Vaadin 6上传组件:如何在不将错误文件保存在服务器上的情况下终止文件上传过程

Question

在我的应用程序中，我有一个上传按钮。当用户选择某个文件时，我必须验证其扩展名。（只允许用户上传.txt文件）。如果是txt，请将其保存在服务器上，否则，不处理此类文件。

我试过这样的东西：

//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);
}

它几乎可以工作，除了上传组件捕捉到一个错误：

com.vaadin.terminal.gwt.server.UploadException：上载在失败com.vaadin.terminal.gwt.server.AbstractCommunicationManager.streamToReceiver（AbstractCommunicationManager.java:623）在com.vaadin.terminal.gwt.server.AbstractCommunicationManager.doHandleSimpleMultipartFileUpload（AbstractCommunicationManager.java:476）在com.vaadin.terminal.gwt.server.CommunicationManager.handleFileUpload（CommunicationManager.java:259）在com.vaadin.terminal.gwt.server.AbstractApplicationServlet.service（AbstractApplicationServlet.java:495）位于org.apache.catalina.core.ApplicationFilterChain.internalDoFilter（ApplicationFilterChain.java:290）在org.apache.catalina.core.ApplicationFilterChain.doFilter（ApplicationFilterChain.java:206）在org.apache.catalina.core.StandardWrapperValv.invoke（StandardWrapperValve.java:233）在org.apache.catalina.core.StandardContextValv.invoke（StandardContextValv.java:191）在org.apache.catalina.authenticator.AuthenticatorBase.ioke（AuthenticatorBase.java:563）在org.apache.catalina.core.StandardHostValv.invoke（StandardHostValve.java:127）在org.apache.catalina.vals.ErrorReportValve.ioke（ErrorReportValve.java:103）在org.apache.catalina.core.StandardEngineValv.invoke（StandardEngineValv.java:109）在org.apache.catalina.connecter.CoyoteAdapter.service（Coyotedapter.java:293）在org.apache.coyote.http11.Http11Processor.process（Http11Processor.java:861）在org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process（Http11Protocol.java:620）在org.apache.tomcat.util.net.JIoEndpoint$Worker.run（JIoEndpoint.java:489）在java.lang.Thread.run（未知源）由以下原因引起：com.vaadin.terminal.gwt.server.NoOutputStreamException位于com.vaadin.terminal.gwt.server.AbstractCommunicationManager.streamToReceiver（AbstractCommunicationManager.java:568）…还有17个

那么，用错误的文件终止Upload的正确方法是什么呢？

Answer 1

返回一个NullOutputStream（扩展OutputStream）而不是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(); 
}

NullOutputStream类是通过"packagecom.vaadin.external.org.apache.commons.io.output"打包的，因此您应该可以使用该类。

如果你有任何问题，请告诉我！