1. Filter 过滤器

2. Filter介绍

3. FilterChain

3. Filter 过滤器的使用

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/demo1")
public class ServletDemo01  extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System.out.println("demo1 执行了");resp.getWriter().write("demo1执行了");}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {super.doGet(req, resp);}
}import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;
/*** Filter基本使用*  @WebFilter("/*") 代表所有都会拦截*/
@WebFilter("/*")
public class FilterDemo01 implements Filter {@Overridepublic void doFilter(ServletRequest request, ServletResponse resp, FilterChain filterChain) throws IOException, ServletException {System.out.println("filter01 执行了");//处理乱码resp.setContentType("text/html;charset=UTF-8");//放行filterChain.doFilter(request,resp);}
}

4. 过滤器使用细节

在web.xml中配置的话 是从上到下在Filterchain中执行，使用注解可以一一对应

5. Filter的声明周期

服务器加载时就创建了,当应用卸载时和服务器停止时执行销毁

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;/*** Filter 生命周期*/
@WebFilter("/*")
public class FilterDemo03 implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {System.out.println("filter 初始化成功");}@Overridepublic void doFilter(ServletRequest request, ServletResponse resp, FilterChain filterChain) throws IOException, ServletException {System.out.println("filter03 执行了");//处理乱码resp.setContentType("text/html;charset=UTF-8");//放行filterChain.doFilter(request,resp);}@Overridepublic void destroy() {System.out.println("filter 销毁了");}
}

6. FilterConfig

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;/*** Filter 过滤器配置对象的使用*/
//@WebFilter("/*")
public class FilterDemo04 implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {System.out.println("filter 初始化成功");//获取过滤器名字String filterName = filterConfig.getFilterName();System.out.println(filterName);// 根据名称获取valueString filter = filterConfig.getInitParameter("filter");System.out.println(filter);}@Overridepublic void doFilter(ServletRequest request, ServletResponse resp, FilterChain filterChain) throws IOException, ServletException {System.out.println("filter03 执行了");//处理乱码resp.setContentType("text/html;charset=UTF-8");//放行filterChain.doFilter(request,resp);}@Overridepublic void destroy() {System.out.println("filter 销毁了");}
}

7. 过滤器五种拦截行为

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"version="4.0"><filter><filter-name>filter05</filter-name><filter-class>com.example.Filter.FilterDemo05</filter-class><async-supported>true</async-supported>
<!--        <init-param>-->
<!--            <param-name>filter</param-name>-->
<!--            <param-value>filter param value</param-value>-->
<!--        </init-param>-->
<!--        配置开启异步支持，当dispatcher配置ASYN时，需要配置此行--></filter><filter-mapping><filter-name>filter05</filter-name><url-pattern>/error.jsp</url-pattern>
<!--        过滤请求：默认值--><dispatcher>REQUEST</dispatcher>
<!--        过滤全局错误页面，当由服务器调用全局错误页面时，过滤器工作-->
<!--        不配置全局配置 不会执行 filter05过滤器调用--><dispatcher>ERROR</dispatcher>
<!--        过滤请求转发 当请求转发时 过滤器工作-->
<!--        不配置全局配置 不会执行过滤器--><dispatcher>FORWARD</dispatcher>
<!--        不配置全局 不会执行过滤器-->
<!--        过滤请求包含 当请求包含时，过滤器工作。它只能过滤动态包含，jsp的include指令是静态包含，过滤器不会--><dispatcher>INCLUDE</dispatcher>
<!--        过滤异步类型，它要求我们filter标签中配置开启异步支持--><dispatcher>ASYNC</dispatcher></filter-mapping><!--    配置全局错误页面--><error-page><exception-type>java.lang.Exception</exception-type><location>/error.jsp</location></error-page><error-page><error-code>404</error-code><location>/error.jsp</location></error-page>
</web-app>