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
WebViewClient.shouldInterceptRequest(WebView view,WebResourceRequest request)方法
首先需要新建一个类，继承WebViewClient：
public class DVDWebViewClient extends WebViewClient
然后实现
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？
@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<String, String> 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
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
//Key 为URL
private Map<String, CacheEntry> 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
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<Boolean>() {
@Override
public Boolean call() throws Exception {
return downloadAndStore(url, cacheEntry);
}
});
final FutureTask<Boolean> 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
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
* <p>
* 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<String, Callable<Boolean>> 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<String, CacheEntry> 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<Boolean>() {
@Override
public Boolean call() throws Exception {
return downloadAndStore(url, cacheEntry);
}
});
final FutureTask<Boolean> 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：
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
* <p>
* 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<Boolean> 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<Object>() {
// @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();
// }
//
// }
}