SpringBoot Interceptor

Interceptor 介紹

攔截器 (Interceptor) 同 Filter 過濾器一樣，它們都是面向切面編程——AOP 的具體實現。

可以使用 Interceptor 來執行某些任務，例如在 Controller 處理請求之前編寫日誌，添加或更新配置等。

在 Spring 中，當請求發送到 Controller 時，在被 Controller 處理之前，必須經過 Interceptors。

過濾器和攔截器的區別

• 過濾器（Filter）：當有一堆東西的時候，只希望選擇符合你要求的某一些東西。定義這些要求的工具，就是過濾器。
• 攔截器（Interceptor）：在一個流程正在進行的時候，希望干預它的進展，甚至終止它進行，這是攔截器做的事情。

自定義 Interceptor

自定義 Interceptor 需要實現 org.springframework.web.servlet.HandlerInterceptor 接口或繼承 org.springframework.web.servlet.handler.HandlerInterceptorAdapter 類，並且需要重寫下面3個方法：

public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
    
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)

public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)

注意： preHandle 方法返回 **true **或 false。如果返回 true，則意味着請求將繼續到達 Controller 被處理。

每個請求可能會通過多個攔截器。

示例

LogInterceptor 用於過濾所有請求：

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

public class LogInterceptor extends HandlerInterceptorAdapter {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        long startTime = System.currentTimeMillis();
        System.out.println("\n-------- LogInterception.preHandle --- ");
        System.out.println("Request URL: " + request.getRequestURL());
        System.out.println("Start Time: " + System.currentTimeMillis());
        request.setAttribute("startTime", startTime);
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("\n-------- LogInterception.postHandle --- ");
        System.out.println("Request URL: " + request.getRequestURL());
        // You can add attributes in the modelAndView
        // and use that in the view page
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("\n-------- LogInterception.afterCompletion --- ");
        long startTime = (Long) request.getAttribute("startTime");
        long endTime = System.currentTimeMillis();
        System.out.println("Request URL: " + request.getRequestURL());
        System.out.println("End Time: " + endTime);
        System.out.println("Time Taken: " + (endTime - startTime));
    }
}

OldLoginInterceptor是一個攔截器，如果用戶輸入已經被廢棄的鏈接“/admin/oldLogin”，它將重定向到新的 “/admin/login”：

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

public class OldLoginInterceptor extends HandlerInterceptorAdapter {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("\n-------- OldLoginInterceptor.preHandle --- ");
        System.out.println("Request URL: " + request.getRequestURL());
        System.out.println("Sorry! This URL is no longer used, Redirect to /admin/login");
        response.sendRedirect(request.getContextPath() + "/admin/login");
        return false;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        // This code will never be run.
        System.out.println("\n-------- OldLoginInterceptor.postHandle --- ");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        // This code will never be run.
        System.out.println("\n-------- QueryStringInterceptor.afterCompletion --- ");
    }
}

AdminInterceptor

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

public class AdminInterceptor extends HandlerInterceptorAdapter {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("\n-------- AdminInterceptor.preHandle --- ");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("\n-------- AdminInterceptor.postHandle --- ");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("\n-------- AdminInterceptor.afterCompletion --- ");
    }
}

配置攔截器

import github.javaguide.springbootfilter.interceptor.AdminInterceptor;
import github.javaguide.springbootfilter.interceptor.LogInterceptor;
import github.javaguide.springbootfilter.interceptor.OldLoginInterceptor;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebConfig implements WebMvcConfigurer {
    
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        // LogInterceptor apply to all URLs.
        registry.addInterceptor(new LogInterceptor());

        // Old Login url, no longer use.
        // Use OldURLInterceptor to redirect to a new URL.
        registry.addInterceptor(new OldLoginInterceptor())
                .addPathPatterns("/admin/oldLogin");

        // This interceptor apply to URL like /admin/*
        // Exclude /admin/oldLogin
        registry.addInterceptor(new AdminInterceptor())
                .addPathPatterns("/admin/*")
                .excludePathPatterns("/admin/oldLogin");
    }
}

自定義 Controller 驗證攔截器

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
public class InterceptorTestController {

    @RequestMapping(value = { "/", "/test" })
    public String test(Model model) {
        System.out.println("\n-------- MainController.test --- ");
        System.out.println(" ** You are in Controller ** ");
        return "test";
    }

    // This path is no longer used.
    // It will be redirected by OldLoginInterceptor
    @Deprecated
    @RequestMapping(value = { "/admin/oldLogin" })
    public String oldLogin(Model model) {
        // Code here never run.
        return "oldLogin";
    }

    @RequestMapping(value = { "/admin/login" })
    public String login(Model model) {
        System.out.println("\n-------- MainController.login --- ");
        System.out.println(" ** You are in Controller ** ");
        return "login";
    }

}

thymeleaf 模板引擎

test.html

<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <meta charset="UTF-8" />
      <title>Spring Boot Mvc Interceptor example</title>
   </head>
   <body>
      <div style="border: 1px solid #ccc;padding: 5px;margin-bottom:10px;">
         <a th:href="@{/}">Home</a>
         &nbsp;&nbsp; | &nbsp;&nbsp;
         <a th:href="@{/admin/oldLogin}">/admin/oldLogin (OLD URL)</a>  
      </div>
      <h3>Spring Boot Mvc Interceptor</h3>
      <span style="color:blue;">Testing LogInterceptor</span>
      <br/><br/>
      See Log in Console..
   </body>
</html>

login.html

<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <meta charset="UTF-8" />
      <title>Spring Boot Mvc Interceptor example</title>
   </head>
   <body>
      <div style="border: 1px solid #ccc;padding: 5px;margin-bottom:10px;">
         <a th:href="@{/}">Home</a>
         &nbsp;&nbsp; | &nbsp;&nbsp;
         <a th:href="@{/admin/oldLogin}">/admin/oldLogin (OLD URL)</a>  
      </div>
      <h3>This is Login Page</h3>
      <span style="color:blue">Testing OldLoginInterceptor &amp; AdminInterceptor</span>
      <br/><br/>
      See more info in the Console.
   </body>
</html>

測試結果

測試用戶訪問 http://localhost:8080/ 的時候， LogInterceptor 記錄相關信息（頁面地址，訪問時間），並計算 Web服務器處理請求的時間。另外，頁面會被渲染成 test.html。

當用戶訪問 http://localhost:8080/admin/oldLogin 也就是舊的登錄頁面（不再使用）時， OldLoginInterceptor 將請求重定向 http://localhost:8080/admin/login 頁面會被渲染成正常的登錄頁面 login.html。