JSP

1. JSP中项目名称的获取

方法1： <%= this.getServletContext().getContextPath() %>

方法2： 使用EL表达式 ${pageContext.request.contextPath}

2. 转发和重定向

转发： request.getRequestDispatcher("/index.jsp").forward(request, response);
重定向： response.sendRedirect("/jsp/index.jsp");

小点：
 1. 转发时空指针 - 原因 ：url 路径不正确
   RequestDispatcher rs=request.getRequestDispatcher(url);
   rs.forward(request, response);
 2. 转发的路径是相对路径

3. request的取值问题

获取request中的属性方法：
  1. ${pageContext.request.name} 
     例： 上下文路径 ${pageContext.request.contextPath}
  2. ${requestscope.name} 
    相当于 Java 的 request.getAttribute("name")

4. 注解式的过滤器，不需在web.xml中配置，tomcat版本 9 ，其他版本未测试

  参考 ：https://www.cnblogs.com/xiaojiayu/p/5946281.html

package com.cy.filter;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;

/**
 * Servlet Filter implementation class UserFilter
 */
@WebFilter(filterName = "userFilter",urlPatterns = "/*")
public class UserFilter implements Filter {

    public UserFilter() {
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see Filter#destroy()
	 */
	public void destroy() {
		// TODO Auto-generated method stub
	}

	/**
	 * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
	 */
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		// TODO Auto-generated method stub
		// place your code here

		// pass the request along the filter chain
		chain.doFilter(request, response);
	}

	/**
	 * @see Filter#init(FilterConfig)
	 */
	public void init(FilterConfig fConfig) throws ServletException {
		// TODO Auto-generated method stub
	}

}