Eine kurze Einführung in den Servlet-Filter Filter (mit Beispielen)

public class UserNoFilter implements Filter { 
    
	private FilterConfig filterConfig; //获取参数配置

	public void init(FilterConfig fConfig) throws ServletException {
		this.filterConfig = fConfig;
	}
	
	/**
	 * 业务逻辑判断
	 */
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		
		String initUser = filterConfig.getInitParameter("userNo");
		String userNo = request.getParameter("userNo");//从提交请求获取用户账号
		
		if(!initUser.equals(userNo)){
			request.setAttribute("message", "用户名不正确");
			request.getRequestDispatcher("/index.jsp").forward(request, response);
			return;
		}
		
		chain.doFilter(request, response);
	} 
	
	public void destroy() {
		 
	} 

}

	<!-- 配置过滤器 -->
	<filter>
		<display-name>UserNoFilter</display-name>
		<filter-name>UserNoFilter</filter-name>
		<filter-class>com.demo.filter.UserNoFilter</filter-class>
		<init-param>
			<param-name>userNo</param-name>
			<param-value>admin</param-value>
		</init-param>
	</filter>
	<filter-mapping>
		<filter-name>UserNoFilter</filter-name>
		<url-pattern>/hello.jsp</url-pattern> 
	</filter-mapping>

request.setCharacterEncoding(encoding);
filterChain.doFilter(request, response);

String userId=(String) session.getAttribute("userId");
if (userId ==null){
}