在這篇文章中，我們將使用Spring MultipartResolver 實現 StandardServletMultipartResolver在Servlet3環境中實現單點和多文件上傳功能。Spring提供了內置的multipart支持來處理Web應用程序文件上傳。

簡短的概述

在這篇文章中，我們將使用Servlet3.0以及javax.servlet.MultipartConfigElement，爲了激活 Servlet3.0環境和Spring 的Multipart支持，你需要做以下：

1.添加 StandardServletMultipartResolver Bean 在 Spring 配置。這是一個標準實現 MultipartResolver 接口，基於Servlet3.0 javax.servlet.http.Part API。

2. 啓用在Servlet3.0環境的多解析(MultiParsing)。要做到這一點，你有多種方案可供選擇。

方案A. 對方案性 Servlet 註冊設置 javax.servlet.MultipartConfigElement。MultipartConfigElement是javax.servlet.annotation.MultipartConfig 的註釋值(如選擇C所述)的簡單Java類表示。這篇文章將特別側重於這個選擇。

方案B. 如果您使用基於XML的配置，可以在web.xml中在servlet配置聲明 multipart-configsection 部分，如下圖所示：

  <servlet>
      <servlet-name>SpringDispatcher</servlet-name>
      <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
      <multipart-config>
          <location>/tmp</location>
          <max-file-size>5242880</max-file-size><!--5MB-->
          <max-request-size>20971520</max-request-size><!--20MB-->
          <file-size-threshold>0</file-size-threshold>
      </multipart-config>
  </servlet>

方案C. 可以創建一個自定義 Servlet 和 javax.servlet.annotation.MultipartConfig 標註其標註，如下圖所示：

@WebServlet(name = "fileUploadServlet", urlPatterns = {"/upload"})
@MultipartConfig(location=/tmp,

               fileSizeThreshold=0,    
               maxFileSize=5242880,       // 5 MB
               maxRequestSize=20971520)   // 20 MB

public class FileUploadServlet extends HttpServlet {

  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
      //handle file upload
  }

話雖這麼說，我們將專注於在這個例子中選擇。

完整的例子

使用以下技術：

Spring 4.2.0.RELEASE
validation-api 1.1.0.Final
Bootstrap v3.3.2
Maven 3
JDK 1.7
Tomcat 8.0.21
Eclipse JUNO Service Release 2

Let’s begin.

項目結構

Spring

在pom.xml聲明依賴關係

4.0.0
com.yiibai.springmvc
Spring4MVCFileUploadMultipartFile
war
1.0.0
Spring4MVCFileUploadMultipartFile Maven Webapp
http://maven.apache.org

<properties>
    <springframework.version>4.2.0.RELEASE</springframework.version>
</properties>

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-webmvc</artifactId>
        <version>${springframework.version}</version>
    </dependency>

    <dependency>
        <groupId>javax.validation</groupId>
        <artifactId>validation-api</artifactId>
        <version>1.1.0.Final</version>
    </dependency>

    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.1.0</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>jstl</artifactId>
        <version>1.2</version>
    </dependency>
</dependencies>


<build>
    <pluginManagement>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>2.4</version>
                <configuration>
                    <warSourceDirectory>src/main/webapp</warSourceDirectory>
                    <warName>Spring4MVCFileUploadMultipartFile</warName>
                    <failOnMissingWebXml>false</failOnMissingWebXml>
                </configuration>
            </plugin>
        </plugins>
    </pluginManagement>

    <finalName>Spring4MVCFileUploadMultipartFile</finalName>
</build>

MultiPartConfigElement的編程註冊

這個註冊提供一個配置，以設置像最大文件大小，請求大小，位置和門限值。文件上傳操作期間暫時存儲在磁盤上的特定屬性。

package com.yiibai.springmvc.configuration;

import javax.servlet.MultipartConfigElement;
import javax.servlet.ServletRegistration;

import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;

public class HelloWorldInitializer extends
AbstractAnnotationConfigDispatcherServletInitializer {

@Override
protected Class<?>\[\] getRootConfigClasses() {
    return new Class\[\] { HelloWorldConfiguration.class };
}

