blocks|key|2597313|text|TL;DR；|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2597314|当用户以编程方式将文件上传到亚马逊S3时，可以指定对象的Content-Type。如果指定了none，正如@Michael-bot所阐明的那样，默认情况下分配的值将是binary/octet-stream。或者，如果决定通过AmazonS3的图形用户界面上传文件，文件将从其文件扩展名获取其Content-Type+(遗憾的是，不是其内容)。如果您可以相信上传文件的人能够正确地设置Content-Type，请继续查看ObjectMetadata，但如果您不能(像我一样)，您将需要另一个解决方案。|offset|length|style|CODE|2597315|因此，如果您正在寻找适用于最常见文件压缩类型的解决方案，Files.probeContentType、Apache+Tika和SimpleMagic似乎是可接受的解决方案。|2597316|最后，我选择了Files.probeContentType，因为它不需要额外的库，并且在Linux机器上运行得很好(只要文件没有错误的扩展名就可以使用，对于这个问题有一个变通办法:删除文件扩展名，让它执行神奇的)。|BOLD|2597317|2597318|测试设置|2597319|首先，人们会认为从亚马逊的S3下载文件时的响应对象包含文件类型。它确实包含这些信息，但是当文件的扩展名与其内容不匹配时，问题就出现了。|2597320|import+com.amazonaws.services.s3.model.S3Object;

final+S3Object+s3Object+=+...;
final+String+contentType+=+s3Object.getObjectMetadata().getContentType();|code-block|syntax|javascript|2597321|即使文件的内容是Rar文件，此代码也会返回application/zip。所以这个解决方案对我不起作用。|2597322|出于这个原因，我花时间构建了一个示例项目，该项目使用不同的方法和可用的库测试各种场景。顺便说一下，我使用的是Java8。|2597323|测试的文件类型包括：|2597324|2597325|带Zip扩展名但不带扩展名的压缩文件|unordered-list-item|2597326|带Rar扩展名、Zip扩展名但不带扩展名的Rar文件|2597327|带7z扩展名、Zip扩展名但不带扩展名的|2597328|+Tar.xz带Tar.xz扩展名、Zip扩展名但不带扩展名|2597329|带Tar.gz扩展名、Zip扩展名但不带扩展名的Tar.gz+|2597330|2597331|请注意，此处提供的实现仅用于测试目的。它们没有以任何方式被认可用于生产代码中，因为它们不会考虑文件锁定问题以及其他我的想象力不会考虑的问题。=)|2597332|2597333|MimetypesFileTypeMap|2597334|实现|2597335|import+java.io.File;
import+javax.activation.MimetypesFileTypeMap;

final+File+file+=+new+File(basePath+%2B+"/"+%2B+fileName);
try+{
++++return+MimetypesFileTypeMap.getDefaultFileTypeMap().getContentType(file);
}+catch+(final+Exception+exception)+{
++++return+"<EXCEPTION:+"+%2B+exception.getMessage()+%2B+">";
}|2597336|结果|2597337|Rar+with+Rar+extension+is:+++++++application/octet-stream
Rar+with+Zip+extension+is:+++++++application/octet-stream
Zip+with+Zip+extension+is:+++++++application/octet-stream
7z+with+7z+extension+is:+++++++++application/octet-stream
7z+with+Zip+extension+is:++++++++application/octet-stream
Tar.xz+with+Tar.xz+extension+is:+application/octet-stream
Tar.xz+with+Zip+extension+is:++++application/octet-stream
Tar.gz+with+Tar.gz+extension+is:+application/octet-stream
Tar.gz+with+Zip+extension+is:++++application/octet-stream
Rar+without+extension+is:++++++++application/octet-stream
Zip+without+extension+is:++++++++application/octet-stream
7z+without+extension+is:+++++++++application/octet-stream
Tar.xz+without+extension+is:+++++application/octet-stream
Tar.gz+without+extension+is:+++++application/octet-stream|2597338|结论|2597339|当文件类型未被识别时，此方法返回的值为application/octet-stream。似乎所有的场景都失败了，所以我们应该放弃这种方法。|2597340|2597341|URLConnection.guessContentTypeFromStream|2597342|2597343|import+java.io.File;
import+java.io.FileInputStream;
import+java.io.InputStream;
import+java.io.BufferedInputStream;
import+java.net.URLConnection;

final+File+file+=+new+File(basePath+%2B+"/"+%2B+fileName);
try+{
++++final+FileInputStream+fileInputStream+=+new+FileInputStream(file);
++++final+InputStream+inputStream+=+new+BufferedInputStream(fileInputStream);

++++return+URLConnection.guessContentTypeFromStream(inputStream);
}+catch+(final+Exception+exception)+{
++++return+"<EXCEPTION:+"+%2B+exception.getMessage()+%2B+">";
}|2597344|2597345|Rar+with+Rar+extension+is:+++++++null
Rar+with+Zip+extension+is:+++++++null
Zip+with+Zip+extension+is:+++++++null
7z+with+7z+extension+is:+++++++++null
7z+with+Zip+extension+is:++++++++null
Tar.xz+with+Tar.xz+extension+is:+null
Tar.xz+with+Zip+extension+is:++++null
Tar.gz+with+Tar.gz+extension+is:+null
Tar.gz+with+Zip+extension+is:++++null
Rar+without+extension+is:++++++++null
Zip+without+extension+is:++++++++null
7z+without+extension+is:+++++++++null
Tar.xz+without+extension+is:+++++null
Tar.gz+without+extension+is:+++++null|2597346|2597347|同样，这种方法不适用于所有场景。It+seems+its+support+is+very+limited。|2597348|2597349|Files.probeContentType|2597350|2597351|import+java.nio.file.Files;
import+java.nio.file.Path;
import+java.nio.file.Paths;

