【12 Filter 学习笔记】

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 {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("demo1 执行了");
        resp.getWriter().write("demo1执行了");
    }

    @Override
    protected 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 {
    @Override
    public 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 {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("filter 初始化成功");
    }

    @Override
    public 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);
    }

    @Override
    public 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 {
    @Override
    public 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value
        String filter = filterConfig.getInitParameter("filter");
        System.out.println(filter);
    }

    @Override
    public 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);
    }

    @Override
    public 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>