package com.decade.interceptor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
@Slf4j
public class LoginInterceptor implements HandlerInterceptor {
    // 在調(diào)用控制器接口方法之前進入，如果放回true就放行，進入下一個攔截器或者控制器，如果返回false就不繼續(xù)往下走
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        // 獲取當前請求路徑
        final String requestURL = request.getRequestURI();
        log.info("攔截到的請求為：{}", requestURL);
        final HttpSession session = request.getSession();
        final Object userSession = session.getAttribute("loginUser");
        // 如果session中存在用戶登錄信息，那么就判定為用戶已登錄，放行
        if (null != userSession) {
            return true;
        } else {
            // model和request都會往請求域中塞信息，所以這里可以使用request傳遞我們需要返回給前端的信息
            request.setAttribute("msg", "請登錄！");
            // 轉(zhuǎn)發(fā)到登錄頁
            request.getRequestDispatcher("/").forward(request, response);
            return false;
        }
    }
    //調(diào)用前提：preHandle返回true
    //調(diào)用時間：Controller方法處理完之后，DispatcherServlet進行視圖的渲染之前，也就是說在這個方法中你可以對ModelAndView進行操作
    //執(zhí)行順序：鏈式Interceptor情況下，Interceptor按照聲明的順序倒著執(zhí)行。
    //備注：postHandle雖然post打頭，但post、get方法都能處理
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        log.info("postHandle執(zhí)行{}", modelAndView);
    }
    //調(diào)用前提：preHandle返回true
    //調(diào)用時間：DispatcherServlet進行視圖的渲染之后
    //多用于清理資源
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        log.info("頁面渲染完成后執(zhí)行");
    }
}

package com.decade.config;
import com.decade.interceptor.LoginInterceptor;
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 MyConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        // addPathPatterns：設置要攔截的請求，如果是/**，那么會攔截包括靜態(tài)資源在內(nèi)的所有請求
        // excludePathPatterns：設置不被攔截的請求，這里我們放行登錄頁請求和靜態(tài)資源
        registry.addInterceptor(new LoginInterceptor())
            .addPathPatterns("/**")
            .excludePathPatterns("/", "/login", "/css/**", "/images/**", "/js/**", "/fonts/**");
    }
}

boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
    for(int i = 0; i < this.interceptorList.size(); this.interceptorIndex = i++) {
        HandlerInterceptor interceptor = (HandlerInterceptor)this.interceptorList.get(i);
        // 如果攔截器的preHandle()返回false，那么就會調(diào)用下面的triggerAfterCompletion()
        if (!interceptor.preHandle(request, response, this.handler)) {
            this.triggerAfterCompletion(request, response, (Exception)null);
            return false;
        }
    }
    return true;
}
// 這個方法里面會從當前遍歷到的攔截器開始，倒序執(zhí)行afterCompletion()方法
void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex) {
    for(int i = this.interceptorIndex; i >= 0; --i) {
        HandlerInterceptor interceptor = (HandlerInterceptor)this.interceptorList.get(i);
        try {
            interceptor.afterCompletion(request, response, this.handler, ex);
        } catch (Throwable var7) {
            logger.error("HandlerInterceptor.afterCompletion threw exception", var7);
        }
    }
}

void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv) throws Exception {
    for(int i = this.interceptorList.size() - 1; i >= 0; --i) {
        HandlerInterceptor interceptor = (HandlerInterceptor)this.interceptorList.get(i);
        interceptor.postHandle(request, response, this.handler, mv);
    }
}

<div class="panel-body">
    <form role="form" th:action="@{/upload}" method="post" enctype="multipart/form-data">
        <div class="form-group">
            <label for="exampleInputEmail1">郵箱</label>
            <input type="email" name="email" class="form-control" id="exampleInputEmail1" placeholder="Enter email">
        </div>
        <div class="form-group">
            <label for="exampleInputPassword1">名字</label>
            <input type="text" name="username" class="form-control" id="exampleInputPassword1" placeholder="Password">
        </div>
        <div class="form-group">
            <label for="exampleInputFile">頭像</label>
            <input type="file" name="headerImg" id="exampleInputFile">
        </div>
        <div class="form-group">
            <label for="exampleInputFile">生活照</label>
            <input type="file" name="photos" multiple>
        </div>
        <div class="checkbox">
            <label>
                <input type="checkbox"> Check me out
            </label>
        </div>
        <button type="submit" class="btn btn-primary">提交</button>
    </form>
</div>

