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这篇教程不错：http://zjutsoft.iteye.com/blog/1084260
自己试验如下：
System.out.println("-----------------servlet-----------------");
System.out.println("realpath null:"+request.getRealPath(""));
System.out.println("realpath index.jsp:"+request.getRealPath("index.jsp"));
System.out.println("realpath ./:"+request.getRealPath("./"));
System.out.println("realpath ../:"+request.getRealPath("../"));
System.out.println("contextpath:"+request.getContextPath());
System.out.println("web项目的全路径:"+request.getSession().getServletContext().getRealPath("/"));
System.out.println("URI:"+request.getRequestURI());
System.out.println("URL:"+request.getRequestURL());
System.out.println("servletpath:"+request.getServletPath());
//System.out.println("页面在服务器的绝对路径:"+new java.io.File(application.getRealPath(request.getRequestURI())).getParent());
System.out.println("~~~~~~~~~~~~~~~页面~~~~~~~~~~~~~~~~~");
System.out.println("realpath null:"+request.getRealPath(""));
System.out.println("realpath index.jsp:"+request.getRealPath("index.jsp"));
System.out.println("realpath ./:"+request.getRealPath("./"));
System.out.println("realpath ../:"+request.getRealPath("../"));
System.out.println("contextpath:"+request.getContextPath());
System.out.println("web项目的全路径:"+request.getSession().getServletContext().getRealPath("/"));
System.out.println("URI:"+request.getRequestURI());
System.out.println("URL:"+request.getRequestURL());
System.out.println("servletpath:"+request.getServletPath());
System.out.println("页面在服务器的绝对路径:"+new java.io.File(application.getRealPath(request.getRequestURI())).getParent());
//结果
-----------------servlet-----------------
realpath null:D:\eclipse-jee-luna-SR1-win32\eclipse\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jyxt
realpath index.jsp:D:\eclipse-jee-luna-SR1-win32\eclipse\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jyxt\index.jsp
realpath ./:D:\eclipse-jee-luna-SR1-win32\eclipse\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jyxt\.
realpath ../:D:\eclipse-jee-luna-SR1-win32\eclipse\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jyxt\..
contextpath:/jyxt
web项目的全路径:D:\eclipse-jee-luna-SR1-win32\eclipse\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jyxtURI:/jyxt/hello
URL:http://localhost:8080/jyxt/hello
servletpath:/hello
~~~~~~~~~~~~~~~页面~~~~~~~~~~~~~~~~~
realpath null:D:\eclipse-jee-luna-SR1-win32\eclipse\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jyxt
realpath index.jsp:D:\eclipse-jee-luna-SR1-win32\eclipse\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jyxt\index.jsp
realpath ./:D:\eclipse-jee-luna-SR1-win32\eclipse\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jyxt\.
realpath ../:D:\eclipse-jee-luna-SR1-win32\eclipse\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jyxt\..
contextpath:/jyxt
web项目的全路径:D:\eclipse-jee-luna-SR1-win32\eclipse\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jyxtURI:/jyxt/WEB-INF/view/index.jsp
URL:http://localhost:8080/jyxt/WEB-INF/view/index.jsp
servletpath:/WEB-INF/view/index.jsp
页面在服务器的绝对路径:D:\eclipse-jee-luna-SR1-win32\eclipse\workspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\jyxt\jyxt\WEB-INF\view
在类中获取路径先不看，其他的只有10种方法。
两种应用场景：.jsp和servlet中。jsp中realPath被抛弃，不过返回值跟servlet中的一样，getRealPath("./ ../")返回值都不太对；页面在服务器的绝对路径 就不能用了。
getContextPath() 和 .getSession().getServletContext().getRealPath("/") 在.jsp和servlet中返回值都一样；URI,URL,servletpath都不一样。
//http
System.out.println("scheme:"+request.getScheme());
//localhost
System.out.println("name:"+request.getServerName());
//8080
System.out.println("port:"+request.getServerPort());
常用方法
在servlet中：getContextPath(), URI, URL, servletPath(), 在jsp中：getContextPath()
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原文地址：http://www.cnblogs.com/wang-jing/p/4620157.html
