1. 在Servlet/Filter等Servlet web环境中，只要获得javax.servlet.ServletContext类型，则可以通过 getRealPath("...") 获得路径。相对路径中最顶层目录可通过参数“"/"”获取。
request.getSession().getServletContext().getRealPath("/");

2. JSP自定义标签javax.servlet.jsp.tagext.TagSupport
((javax.servlet.ServletContext)pageContext).getRealPath("");

3. 普通Java Class对象文件中使用：
this.getClass().getResource("???");
如果Class文件在顶层目录（包）中，且“???”为空白字符串（“""”），及此方法在jar文件中执行则会返回null。在顶层目录（包）以下的各层目录（包）则会返回包含协议的URL。各层文件夹（包）之间使用“/”分隔。


项目位置：D:/BeyondTrack--reference/jBPMWebDesigner

javacode 位置：D:/BeyondTrack--reference/jBPMWebDesigner/build/web/classes/net/java/dev/beyondtrack/web/workflow/designer/japplet

文件位置：D:/BeyondTrack--reference/jBPMWebDesigner/src/java/net/java/dev/beyondtrack/web/workflow/designer/icon



/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package net.java.dev.beyondtrack.web.workflow.designer.japplet;

import javax.swing.ImageIcon;

/**
 *
 * @author pub32
 */
public class NewMain {

 public NewMain () {
  System.out.println(this.getClass().getResource(""));
  System.out.println(this.getClass().getResource("."));
  System.out.println(this.getClass().getResource(".."));
  System.out.println(this.getClass().getResource("/"));
  System.out.println(this.getClass().getResource("point.png"));
  System.out.println(this.getClass().getResource("/point.png"));
  System.out.println(this.getClass().getResource("./point.png"));
  System.out.println(this.getClass().getResource("../point.png"));
  System.out.println(this.getClass().getResource("icon/point.png"));
  System.out.println(this.getClass().getResource("/icon/point.png"));
  System.out.println(this.getClass().getResource("./icon/point.png"));
  System.out.println(this.getClass().getResource("../icon/point.png"));
 }

 public static void main(String[] args) {
  System.out.println("====== Test.class ======");
  NewMain test = new NewMain();
 }
}



====== Test.class ======
file:/D:/BeyondTrack--reference/jBPMWebDesigner/build/web/WEB-INF/classes/net/java/dev/beyondtrack/web/workflow/designer/japplet/
file:/D:/BeyondTrack--reference/jBPMWebDesigner/build/web/WEB-INF/classes/net/java/dev/beyondtrack/web/workflow/designer/japplet/
file:/D:/BeyondTrack--reference/jBPMWebDesigner/build/web/WEB-INF/classes/net/java/dev/beyondtrack/web/workflow/designer/
file:/D:/BeyondTrack--reference/jBPMWebDesigner/build/web/WEB-INF/classes/
null
null
null
null
null
null
null
file:/D:/BeyondTrack--reference/jBPMWebDesigner/build/web/WEB-INF/classes/net/java/dev/beyondtrack/web/workflow/designer/icon/point.png
BUILD SUCCESSFUL (total time: 0 seconds)