Filter学习
Filter功能
- 拦截jsp、静态图片文件、静态html资源文件
- 实现URL级别的权限访问控制
- 过滤敏感词汇
- 压缩相应信息
Filter的工作原理
看源码可以看出来，Filter接口中有3个方法：init、doFilter、destory
init方法，初始化Filter，Filter在服务器启动阶段被实例化。并且调用init方法，init方法只执行一次，因为Filter只被实例化一次。
destory方法也好理解，就是销毁Filter，释放内存，在运行结束时调用此方法当。长时间没有用户访问，或者项目重新部署，或者服务器重新启动的时候，会销毁所有的Filter对象，销毁之前会先调用Filter对象的destroy方法，完成销毁前的准备工作。也是只执行一次。
doFilter方法提供给开发者重写过滤逻辑。
多个Filter的实现
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public class AFilter implements Filter { @Override public void init(FilterConfig filterConfig) throws ServletException { System.out.println("输出filter2的init方法"); } @Override public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { HttpServletResponse response = (HttpServletResponse) servletResponse; HttpServletRequest request = (HttpServletRequest) servletRequest; System.out.println("输出filter2的doFilter方法之前"); filterChain.doFilter(request, response); System.out.println("输出filter2的doFilter方法之后"); } @Override public void destroy() { System.out.println("输出filter2的destroy方法"); }} |
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public class BFilter implements Filter { @Override public void init(FilterConfig filterConfig) throws ServletException { System.out.println("输出filter1的init方法"); } @Override public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { HttpServletResponse response = (HttpServletResponse) servletResponse; HttpServletRequest request = (HttpServletRequest) servletRequest; System.out.println("输出filter1的doFilter方法之前"); filterChain.doFilter(request, response); System.out.println("输出filter1的doFilter方法之后"); } @Override public void destroy() { System.out.println("输出filter1的destroy方法"); }} |
配置Filter的过滤顺序，通过setOrder方法执行FilterChain的顺序，数字越小，优先级越高。
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@Configurationpublic class WebConfig { @Bean public FilterRegistrationBean filter1() { FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(); AFilter aFilter = new AFilter(); filterRegistrationBean.setFilter(aFilter); filterRegistrationBean.setOrder(1); return filterRegistrationBean; } @Bean public FilterRegistrationBean filter2() { FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(); BFilter bFilter = new BFilter(); filterRegistrationBean.setFilter(bFilter); filterRegistrationBean.setOrder(2); return filterRegistrationBean; }} |
Filter的执行逻辑
总结
本篇文章就到这里了，希望能给你带来帮助，也希望您能够多多关注服务器之家的更多内容！
原文链接：https://blog.csdn.net/u011133007/article/details/119880215
