过滤器 - 基础篇

<?xmlversion="1.0"encoding="UTF-8"?><web-appxmlns: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>FilterDemo</display-name><welcome-file-list><welcome-file>index.jsp</welcome-file></welcome-file-list><!--字符集编码过滤器配置--><filter><filter-name>characterEncodingFilter</filter-name><filter-class>filter.CharacterEncodingFilter</filter-class><init-param><param-name>charset</param-name><param-value>UTF-8</param-value></init-param></filter><filter-mapping><filter-name>characterEncodingFilter</filter-name><url-pattern>/*</url-pattern></filter-mapping><!-- 用户登录安全控制过滤器配置 --><filter><filter-name>sessionFilter</filter-name><filter-class>filter.SessionFilter</filter-class></filter><filter-mapping><filter-name>sessionFilter</filter-name><url-pattern>/message.jsp</url-pattern></filter-mapping></web-app>

packagefilter;
importjava.io.IOException;
importjavax.servlet.Filter;
importjavax.servlet.FilterChain;
importjavax.servlet.FilterConfig;
importjavax.servlet.ServletException;
importjavax.servlet.ServletRequest;
importjavax.servlet.ServletResponse;
importjavax.servlet.http.HttpServletRequest;
importjavax.servlet.http.HttpServletResponse;
/*** 用户登录安全控制过滤器*/publicclassSessionFilterimplementsFilter {
@Overridepublicvoiddestroy() {
    }
@OverridepublicvoiddoFilter(ServletRequestrequest, ServletResponseresponse, FilterChainchain)
throwsIOException, ServletException {
HttpServletRequesthrequest= (HttpServletRequest) request;// 涉及到HTTP请求处理，转型处理HttpServletResponsehresponse= (HttpServletResponse) response;// 涉及到HTTP请求处理，转型处理StringloginUser= (String) hrequest.getSession().getAttribute("loginUser");// 判断用户是否完成了登录操作，session中是否存储用户名if (loginUser==null) {
hresponse.sendRedirect(hrequest.getContextPath() +"/index.jsp?flag=1");// 未登录，系统强制重定向至登录页面return;
        } else {
chain.doFilter(hrequest, hresponse);
return;
        }
    }
@Overridepublicvoidinit(FilterConfigconfig) throwsServletException {
    }
}

packagefilter;
/*** 字符集编码过滤器*/importjava.io.IOException;
importjavax.servlet.Filter;
importjavax.servlet.FilterChain;
importjavax.servlet.FilterConfig;
importjavax.servlet.ServletException;
importjavax.servlet.ServletRequest;
importjavax.servlet.ServletResponse;
publicclassCharacterEncodingFilterimplementsFilter {
privateFilterConfigconfig;
@Overridepublicvoiddestroy() {
    }
@OverridepublicvoiddoFilter(ServletRequestrequest, ServletResponseresponse, FilterChainchain)
throwsIOException, ServletException {
request.setCharacterEncoding(config.getInitParameter("charset")); // 根据过滤器配置字符集，设置请求字符集编码// System.out.println("characterEncodingFilter 请求预处理"); // 测试过滤器（链）工作流程使用chain.doFilter(request, response); // 通知web服务器已经完成，或请求下一个过滤器// System.out.println("characterEncodingFilter 响应后处理"); // 测试过滤器（链）工作流程使用    }
@Overridepublicvoidinit(FilterConfigconfig) throwsServletException {
this.config=config;
    }
publicFilterConfiggetConfig() {
returnconfig;
    }
publicvoidsetConfig(FilterConfigconfig) {
this.config=config;
    }
}

@OverridepublicvoiddoFilter(ServletRequestservletRequest, ServletResponseservletResponse, FilterChainfilterChain) throwsIOException, ServletException {
System.out.println("Filter 开始》》》》》》》》》》》》》》");
/*filterChain.doFilter(servletRequest, servletResponse);*/System.out.println("首次监听启动");
servletRequest.getRequestDispatcher("main.jsp").forward(servletRequest, servletResponse);
// 重定向省略...System.out.println("Filter 结束》》》》》》》》》》》》》》");
}

<filter><filter-name>SimpleFilter</filter-name><filter-class>SimpleFilter</filter-class></filter><filter-mapping><filter-name>SimpleFilter</filter-name><url-pattern>/index.jsp</url-pattern></filter-mapping><filter-mapping><filter-name>SimpleFilter</filter-name><url-pattern>/main.jsp</url-pattern></filter-mapping>

<!--过滤顺序：谁的写在上面，谁先被过滤--><filter><filter-name>FilterTest01</filter-name><filter-class>com.Higgin.web.filter.FilterTest01</filter-class></filter><filter-mapping><filter-name>FilterTest01</filter-name><url-pattern>/*</url-pattern> <!-- 过滤所有 --></filter-mapping><filter><filter-name>FilterTest02</filter-name><filter-class>com.Higgin.web.filter.FilterTest02</filter-class></filter><filter-mapping><filter-name>FilterTest02</filter-name><url-pattern>/*</url-pattern> <!-- 过滤所有 --></filter-mapping>