WebViewAssetLoader


class WebViewAssetLoader


Helper class to load local files including application's static assets and resources using http(s):// URLs inside a android.webkit.WebView class. Loading local files using web-like URLs instead of "file://" is desirable as it is compatible with the Same-Origin policy.

For more context about application's assets and resources and how to normally access them please refer to Android Developer Docs: App resources overview.

This class is expected to be used within shouldInterceptRequest, which is invoked on a different thread than application's main thread. Although instances are themselves thread-safe (and may be safely constructed on the application's main thread), exercise caution when accessing private data or the view system.

Using http(s):// URLs to access local resources may conflict with a real website. This means that local files should only be hosted on domains your organization owns (at paths reserved for this purpose) or the default domain reserved for this: appassets.androidplatform.net.

A typical usage would be like:

final WebViewAssetLoader assetLoader = new WebViewAssetLoader.Builder()
         .addPathHandler("/assets/", new AssetsPathHandler(this))
         .build();

      

webView.setWebViewClient(new WebViewClientCompat() { @Override public WebResourceResponse shouldInterceptRequest(WebView view, WebResourceRequest request) { return assetLoader.shouldInterceptRequest(request.getUrl()); }

@Override @SuppressWarnings("deprecation") // for API < 21 public WebResourceResponse shouldInterceptRequest(WebView view, String url) { return assetLoader.shouldInterceptRequest(Uri.parse(url)); } });

WebSettings webViewSettings = webView.getSettings(); // Setting this off for security. Off by default for SDK versions >= 16. webViewSettings.setAllowFileAccessFromFileURLs(false); // Off by default, deprecated for SDK versions >= 30. webViewSettings.setAllowUniversalAccessFromFileURLs(false); // Keeping these off is less critical but still a good idea, especially if your app is not // using file:// or content:// URLs. webViewSettings.setAllowFileAccess(false); webViewSettings.setAllowContentAccess(false);

// Assets are hosted under http(s)://appassets.androidplatform.net/assets/... . // If the application's assets are in the "main/assets" folder this will read the file // from "main/assets/www/index.html" and load it as if it were hosted on: // https://appassets.androidplatform.net/assets/www/index.html webview.loadUrl("https://appassets.androidplatform.net/assets/www/index.html");

Summary

Nested types

Handler class to open a file from assets directory in the application APK.

A builder class for constructing WebViewAssetLoader objects.

Handler class to open files from application internal storage.

A handler that produces responses for a registered path.

Handler class to open a file from resources directory in the application APK.

Constants

const String!
DEFAULT_DOMAIN = "appassets.androidplatform.net"

An unused domain reserved for Android applications to intercept requests for app assets.

Public functions

WebResourceResponse?

Attempt to resolve the url to an application resource or asset, and return a WebResourceResponse for the content.

Constants

DEFAULT_DOMAIN

Added in 1.1.0
const val DEFAULT_DOMAIN = "appassets.androidplatform.net": String!

An unused domain reserved for Android applications to intercept requests for app assets.

It is used by default unless the user specified a different domain.

Public functions

shouldInterceptRequest

Added in 1.1.0
@WorkerThread
fun shouldInterceptRequest(url: Uri): WebResourceResponse?

Attempt to resolve the url to an application resource or asset, and return a WebResourceResponse for the content.

This method should be invoked from within shouldInterceptRequest.

Parameters
url: Uri

the URL to process.

Returns
WebResourceResponse?

WebResourceResponse if the request URL matches a registered URL, null otherwise.