SpringBoot文件上傳的原理解析

更新時間：2023年10月10日 10:27:42 作者：劉婉晴

這篇文章主要介紹了SpringBoot文件上傳的原理解析,SpringBoot 文件上傳是一種方便快捷的方式,可以將文件上傳到服務(wù)器,通過使用SpringBoot的文件上傳功能,可以輕松地實現(xiàn)文件上傳功能,需要的朋友可以參考下

一、請求進(jìn)入,使用文件上傳解析器判斷并封裝

文件上傳解析器：只能接收標(biāo)準(zhǔn)的 Servlet 方式上傳的文件

@ConditionalOnMissingBean({MultipartResolver.class}) 判斷容器中無文件上傳解析器，若無自動創(chuàng)建

    @ConditionalOnMissingBean({MultipartResolver.class}) // 判斷注解
    public StandardServletMultipartResolver multipartResolver() {
        StandardServletMultipartResolver multipartResolver = new StandardServletMultipartResolver();
        multipartResolver.setResolveLazily(this.multipartProperties.isResolveLazily());
        return multipartResolver;
    }

DispatcherServlet.class —— doDispatch（）方法

與文件上傳相關(guān)功能有關(guān)的語句，請見下面的注釋：

    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;
        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
        try {
            try {
                ModelAndView mv = null;
                Exception dispatchException = null;
                try {
                    processedRequest = this.checkMultipart(request);
                    multipartRequestParsed = processedRequest != request; // 判斷是否是文件上傳請求（封裝好的文件上傳請求與原請求不相等，則判斷是文件上傳請求）
                    mappedHandler = this.getHandler(processedRequest); // 找誰能處理文件上傳請求
                    if (mappedHandler == null) {
                        this.noHandlerFound(processedRequest, response);
                        return;
                    }
                    HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());
                    String method = request.getMethod();
                    boolean isGet = "GET".equals(method);
                    if (isGet || "HEAD".equals(method)) {
                        long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                        if ((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) {
                            return;
                        }
                    }
                    if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                        return;
                    }
                    mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
                    if (asyncManager.isConcurrentHandlingStarted()) {
                        return;
                    }
                    this.applyDefaultViewName(processedRequest, mv);
                    mappedHandler.applyPostHandle(processedRequest, response, mv);
                } catch (Exception var20) {
                    dispatchException = var20;
                } catch (Throwable var21) {
                    dispatchException = new NestedServletException("Handler dispatch failed", var21);
                }
                this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException);
            } catch (Exception var22) {
                this.triggerAfterCompletion(processedRequest, response, mappedHandler, var22);
            } catch (Throwable var23) {
                this.triggerAfterCompletion(processedRequest, response, mappedHandler, new NestedServletException("Handler processing failed", var23));
            }
        } finally {
            if (asyncManager.isConcurrentHandlingStarted()) {
                if (mappedHandler != null) {
                    mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
                }
            } else if (multipartRequestParsed) {
                this.cleanupMultipart(processedRequest);
            }
        }
    }

（1） processedRequest = this.checkMultipart(request) —— 用于判斷是否是文件上傳請求

Step Into 查看：發(fā)現(xiàn)使用 multipartResolver 判斷是否是文件上傳請求

   protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
        if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) { // 判斷是否是文件上傳請求
            if (WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class) != null) {
                if (request.getDispatcherType().equals(DispatcherType.REQUEST)) {
                    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 {
                    return this.multipartResolver.resolveMultipart(request); // 解析文件上傳請求
                } catch (MultipartException var3) {
                    if (request.getAttribute("javax.servlet.error.exception") == null) {
                        throw var3;
                    }
                }
                this.logger.debug("Multipart resolution failed for error dispatch", var3);
            }
        }
        return request;
    }

StepInto—— multipartResolver 判斷是否是文件上傳請求方式

用 String 工具類判斷是否以 multipart/ 開頭（這也解釋了為什么我們在寫前端表單接收文件時，必須使用multipart）

    public boolean isMultipart(HttpServletRequest request) {
        return StringUtils.startsWithIgnoreCase(request.getContentType(), "multipart/");
    }