try+{
++++final+Path+path+=+Paths.get(basePath+%2B+"/"+%2B+fileName);
++++return+Files.probeContentType(path);
}+catch+(final+Exception+exception)+{
++++return+"<EXCEPTION:+"+%2B+exception.getMessage()+%2B+">";
}|2597352|2597353|Rar+with+Rar+extension+is:+++++++application/vnd.rar
Rar+with+Zip+extension+is:+++++++application/zip
Zip+with+Zip+extension+is:+++++++application/zip
7z+with+7z+extension+is:+++++++++application/x-7z-compressed
7z+with+Zip+extension+is:++++++++application/zip
Tar.xz+with+Tar.xz+extension+is:+application/x-xz-compressed-tar
Tar.xz+with+Zip+extension+is:++++application/zip
Tar.gz+with+Tar.gz+extension+is:+application/x-compressed-tar
Tar.gz+with+Zip+extension+is:++++application/zip
Rar+without+extension+is:++++++++application/vnd.rar
Zip+without+extension+is:++++++++application/zip
7z+without+extension+is:+++++++++application/x-7z-compressed
Tar.xz+without+extension+is:+++++application/x-xz
Tar.gz+without+extension+is:+++++application/gzip|2597354|2597355|这种方法工作得出奇地好，但不要被愚弄了，有一种情况是它总是失败。如果文件具有错误的扩展名(与内容不匹配的扩展名)，它将报告文件类型为该扩展名。这种情况不应该经常发生，但如果一个人非常挑剔，就不应该使用这种方法。|2597356|还有，some+warn+that+his+approach+doesn't+work+well+in+Windows。|2597357|2597358|+变通方法：如果有人设法从文件名中删除扩展名，这将为所有给定的场景返回正确的值。|blockquote|2597359|2597360|2597361|2597362|Apache+Tika+(tika-eval+1.18)|2597363|似乎有many+flavors+of+this+library+(应用程序、服务器、eval等)，但网络上的许多人抱怨它有点“依赖重”。|2597364|2597365|import+org.apache.tika.Tika;

try+{
++++return+new+Tika().detect(new+File(basePath+%2B+"/"+%2B+fileName));
}+catch+(final+Exception+exception)+{
++++return+"<EXCEPTION:+"+%2B+exception.getMessage()+%2B+">";
}|2597366|2597367|Rar+with+Rar+extension+is:+++++++application/x-rar-compressed
Rar+with+Zip+extension+is:+++++++application/x-rar-compressed
Zip+with+Zip+extension+is:+++++++application/zip
7z+with+7z+extension+is:+++++++++application/x-7z-compressed
7z+with+Zip+extension+is:++++++++application/x-7z-compressed
Tar.xz+with+Tar.xz+extension+is:+application/x-xz
Tar.xz+with+Zip+extension+is:++++application/x-xz
Tar.gz+with+Tar.gz+extension+is:+application/gzip
Tar.gz+with+Zip+extension+is:++++application/gzip
Rar+without+extension+is:++++++++application/x-rar-compressed
Zip+without+extension+is:++++++++application/zip
7z+without+extension+is:+++++++++application/x-7z-compressed
Tar.xz+without+extension+is:+++++application/x-xz
Tar.gz+without+extension+is:+++++application/gzip|2597368|2597369|所有的文件都被正确地识别出来了，但是它有它的优点，也有它的缺点。|2597370|优点：|2597371|由Apache维护的|2597372|。|2597373|不会被扩展欺骗。|2597374|2597375|缺点：|2597376|2597377|真的很重，特别是当你只想检查文件类型的时候。Tika-eval+Jar重量%2B40MB。|2597378|2597379|2597380|URLConnection|2597381|2597382|import+java.net.URL;
import+java.net.URLConnection;

try+{
++++final+URL+url+=+new+URL("file://"+%2B+basePath+%2B+"/"+%2B+fileName);
++++final+URLConnection+urlConnection+=+url.openConnection();
++++return+urlConnection.getContentType();
}+catch+(final+Exception+exception)+{
++++return+"<EXCEPTION:+"+%2B+exception.getMessage()+%2B+">";
}|2597383|2597384|Rar+with+Rar+extension+is:+++++++content/unknown
Rar+with+Zip+extension+is:+++++++application/zip
Zip+with+Zip+extension+is:+++++++application/zip
7z+with+7z+extension+is:+++++++++content/unknown
7z+with+Zip+extension+is:++++++++application/zip
Tar.xz+with+Tar.xz+extension+is:+content/unknown
Tar.xz+with+Zip+extension+is:++++application/zip
Tar.gz+with+Tar.gz+extension+is:+application/octet-stream
Tar.gz+with+Zip+extension+is:++++application/zip
Rar+without+extension+is:++++++++content/unknown
Zip+without+extension+is:++++++++content/unknown
7z+without+extension+is:+++++++++content/unknown
Tar.xz+without+extension+is:+++++content/unknown
Tar.gz+without+extension+is:+++++content/unknown|2597385|2597386|它很难识别任何文件压缩格式，并通过扩展名引导自己，而不是其内容。|2597387|2597388|SimpleMagic+1.14|2597389|这个项目似乎更新了at+least+once+a+year。|2597390|2597391|import+com.j256.simplemagic.ContentInfo;
import+com.j256.simplemagic.ContentInfoUtil;

try+{
++++final+ContentInfoUtil+util+=+new+ContentInfoUtil();
++++final+ContentInfo+info+=+util.findMatch(basePath+%2B+"/"+%2B+fileName);

