Vaadin 6 Upload component: how to terminate file upload proccess without saving wrong file on a server

Question

In my app i have an Upload button. When a user selects some file, i have to validate its extention. (Let user upload only .txt files). And if it is txt - save it on server, otherwise - do nothing with such file.

I've tried something like that:

//Check file type on start event:
@Override
public void uploadStarted(StartedEvent event) {
    String contentType = event.getFilename();
    if (!contentType.endsWith("txt")) {
        isValid = false;
        upload.interruptUpload();
    }
}

//If it is txt, do some actions:
@Override
public OutputStream receiveUpload(String filename, String mimeType) {
    FileOutputStream fos = null;
    if(isValid) {
        try {
            createUserDir(filename);
            fos = new FileOutputStream(file);
            //some more actions
        } catch (final java.io.FileNotFoundException e) {
            log.error(e);
            return null;
        }
    }
    return fos;
}

//Error msg for a user
@Override
public void uploadFailed(Upload.FailedEvent event) {
    root.getWindow().showNotification("Error Header", "Error Msg",
            Window.Notification.TYPE_ERROR_MESSAGE);
}

It nearly works, with the exception of the fact, upload component catches an error:

com.vaadin.terminal.gwt.server.UploadException: Upload failed at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.streamToReceiver(AbstractCommunicationManager.java:623) at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.doHandleSimpleMultipartFileUpload(AbstractCommunicationManager.java:476) at com.vaadin.terminal.gwt.server.CommunicationManager.handleFileUpload(CommunicationManager.java:259) at com.vaadin.terminal.gwt.server.AbstractApplicationServlet.service(AbstractApplicationServlet.java:495) at javax.servlet.http.HttpServlet.service(HttpServlet.java:723) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:563) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:620) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Unknown Source) Caused by: com.vaadin.terminal.gwt.server.NoOutputStreamException at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.streamToReceiver(AbstractCommunicationManager.java:568) ... 17 more

So, what is the right way to terminate Upload with a wrong file?

Answer 1

Return a NullOutputStream (which extends OutputStream) instead of null:

//Check file type on start event:
@Override
public void uploadStarted(StartedEvent event) {
    String contentType = event.getFilename();
    if (!contentType.endsWith("txt")) {
        isValid = false;
        upload.interruptUpload();    
    }
}

//If it is txt, do some actions:
@Override
public OutputStream receiveUpload(String filename, String mimeType) {
    FileOutputStream fos = null; // Stream to write to
    if (filename != null && !filename.isEmpty() && isValid) {
        try {
            createUserDir(filename);
            fos = new FileOutputStream(file);
            return fos;
        } catch (final java.io.FileNotFoundException e) {
            log.error(e);
            return new NullOutputStream();
        }
    } else {/*Show error "Please select a file to upload."*/};

    uploadControl.interruptUpload();
    return new NullOutputStream(); 
}

The NullOutputStream class is packaged via "package com.vaadin.external.org.apache.commons.io.output" so you should have the class available to you.

Please let me know if you have any questions!