Tomcat与web开发技术详解读书笔记（二）过滤器

1.简介

• 过滤器能够在Servlet、JSP或HTML等web组件被调用之前检查ServletRequest对象，修改请求头和请求正文的内容或者对请求进行预处理操作
• 能够在Servlet、JSP或HTML等web组件被调用之后检查ServletReponse对象，修改响应头和响应正文。
• 利用包装类ServletRequestWrapper和ServletResponseWrapper来修改ServletRequest对象和ServletResponse对象。

2.如何创建过滤器？

必须实现javax.servlet.Filter接口。

• init(FilterConfig config)：过滤器初始化方法。Web应用启动时，Servlet容器首先创建FilterConfig对象（包含过滤器配置信息），然后创建Filter对象，接着调用Filter对象的init(FilterConfig config)方法，读取web.xml中的配置参数。

•  public class LoginFilter implements Filter{
      private FilterConfig config;
      
      private String username;
  
      @Override
      public void destroy() {
          this.config = null;
      }
  
      @Override
      public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException,
          ServletException {
          //HttpServletRequest httpRequest = (HttpServletRequest)request;
          HttpServletResponse httpResponse = (HttpServletResponse)response;
          System.out.println("登录过滤器验证");
          if(StringUtils.equalsIgnoreCase(username, "flyer")){
              System.out.println("验证通过");
              chain.doFilter(request, response);
          }else {
              System.out.println("验证被拦截");
              httpResponse.sendRedirect("login.jsp");
          }
      }
  
      @Override
      public void init(FilterConfig config) throws ServletException {
          this.config = config;
          username = config.getInitParameter("username");
      }
  
  }

  ??web.xml中添加过滤器配置

  ?

  ?

  Xml代码?

  1. <filter>??
  2. ????????<filter-name>loginFilter</filter-name>??
  3. ????????<filter-class>com.flyer.filter.LoginFilter</filter-class>??
  4. ????????<init-param>??
  5. ????????????<param-name>username</param-name>??
  6. ????????????<param-value>flyer</param-value>??
  7. ????????</init-param>??
  8. ????</filter>??
  9. ????<filter-mapping>??
  10. ????????<filter-name>loginFilter</filter-name>??
  11. ????????<url-pattern>??
  12. ????????????/*??
  13. ????????</url-pattern>??
  14. ????</filter-mapping>??
  ?web开发中常用的字符集编码过滤器

  ?

  ?

  Xml代码?

  1. <filter>??
  2. ????????<filter-name>encodingFilter</filter-name>??
  3. ????????<filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>??
  4. ????????<init-param>??
  5. ????????????<param-name>encoding</param-name>??
  6. ????????????<param-value>??
  7. ????????????????UTF-8??
  8. ????????????</param-value>??
  9. ????????</init-param>??
  10. ????</filter>??
  11. ????<!--?过滤器能为所有的url过滤?-->??
  12. ????<filter-mapping>??
  13. ????????<filter-name>encodingFilter</filter-name>??
  14. ????????<url-pattern>??
  15. ????????????/*??
  16. ????????</url-pattern>??
  17. ????</filter-mapping>??
  ?补充：Servlet监听器 ??类似与Swing界面应用开发，Servlet也可以创建监听器，以对Servlet容器，或Servlet中以象的事件做出反应。Servlet监听器主要有以下几种： ServletRequestListener ,ServletRequestAttributeListener， HttpSessionActivationListener ,HttpSessionBindingListener , HttpSessionAttributeListener,HttpSessionListener, ServletContextListener等等。 ??这些监听器主要用来监听session,request,application这三个对象里存取数据的变化。?

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