++++return+info.getMimeType();
}+catch+(final+Exception+exception)+{
++++return+"<EXCEPTION:+"+%2B+exception.getMessage()+%2B+">";
}|2597392|2597393|Rar+with+Rar+extension+is:+++++++application/x-rar
Rar+with+Zip+extension+is:+++++++application/x-rar
Zip+with+Zip+extension+is:+++++++application/zip
7z+with+7z+extension+is:+++++++++application/x-7z-compressed
7z+with+Zip+extension+is:++++++++application/x-7z-compressed
Tar.xz+with+Tar.xz+extension+is:+<EXCEPTION:+null>
Tar.xz+with+Zip+extension+is:++++<EXCEPTION:+null>
Tar.gz+with+Tar.gz+extension+is:+application/x-gzip
Tar.gz+with+Zip+extension+is:++++application/x-gzip
Rar+without+extension+is:++++++++application/x-rar
Zip+without+extension+is:++++++++application/zip
7z+without+extension+is:+++++++++application/x-7z-compressed
Tar.xz+without+extension+is:+++++<EXCEPTION:+null>
Tar.gz+without+extension+is:+++++application/x-gzip|2597394|2597395|它几乎适用于我们所有的场景，但似乎对于像Tar.xz这样的最“模糊”的压缩格式，它未能检测到它们(并在过程中抛出了一个异常)。|2597396|2597397|MimeUtil+2.1.3|2597398|这个项目是has+not+been+modified+since+2010的，所以不要期待支持或更新。这里只是为了完成而在这里列出。|2597399|2597400|import+eu.medsea.mimeutil.MimeUtil2;

try+{
++++final+MimeUtil2+mimeUtil+=+new+MimeUtil2();
++++++++mimeUtil.registerMimeDetector("eu.medsea.mimeutil.detector.MagicMimeMimeDetector");

++++return+MimeUtil2.getMostSpecificMimeType(mimeUtil.getMimeTypes(basePath+%2B+"/"+%2B+fileName)).toString();
}+catch+(final+Exception+exception)+{
++++return+"<EXCEPTION:+"+%2B+exception.getMessage()+%2B+">";
}|2597401|2597402|Rar+with+Rar+extension+is:+++++++application/x-rar
Rar+with+Zip+extension+is:+++++++application/x-rar
Zip+with+Zip+extension+is:+++++++application/zip
7z+with+7z+extension+is:+++++++++application/octet-stream
7z+with+Zip+extension+is:++++++++application/octet-stream
Tar.xz+with+Tar.xz+extension+is:+application/octet-stream
Tar.xz+with+Zip+extension+is:++++application/octet-stream
Tar.gz+with+Tar.gz+extension+is:+application/x-gzip
Tar.gz+with+Zip+extension+is:++++application/x-gzip
Rar+without+extension+is:++++++++application/x-rar
Zip+without+extension+is:++++++++application/zip
7z+without+extension+is:+++++++++application/octet-stream
Tar.xz+without+extension+is:+++++application/octet-stream
Tar.gz+without+extension+is:+++++application/x-gzip|2597403|2597404|它识别了一些最流行的文件类型，但在Tar.xz和7z中失败。|2597405|2597406|文件-命令行|2597407|这不是最好的解决方案，但必须尝试一下：Ubuntu+file+command。|2597408|2597409|import+java.io.BufferedReader;
import+java.io.InputStreamReader;

try+{
++++final+Process+process+=+Runtime.getRuntime().exec("file+--mime-type+"+%2B+basePath+%2B+"/"+%2B+fileName);

++++final+BufferedReader+stdInput+=+new+BufferedReader(new+InputStreamReader(process.getInputStream()));

++++String+text+=+"";

++++String+s;
++++while+((s+=+stdInput.readLine())+!=+null)+{
++++++++text+%2B=+s;
++++}