package com.decade.controller;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RequestPart;
import org.springframework.web.multipart.MultipartFile;
import java.io.File;
import java.io.IOException;
@Controller
@Slf4j
public class FileUploadController {
    /**
     * 頁面跳轉(zhuǎn)，跳轉(zhuǎn)到文件上傳頁面
     * @return 跳轉(zhuǎn)到文件上傳頁面
     */
    @GetMapping(value = "/form_layouts")
    public String uploadPage() {
        return "form/form_layouts";
    }
    /**
     * 文件上傳請求
     * @param email 郵件
     * @param username 用戶名
     * @param headerImg 頭像文件
     * @param photos 生活照
     * @return 如果上傳文件成功，跳轉(zhuǎn)到首頁
     */
    @PostMapping(value = "/upload")
    public String uploadFile(@RequestParam(name = "email") String email,
        @RequestParam(name = "username") String username, @RequestPart("headerImg") MultipartFile headerImg,
        @RequestPart("photos") MultipartFile[] photos) {
        log.info("請求參數(shù)email{}, username{}, 頭像headerImg大小{}, 生活照photos張數(shù){}",
            email, username, headerImg.getSize(), photos.length);
        try {
            // 判斷頭像文件是否為空，如果不是為空，那么就保存到本地
            if (!headerImg.isEmpty()) {
                final String filename = headerImg.getOriginalFilename();
                headerImg.transferTo(new File("D:\\test1\\" + filename));
            }
            // 判斷生活照是否上傳，循環(huán)保存到本地
            if (photos.length > 0) {
                for (MultipartFile photo : photos) {
                    final String originalFilename = photo.getOriginalFilename();
                    photo.transferTo(new File("D:\\test1\\" + originalFilename));
                }
            }
        } catch (IOException e) {
            log.error("上傳文件出錯！", e);
        }
        return "redirect:/main.html";
    }
}

# 單個文件最大限制
spring.servlet.multipart.max-file-size=10MB
# 單次請求最大限制
spring.servlet.multipart.max-request-size=100MB

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    HttpServletRequest processedRequest = request;
    HandlerExecutionChain mappedHandler = null;
    // 設置文件解析默認值為false
    boolean multipartRequestParsed = false;
    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
    try {
        try {
            ModelAndView mv = null;
            Object dispatchException = null;
            try {
            	// 檢查當前請求是否涉及文件上傳
                processedRequest = this.checkMultipart(request);
                // 將文件解析設置為true，表明當前請求涉及文件上傳
                multipartRequestParsed = processedRequest != request;

protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
	// 如果文件上傳解析器不為空，那么就調(diào)用StandardServletMultipartResolver類中的isMultipart()判斷當前請求是否涉及文件上傳
    if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
        if (WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class) != null) {
            if (DispatcherType.REQUEST.equals(request.getDispatcherType())) {
                this.logger.trace("Request already resolved to MultipartHttpServletRequest, e.g. by MultipartFilter");
            }
        } else if (this.hasMultipartException(request)) {
            this.logger.debug("Multipart resolution previously failed for current request - skipping re-resolution for undisturbed error rendering");
        } else {
            try {
            	// 將原生的請求封裝成一個StandardMultipartHttpServletRequest請求，把文件相關信息解析放進Map中
                return this.multipartResolver.resolveMultipart(request);

@Nullable
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer, NativeWebRequest request, @Nullable WebDataBinderFactory binderFactory) throws Exception {
    HttpServletRequest servletRequest = (HttpServletRequest)request.getNativeRequest(HttpServletRequest.class);
    Assert.state(servletRequest != null, "No HttpServletRequest");
    RequestPart requestPart = (RequestPart)parameter.getParameterAnnotation(RequestPart.class);
    boolean isRequired = (requestPart == null || requestPart.required()) && !parameter.isOptional();
    // 獲取文件上傳的參數(shù)名稱
    String name = this.getPartName(parameter, requestPart);
    parameter = parameter.nestedIfOptional();
    Object arg = null;
    // 根據(jù)參數(shù)名稱去獲取前面map中的value，也就是MultipartFile對象
    Object mpArg = MultipartResolutionDelegate.resolveMultipartArgument(name, parameter, servletRequest);