java - Vaadin 6 上传组件 : how to terminate file upload proccess without saving wrong file on a server

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。 (让用户仅上传 .txt 文件)。如果它是 txt - 将其保存在服务器上，否则 - 对此类文件不执行任何操作。

我尝试过类似的事情:

//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，除了上传组件捕获错误:

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

那么，终止上传错误文件的正确方法是什么？

Answer 1

返回一个 NullOutputStream (其中 extends 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“package com.vaadin.external.org.apache.commons.io.output”打包的，因此您应该可以使用该类。

如果您有任何疑问，请告诉我!