++++return+text.split(":+")[1];
}+catch+(final+Exception+exception)+{
++++return+"<EXCEPTION:+"+%2B+exception.getMessage()+%2B+">";
}|2597410|2597411|Rar+with+Rar+extension+is:+++++++application/x-rar
Rar+with+Zip+extension+is:+++++++application/x-rar
Zip+with+Zip+extension+is:+++++++application/zip
7z+with+7z+extension+is:+++++++++application/x-7z-compressed
7z+with+Zip+extension+is:++++++++application/x-7z-compressed
Tar.xz+with+Tar.xz+extension+is:+application/x-xz
Tar.xz+with+Zip+extension+is:++++application/x-xz
Tar.gz+with+Tar.gz+extension+is:+application/gzip
Tar.gz+with+Zip+extension+is:++++application/gzip
Rar+without+extension+is:++++++++application/x-rar
Zip+without+extension+is:++++++++application/zip
7z+without+extension+is:+++++++++application/x-7z-compressed
Tar.xz+without+extension+is:+++++application/x-xz
Tar.gz+without+extension+is:+++++application/gzip|2597412|2597413|它适用于我们的所有场景，但同样，这依赖于运行代码的系统上是否存在命令File。|2597414|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/javase/7/docs/api/java/nio/file/Files.html#probeContentType%2528java.nio.file.Path%2529|1|https://tika.apache.org/|2|https://github.com/j256/simplemagic|3|https://stackoverflow.com/questions/34722106/why-does-conversion-of-bytearray-to-mime-type-returns-null/34722480#34722480|4|https://stackoverflow.com/questions/51438/getting-a-files-mime-type-in-java/8973468#comment30001895_8973468|5|https://tika.apache.org/download.html|6|https://mvnrepository.com/artifact/com.j256.simplemagic/simplemagic|7|https://mvnrepository.com/artifact/eu.medsea.mimeutil/mime-util|8|http://manpages.ubuntu.com/manpages/xenial/man1/file.1.html^0|0|S|C|2B|J|41|C|5B|C|5T|E|0|S|M|0|1F|B|1|1R|B|2|0|7|M|23|U|0|0|0|0|0|L|F|0|1I|5|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|J|O|0|0|0|0|0|0|0|0|G|10|3|0|0|0|0|0|0|0|0|0|3|1K|4|0|0|1|4|0|0|0|0|0|3|S|5|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|9|K|6|0|0|0|0|0|0|0|0|0|5|W|7|0|0|0|0|0|0|0|0|0|J|J|8|0|0|0|0|0|0|Y|4|0^^$0|@$1|2|3|4|5|6|7|5R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|5S|8|@$D|5T|E|5U|F|G]|$D|5V|E|5W|F|G]|$D|5X|E|5Y|F|G]|$D|5Z|E|60|F|G]|$D|61|E|62|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|63|8|@]|9|@$D|64|E|65|1|66]|$D|67|E|68|1|69]|$D|6A|E|6B|1|6C]]|A|$]]|$1|J|3|K|5|6|7|6D|8|@$D|6E|E|6F|F|G]|$D|6G|E|6H|F|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|6I|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|6J|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|6K|8|@]|9|@]|A|$]]|$1|R|3|S|5|T|7|6L|8|@]|9|@]|A|$U|V]]|$1|W|3|X|5|6|7|6M|8|@$D|6N|E|6O|F|G]]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|6P|8|@$D|6Q|E|6R|F|L]]|9|@]|A|$]]|$1|10|3|11|5|6|7|6S|8|@]|9|@]|A|$]]|$1|12|3|-4|5|6|7|6T|8|@]|9|@]|A|$]]|$1|13|3|14|5|15|7|6U|8|@]|9|@]|A|$]]|$1|16|3|17|5|15|7|6V|8|@]|9|@]|A|$]]|$1|18|3|19|5|15|7|6W|8|@]|9|@]|A|$]]|$1|1A|3|1B|5|15|7|6X|8|@]|9|@]|A|$]]|$1|1C|3|1D|5|15|7|6Y|8|@]|9|@]|A|$]]|$1|1E|3|-4|5|6|7|6Z|8|@]|9|@]|A|$]]|$1|1F|3|1G|5|6|7|70|8|@]|9|@]|A|$]]|$1|1H|3|-4|5|6|7|71|8|@]|9|@]|A|$]]|$1|1I|3|1J|5|6|7|72|8|@]|9|@]|A|$]]|$1|1K|3|1L|5|6|7|73|8|@]|9|@]|A|$]]|$1|1M|3|1N|5|T|7|74|8|@]|9|@]|A|$U|V]]|$1|1O|3|1P|5|6|7|75|8|@]|9|@]|A|$]]|$1|1Q|3|1R|5|T|7|76|8|@]|9|@]|A|$U|V]]|$1|