[FIXED] How to not hardcoding image extensions in Java?

Issue

How to not hardcoding image extensions in Java?

            switch(extension) {
                case "zip" -> {
                    FileUtil.saveFile(multipartFile, historyFolder, FileType.ZIP, backupFilePath);
                    FileUtil.saveFile(multipartFile, target, FileType.ZIP, filePath);
                }
                case "jpg", "jpeg", "png", ".bmp", ".svg", "webp", "jfif", "pjpeg", "pjp", "apng", "avif" -> {
                    FileUtil.saveFile(multipartFile, historyFolder, FileType.IMAGE, backupFilePath);
                    FileUtil.saveFile(multipartFile, target, FileType.IMAGE, filePath);
                }
                default -> throw new GlobalCustomException(ErrorCode.ILLIGAL_FILE_TYPE);
            }

Above is my code.

In the case statement, I have listed strings as hard-coded as jpg, jpeg....

This code is not flexible, so I'm sure there must be a better way.

I'd appreciate it if you could give me a solution that I'm not aware of.

Solution

As one of possible ways, you can use URLConnection.guessContentTypeFromName() like this.

String mimeType = java.net.URLConnection.guessContentTypeFromName("test." + extension);
boolean isImage = mimeType != null && mimeType.startWith("image/")

You can add custom extensions to the $JAVA_HOME/jre/lib/content-types.properties file.

Also see these questions.

• How to get a file's Media Type (MIME type)?
• How to reliably detect file types?

Answered By - relent95
Answer Checked By - Pedro (JavaFixing Volunteer)