2019独角兽企业重金招聘Python工程师标准>>> 
如果带WebRoot，那么js、css、img都应该放到WebRoot目录下，否则访问会有问题。千万不要放在WEB-INF下，因为WEB-INF下的内容只有服务器转发可以访问到，出于安全考虑。
如果不带有WebRoot目录，那么可以放在WEB-INF外面（建立的文件夹中）。
一、JSP、Servlet中的相对路径
a) 在JSP中
“/”代表站点（服务器）根目录http://127.0.0.1/
b) 在Servlet中
“/”代表Web应用的根目录http://127.0.0.1/JSP_Servlet_Path/
request.getRequestDispatcher("/a/a.jsp").forward(request, response);
相对路径/a/a.jsp中/相对于web应用的根目录，所以相当于请求跳转到绝对路径
http://127.0.0.1/JSP_Servlet_Path/a/a.jsp
response.sendRedirect("/JSP_Servlet_Path/b/b.jsp");
因为重定向中的方法是传递给浏览器，用于重新发送请求的，而在浏览器端“/”代表，相对于站点根目录http://127.0.0.1/，所以这里必须要加上/JSP_Servlet_Path，这样浏览器重新请求的地址为：http://127.0.0.1/JSP_Servlet_Path/b/b.jsp
package com.jsp_servlet_path.rqq;import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class JSP_Servlet extends HttpServlet {@Overridepublic voiddoGet(HttpServletRequest request, HttpServletResponse response)throwsServletException, IOException {doPost(request,response);}@Overridepublic voiddoPost(HttpServletRequest request, HttpServletResponse response)throwsServletException, IOException {System.out.println(request.getContextPath());//请求转发，在服务器端，"/"代表（相对于）web应用http://localhost:8000/JSP_Servlet_Path///所以请求转发的绝对路径为http://localhost:8000/JSP_Servlet_Path/a/a.jsp// request.getRequestDispatcher("/a/a.jsp").forward(request,response);//请求重定向，将方法中的地址参数传递给浏览器，让浏览器重新发送请求，//"/"代表（相对于）服务器站点http://localhost:8000///所以相当于浏览器重新请求了绝对路径http://localhost:8000/JSP_Servlet_Path/b/b.jspresponse.sendRedirect("/JSP_Servlet_Path/b/b.jsp");//response.sendRedirect(request.getContextPath()+ "/b/b.jsp");}
}二、JSP中加入basePath
<%String path = request.getContextPath();String basePath= request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<head>
<base href="<%=basePath%>">注：相当于所有的href相对路径前面都加入了：
http://localhost:8000/JSP_Servlet_Path/
三、JSP与Servlet相互访问
<?xmlversion="1.0"encoding="UTF-8"?>
<web-appversion="2.5"xmlns="http://java.sun.com/xml/ns/javaee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://java.sun.com/xml/ns/javaeehttp://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"><servlet><servlet-name>JSP_Servlet</servlet-name><servlet-class>com.jsp_servlet_path.rqq.JSP_Servlet</servlet-class></servlet><servlet><servlet-name>CopyOfJSP_Servlet</servlet-name><servlet-class>com.jsp_servlet_path.rqq.CopyOfJSP_Servlet</servlet-class></servlet><servlet-mapping><servlet-name>JSP_Servlet</servlet-name><url-pattern>/servlet/JSP_Servlet</url-pattern></servlet-mapping><servlet-mapping><servlet-name>CopyOfJSP_Servlet</servlet-name><url-pattern>/servlet/CopyOfJSP_Servlet</url-pattern></servlet-mapping><welcome-file-list><welcome-file>index.jsp</welcome-file></welcome-file-list>
</web-app><%@ page language="java"import="java.util.*"pageEncoding="GBK"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPEHTMLPUBLIC "-//W3C//DTDHTML 4.01 Transitional//EN">
<html><head><basehref="<%=basePath%>"><title>My JSP 'index.jsp' starting page</title><metahttp-equiv="pragma"content="no-cache"><metahttp-equiv="cache-control"content="no-cache"><metahttp-equiv="expires"content="0"> <metahttp-equiv="keywords"content="keyword1,keyword2,keyword3"><metahttp-equiv="description"content="This is my page"><!--<linkrel="stylesheet" type="text/css"href="styles.css">--></head><bodybackground="/JSP_Servlet_Path/img/main1.jpg">This is index.jsp page. <br><%--href中隐含了basePath，因为<basehref="<%=basePath%>">--%><ahref="a/a.jsp">a.jsp(a/a.jsp)</a><br/><ahref="/JSP_Servlet_Path/a/a.jsp">a.jsp(/JSP_Servlet_Path/a/a.jsp)</a><br/><ahref="a/c/c.jsp">c.jsp(a/c/c.jsp)</a><br/><ahref="a/c/e/e.jsp">e.jsp(a/c/e/e.jsp)</a><br/><imgsrc="/JSP_Servlet_Path/img/2012317253390833.jpg"><br/><imgsrc="a/main1.jpg"><br/><ahref="servlet/JSP_Servlet?i=0">JSP_Servlet(servlet/JSP_Servlet)</a>
<a href="/JSP_Servlet_Path/servlet/JSP_Servlet?i=0">
JSP_Servlet(/JSP_Servlet_Path/servlet/JSP_Servlet)</a><br/><ahref="servlet/JSP_Servlet?i=100">请求JSP_Servlet，并转发给CopyOfJSP_Servlet</a></body>
</html>package com.jsp_servlet_path.rqq;import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class JSP_Servlet extends HttpServlet {@Overridepublic voiddoGet(HttpServletRequest request, HttpServletResponse response)throwsServletException, IOException {doPost(request,response);}@Overridepublic voiddoPost(HttpServletRequest request, HttpServletResponse response)throwsServletException, IOException {System.out.println(request.getContextPath());//请求转发，在服务器端，"/"代表（相对于）web应用http://localhost:8000/JSP_Servlet_Path///所以请求转发的绝对路径为http://localhost:8000/JSP_Servlet_Path/a/a.jsp// request.getRequestDispatcher("/a/a.jsp").forward(request,response);//请求重定向，将方法中的地址参数传递给浏览器，让浏览器重新发送请求，//"/"代表（相对于）服务器站点http://localhost:8000///所以相当于浏览器重新请求了绝对路径http://localhost:8000/JSP_Servlet_Path/b/b.jspresponse.sendRedirect("/JSP_Servlet_Path/b/b.jsp");//response.sendRedirect(request.getContextPath()+ "/b/b.jsp");Stringstr_i = request.getParameter("i");int i =new Integer(str_i);switch(i) {case 0:request.getRequestDispatcher("/index.jsp").forward(request,response);System.out.println("index.jsp");break;case 1:request.getRequestDispatcher("/a/a.jsp").forward(request, response);System.out.println("a.jsp");break;case 2:request.getRequestDispatcher("/b/b.jsp").forward(request,response);System.out.println("b.jsp");break;case 3:request.getRequestDispatcher("/a/c/c.jsp").forward(request,response);System.out.println("c.jsp");break;case 100:request.getRequestDispatcher("/servlet/CopyOfJSP_Servlet").forward(request,response);System.out.println("forward to CopyOfJSP_Servlet");break;default:System.out.println("default");return;}}
}
