java 的Class中获得相对路径，绝对路径的方法

import java.io.File;      public class FileTest {       public static void main(String[] args) throws Exception {           System.out.println(Thread.currentThread().getContextClassLoader().getResource(""));              System.out.println(FileTest.class.getClassLoader().getResource(""));              System.out.println(ClassLoader.getSystemResource(""));           System.out.println(FileTest.class.getResource(""));           System.out.println(FileTest.class.getResource("/"));         //Class文件所在路径         System.out.println(new File("/").getAbsolutePath());           System.out.println(System.getProperty("user.dir"));       }   }