您可以使用
Map来保存您的解决方案：
Map<String,String> extensionToMimeType = new HashMap<String,String>();extensionToMimeType.put("pdf", "application/pdf");extensionToMimeType.put("doc", "application/msword");// and the restint lastDot = fileName.lastIndexOf(".");String mimeType;if (lastDot == -1) { mimeType = NO_EXTENSION_MIME_TYPE;} else { String extension = fileName.substring(lastDot+1); mimeType = extensionToMimeType.getOrDefault(extension, UNKNOWN_EXTENSION_MIME_TYPE);}为了使此代码起作用，您需要像在类中那样进行定义
NO_EXTENSION_MIME_TYPE和定义
UNKNOWN_EXTENSION_MIME_TYPE，如下所示：
private static final String NO_EXTENSION_MIME_TYPE = "application/octet-stream";private static final String UNKNOWN_EXTENSION_MIME_TYPE = "text/plain";