1S|3|1T|5|6|7|77|8|@]|9|@]|A|$]]|$1|1U|3|1V|5|6|7|78|8|@$D|79|E|7A|F|G]]|9|@]|A|$]]|$1|1W|3|-4|5|6|7|7B|8|@]|9|@]|A|$]]|$1|1X|3|1Y|5|6|7|7C|8|@]|9|@]|A|$]]|$1|1Z|3|1L|5|6|7|7D|8|@]|9|@]|A|$]]|$1|20|3|21|5|T|7|7E|8|@]|9|@]|A|$U|V]]|$1|22|3|1P|5|6|7|7F|8|@]|9|@]|A|$]]|$1|23|3|24|5|T|7|7G|8|@]|9|@]|A|$U|V]]|$1|25|3|1T|5|6|7|7H|8|@]|9|@]|A|$]]|$1|26|3|27|5|6|7|7I|8|@]|9|@$D|7J|E|7K|1|7L]]|A|$]]|$1|28|3|-4|5|6|7|7M|8|@]|9|@]|A|$]]|$1|29|3|2A|5|6|7|7N|8|@]|9|@]|A|$]]|$1|2B|3|1L|5|6|7|7O|8|@]|9|@]|A|$]]|$1|2C|3|2D|5|T|7|7P|8|@]|9|@]|A|$U|V]]|$1|2E|3|1P|5|6|7|7Q|8|@]|9|@]|A|$]]|$1|2F|3|2G|5|T|7|7R|8|@]|9|@]|A|$U|V]]|$1|2H|3|1T|5|6|7|7S|8|@]|9|@]|A|$]]|$1|2I|3|2J|5|6|7|7T|8|@]|9|@]|A|$]]|$1|2K|3|2L|5|6|7|7U|8|@]|9|@$D|7V|E|7W|1|7X]]|A|$]]|$1|2M|3|-4|5|6|7|7Y|8|@]|9|@]|A|$]]|$1|2N|3|2O|5|2P|7|7Z|8|@$D|80|E|81|F|L]]|9|@]|A|$]]|$1|2Q|3|-4|5|6|7|82|8|@]|9|@]|A|$]]|$1|2R|3|-4|5|6|7|83|8|@]|9|@]|A|$]]|$1|2S|3|-4|5|6|7|84|8|@]|9|@]|A|$]]|$1|2T|3|2U|5|6|7|85|8|@]|9|@]|A|$]]|$1|2V|3|2W|5|6|7|86|8|@]|9|@$D|87|E|88|1|89]]|A|$]]|$1|2X|3|1L|5|6|7|8A|8|@]|9|@]|A|$]]|$1|2Y|3|2Z|5|T|7|8B|8|@]|9|@]|A|$U|V]]|$1|30|3|1P|5|6|7|8C|8|@]|9|@]|A|$]]|$1|31|3|32|5|T|7|8D|8|@]|9|@]|A|$U|V]]|$1|33|3|1T|5|6|7|8E|8|@]|9|@]|A|$]]|$1|34|3|35|5|6|7|8F|8|@]|9|@]|A|$]]|$1|36|3|37|5|6|7|8G|8|@]|9|@]|A|$]]|$1|38|3|39|5|6|7|8H|8|@]|9|@]|A|$]]|$1|3A|3|3B|5|15|7|8I|8|@]|9|@]|A|$]]|$1|3C|3|3D|5|15|7|8J|8|@]|9|@]|A|$]]|$1|3E|3|-4|5|6|7|8K|8|@]|9|@]|A|$]]|$1|3F|3|3G|5|6|7|8L|8|@]|9|@]|A|$]]|$1|3H|3|-4|5|6|7|8M|8|@]|9|@]|A|$]]|$1|3I|3|3J|5|15|7|8N|8|@]|9|@]|A|$]]|$1|3K|3|-4|5|6|7|8O|8|@]|9|@]|A|$]]|$1|3L|3|-4|5|6|7|8P|8|@]|9|@]|A|$]]|$1|3M|3|3N|5|6|7|8Q|8|@]|9|@]|A|$]]|$1|3O|3|1L|5|6|7|8R|8|@]|9|@]|A|$]]|$1|3P|3|3Q|5|T|7|8S|8|@]|9|@]|A|$U|V]]|$1|3R|3|1P|5|6|7|8T|8|@]|9|@]|A|$]]|$1|3S|3|3T|5|T|7|8U|8|@]|9|@]|A|$U|V]]|$1|3U|3|1T|5|6|7|8V|8|@]|9|@]|A|$]]|$1|3V|3|3W|5|6|7|8W|8|@]|9|@]|A|$]]|$1|3X|3|-4|5|6|7|8X|8|@]|9|@]|A|$]]|$1|3Y|3|3Z|5|6|7|8Y|8|@]|9|@]|A|$]]|$1|40|3|41|5|6|7|8Z|8|@]|9|@$D|90|E|91|1|92]]|A|$]]|$1|42|3|1L|5|6|7|93|8|@]|9|@]|A|$]]|$1|43|3|44|5|T|7|94|8|@]|9|@]|A|$U|V]]|$1|45|3|1P|5|6|7|95|8|@]|9|@]|A|$]]|$1|46|3|47|5|T|7|96|8|@]|9|@]|A|$U|V]]|$1|48|3|1T|5|6|7|97|8|@]|9|@]|A|$]]|$1|49|3|4A|5|6|7|98|8|@]|9|@]|A|$]]|$1|4B|3|-4|5|6|7|99|8|@]|9|@]|A|$]]|$1|4C|3|4D|5|6|7|9A|8|@]|9|@]|A|$]]|$1|4E|3|4F|5|6|7|9B|8|@]|9|@$D|9C|E|9D|1|9E]]|A|$]]|$1|4G|3|1L|5|6|7|9F|8|@]|9|@]|A|$]]|$1|4H|3|4I|5|T|7|9G|8|@]|9|@]|A|$U|V]]|$1|4J|3|1P|5|6|7|9H|8|@]|9|@]|A|$]]|$1|4K|3|4L|5|T|7|9I|8|@]|9|@]|A|$U|V]]|$1|4M|3|1T|5|6|7|9J|8|@]|9|@]|A|$]]|$1|4N|3|4O|5|6|7|9K|8|@]|9|@]|A|$]]|$1|4P|3|-4|5|6|7|9L|8|@]|9|@]|A|$]]|$1|4Q|3|4R|5|6|7|9M|8|@]|9|@]|A|$]]|$1|4S|3|4T|5|6|7|9N|8|@]|9|@$D|9O|E|9P|1|9Q]]|A|$]]|$1|4U|3|1L|5|6|7|9R|8|@]|9|@]|A|$]]|$1|4V|3|4W|5|T|7|9S|8|@]|9|@]|A|$U|V]]|$1|4X|3|1P|5|6|7|9T|8|@]|9|@]|A|$]]|$1|4Y|3|4Z|5|T|7|9U|8|@]|9|@]|A|$U|V]]|$1|50|3|1T|5|6|7|9V|8|@]|9|@]|A|$]]|$1|51|3|52|5|6|7|9W|8|@$D|9X|E|9Y|F|G]]|9|@]|A|$]]|$1|53|3|-4|5|6|7|9Z|8|@]|9|@]|A|$]]]|54|$55|$5|56|57|58|A|$59|5A]]|5B|$5|56|57|58|A|$59|5C]]|5D|$5|56|57|58|A|$59|5E]]|5F|$5|56|57|58|A|$59|5G]]|5H|$5|56|57|58|A|$59|5I]]|5J|$5|56|57|58|A|$59|5K]]|5L|$5|56|57|58|A|$59|5M]]|5N|$5|56|57|58|A|$59|5O]]|5P|$5|56|57|58|A|$59|5Q]]]]