@Override
protected Class<?>\[\] getServletConfigClasses() {
    return null;
}

@Override
protected String\[\] getServletMappings() {
    return new String\[\] { "/" };
}

@Override
protected void customizeRegistration(ServletRegistration.Dynamic registration) {
    registration.setMultipartConfig(getMultipartConfigElement());
}

private MultipartConfigElement getMultipartConfigElement() {
    MultipartConfigElement multipartConfigElement = new MultipartConfigElement(    LOCATION, MAX\_FILE\_SIZE, MAX\_REQUEST\_SIZE, FILE\_SIZE\_THRESHOLD);
    return multipartConfigElement;
}

private static final String LOCATION = "C:/temp/"; // Temporary location where files will be stored

private static final long MAX\_FILE\_SIZE = 5242880; // 5MB : Max file size.
                                                    // Beyond that size spring will throw exception.
private static final long MAX\_REQUEST\_SIZE = 20971520; // 20MB : Total request size containing Multi part.

private static final int FILE\_SIZE\_THRESHOLD = 0; // Size threshold after which files will be written to disk

}

請注意，我們如何才能註冊所需的 MultiPartConfigElement 到 DispatcherServlet 的重寫函數 customizeRegistration。

創建配置

配置StandardServletMultipartResolver Bean。這是一個標準實現MultipartResolver接口，基於Servlet3.0 javax.servlet.http.Part API。

package com.yiibai.springmvc.configuration;

import org.springframework.context.MessageSource;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.ResourceBundleMessageSource;
import org.springframework.web.multipart.support.StandardServletMultipartResolver;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.ViewResolverRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
import org.springframework.web.servlet.view.InternalResourceViewResolver;
import org.springframework.web.servlet.view.JstlView;

@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "com.yiibai.springmvc")
public class HelloWorldConfiguration extends WebMvcConfigurerAdapter {

@Bean(name = "multipartResolver")
public StandardServletMultipartResolver resolver() {
    return new StandardServletMultipartResolver();
}

@Override
public void configureViewResolvers(ViewResolverRegistry registry) {
    InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
    viewResolver.setViewClass(JstlView.class);
    viewResolver.setPrefix("/WEB-INF/views/");
    viewResolver.setSuffix(".jsp");
    registry.viewResolver(viewResolver);
}

@Bean
public MessageSource messageSource() {
    ResourceBundleMessageSource messageSource = new ResourceBundleMessageSource();
    messageSource.setBasename("messages");
    return messageSource;
}

@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
    registry.addResourceHandler("/static/\*\*").addResourceLocations( "/static/");
}

}

以XML格式配置類將是：

<context:component-scan base-package="com.yiibai.springmvc" />
<mvc:annotation-driven />

<bean id="multipartResolver" class="org.springframework.web.multipart.support.StandardServletMultipartResolver"/>

<mvc:resources mapping="/static/\*\*" location="/static/" />
<mvc:default-servlet-handler />


<bean id="messageSource" class="org.springframework.context.support.ResourceBundleMessageSource">
    <property name="basename">
        <value>messages</value>
    </property>
</bean>


<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="prefix">
        <value>/WEB-INF/views/</value>
    </property>
    <property name="suffix">
        <value>.jsp</value>
    </property>
</bean>

創建模型類

Spring提供 org.springframework.web.multipart.MultipartFile，這是一個 multipart 請求獲得上傳文件的表示。它提供了方便的方法，如getName()，getContentType()，GetBytes()，getInputStream()等。這讓我們處理更容易一點，同時檢索有關被上傳文件的信息。

