Restricting file types upload component

问题

I'm using the upload component of vaadin(7.1.9), now my trouble is that I'm not able to restrict what kind of files that can be sent with the upload component to the server, but I haven't found any API for that purpose. The only way is that of discarding file of wrong types after the upload.

public OutputStream receiveUpload(String filename, String mimeType) {

    if(!checkIfAValidType(filename)){
        upload.interruptUpload();
    }          

    return out;
}

Is this a correct way?

回答1:

No, its not the correct way. The fact is, Vaadin does provide many useful interfaces that you can use to monitor when the upload started, interrupted, finished or failed. Here is a list:

com.vaadin.ui.Upload.FailedListener;
com.vaadin.ui.Upload.FinishedListener;
com.vaadin.ui.Upload.ProgressListener;
com.vaadin.ui.Upload.Receiver;
com.vaadin.ui.Upload.StartedListener;

Here is a code snippet to give you an example:

@Override
public void uploadStarted(StartedEvent event) {
    // TODO Auto-generated method stub
    System.out.println("***Upload: uploadStarted()");

    String contentType = event.getMIMEType();
    boolean allowed = false;
    for(int i=0;i<allowedMimeTypes.size();i++){
        if(contentType.equalsIgnoreCase(allowedMimeTypes.get(i))){
            allowed = true;
            break;
        }
    }
    if(allowed){
        fileNameLabel.setValue(event.getFilename());
        progressBar.setValue(0f);
        progressBar.setVisible(true);
        cancelButton.setVisible(true);
        upload.setEnabled(false);
    }else{
        Notification.show("Error", "\nAllowed MIME: "+allowedMimeTypes, Type.ERROR_MESSAGE);
        upload.interruptUpload();
    }

}

Here, allowedMimeTypes is an array of mime-type strings.

ArrayList<String> allowedMimeTypes = new ArrayList<String>();
allowedMimeTypes.add("image/jpeg");
allowedMimeTypes.add("image/png");

I hope it helps you.

回答2:

Can be done.

You can add this and it will work (all done by HTML 5 and most browsers now support accept attribute) - this is example for .csv files:

upload.setButtonCaption("Import");
JavaScript.getCurrent().execute("document.getElementsByClassName('gwt-FileUpload')[0].setAttribute('accept', '.csv')");

回答3:

I think it's better to throw custom exception from Receiver's receiveUpload:

Upload upload = new Upload(null, new Upload.Receiver() {
    @Override
    public OutputStream receiveUpload(String filename, String mimeType) {
        boolean typeSupported = /* do your check*/;
        if (!typeSupported) {
            throw new UnsupportedImageTypeException();
        }
        // continue returning correct stream
    }
});

The exception is just a simple custom exception:

public class UnsupportedImageTypeException extends RuntimeException {
}

Then you just simply add a listener if the upload fails and check whether the reason is your exception:

upload.addFailedListener(new Upload.FailedListener() {
    @Override
    public void uploadFailed(Upload.FailedEvent event) {
        if (event.getReason() instanceof UnsupportedImageTypeException) {
            // do your stuff but probably don't log it as an error since it's not 'real' error
            // better would be to show sth like a notification to inform your user
        } else {
            LOGGER.error("Upload failed, source={}, component={}", event.getSource(), event.getComponent());
        }
    }
});

回答4:

public static boolean checkFileType(String mimeTypeToCheck) { ArrayList allowedMimeTypes = new ArrayList();

    allowedMimeTypes.add("image/jpeg");
    allowedMimeTypes.add("application/pdf");
    allowedMimeTypes.add("application/vnd.openxmlformats-officedocument.wordprocessingml.document");
    allowedMimeTypes.add("image/png");
    allowedMimeTypes.add("application/vnd.openxmlformats-officedocument.presentationml.presentation");
    allowedMimeTypes.add("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");

    for (int i = 0; i < allowedMimeTypes.size(); i++) {
        String temp = allowedMimeTypes.get(i);
        if (temp.equalsIgnoreCase(mimeTypeToCheck)) {
            return true;
        }
    }

    return false;
}

来源：https://stackoverflow.com/questions/21913526/restricting-file-types-upload-component