Android webview, loading javascript file in assets folder

I tried the same thing, loading a bookmarklet (the javascript code in your loadUrl() call) into a third-party page. My bookmarklet also depends on other assets (javascript and css files) which would not load with a file:///android_asset URL.

That's because the security context of the page is still that of, e.g., http://www.google.com, and that's not allowed access to file: URLs. You should be able to see the errors if you supply/override a WebChromeClient.onConsoleMessage().

I ended up with a kludge where I changed the bookmarklet's asset references to a bogus URL scheme, like:

asset:foo/bar/baz.js

and added a WebViewClient.shouldInterceptRequest() override which looks for those and loads them from assets using AssetManager.open().

One thing I don't like about this kludge is that the asset: scheme is open to any third-party HTML/Javascript on any page my view loads, giving them access to my app's assets.

One alternative, which I didn't try, would be to embed the sub-assets in the bookmarklet using data: URLs, but that can get unwieldy.

I'd much prefer it if there was a way to manipulate the security context of just the JS bookmarklet I'm loading in loadUrl(), but I can't find anything like that.

Here's a snippet:

import android.webkit.WebResourceResponse;
...
    private final class FooViewClient extends WebViewClient
    {
    private final String bookmarklet;
    private final String scheme;

    private FooViewClient(String bookmarklet, String scheme)
        {
        this.bookmarklet = bookmarklet;
        this.scheme = scheme;
        }

    @Override
    public void onPageFinished(WebView view, String url)
        {
        view.loadUrl(bookmarklet);
        }

    @Override
    public WebResourceResponse shouldInterceptRequest(WebView view, String url)
        {
        if (url.startsWith(scheme))
            try
                {
                return new WebResourceResponse(url.endsWith("js") ? "text/javascript" : "text/css", "utf-8",
                        Foo.this.getAssets().open(url.substring(scheme.length())));
                }
            catch (IOException e)
                {
                Log.e(getClass().getSimpleName(), e.getMessage(), e);
                }

        return null;
        }
    }

I think the iceam cream webview client of cordova does the very thing you want to do.

It would be nice if this was documented somewhere but, as far as I can see, it is not.

Take a look at cordova's android github: https://github.com/apache/incubator-cordova-android/blob/master/framework/src/org/apache/cordova/IceCreamCordovaWebViewClient.java

Here is how i ended up doing it. I used the Content:// protocol and set up a contentprovider to handle returning a file descriptor to the system

Here is my fileContentProvider:

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;

import org.apache.commons.io.IOUtils;


import android.content.ContentProvider;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.os.ParcelFileDescriptor;
import android.util.Log;

public class FileContentProvider extends ContentProvider {
    @Override
    public ParcelFileDescriptor openFile(Uri uri, String mode) {

        Log.d("FileContentProvider","fetching: " + uri);

        ParcelFileDescriptor parcel = null;

        String fileNameRequested = uri.getLastPathSegment();
        String[] name=fileNameRequested.split("\\.");
        String prefix=name[0];
        String suffix=name[1];
       // String path = getContext().getFilesDir().getAbsolutePath() + "/" + uri.getPath();
        //String path=file:///android_asset/"+Consts.FILE_JAVASCRIPT+"

/*check if this is a javascript file*/

        if(suffix.equalsIgnoreCase("js")){
        InputStream is = null;
        try {
            is = getContext().getAssets().open("www/"+Consts.FILE_JAVASCRIPT);
        } catch (IOException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }


        File file = stream2file(is,prefix,suffix);
        try {
            parcel = ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY);
        } catch (FileNotFoundException e) {
            Log.e("FileContentProvider", "uri " + uri.toString(), e);
        }
        }
        return parcel;
    }

    /*converts an inputstream to a temp file*/

    public File stream2file (InputStream in,String prefix,String suffix) {
        File tempFile = null;
        try {
            tempFile = File.createTempFile(prefix, suffix);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        tempFile.deleteOnExit();

            FileOutputStream out = null;
            try {
                out = new FileOutputStream(tempFile);
            } catch (FileNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } 

            try {
                IOUtils.copy(in, out);
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        return tempFile;
    }


    @Override
    public boolean onCreate() {
        return true;
    }

    @Override
    public int delete(Uri uri, String s, String[] as) {
        throw new UnsupportedOperationException("Not supported by this provider");
    }

    @Override
    public String getType(Uri uri) {
        throw new UnsupportedOperationException("Not supported by this provider");
    }

    @Override
    public Uri insert(Uri uri, ContentValues contentvalues) {
        throw new UnsupportedOperationException("Not supported by this provider");
    }

    @Override
    public Cursor query(Uri uri, String[] as, String s, String[] as1, String s1) {
        throw new UnsupportedOperationException("Not supported by this provider");
    }

    @Override
    public int update(Uri uri, ContentValues contentvalues, String s, String[] as) {
        throw new UnsupportedOperationException("Not supported by this provider");
    }
}

in the manifest i defined the provider:

<provider android:name="com.example.mypackage.FileContentProvider"
          android:authorities="com.example.fileprovider"
        />

Here is the javascript o inject into the webview:

webView.loadUrl("javascript:(function() { "

           + "var script=document.createElement('script'); "
           + " script.setAttribute('type','text/javascript'); "
           + " script.setAttribute('src', 'content://com.example.fileprovider/myjavascriptfile.js'); "
      /*      + " script.onload = function(){ "
           + "     test(); "
           + " }; "
      */     + "document.body.appendChild(script); "
           + "})();");

and here is the myjavascriptfile.js (as an example):

   function changeBackground(color) {
       document.body.style.backgroundColor = color;
   }