JavaWeb中的组件Filter过滤器解析

<!-- 配置Filter要拦截的目标资源 -->
<filter-mapping>
    <!-- 指定这个mapping对应的Filter名称 -->
    <filter-name>FilterDemo01</filter-name>

    <!-- 通过请求地址模式来设置要拦截的资源 -->
    <url-pattern>/servletDemo01</url-pattern>
</filter-mapping>

<filter-mapping>
    <filter-name>Target02Filter</filter-name>

    <!-- 模糊匹配：前杠后星 -->
    <!--
        /user/demo01
        /user/demo02
        /user/demo03
		/demo04
    -->
    <url-pattern>/user/*</url-pattern>
</filter-mapping>

<filter>
    <filter-name>Target04Filter</filter-name>
    <filter-class>com.carson.filter.Target04Filter</filter-class>
</filter>
<filter-mapping>
    <filter-name>Target04Filter</filter-name>
    <url-pattern>*.png</url-pattern>
</filter-mapping>

<filter-mapping>
    <filter-name>Target05Filter</filter-name>
    <!-- 根据Servlet名称匹配 -->
    <servlet-name>Target01Servlet</servlet-name>
</filter-mapping>

public class ServletDemo01 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("ServletDemo01接收到了请求...");
    }
}

<servlet>
    <servlet-name>servletDemo01</servlet-name>
    <servlet-class>com.carson.ServletDemo01</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>servletDemo01</servlet-name>
    <url-pattern>/ServletDemo01</url-pattern>
</servlet-mapping>

<!--创建多个Filter拦截Servlet：-->
<filter-mapping>
    <filter-name>TargetChain03Filter</filter-name>
    <url-pattern>/ServletDemo01</url-pattern>
</filter-mapping>
<filter-mapping>
    <filter-name>TargetChain02Filter</filter-name>
    <url-pattern>/ServletDemo01</url-pattern>
</filter-mapping>
<filter-mapping>
    <filter-name>TargetChain01Filter</filter-name>
    <url-pattern>/ServletDemo01</url-pattern>
</filter-mapping>

<dependencies>
        <!--JSP依赖-->
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.3.3</version>
        </dependency>
        <!--Servlet依赖-->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
        </dependency>
        <!--JSTL表达式的依赖-->
        <dependency>
            <groupId>javax.servlet.jsp.jstl</groupId>
            <artifactId>jstl-api</artifactId>
            <version>1.2</version>
        </dependency>
        <!--standard标签库-->
        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
            <version>1.1.2</version>
        </dependency>
        <!--链接数据库-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.19</version>
        </dependency>
    </dependencies>

package com.carson.filter;

import javax.servlet.*;
import java.io.IOException;

public class CharacterEncodingFilter implements Filter {
    //初始化:当web服务器启动时,就自动初始化了,随时等待过滤对象的出现
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("CharacterEncodingFilter已经初始化");

    }

    /*
    1:过滤器中的所有代码,在过滤特定请求的时候都会执行
    2:必须写chain.foFilter()方法让过滤器继续前进
    */

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
		//转换request和response为HttpServlet类型
		HttpServletRequest request = (HttpServletRequest) request;
		HttpServletResponse response = (HttpServletResponse) response;
		解决请求参数的中文乱码问题
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=UTF-8");

        System.out.println("CharacterEncodingFilter执行前");
        //让我们的请求继续走,如果不写,程序到这里就会被拦截停止
        //即这句代码表示放行
        filterChain.doFilter(servletRequest,servletResponse);
        System.out.println("CharacterEncodingFilter执行后");

    }
    //销毁:当web服务器关闭的时候,会进行销毁
    public void destroy() {
        System.out.println("CharacterEncodingFilter已经销毁");

    }
}

<!--注册filter过滤器,类似注册servlet-->
    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.carson.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <!--filter的路径配置:只要是/servlet的任何请求,都会经过这个过滤器-->
        <!--即设置过滤器的过滤请求路径-->
        <url-pattern>/servlet/*</url-pattern>
    </filter-mapping>