);
-
if (!renameResult) {
-
Log.w(LOG_TAG, "rename file failed, " + tempFilePath);
-
}
- // Log.d(LOG_TAG, "Cache file: " + cacheEntry.fileName + " stored. ");
-
return true;
-
} catch (Exception e) {
-
Log.e(LOG_TAG, "", e);
-
} finally {
-
if (urlInput != null) {
-
urlInput.close();
-
}
-
if (fileOutputStream != null) {
-
fileOutputStream.close();
-
}
-
}
-
return false;
-
}
-
private boolean isReadFromCache(String url) {
-
return true;
-
}
- }
ThreadPoolManager 很简单:
Java 代码
- package com.davdian.seller.util;
- import android.util.Log;
- import java.util.concurrent.Callable;
- import java.util.concurrent.ExecutorService;
- import java.util.concurrent.Executors;
- import java.util.concurrent.FutureTask;
- /**
-
- 线程池
-
-
- Created by hongminghuangfu on 16/9/9.
- */
- public class ThreadPoolManager {
-
private static final String LOG_TAG = "ThreadPoolManager";
-
private static final ThreadPoolManager instance = new ThreadPoolManager();
-
private ExecutorService threadPool = Executors.newFixedThreadPool(100);
-
public static ThreadPoolManager getInstance() {
-
return instance;
-
}
-
/**
-
* @param runnable 不返回执行结果的异步任务
-
*/
-
public void addTask(Runnable runnable) {
-
try {
-
if (runnable != null) {
-
threadPool.execute(runnable);
-
}
-
} catch (Exception e) {
-
Log.e(LOG_TAG, "", e);
-
}
-
}
-
/**
-
* @param callback 异步任务
-
* @return 你可以获取相应的执行结果
-
*/
-
public FutureTask addTaskCallback(Callable callback) {
-
if (callback == null) {
-
return null;
-
} else {
-
FutureTask futureTask = new FutureTask<>(callback);
-
threadPool.submit(futureTask);
-
return futureTask;
-
}
-
}
- // 这是一个 demo,如果你看不懂,可以打开跑一下
- // public static void main(String args[]) {
- // FutureTask ft = ThreadPoolManager.getInstance().addTaskCallback(new Callable() {
- // @Override
- // public Object call() throws Exception {
- // int sum = 0;
- // for (int i = 0; i < 1000; i++) {
- // sum++;
- // }
- // return sum;
- // }
- // });
- // try {
- // System.out.println("执行结果是:" + ft.get());
- // } catch (InterruptedException | ExecutionException e) {
- // e.printStackTrace();
- // }
- //
- // }
- }
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