新版Servlet3.0的注解开发自定义Filter——拦截器和过滤器使用

使用Servlet3.0的注解进行配置步骤

启动类里面增加 @ServletComponentScan，进行扫描
新建一个Filter类，implements Filter，并实现对应的接口
@WebFilter 标记一个类为filter，被spring进行扫描
urlPatterns：拦截规则，支持正则
控制chain.doFilter的方法的调用，来实现是否通过放行
不放行，web应用resp.sendRedirect("/index.html") 或者 返回json字符串

package com.example.demo.filter;


import com.example.demo.tools.JsonData;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.apache.commons.lang.StringUtils;

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

//TODO  暂时不需要拦截器  Filter   所以为测试  Controller
@WebFilter(urlPatterns = "/Controller/*",filterName = "测试")
public class KnowledgeFilter implements Filter {
    private static final ObjectMapper objectMapper = new ObjectMapper();
    /**
     * 容器加载的时候
     * @param filterConfig
     * @throws ServletException
     */
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

        HttpServletRequest req = (HttpServletRequest) request;
        HttpServletResponse resp = (HttpServletResponse) response;

        String token =  req.getHeader("token");
        if (StringUtils.isEmpty(token)){
            token = req.getParameter("token");
        }
        if (StringUtils.isEmpty(token)){
            JsonData jsonData = JsonData.buildError("登录失败，token无效！",-2);
            String jsonStr = objectMapper.writeValueAsString(jsonData);
            renderJson(resp,jsonStr);
        }else {
            chain.doFilter(request,response);
            //TODO  判断是否合法    比如说判断此token是否在user表里面，如果是。。。。

        }

    }

    private void renderJson(HttpServletResponse response,String json){
        response.setCharacterEncoding("GBK");
        response.setContentType("application/json");

        try (PrintWriter writer = response.getWriter()){
            writer.println(json);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * 容器销毁的时候
     */
    @Override
    public void destroy() {

    }
}

拦截器不生效常见问题：

- 是否有加@Configuration
- 拦截路径是否有问题 ** 和 *
- 拦截器最后路径一定要 /** 如果是目录的话则是 /*/

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

/**
 * 拦截器配置类
 */
@Configuration
public class CustomWebMvcConfigurer implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {

        registry.addInterceptor(getLoginIntercepter()).addPathPatterns("/Controller1/*");
        WebMvcConfigurer.super.addInterceptors(registry);
    }
    public LoginIntercepter getLoginIntercepter(){
        return new LoginIntercepter();
    }
}

package com.example.demo.intercepter;

import com.example.demo.tools.JsonData;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.apache.commons.lang.StringUtils;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.PrintWriter;

public class LoginIntercepter implements HandlerInterceptor {
    private static final ObjectMapper objectMapper = new ObjectMapper();
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {

        HttpServletRequest req = (HttpServletRequest) request;
        HttpServletResponse resp = (HttpServletResponse) response;

        String token =  req.getHeader("token");
        if (StringUtils.isEmpty(token)){
            token = req.getParameter("token");
        }
        if (StringUtils.isEmpty(token)){
            JsonData jsonData = JsonData.buildError("登录失败，token无效！",-2);
            String jsonStr = objectMapper.writeValueAsString(jsonData);
            renderJson(resp,jsonStr);
            return false;
        }else {
            return true;
            //TODO  判断是否合法    比如说判断此token是否在user表里面，如果是。。。。

        }
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {

    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {

    }

    private void renderJson(HttpServletResponse response,String json){
        response.setCharacterEncoding("GBK");
        response.setContentType("application/json");

        try (PrintWriter writer = response.getWriter()){
            writer.println(json);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

和Filter过滤器的区别

Filter和Interceptor二者都是AOP编程思想的体现，功能基本都可以实现

拦截器功能更强大些，Filter能做的事情它都能做

Filter在只在Servlet前后起作用，而Interceptor够深入到方法前后、异常抛出前后等

filter依赖于Servlet容器即web应用中，而Interceptor不依赖于Servlet容器所以可以运行在多种环境。

在接口调用的生命周期里，Interceptor可以被多次调用，而Filter只能在容器初始化时调用一次。

Filter和Interceptor的执行顺序

过滤前->拦截前->action执行->拦截后->过滤后

补充知识点

如何配置不拦截某些路径？
registry.addInterceptor(new LoginIntercepter()).addPathPatterns("/api/v1/pri/**")
//配置不拦截某些路径，比如静态资源
.excludePathPatterns("/**/*.html","/**/*.js");

/**
 * 拦截器配置类
 */
@Configuration
public class CustomWebMvcConfigurer implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {

        registry.addInterceptor(getLoginIntercepter()).addPathPatterns("/Controller1/*")
        .excludePathPatterns("/Controller/register");
        WebMvcConfigurer.super.addInterceptors(registry);
    }
    public LoginIntercepter getLoginIntercepter(){
        return new LoginIntercepter();
    }
}