如何从webview到textview中提取html代码？

public interface OnHtmlExtractedListener {
    void onHtmlExtracted(String html);
}

public class MainActivity extends AppCompatActivity implements OnHtmlExtractedListener {
    private TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = findViewById(R.id.textView);

        WebView webView = findViewById(R.id.webView);
        webView.setWebViewClient(new WebViewClient() {
            @Override
            public void onPageFinished(WebView view, String url) {
                view.loadUrl("javascript:window.android.onHtmlExtracted(document.documentElement.outerHTML);");
            }
        });
        webView.loadUrl("http://example.com");
    }

    @Override
    public void onHtmlExtracted(String html) {
        textView.setText(Html.fromHtml(html));
    }
}

<script>
    window.android = {
        onHtmlExtracted: function(html) {
            // 将html传递给Android端
            if (typeof onHtmlExtractedListener !== 'undefined') {
                onHtmlExtractedListener.onHtmlExtracted(html);
            }
        }
    };
</script>