java获取文件名后缀

public class filename {

    public static void main(String[] args) {
        File file = new File("/Users/pankaj/book.txt");
        System.out.println("File extension is: " + getFileExtension(file));

        file = new File("/Users/pankaj/header.png");
        System.out.println("File extension is: " + getFileExtension(file));

        file = new File("/Users/pankaj/java.util.txt");
        System.out.println("File extension is: " + getFileExtension(file));

        file = new File("/Users/pankaj/snow");
        System.out.println("File extension is: " + getFileExtension(file));
    }

    private static String getFileExtension(File file) {
        String fileName = file.getName();
        if (fileName.lastIndexOf(".") != -1 && fileName.lastIndexOf(".") != 0)
            return fileName.substring(fileName.lastIndexOf(".") + 1);
        else return " ";
    }

}

　　

运行结果：