讓我們寫一個包裝類，進一步簡化我們應用程序的使用。

package com.yiibai.springmvc.model;

import org.springframework.web.multipart.MultipartFile;

public class FileBucket {

MultipartFile file;

public MultipartFile getFile() {
    return file;
}

public void setFile(MultipartFile file) {
    this.file = file;
}

}

爲了展示Multiple上傳的例子，讓我們再創建一個包裝類。

package com.yiibai.springmvc.model;

import java.util.ArrayList;
import java.util.List;

public class MultiFileBucket {

List<FileBucket> files = new ArrayList<FileBucket>();

public MultiFileBucket(){
    files.add(new FileBucket());
    files.add(new FileBucket());
    files.add(new FileBucket());
}

public List<FileBucket> getFiles() {
    return files;
}

public void setFiles(List<FileBucket> files) {
    this.files = files;
}

}

這個類可以處理多達3個文件上傳。

創建控制器

package com.yiibai.springmvc.controller;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.validation.Valid;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.util.FileCopyUtils;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.InitBinder;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.multipart.MultipartFile;

import com.yiibai.springmvc.model.FileBucket;
import com.yiibai.springmvc.model.MultiFileBucket;
import com.yiibai.springmvc.util.FileValidator;
import com.yiibai.springmvc.util.MultiFileValidator;

@Controller
public class FileUploadController {

private static String UPLOAD\_LOCATION="C:/mytemp/";

@Autowired
FileValidator fileValidator;

@Autowired
MultiFileValidator multiFileValidator;

@InitBinder("fileBucket")
protected void initBinderFileBucket(WebDataBinder binder) {
    binder.setValidator(fileValidator);
}

@InitBinder("multiFileBucket")
protected void initBinderMultiFileBucket(WebDataBinder binder) {
    binder.setValidator(multiFileValidator);
}

@RequestMapping(value = { "/", "/welcome" }, method = RequestMethod.GET)
public String getHomePage(ModelMap model) {
    return "welcome";
}

@RequestMapping(value = "/singleUpload", method = RequestMethod.GET)
public String getSingleUploadPage(ModelMap model) {
    FileBucket fileModel = new FileBucket();
    model.addAttribute("fileBucket", fileModel);
    return "singleFileUploader";
}

@RequestMapping(value = "/singleUpload", method = RequestMethod.POST)
public String singleFileUpload(@Valid FileBucket fileBucket,
        BindingResult result, ModelMap model) throws IOException {

    if (result.hasErrors()) {
        System.out.println("validation errors");
        return "singleFileUploader";
    } else {
        System.out.println("Fetching file");
        MultipartFile multipartFile = fileBucket.getFile();

        // Now do something with file...
        FileCopyUtils.copy(fileBucket.getFile().getBytes(), new File( UPLOAD\_LOCATION + fileBucket.getFile().getOriginalFilename()));
        String fileName = multipartFile.getOriginalFilename();
        model.addAttribute("fileName", fileName);
        return "success";
    }
}

@RequestMapping(value = "/multiUpload", method = RequestMethod.GET)
public String getMultiUploadPage(ModelMap model) {
    MultiFileBucket filesModel = new MultiFileBucket();
    model.addAttribute("multiFileBucket", filesModel);
    return "multiFileUploader";
}

@RequestMapping(value = "/multiUpload", method = RequestMethod.POST)
public String multiFileUpload(@Valid MultiFileBucket multiFileBucket,
        BindingResult result, ModelMap model) throws IOException {

    if (result.hasErrors()) {
        System.out.println("validation errors in multi upload");
        return "multiFileUploader";
    } else {
        System.out.println("Fetching files");
        List<String> fileNames = new ArrayList<String>();
        // Now do something with file...
        for (FileBucket bucket : multiFileBucket.getFiles()) {
            FileCopyUtils.copy(bucket.getFile().getBytes(), new File(UPLOAD\_LOCATION + bucket.getFile().getOriginalFilename()));
            fileNames.add(bucket.getFile().getOriginalFilename());
        }

        model.addAttribute("fileNames", fileNames);
        return "multiSuccess";
    }
}

}

以上控制器是相當微不足道。它處理上傳視圖的GET和POST請求的文件。當文件從文件選擇器，用戶選擇點擊上傳，我們只是創建具有相同的名稱和字節的內容作爲原始文件的新文件，從原始複製文件的字節數。爲此，我們正在使用Spring FileCopyUtils工具類流從源複製到目的地。在這個例子中，我們指定的目的地是 C:/mytemp 文件夾，所有文件將存在這個文件夾中。

