java – 某些条件不正确时中断文件上载
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我想实现这个：在上传文件检查文件扩展名时,如果它不是.zip,上传将被中断,并向用户显示一条消息,所以我写了这个：
// Implement both receiver that saves upload in a file and
// listener for successful upload
class ReportUploader implements Receiver, SucceededListener {
public File file;
public OutputStream receiveUpload(String filename, String mimeType) {
// Create upload stream
FileOutputStream fos = null; // Stream to write to
String userHome = System.getProperty("user.home");
String ext = filename.substring(filename.lastIndexOf('.'));
System.out.println("+++++++++++>" + ext);
if (!ext.equals(".zip")) {
Notification.show("Could not upload file", Notification.TYPE_ERROR_MESSAGE);
return null;
}
try {
file = new File(userHome + "/uploads/report/" + filename);
fos = new FileOutputStream(file);
} catch (final java.io.FileNotFoundException e) {
Notification.show("Could not open file", e.getMessage(), Notification.TYPE_ERROR_MESSAGE);
return null;
}
return fos;
}
public void uploadSucceeded(SucceededEvent event) {
String filename;
String basepath;
String folderName;
String uploadDir;
filename = event.getFilename();
basepath = VaadinService.getCurrent().getBaseDirectory().getAbsolutePath();
uploadDir = Utilities.getProperty("uploadDir", basepath + "/WEB-INF/properties/config.properties");
file = new File(uploadDir + filename);
folderName = filename.substring(0, filename.length() - 5);
Utilities.unZipFolder(uploadDir + filename, uploadDir + folderName);
addFilename(folderName);
try {
Utilities.deleteCompressedReport(file);
} catch (IOException e) {
e.printStackTrace();
}
Notification.show("upload finished", Notification.TYPE_HUMANIZED_MESSAGE);
}
private void addFilename(String sFilename) {
reportDirList.add(sFilename);
selectDir.addItem(sFilename);
}
}
当扩展名不是.zip时,会产生以下错误：
com.vaadin.server.UploadException: Upload failed
at com.vaadin.server.communication.FileUploadHandler.streamToReceiver(FileUploadHandler.java:581)
at com.vaadin.server.communication.FileUploadHandler.handleFileUploadValidationAndData(FileUploadHandler.java:419)
at com.vaadin.server.communication.FileUploadHandler.doHandleSimpleMultipartFileUpload(FileUploadHandler.java:382)
at com.vaadin.server.communication.FileUploadHandler.handleRequest(FileUploadHandler.java:267)
at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1329)
at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:236)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:462)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:562)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:395)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:250)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)
Caused by: com.vaadin.server.NoOutputStreamException
at com.vaadin.server.communication.FileUploadHandler.streamToReceiver(FileUploadHandler.java:518)
... 22 more
那么如何中断上传并显示消息？
解决方法:
如您所见,您需要调用Upload的interruptUpload方法.其他一些观点：
>您的Receiver在显示错误后返回null.我发现这会导致日志中的堆栈跟踪,如果用户将鼠标悬停在Upload组件上,则部分堆栈跟踪甚至可供用户看到.我避免这种情况的方法是返回NullOutputStream而不是null.
>如果用户在未先选择文件的情况下尝试上传,您可能还希望在receiveUpload中防止异常(再次生成堆栈跟踪).检查空文件名,显示错误,然后返回NullOutputStream.
这是一个示例receiveUpload,它具有上述两个保护. (注意：Utilities.showError只是创建了通常的Vaadin Notification对话框,没有什么神奇之处.)
public OutputStream receiveUpload(String filename, String mimeType) {
if (filename != null && !filename.isEmpty()) {
// Create upload stream
FileOutputStream fos = null; // Stream to write to
try {
// Open the file for writing.
file = new File(FileHandler.DEST_PATH + filename);
fos = new FileOutputStream(file);
return fos;
} catch (final java.io.FileNotFoundException e) {
Utilities.showError("Could not open file<br>", e.getMessage());
}
} else {
Utilities.showError("You must first select a spreadsheet file to upload.");
}
uploadControl.interruptUpload();
return new NullOutputStream(); // to prevent a stack trace from being thrown by Vaadin
}
>此外,您可能还需要StartedListener.这是检查文件太大的最简单的地方 – 你可能不想让别人用一个千兆字节的文件来抨击你. uploadStarted方法可能如下所示：
public void uploadStarted(StartedEvent event) {
if (event.getFilename().isEmpty()) {
uploadControl.interruptUpload();
Utilities.showError("You must first select a file to upload.");
} else if (event.getContentLength() > FileHandler.MAX_UPLOAD_BYTES) {
uploadControl.interruptUpload();
Utilities.showError("File is too big. Please check that you selected the correct file.");
} else if (!FileHandler.isValidUploadMIMEType(event.getMIMEType())) {
uploadControl.interruptUpload();
Utilities.showError("Unexpected file type. Please check that you selected the correct file.");
} else {
progressBar.setValue(0.0f);
progressBar.setVisible(true);
}
}
这种方法的一个缺点是我通过避免异常来避免堆栈跟踪.哪个没问题,但上传组件清除了有问题的文件名.如果您抛出异常,您会看到堆栈跟踪,但用户可以看到他们选择的文件,并可能弄清楚他们做错了什么.我觉得这很小.
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