这个已经有人问过了，我已经回答过了，亲测完全没问题。https://segmentfault.com/q/1010000005980836

Github上有个Os-FileUp项目提供了一些方法.

        webView.setWebChromeClient(new WebChromeClient(){
            //For Android 3.0+
            public void openFileChooser(ValueCallback<Uri> uploadMsg){
                mUM = uploadMsg;
                Intent i = new Intent(Intent.ACTION_GET_CONTENT);
                i.addCategory(Intent.CATEGORY_OPENABLE);
                i.setType("image/*");
                MainActivity.this.startActivityForResult(Intent.createChooser(i,"File Chooser"), FCR);
            }
            // For Android 3.0+, above method not supported in some android 3+ versions, in such case we use this
            public void openFileChooser(ValueCallback uploadMsg, String acceptType){
                mUM = uploadMsg;
                Intent i = new Intent(Intent.ACTION_GET_CONTENT);
                i.addCategory(Intent.CATEGORY_OPENABLE);
                i.setType("*/*");
                MainActivity.this.startActivityForResult(
                        Intent.createChooser(i, "File Browser"),
                        FCR);
            }
            //For Android 4.1+
            public void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType, String capture){
                mUM = uploadMsg;
                Intent i = new Intent(Intent.ACTION_GET_CONTENT);
                i.addCategory(Intent.CATEGORY_OPENABLE);
                i.setType("image/*");
                MainActivity.this.startActivityForResult(Intent.createChooser(i, "File Chooser"), MainActivity.FCR);
            }
            //For Android 5.0+
            public boolean onShowFileChooser(
                    WebView webView, ValueCallback<Uri[]> filePathCallback,
                    WebChromeClient.FileChooserParams fileChooserParams){
                if(mUMA != null){
                    mUMA.onReceiveValue(null);
                }
                mUMA = filePathCallback;
                Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                if(takePictureIntent.resolveActivity(MainActivity.this.getPackageManager()) != null){
                    File photoFile = null;
                    try{
                        photoFile = createImageFile();
                        takePictureIntent.putExtra("PhotoPath", mCM);
                    }catch(IOException ex){
                        Log.e(TAG, "Image file creation failed", ex);
                    }
                    if(photoFile != null){
                        mCM = "file:" + photoFile.getAbsolutePath();
                        takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(photoFile));
                    }else{
                        takePictureIntent = null;
                    }
                }
                Intent contentSelectionIntent = new Intent(Intent.ACTION_GET_CONTENT);
                contentSelectionIntent.addCategory(Intent.CATEGORY_OPENABLE);
                contentSelectionIntent.setType("image/*");
                Intent[] intentArray;
                if(takePictureIntent != null){
                    intentArray = new Intent[]{takePictureIntent};
                }else{
                    intentArray = new Intent[0];
                }

                Intent chooserIntent = new Intent(Intent.ACTION_CHOOSER);
                chooserIntent.putExtra(Intent.EXTRA_INTENT, contentSelectionIntent);
                chooserIntent.putExtra(Intent.EXTRA_TITLE, "Image Chooser");
                chooserIntent.putExtra(Intent.EXTRA_INITIAL_INTENTS, intentArray);
                startActivityForResult(chooserIntent, FCR);
                return true;
            }
        });
}