創建驗證類

我們使用的是一些驗證，以驗證用戶確實選擇了要上傳的文件。它們如下所示。

package com.yiibai.springmvc.util;

import org.springframework.stereotype.Component;
import org.springframework.validation.Errors;
import org.springframework.validation.Validator;

import com.yiibai.springmvc.model.FileBucket;

@Component
public class FileValidator implements Validator {

public boolean supports(Class<?> clazz) {
    return FileBucket.class.isAssignableFrom(clazz);
}

public void validate(Object obj, Errors errors) {
    FileBucket file = (FileBucket) obj;

    if(file.getFile()!=null){
        if (file.getFile().getSize() == 0) {
            errors.rejectValue("file", "missing.file");
        }
    }
}

}

package com.yiibai.springmvc.util;

import org.springframework.stereotype.Component;
import org.springframework.validation.Errors;
import org.springframework.validation.Validator;

import com.yiibai.springmvc.model.FileBucket;
import com.yiibai.springmvc.model.MultiFileBucket;

@Component
public class MultiFileValidator implements Validator {

public boolean supports(Class<?> clazz) {
    return MultiFileBucket.class.isAssignableFrom(clazz);
}

public void validate(Object obj, Errors errors) {
    MultiFileBucket multiBucket = (MultiFileBucket) obj;

    int index=0;

    for(FileBucket file : multiBucket.getFiles()){
        if(file.getFile()!=null){
            if (file.getFile().getSize() == 0) {
                errors.rejectValue("files\["+index+"\].file", "missing.file");
            }
        }
        index++;
    }

}

}

messages.properties

missing.file= Please select a file.

創建視圖

singleFileUploader.jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form"%>

Spring 4 MVC File Upload Example

<div class="form-container">
    <h1>Spring 4 MVC File Upload Example </h1>
    <form:form method="POST" modelAttribute="fileBucket" enctype="multipart/form-data" class="form-horizontal">

        <div class="row">
            <div class="form-group col-md-12">
                <label class="col-md-3 control-lable" for="file">Upload a file</label>
                <div class="col-md-7">
                    <form:input type="file" path="file" id="file" class="form-control input-sm"/>
                    <div class="has-error">
                        <form:errors path="file" class="help-inline"/>
                    </div>
                </div>
            </div>
        </div>

        <div class="row">
            <div class="form-actions floatRight">
                <input type="submit" value="Upload" class="btn btn-primary btn-sm">
            </div>
        </div>
    </form:form>
    <a href="<c:url value='/welcome' />">Home</a>
</div>

success.jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

File Upload Success

File ${fileName} uploaded successfully.

Home

multiFileUploader.jsp

Spring 4 MVC File Multi Upload Example

<div class="form-container">
    <h1>Spring 4 MVC Multi File Upload Example </h1>
    <form:form method="POST" modelAttribute="multiFileBucket" enctype="multipart/form-data" class="form-horizontal">

        <c:forEach var="v" varStatus="vs" items="${multiFileBucket.files}">
            <form:input type="file" path="files\[${vs.index}\].file" id="files\[${vs.index}\].file" class="form-control input-sm"/>
            <div class="has-error">
                <form:errors path="files\[${vs.index}\].file" class="help-inline"/>
            </div>
        </c:forEach>
        <br/>
        <div class="row">
            <div class="form-actions floatRight">
                <input type="submit" value="Upload" class="btn btn-primary btn-sm">
            </div>
        </div>
    </form:form>

    <br/>
    <a href="<c:url value='/welcome' />">Home</a>
</div>

multiSuccess.jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

File Upload Success

File ${fileName} uploaded successfully

Home

welcome.jsp

<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

Spring 4 MVC File Upload Example

Welcome to FileUploader Example

    Click on below links to see FileUpload in action.<br/><br/>

    <a href="<c:url value='/singleUpload' />">Single File Upload</a>  OR  <a href="<c:url value='multiUpload' />">Multi File Upload</a>
</div>

構建，部署和運行應用程序

現在構建 war(前面的Eclipse教程)或通過Maven的命令行( mvn clean install).部署 war 到Servlet3.0容器。

打開瀏覽器，瀏覽 http://localhost:8080/Spring4MVCFileUploadMultipart/

Spring