Setting file type in java

Getting a File’s Mime Type in Java

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Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.

The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.

Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.

Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you’ll have results within minutes:

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To avoid overspending on your Kubernetes cluster, definitely have a look at the free K8s cost monitoring tool from the automation platform CAST AI. You can view your costs in real time, allocate them, calculate burn rates for projects, spot anomalies or spikes, and get insightful reports you can share with your team.

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1. Overview

In this tutorial, we’ll take a look at various strategies for getting MIME types of a file. We’ll look at ways to extend the MIME types available to the strategies, wherever applicable.

We’ll also point out where we should favor one strategy over the other.

2. Using Java 7

Let’s start with Java 7 – which provides the method Files.probeContentType(path) for resolving the MIME type:

@Test public void whenUsingJava7_thenSuccess() < Path path = new File("product.png").toPath(); String mimeType = Files.probeContentType(path); assertEquals(mimeType, "image/png"); >

This method makes use of the installed FileTypeDetector implementations to probe the MIME type. It invokes the probeContentType of each implementation to resolve the type.

Now, if the file is recognized by any of the implementations, the content type is returned. However, if that doesn’t happen, a system-default file type detector is invoked.

However, the default implementations are OS specific and might fail depending on the OS that we are using.

In addition to that, it’s also important to note that the strategy will fail if the file isn’t present in the filesystem. Furthermore, if the file doesn’t have an extension, it will result in failure.

3. Using URLConnection

URLConnection provides several APIs for detecting MIME types of a file. Let’s briefly explore each of them.

3.1. Using getContentType()

We can use getContentType() method of URLConnection to retrieve a file’s MIME type:

@Test public void whenUsingGetContentType_thenSuccess()< File file = new File("product.png"); URLConnection connection = file.toURL().openConnection(); String mimeType = connection.getContentType(); assertEquals(mimeType, "image/png"); >

However, a major drawback of this approach is that it’s very slow.

3.2. Using guessContentTypeFromName()

Next, let’s see how we can make use of the guessContentTypeFromName() for the purpose:

@Test public void whenUsingGuessContentTypeFromName_thenSuccess()< File file = new File("product.png"); String mimeType = URLConnection.guessContentTypeFromName(file.getName()); assertEquals(mimeType, "image/png"); >

This method makes use of the internal FileNameMap to resolve the MIME type from the extension.

We also have the option of using guessContentTypeFromStream() instead, which uses the first few characters of the input stream, to determine the type.

3.3. Using getFileNameMap()

A faster way to obtain the MIME type using URLConnection is using the getFileNameMap() method:

@Test public void whenUsingGetFileNameMap_thenSuccess()< File file = new File("product.png"); FileNameMap fileNameMap = URLConnection.getFileNameMap(); String mimeType = fileNameMap.getContentTypeFor(file.getName()); assertEquals(mimeType, "image/png"); >

The method returns the table of MIME types used by all instances of URLConnection. This table is then used to resolve the input file type.

The built-in table of MIME types is very limited when it comes to URLConnection.

By default, the class uses content-types.properties file in JRE_HOME/lib. We can, however, extend it, by specifying a user-specific table using the content.types.user.table property:

System.setProperty("content.types.user.table",""); 

4. Using MimeTypesFileTypeMap

MimeTypesFileTypeMap resolves MIME types by using file’s extension. This class came with Java 6, and hence comes very handy when we’re working with JDK 1.6.

Now let’s see how to use it:

@Test public void whenUsingMimeTypesFileTypeMap_thenSuccess() < File file = new File("product.png"); MimetypesFileTypeMap fileTypeMap = new MimetypesFileTypeMap(); String mimeType = fileTypeMap.getContentType(file.getName()); assertEquals(mimeType, "image/png"); >

Here, we can either pass the name of the file or the File instance itself as the parameter to the function. However, the function with File instance as the parameter internally calls the overloaded method that accepts the filename as the parameter.

Internally, this method looks up a file called mime.types for the type resolution. It’s very important to note that the method searches for the file in a specific order:

1. Programmatically added entries to the MimetypesFileTypeMap instance
2. .mime.types in the user’s home directory
3. /lib/mime.types
4. resources named META-INF/mime.types
5. resource named META-INF/mimetypes.default (usually found only in the activation.jar file)

However, if no file is found, it will return application/octet-stream as the response.

