SpringBoot拦截器与文件上传实现方法与源码分析

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 {
    // 在调用控制器接口方法之前进入，如果放回true就放行，进入下一个拦截器或者控制器，如果返回false就不继续往下走
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        // 获取当前请求路径
        final String requestURL = request.getRequestURI();
        log.info("拦截到的请求为：{}", requestURL);
        final HttpSession session = request.getSession();
        final Object userSession = session.getAttribute("loginUser");
        // 如果session中存在用户登录信息，那么就判定为用户已登录，放行
        if (null != userSession) {
            return true;
        } else {
            // model和request都会往请求域中塞信息，所以这里可以使用request传递我们需要返回给前端的信息
            request.setAttribute("msg", "请登录！");
            // 转发到登录页
            request.getRequestDispatcher("/").forward(request, response);
            return false;
        }
    }
    //调用前提：preHandle返回true
    //调用时间：Controller方法处理完之后，DispatcherServlet进行视图的渲染之前，也就是说在这个方法中你可以对ModelAndView进行操作
    //执行顺序：链式Interceptor情况下，Interceptor按照声明的顺序倒着执行。
    //备注：postHandle虽然post打头，但post、get方法都能处理
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        log.info("postHandle执行{}", modelAndView);
    }
    //调用前提：preHandle返回true
    //调用时间：DispatcherServlet进行视图的渲染之后
    //多用于清理资源
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        log.info("页面渲染完成后执行");
    }
}

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：设置要拦截的请求，如果是/**，那么会拦截包括静态资源在内的所有请求
        // excludePathPatterns：设置不被拦截的请求，这里我们放行登录页请求和静态资源
        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);
        // 如果拦截器的preHandle()返回false，那么就会调用下面的triggerAfterCompletion()
        if (!interceptor.preHandle(request, response, this.handler)) {
            this.triggerAfterCompletion(request, response, (Exception)null);
            return false;
        }
    }
    return true;
}
// 这个方法里面会从当前遍历到的拦截器开始，倒序执行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">邮箱</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">头像</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 {
    /**
     * 页面跳转，跳转到文件上传页面
     * @return 跳转到文件上传页面
     */
    @GetMapping(value = "/form_layouts")
    public String uploadPage() {
        return "form/form_layouts";
    }
    /**
     * 文件上传请求
     * @param email 邮件
     * @param username 用户名
     * @param headerImg 头像文件
     * @param photos 生活照
     * @return 如果上传文件成功，跳转到首页
     */
    @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("请求参数email{}, username{}, 头像headerImg大小{}, 生活照photos张数{}",
            email, username, headerImg.getSize(), photos.length);
        try {
            // 判断头像文件是否为空，如果不是为空，那么就保存到本地
            if (!headerImg.isEmpty()) {
                final String filename = headerImg.getOriginalFilename();
                headerImg.transferTo(new File("D:\\test1\\" + filename));
            }
            // 判断生活照是否上传，循环保存到本地
            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("上传文件出错！", e);
        }
        return "redirect:/main.html";
    }
}

# 单个文件最大限制
spring.servlet.multipart.max-file-size=10MB
# 单次请求最大限制
spring.servlet.multipart.max-request-size=100MB

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    HttpServletRequest processedRequest = request;
    HandlerExecutionChain mappedHandler = null;
    // 设置文件解析默认值为false
    boolean multipartRequestParsed = false;
    WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
    try {
        try {
            ModelAndView mv = null;
            Object dispatchException = null;
            try {
            	// 检查当前请求是否涉及文件上传
                processedRequest = this.checkMultipart(request);
                // 将文件解析设置为true，表明当前请求涉及文件上传
                multipartRequestParsed = processedRequest != request;

protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
	// 如果文件上传解析器不为空，那么就调用StandardServletMultipartResolver类中的isMultipart()判断当前请求是否涉及文件上传
    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 {
            	// 将原生的请求封装成一个StandardMultipartHttpServletRequest请求，把文件相关信息解析放进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();
    // 获取文件上传的参数名称
    String name = this.getPartName(parameter, requestPart);
    parameter = parameter.nestedIfOptional();
    Object arg = null;
    // 根据参数名称去获取前面map中的value，也就是MultipartFile对象
    Object mpArg = MultipartResolutionDelegate.resolveMultipartArgument(name, parameter, servletRequest);