Filter过滤器

今天刚刚学到Filter过滤器，说下今天所学的，什么是过滤器

JavaWeb中的过滤器的概念： 对请求和响应进行拦截或者增强的对象，就是过滤器

由于Tomcat服务器的不断更新换代，8之后解决了get里的编码问题，不过post里还是要加一句，这样的：request.setCharacterEncoding("UTF-8");

protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        doGet(request, response);
    } 

我说的是如果，如果你的javaweb里只用到一个或两个不相干的过滤器，可以直接用注解代替配置文件web.xml，如果涉及到彼此的那两个过滤器相互有影响了，比如过滤器AuthorityFilter是过滤用户身份的，是管理员或不是管理员，

public class AuthorityFilter implements Filter {

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		System.out.println("---具体权限（xxx管理员）---");
		HttpServletRequest httpRequest = (HttpServletRequest)request;
		HttpSession session = httpRequest.getSession();
		User user = (User)session.getAttribute("user");
		if(user.getFlag() == 1) {	//仓库管理员
			chain.doFilter(request, response);
		} else {	//其他人员
			System.out.println("权限不足...");
			httpRequest.getRequestDispatcher("/index.jsp")
				       .forward(httpRequest, response);
		}
	}

PrivilegeFilter是过滤是否已登录或是未登录又怎么办，也就是我们最开始时候肯定是未登录状态，那么session里一定是空的，

public class PrivilegeFilter implements Filter {

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		System.out.println("-------登录权限判断-------");
		HttpServletRequest httpRequest = (HttpServletRequest)request;
		HttpSession session = httpRequest.getSession();
		if(session.getAttribute("user") == null) {	//未登录
			httpRequest.setAttribute("info", "请先登录.");
			httpRequest.getRequestDispatcher("/login.jsp")
					   .forward(httpRequest, response); 
		} else {	//已登录
			chain.doFilter(request, response);
		}
	}

那么sessionli对象user里也是空的,过滤器AuthorityFilter会影响用户的首次登陆，所以为了避免这样的情况，我们不能再用注解配置了，应该在web.xml里给过滤器配置，并且要注意顺序，因为配置文件xml文件的解析是从上到下的顺序，所以要先放什么，后放什么，例如：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>web1029</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <context-param>
    <param-name>encode</param-name>
    <param-value>UTF-8</param-value>
  </context-param>
  <filter>
  	<filter-name>PrivilegeFilter</filter-name>
  	<filter-class>com.igeek.web.filter.PrivilegeFilter</filter-class>
  </filter>
   <filter>
  	<filter-name>AuthorityFilter</filter-name>
  	<filter-class>com.igeek.web.filter.AuthorityFilter</filter-class>
  </filter>
  
  <filter-mapping>
  	<filter-name>PrivilegeFilter</filter-name>
  	<url-pattern>/users/*</url-pattern>
  </filter-mapping>
   <filter-mapping>
  	<filter-name>AuthorityFilter</filter-name>
  	<url-pattern>/users/storage/*</url-pattern>
  </filter-mapping>
</web-app>

 注意先后顺序，还有最后要说的是，servlet里不只能用一个注解配置，可以多个