根据文件扩展名验证文件 [英] Validation of files based on their file extensions

问题描述

我从Java中的队列中获取文件。他们可能是以下格式。

1. docx


2. pdf




4. xls


5. xlsx


6. txt


7. rtf

阅读扩展名后，我想验证是否实际上是这些类型的文件。

例如，我有一个文件，并检查它有扩展名.xls。之后，我想检查它是否实际上是一个.xls文件或某人上传的其他格式的文件，在更改其扩展名后。

编辑：我想通过实际检查其内容而不是其扩展名来检查文件的MIME类型。如何做？

解决方案

不使用外部库：

您可以使用MimetypesFileTypeMap获取文件mimetype：

 文件f = new File（...）; 
 System.out.println（new MimetypesFileTypeMap（）。getContentType（f））; 
  

您可以得到类似的结果：
URLConnection.guessContentTypeFromName
两者根据文档，这些解决方案仅查看扩展名。

一个更好的选择： URLConnection.guessContentTypeFromStream

 文件f = new File（...）; 
 System.out.println（URLConnection.guessContentTypeFromStream（new FileInputStream（f）））; 
  

这个尝试从文件的第一个字节猜测 - 警告这只是一个猜测 - 我发现它在大多数情况下起作用，但无法检测到一些明显的类型。

我推荐两者的组合。

I get files from queues in Java. They may be of following formats.

1. docx
2. pdf
3. doc
4. xls
5. xlsx
6. txt
7. rtf

After reading their extensions, I want to validate whether they are actually files of these types.

For example, I got a file and checked that it has extension .xls. Afterwards, I want to check whether it is actually an .xls file or someone uploaded file of some other format after changing its extension.

EDIT: I'd like to check the file's MIME type by actually checking its content, not its extension. How it can be done?

解决方案

Without using external libraries:

You can get the file mimetype using MimetypesFileTypeMap:

    File f = new File(...);
    System.out.println(new MimetypesFileTypeMap().getContentType(f));

You can get a similar result with: URLConnection.guessContentTypeFromName Both these solutions, according to the documentation, look only at the extension.

A better option: URLConnection.guessContentTypeFromStream

    File f= new File(...);
    System.out.println(URLConnection.guessContentTypeFromStream(new FileInputStream(f)));

This try to guess from the first bytes of the file - be warned this is only a guess - I found it works in most cases, but fails to detect some obvious types.

I recommend a combination of both.

这篇关于根据文件扩展名验证文件的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！