<h1>TL;DR;</h1>

<p>When one uploads a file to Amazon S3 programatically, one could specify the object's <code>Content-Type</code>. If one specifies none, as @Michael-bot clarifies, the value assigned by default will be <code>binary/octet-stream</code>. Or if one decides to upload the file through Amazon S3's GUI, the file gets its <code>Content-Type</code> from its file extension (sadly, not its contents). If you can trust whoever uploaded the file to set the <code>Content-Type</code> correctly, go ahead and look at the <code>ObjectMetadata</code>, but if you can't (like me), you would need another solution.</p>

<p>So, if you are looking for a solution that works on the most common file compression types, <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/file/Files.html#probeContentType%28java.nio.file.Path%29" rel="nofollow noreferrer">Files.probeContentType</a>, <a href="https://tika.apache.org/" rel="nofollow noreferrer">Apache Tika</a> and <a href="https://github.com/j256/simplemagic" rel="nofollow noreferrer">SimpleMagic</a> seem to be acceptable solutions. </p>

<p>In the end I chose <code>Files.probeContentType</code> as it required no extra libraries and works just fine on a Linux machine (<strong>as long as the file doesn't have the wrong extension, for which there is a workaround: remove the file extension and let it do its magic</strong>).</p>

<hr>

<h1>The Test Setup</h1>

<p>At first one would think that the response object when downloading the file from Amazon's S3 includes the file type. And it does contain this information, but the problem arises when the extension of the file doesn't match its contents.</p>

<pre><code>import com.amazonaws.services.s3.model.S3Object;

final S3Object s3Object = ...;
final String contentType = s3Object.getObjectMetadata().getContentType();
</code></pre>

<p>This code would return <code>application/zip</code> even if the contents of the file are of a Rar file. So this solution doesn't work for me.</p>

<p>For this reason I took the time to build a sample project that tested various scenarios with the different approaches and libraries available. I'm using <strong>Java 8</strong> by the way.</p>

<p>The files types tested are:</p>

<ul>
<li>A Zip file with Zip extension and without extension</li>
<li>A Rar file with Rar extension, Zip extension and without extension</li>
<li>A 7z file with 7z extension, Zip extension and without extension</li>
<li>A Tar.xz with Tar.xz extension, Zip extension and without extension</li>
<li>A Tar.gz with Tar.gz extension, Zip extension and without extension</li>
</ul>

<p>Beware, the implementations presented here are only for testing purposes. They are not in any way endorsed to be used in production code, as they don't consider file locking problems among other things that my imagination couldn't bother to consider. =)</p>

<hr>

<h1>MimetypesFileTypeMap</h1>

<h2>Implementation</h2>

<pre><code>import java.io.File;
import javax.activation.MimetypesFileTypeMap;

final File file = new File(basePath + "/" + fileName);
try {
    return MimetypesFileTypeMap.getDefaultFileTypeMap().getContentType(file);
} catch (final Exception exception) {
    return "&lt;EXCEPTION: " + exception.getMessage() + "&gt;";
}
</code></pre>

<h2>Results</h2>

<pre><code>Rar with Rar extension is:       application/octet-stream
Rar with Zip extension is:       application/octet-stream
Zip with Zip extension is:       application/octet-stream
7z with 7z extension is:         application/octet-stream
7z with Zip extension is:        application/octet-stream
Tar.xz with Tar.xz extension is: application/octet-stream
Tar.xz with Zip extension is:    application/octet-stream
Tar.gz with Tar.gz extension is: application/octet-stream
Tar.gz with Zip extension is:    application/octet-stream
Rar without extension is:        application/octet-stream
Zip without extension is:        application/octet-stream
7z without extension is:         application/octet-stream
Tar.xz without extension is:     application/octet-stream
Tar.gz without extension is:     application/octet-stream
</code></pre>

<h2>Conclusion</h2>

<p>The value returned by this approach when a file type has not been recognized is <code>application/octet-stream</code>. It seems all scenarios failed so we should discard this approach.</p>

<hr>

<h1>URLConnection.guessContentTypeFromStream</h1>

<h2>Implementation</h2>

<pre><code>import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.BufferedInputStream;
import java.net.URLConnection;

final File file = new File(basePath + "/" + fileName);
try {
    final FileInputStream fileInputStream = new FileInputStream(file);
    final InputStream inputStream = new BufferedInputStream(fileInputStream);

    return URLConnection.guessContentTypeFromStream(inputStream);
} catch (final Exception exception) {
    return "&lt;EXCEPTION: " + exception.getMessage() + "&gt;";
}
</code></pre>

<h2>Results</h2>

<pre><code>Rar with Rar extension is:       null
Rar with Zip extension is:       null
Zip with Zip extension is:       null
7z with 7z extension is:         null
7z with Zip extension is:        null
Tar.xz with Tar.xz extension is: null
Tar.xz with Zip extension is:    null
Tar.gz with Tar.gz extension is: null
Tar.gz with Zip extension is:    null
Rar without extension is:        null
Zip without extension is:        null
7z without extension is:         null
Tar.xz without extension is:     null
Tar.gz without extension is:     null
</code></pre>

<h2>Conclusion</h2>

<p>Again, this method fails all scenarios. <a href="https://stackoverflow.com/questions/34722106/why-does-conversion-of-bytearray-to-mime-type-returns-null/34722480#34722480">It seems its support is very limited</a>.</p>

<hr>

<h1>Files.probeContentType</h1>

<h2>Implementation</h2>

<pre><code>import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

try {
    final Path path = Paths.get(basePath + "/" + fileName);
    return Files.probeContentType(path);
} catch (final Exception exception) {
    return "&lt;EXCEPTION: " + exception.getMessage() + "&gt;";
}
</code></pre>

