android怎么让webview里的资源访问本地缓存

android如何让webview里的资源访问本地缓存
继承并实现一个ContentProvider
package com.packagename.provider;
public class MyProvider extends ContentProvider {
     @Override
     public ParcelFileDescriptor openFile(Uri uri, String mode){
        URI fileURI = URI.create( "file://" + uri.getPath() );
        File file = new File( fileURI );

        ParcelFileDescriptor parcel = null;
        try {
            parcel = ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY);
        } catch (FileNotFoundException e) {
            Log.e( TAG, "Error finding: " + fileURI + "\n" + e.toString() );
        }

        return parcel;
     }
}

注册AndroidManifest.xml
<provider
        android:name=".provider.MyProvider"
        android:authorities="com.packagename" />

资源url
content://com.packagename/sdcard/Android/data/com.packagename/image.jpg