拦截器Filter（过滤器）

拦截器也叫过滤器，拦截器就是前端和servlet之间的一个东西，可以用拦截器进行编码统一和拦截没登陆就进页面的

实现Filter（Servlet包下的）

那三个方法是init、doFilter、destroy，它们是生命周期

init是初始化，doFilter是内容，destroy是销毁

拦截没登陆的

1.置web.xml方法

这里的配置替代的是java文件中的注解（java文件也要有只是可以不写注解），个人认为还是注解更方便

    <!-- 配置过滤器 -->
    <filter>
        <filter-name>LoginFilter</filter-name>
        <filter-class>com.hz.filter.LoginFilter</filter-class>
    </filter>

    <!-- 配置过滤器映射 -->
    <filter-mapping>
        <filter-name>LoginFilter</filter-name>
        <url-pattern>/servlet/*</url-pattern>  <!-- 只拦截 /secure 路径下的请求 -->
    </filter-mapping>

2.使用注解配置：

package com.hz.filter;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebFilter("/servlet/*")
public class LoginFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // Filter 初始化，可以不做任何事
        Filter.super.init(filterConfig);
    }

    @Override
    public void doFilter(ServletRequest servletRequest,
                         ServletResponse servletResponse,
                         FilterChain filterChain) throws IOException, ServletException {

        //转换类型，创建session对
        HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
        HttpServletResponse httpServletResponse = (HttpServletResponse) servletResponse;
        HttpSession session = httpServletRequest.getSession();


        if (session.getAttribute("smbmsProvider")==null){
//            如果没有登录，返回登录页
            httpServletResponse.sendRedirect("/login.jsp");

        }else {
//放行

            filterChain.doFilter(servletRequest,servletResponse);
        }

    }
    @Override
    public void destroy() {
        Filter.super.destroy();
    }
}

统一设置编码：

1、使用注解配置：

@WebFilter("/*")

package com.hz.filter;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebFilter("/*")
public class CharacterEncodingFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        Filter.super.init(filterConfig);
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
        HttpServletResponse httpServletResponse = (HttpServletResponse) servletResponse;

        // 设置请求的字符编码
        httpServletRequest.setCharacterEncoding("UTF-8");

        // 设置响应的字符编码
        httpServletResponse.setCharacterEncoding("UTF-8");
        httpServletResponse.setContentType("text/html;charset=UTF-8");

        // 继续执行过滤链
        filterChain.doFilter(httpServletRequest, httpServletResponse);
    }

    @Override
    public void destroy() {
        Filter.super.destroy();
    }
}

2.使用web.xml配置文件

    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.hz.filter.CharacterEncodingFilter</filter-class>
    </filter>

    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/*</url-pattern>  <!-- 拦截所有请求 -->
    </filter-mapping>