<h2>Results</h2>

<pre><code>Rar with Rar extension is:       application/vnd.rar
Rar with Zip extension is:       application/zip
Zip with Zip extension is:       application/zip
7z with 7z extension is:         application/x-7z-compressed
7z with Zip extension is:        application/zip
Tar.xz with Tar.xz extension is: application/x-xz-compressed-tar
Tar.xz with Zip extension is:    application/zip
Tar.gz with Tar.gz extension is: application/x-compressed-tar
Tar.gz with Zip extension is:    application/zip
Rar without extension is:        application/vnd.rar
Zip without extension is:        application/zip
7z without extension is:         application/x-7z-compressed
Tar.xz without extension is:     application/x-xz
Tar.gz without extension is:     application/gzip
</code></pre>

<h2>Conclusion</h2>

<p>This method worked surprisingly well, but don't be fooled, there is a scenario where it consistently fails. If a file has the wrong extension (one that doesn't match is content) it will report the file type to be the extension. It should not happen very often, but if one is very picky this method is not to be used.</p>

<p>Also, <a href="https://stackoverflow.com/questions/51438/getting-a-files-mime-type-in-java/8973468#comment30001895_8973468">some warn that his approach doesn't work well in Windows</a>.</p>

<blockquote>
  <p><strong>Workaround</strong>: If one manages to remove the extension from the filename, this would return the proper value for all the given scenarios.</p>
</blockquote>

<hr>

<h1>Apache Tika (tika-eval 1.18)</h1>

<p>There seem to be <a href="https://tika.apache.org/download.html" rel="nofollow noreferrer">many flavors of this library</a> (app, server, eval, etc), but many around the web complain about it being somewhat "dependency-heavy".</p>

<h2>Implementation</h2>

<pre><code>import org.apache.tika.Tika;

try {
    return new Tika().detect(new File(basePath + "/" + fileName));
} catch (final Exception exception) {
    return "&lt;EXCEPTION: " + exception.getMessage() + "&gt;";
}
</code></pre>

<h2>Results</h2>

<pre><code>Rar with Rar extension is:       application/x-rar-compressed
Rar with Zip extension is:       application/x-rar-compressed
Zip with Zip extension is:       application/zip
7z with 7z extension is:         application/x-7z-compressed
7z with Zip extension is:        application/x-7z-compressed
Tar.xz with Tar.xz extension is: application/x-xz
Tar.xz with Zip extension is:    application/x-xz
Tar.gz with Tar.gz extension is: application/gzip
Tar.gz with Zip extension is:    application/gzip
Rar without extension is:        application/x-rar-compressed
Zip without extension is:        application/zip
7z without extension is:         application/x-7z-compressed
Tar.xz without extension is:     application/x-xz
Tar.gz without extension is:     application/gzip
</code></pre>

<h2>Conclusion</h2>

<p>All files were properly identified, but as it has its advantages it also has its disadvantages.</p>

<p>Pros:</p>

<ul>
<li>Maintained by Apache.</li>
<li>Does not get fooled by extensions.</li>
</ul>

<p>Cons:</p>

<ul>
<li>Really heavy, specially if one only wants to check get the file type. The Tika-eval Jar weights +40MB.</li>
</ul>

<hr>

<h1>URLConnection</h1>

<h2>Implementation</h2>

<pre><code>import java.net.URL;
import java.net.URLConnection;

try {
    final URL url = new URL("file://" + basePath + "/" + fileName);
    final URLConnection urlConnection = url.openConnection();
    return urlConnection.getContentType();
} catch (final Exception exception) {
    return "&lt;EXCEPTION: " + exception.getMessage() + "&gt;";
}
</code></pre>

<h2>Results</h2>

<pre><code>Rar with Rar extension is:       content/unknown
Rar with Zip extension is:       application/zip
Zip with Zip extension is:       application/zip
7z with 7z extension is:         content/unknown
7z with Zip extension is:        application/zip
Tar.xz with Tar.xz extension is: content/unknown
Tar.xz with Zip extension is:    application/zip
Tar.gz with Tar.gz extension is: application/octet-stream
Tar.gz with Zip extension is:    application/zip
Rar without extension is:        content/unknown
Zip without extension is:        content/unknown
7z without extension is:         content/unknown
Tar.xz without extension is:     content/unknown
Tar.gz without extension is:     content/unknown
</code></pre>

<h2>Conclusion</h2>

<p>It hardly identifies any file compression format, and guides itself by the extension, not its contents.</p>

<hr>

<h1>SimpleMagic 1.14</h1>

<p>This project seems to be updated <a href="https://mvnrepository.com/artifact/com.j256.simplemagic/simplemagic" rel="nofollow noreferrer">at least once a year</a>.</p>

<h2>Implementation</h2>

<pre><code>import com.j256.simplemagic.ContentInfo;
import com.j256.simplemagic.ContentInfoUtil;

try {
    final ContentInfoUtil util = new ContentInfoUtil();
    final ContentInfo info = util.findMatch(basePath + "/" + fileName);

    return info.getMimeType();
} catch (final Exception exception) {
    return "&lt;EXCEPTION: " + exception.getMessage() + "&gt;";
}
</code></pre>

<h2>Results</h2>

<pre><code>Rar with Rar extension is:       application/x-rar
Rar with Zip extension is:       application/x-rar
Zip with Zip extension is:       application/zip
7z with 7z extension is:         application/x-7z-compressed
7z with Zip extension is:        application/x-7z-compressed
Tar.xz with Tar.xz extension is: &lt;EXCEPTION: null&gt;
Tar.xz with Zip extension is:    &lt;EXCEPTION: null&gt;
Tar.gz with Tar.gz extension is: application/x-gzip
Tar.gz with Zip extension is:    application/x-gzip
Rar without extension is:        application/x-rar
Zip without extension is:        application/zip
7z without extension is:         application/x-7z-compressed
Tar.xz without extension is:     &lt;EXCEPTION: null&gt;
Tar.gz without extension is:     application/x-gzip
</code></pre>

