在Android Web view中实现文件选择功能需要设置WebChromeClient以覆盖onShowFileChooser方法。以下是一个简单的示例代码：

public class MyWebChromeClient extends WebChromeClient {
   @Override
   public boolean onShowFileChooser(WebView webView, ValueCallback filePathCallback, WebChromeClient.FileChooserParams fileChooserParams) {
       if (ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.READ_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
           ActivityCompat.requestPermissions(MainActivity.this,
                   new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                  FILE_PERMISSION_REQUEST_CODE);
           return false;
        }
       else {
           openFileChooser(webView, filePathCallback);
           return true;
       }
   }

   public void openFileChooser(WebView webView, ValueCallback filePathCallback) {
        Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
        intent.setType("*/*");
        intent.addCategory(Intent.CATEGORY_OPENABLE);

        try {
            startActivityForResult(Intent.createChooser(intent, "Choose File to Upload"), REQUEST_FILE_UPLOAD);
        } catch (Exception ex) {
            Log.e(TAG, "Exception: " + ex);
        }
        uploadFilePathCallback = filePathCallback;
    }

   @Override
   public void onActivityResult(int requestCode, int resultCode, Intent data) {
       if (requestCode == REQUEST_FILE_UPLOAD && resultCode == RESULT_OK) {
           if (uploadFilePathCallback != null) {
               Uri[] uris = new Uri[]{data.getData()};
               uploadFilePathCallback.onReceiveValue(uris);
           }
       }
    }
}

在MainActivity中，将WebView设置为如下：

webView.setWebChromeClient(new MyWebChromeClient());

在这种设置后，Android WebView就可以从打开对话框中选择文件。