（2） this.multipartResolver.resolveMultipart(request) 解析文件上傳請求

其將文件上傳請求封裝為 MultipartHttpServletRequest 類返回

    public MultipartHttpServletRequest resolveMultipart(HttpServletRequest request) throws MultipartException {
        return new StandardMultipartHttpServletRequest(request, this.resolveLazily);
    }

二、參數(shù)解析器解析請求中的文件內(nèi)容封裝成 MultipartFile

文件請求參數(shù)解析器：

在這里插入圖片描述

(1) InvocableHandlerMethod.class 找到參數(shù)解析器，執(zhí)行文件上傳代理

  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();
        String name = this.getPartName(parameter, requestPart);
        parameter = parameter.nestedIfOptional();
        Object arg = null;
        Object mpArg = MultipartResolutionDelegate.resolveMultipartArgument(name, parameter, servletRequest); // 文件上傳代理
        if (mpArg != MultipartResolutionDelegate.UNRESOLVABLE) {
            arg = mpArg;
        } else {
            try {
                HttpInputMessage inputMessage = new RequestPartServletServerHttpRequest(servletRequest, name);
                arg = this.readWithMessageConverters(inputMessage, parameter, parameter.getNestedGenericParameterType());
                if (binderFactory != null) {
                    WebDataBinder binder = binderFactory.createBinder(request, arg, name);
                    if (arg != null) {
                        this.validateIfApplicable(binder, parameter);
                        if (binder.getBindingResult().hasErrors() && this.isBindExceptionRequired(binder, parameter)) {
                            throw new MethodArgumentNotValidException(parameter, binder.getBindingResult());
                        }
                    }
                    if (mavContainer != null) {
                        mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult());
                    }
                }
            } catch (MultipartException | MissingServletRequestPartException var13) {
                if (isRequired) {
                    throw var13;
                }
            }
        }
  }

（2）確定每個參數(shù)的值

       Object[] args = this.getMethodArgumentValues(request, mavContainer, providedArgs);

（3）解析所有參數(shù)

           for(int i = 0; i < parameters.length; ++i) {
                MethodParameter parameter = parameters[i];
                parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
                args[i] = findProvidedArgument(parameter, providedArgs);
                if (args[i] == null) {
                    if (!this.resolvers.supportsParameter(parameter)) {
                        throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
                    }
                    try {
                        args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
                    } catch (Exception var10) {
                        if (logger.isDebugEnabled()) {
                            String exMsg = var10.getMessage();
                            if (exMsg != null && !exMsg.contains(parameter.getExecutable().toGenericString())) {
                                logger.debug(formatArgumentError(parameter, exMsg));
                            }
                        }
                        throw var10;
                    }
                }
            }

三、將 request 文件封裝為一個 Map (Map<String, MultipartFile>)

AbstractMultipartHttpServletRequest.class

    public List<MultipartFile> getFiles(String name) {
        List<MultipartFile> multipartFiles = (List)this.getMultipartFiles().get(name);
        return multipartFiles != null ? multipartFiles : Collections.emptyList();
    }

public Map<String, MultipartFile> getFileMap() {
        return this.getMultipartFiles().toSingleValueMap();
    }

總結(jié)：

請求進(jìn)入，使用文件上傳解析器判斷（isMultipart）并封裝（resolveMultipart，返回MultipartHttpServletRequest）文件上傳請求
參數(shù)解析器解析請求中的文件內(nèi)容封裝成 MultipartFile
將 request 文件封裝為一個 Map (Map<String, MultipartFile>)

通過觀察源碼，可以得到許多 SpringBoot 為我們封裝好的文件工具類，如 FileCopyUtils 實現(xiàn)文件流的拷貝

到此這篇關(guān)于SpringBoot文件上傳的原理解析的文章就介紹到這了,更多相關(guān)SpringBoot文件上傳內(nèi)容請搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！

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