<h2>Conclusion</h2>

<p>It worked for almost all our scenarios, but it seems that for the most "obscure" compression formats like Tar.xz it failed to detect them (and threw an exception in the process).</p>

<hr>

<h1>MimeUtil 2.1.3</h1>

<p>This project <a href="https://mvnrepository.com/artifact/eu.medsea.mimeutil/mime-util" rel="nofollow noreferrer">has not been modified since 2010</a>, so don't expect support or updates. It is just listed here for the sake of completion.</p>

<h2>Implementation</h2>

<pre><code>import eu.medsea.mimeutil.MimeUtil2;

try {
    final MimeUtil2 mimeUtil = new MimeUtil2();
        mimeUtil.registerMimeDetector("eu.medsea.mimeutil.detector.MagicMimeMimeDetector");

    return MimeUtil2.getMostSpecificMimeType(mimeUtil.getMimeTypes(basePath + "/" + fileName)).toString();
} catch (final Exception exception) {
    return "&lt;EXCEPTION: " + exception.getMessage() + "&gt;";
}
</code></pre>

<h2>Results</h2>

<pre><code>Rar with Rar extension is:       application/x-rar
Rar with Zip extension is:       application/x-rar
Zip with Zip extension is:       application/zip
7z with 7z extension is:         application/octet-stream
7z with Zip extension is:        application/octet-stream
Tar.xz with Tar.xz extension is: application/octet-stream
Tar.xz with Zip extension is:    application/octet-stream
Tar.gz with Tar.gz extension is: application/x-gzip
Tar.gz with Zip extension is:    application/x-gzip
Rar without extension is:        application/x-rar
Zip without extension is:        application/zip
7z without extension is:         application/octet-stream
Tar.xz without extension is:     application/octet-stream
Tar.gz without extension is:     application/x-gzip
</code></pre>

<h2>Conclusion</h2>

<p>It identifies some of the most popular file types, but fails with Tar.xz and 7z.</p>

<hr>

<h1>file - Command Line</h1>

<p>Not the prettiest solution, but it had to be tried: <a href="http://manpages.ubuntu.com/manpages/xenial/man1/file.1.html" rel="nofollow noreferrer">Ubuntu file command</a>.</p>

<h2>Implementation</h2>

<pre><code>import java.io.BufferedReader;
import java.io.InputStreamReader;

try {
    final Process process = Runtime.getRuntime().exec("file --mime-type " + basePath + "/" + fileName);

    final BufferedReader stdInput = new BufferedReader(new InputStreamReader(process.getInputStream()));

    String text = "";

    String s;
    while ((s = stdInput.readLine()) != null) {
        text += s;
    }

    return text.split(": ")[1];
} catch (final Exception exception) {
    return "&lt;EXCEPTION: " + exception.getMessage() + "&gt;";
}
</code></pre>

<h2>Results</h2>

<pre><code>Rar with Rar extension is:       application/x-rar
Rar with Zip extension is:       application/x-rar
Zip with Zip extension is:       application/zip
7z with 7z extension is:         application/x-7z-compressed
7z with Zip extension is:        application/x-7z-compressed
Tar.xz with Tar.xz extension is: application/x-xz
Tar.xz with Zip extension is:    application/x-xz
Tar.gz with Tar.gz extension is: application/gzip
Tar.gz with Zip extension is:    application/gzip
Rar without extension is:        application/x-rar
Zip without extension is:        application/zip
7z without extension is:         application/x-7z-compressed
Tar.xz without extension is:     application/x-xz
Tar.gz without extension is:     application/gzip
</code></pre>

<h2>Conclusion</h2>

<p>It works for all our scenarios, but again, this relies on the command <code>File</code> being present on the System running the code.</p>


<p>A client is supposed to upload a compressed file into an S3 folder. Then the compressed file is downloaded and decompressed to perform various operations on its contained files. Originally we told our client to compress its files into a <strong>ZIP</strong> file, but this proved too difficult for our client. Instead it submitted a <em>RAR</em> file with ZIP extension... how clever. For obvious reasons one can't decompress a <em>RAR</em> file using a <em>ZIP</em> decompressing algorithm.</p>

<p>So, I'm looking for a way to find out the file type of the S3 downloaded files given that I'm working on a Java project with Amazon's SDK on a Linux OS. I'll take care of how to decompress the file depending on the obtained file type.</p>

<p>I've looked at many stack overflow questions, like <a href="https://stackoverflow.com/questions/51438/getting-a-files-mime-type-in-java">this one</a>, but none seem 100% effective just by looking at them (and its comments). </p>

<p>What would be the best approach to find out the compressed file's type?</p>


Find out MIME Type of compressed files downloaded from S3 for Java

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客户端应该将压缩文件上传到S3文件夹中。然后下载并解压缩压缩文件以对其包含的文件执行各种操作。最初我们告诉客户端将其文件压缩为ZIP文件，但事实证明这对我们的客户端来说太难了。相反，它提交了一个带有ZIP扩展名的RAR文件...多聪明啊。由于显而易见的原因，我们不能使用ZIP解压缩算法来解压缩RAR文件。因此，我正在寻...

问查找从S3下载的压缩文件的MIME类型
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