SpringBoot中过滤器、监听器、拦截器

目录

1.使用Servlet3.0的注解过滤器

  • 启动类添加@ServletComponentScan进行扫描

  • 新建一个Filter类，implements Filter，并实现对应的接口

    package com.gen.filter;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.gen.mo.User;
import com.gen.service.impl.UserServiceImpl;
import com.gen.util.JsonData;
import org.springframework.util.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;

/**
 * 登录过滤器
 * @WebFilter：标记一个类为filter，被Spring进行扫描 urlPatterns：拦截规则，支持正则
 */
@WebFilter(urlPatterns = "/api/v1/pri/*", filterName = "loginFilter")
public class LoginFilter implements Filter {

    private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();

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

        // 获取token
        String token = request.getHeader("token");
        if (!StringUtils.hasLength(token)) {
            token = request.getParameter("token");
        }
        if (StringUtils.hasLength(token)) {
            // 判断token是否合法
            User user = UserServiceImpl.sessionMap.get(token);
            if (user != null) {
                // token合法，放行
                filterChain.doFilter(request, response);
            } else {
                // token失效
                JsonData jsonData = JsonData.buildError(-2, "token失效");
                String jsonStr = OBJECT_MAPPER.writeValueAsString(jsonData);
                renderJson(response, jsonStr);
            }
        } else {
            // 未登录
            JsonData jsonData = JsonData.buildError(-3, "未登录");
            String jsonStr = OBJECT_MAPPER.writeValueAsString(jsonData);
            renderJson(response, jsonStr);
        }
    }

    /**
     * 工具类：返回json字符串
     */
    private void renderJson(HttpServletResponse response, String json) {
        response.setCharacterEncoding("utf-8");
        response.setContentType("application/json");

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

}

2.使用Servlet3.0的注解原生Servlet

package com.gen.servlet;

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;
import java.io.PrintWriter;

@WebServlet(name = "userServlet", urlPatterns = "/api/v1/test/servlet")
public class UserServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        PrintWriter writer = resp.getWriter();
        writer.print("this is my servlet");
        writer.flush();
        writer.close();
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

3.使用Servlet3.0的注解监听器

  • 什么是监听器

    监听器是一个实现了特定接口的普通Java类，用于监听其他对象的创建和销毁，监听其他对象的方法执行和属性改变

  • 监听器分类

    • ServletContextListener 应用启动监听
    • HttpSessionListener 会话监听
    • ServletRequestListener 请求监听
    package com.gen.listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

/**
 * 应用上下文监听
 */
@WebListener
public class ApplicationListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.out.println("contextInitialized===========");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        System.out.println("contextDestroyed===========");
    }
}

4.拦截器

  • SpringBoot2.x新版本配置拦截器 implements WebMvcConfigurer，代码如下：

    package com.gen.interceptor;

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(new LoginInterceptor()).addPathPatterns("/api/v1/pri/**");
    }
}

  • 自定义拦截器HandlerInterceptor

    • preHandle：调用Controller某个方法之前

    • postHandle：Controller之后调用，视图渲染之前，如果控制器Controller出现了异常，则不会执行此方法

    • afterCompletion：不管有没有异常，这个方法都会被调用，用于资源清理

    • 登录拦截器代码示例

      package com.gen.interceptor;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.gen.mo.User;
import com.gen.service.impl.UserServiceImpl;
import com.gen.util.JsonData;
import org.springframework.util.StringUtils;
import org.springframework.web.servlet.HandlerInterceptor;

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

/**
 * 登录拦截器
 */
public class LoginInterceptor implements HandlerInterceptor {
    private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        // 获取token
        String token = request.getHeader("token");
        if (!StringUtils.hasLength(token)) {
            token = request.getParameter("token");
        }
        if (StringUtils.hasLength(token)) {
            // 判断token是否合法
            User user = UserServiceImpl.sessionMap.get(token);
            if (user != null) {
                // token合法，放行
                return true;
            } else {
                // token失效
                JsonData jsonData = JsonData.buildError(-2, "token失效");
                String jsonStr = OBJECT_MAPPER.writeValueAsString(jsonData);
                renderJson(response, jsonStr);
                return false;
            }
        } else {
            // 未登录
            JsonData jsonData = JsonData.buildError(-3, "未登录");
            String jsonStr = OBJECT_MAPPER.writeValueAsString(jsonData);
            renderJson(response, jsonStr);
            return false;
        }
    }

    /**
     * 工具类：返回json字符串
     */
    private void renderJson(HttpServletResponse response, String json) {
        response.setCharacterEncoding("utf-8");
        response.setContentType("application/json");

        try (PrintWriter writer = response.getWriter()) {
            writer.print(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，Filter能做的事情它都能做
    • Filter只在Servlet前后起作用，而Interceptor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
posted @ 2021-03-04 17:23  Gen2021  阅读(183)  评论(0)    收藏  举报