5. Using jMimeMagic

jMimeMagic is a restrictively licensed library that we can use to obtain the MIME type of a file.

Let’s start by configuring the Maven dependency:

 net.sf.jmimemagic jmimemagic 0.1.5 

We can find the latest version of this library on Maven Central.

Next, we’ll explore how to work with the library:

@Test public void whenUsingJmimeMagic_thenSuccess() < File file = new File("product.png"); Magic magic = new Magic(); MagicMatch match = magic.getMagicMatch(file, false); assertEquals(match.getMimeType(), "image/png"); >

This library can work with a stream of data and hence doesn’t require the file to be present in the file system.

6. Using Apache Tika

Apache Tika is a toolset that detects and extracts metadata and text from a variety of files. It has a rich and powerful API and comes with tika-core which we can make use of, for detecting MIME type of a file.

Let’s begin by configuring the Maven dependency:

 org.apache.tika tika-core 1.18 

Next, we’ll make use of the detect() method to resolve the type:

@Test public void whenUsingTika_thenSuccess() < File file = new File("product.png"); Tika tika = new Tika(); String mimeType = tika.detect(file); assertEquals(mimeType, "image/png"); >

The library relies on magic markers in the stream prefix, for type resolution.

7. Conclusion

In this article, we’ve looked at the various strategies of obtaining the MIME type of a file. Furthermore, we have also analyzed the tradeoffs of the approaches. We have also pointed out the scenarios where we should favor one strategy over the other.

The full source code that is used in this article is available over at GitHub, as always.

Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.

The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.

Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.

Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you’ll have results within minutes:

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Определение типов файлов в Java

Программно определить тип файла может быть удивительно сложно, и было предложено и реализовано много подходов идентификации файлов на основе контента . Существует несколько реализаций, доступных в Java для обнаружения типов файлов, и большинство из них в значительной степени или исключительно основаны на расширениях файлов. В этом посте рассматриваются некоторые из наиболее распространенных реализаций обнаружения типов файлов в Java.

В этом посте демонстрируется несколько подходов к идентификации типов файлов в Java. Каждый подход кратко описан, проиллюстрирован листингом кода, а затем связан с выводом, который демонстрирует, как различные общие файлы печатаются на основе расширений. Некоторые из подходов являются настраиваемыми, но все показанные здесь примеры используют сопоставления «по умолчанию», как это предусмотрено «из коробки», если не указано иное.

О примерах

Снимки экрана, показанные в этом посте, представляют собой каждый из перечисленных фрагментов кода, запускаемых для определенных тематических файлов, созданных для тестирования различных реализаций обнаружения типов файлов в Java. Прежде чем рассказать об этих подходах и продемонстрировать тип, который обнаруживает каждый из них, я перечисляю тестируемые файлы, их имена и имена.

файл название	файл расширение	файл Тип	Тип совпадений Конвенция о продлении?
actualXml.xml	XML	XML	да
blogPostPDF		PDF	нет
blogPost.pdf	PDF	PDF	да
blogPost.gif	GIF	GIF	да
blogPost.jpg	JPG	JPEG	да
blogPost.png	PNG	PNG	да
blogPostPDF.txt	текст	PDF	нет
blogPostPDF.xml	XML	PDF	нет
blogPostPNG.gif	GIF	PNG	нет
blogPostPNG.jpg	JPG	PNG	нет
dustin.txt	текст	Текст	да
dustin.xml	XML	Текст	нет
Дастин		Текст	нет

Files.probeContentType (Path) [JDK 7]

Java SE 7 представила высоко утилитарный класс Files, и Javadoc этого класса кратко описывает его использование: «Этот класс состоит исключительно из статических методов, которые работают с файлами, каталогами или другими типами файлов» и «в большинстве случаев с методами, определенными здесь делегирует соответствующему провайдеру файловой системы для выполнения файловых операций ».

Класс java.nio.file.Files предоставляет метод probeContentType (Path), который «проверяет тип содержимого файла» посредством использования «установленных реализаций FileTypeDetector» (Javadoc также отмечает, что «данный вызов виртуальной машины Java») ведет общесистемный список детекторов типов файлов »).

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