如何在Spring MVC应用中显示上传的图片

Question

我有一个Spring MVC应用程序，我想把用户上传的图像放到resources/uploads文件夹中。显然，我希望在我的网站上提供它们。但是当我尝试将sample.png放入resources文件夹中进行测试时，Web服务器回答“未找到”。我重新构建了项目，图片就变得可以访问了。我删除了图片，它仍然可以访问。我重新构建了项目，服务器回答了应该回答的内容（“未找到”）。

这是什么奇怪的行为？资源是否被构建到最终的jar文件中？这是否意味着，在重新构建项目之前，所有上传的用户图片都将无法访问？ 如果是这样，我完全不应该将上传的文件放入资源文件夹中，那么应该将它们放在哪里？ 为什么会发生这种情况，我该如何提供这些图片？

非常感谢。

Context.xml:

<!-- DispatcherServlet Context: defines this servlet's request-processing infrastructure -->

    <!-- Enables the Spring MVC @Controller programming model -->
    <annotation-driven>
        <message-converters>
          <beans:bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
              <beans:property name="objectMapper" ref="customObjectMapper"/>
          </beans:bean>
      </message-converters>
    </annotation-driven>

    <!-- Handles HTTP GET requests for /resources/** by efficiently serving up static resources in the ${webappRoot}/resources directory -->
    <resources mapping="/resources/**" location="/resources/" />


    <!-- mustache.java -->
    <beans:bean id="viewResolver" class="org.springframework.web.servlet.view.mustache.MustacheViewResolver">
        <beans:property name="cache" value="false" />
        <beans:property name="prefix" value="/WEB-INF/views/" />
        <beans:property name="suffix" value=".mustache" />
        <beans:property name="templateLoader">
            <beans:bean class="org.springframework.web.servlet.view.mustache.MustacheTemplateLoader" />
        </beans:property>
    </beans:bean>


    <!-- Standard template engine -->
    <!-- Resolves views selected for rendering by @Controllers to .jsp resources in the /WEB-INF/views directory -->
    <!--
    <beans:bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <beans:property name="prefix" value="/WEB-INF/views/" />
        <beans:property name="suffix" value=".jsp" />
    </beans:bean>
    -->

    <context:component-scan base-package="com.me.myproject" />


    <!-- JDBC Data Source. It is assumed you have MySQL running on localhost port 3306 with 
       username root and blank password. Change below if it's not the case -->
      <beans:bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
    <beans:property name="driverClassName" value="com.mysql.jdbc.Driver"/>
    <beans:property name="url" value="jdbc:mysql://localhost:3306/myproject"/>
    <beans:property name="username" value="someone"/>
    <beans:property name="password" value="something"/>
    <beans:property name="validationQuery" value="SELECT 1"/>
  </beans:bean>


  <!-- FlyWay -->
  <beans:bean id="flyway" class="com.googlecode.flyway.core.Flyway" init-method="migrate">
    <beans:property name="dataSource" ref="myDataSource"/>
  </beans:bean>

  <!-- Hibernate Session Factory -->
  <beans:bean id="mySessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean" depends-on="flyway">
    <beans:property name="dataSource" ref="myDataSource"/>
    <beans:property name="packagesToScan">
      <beans:array>
        <beans:value>com.me.myproject</beans:value>
      </beans:array>
    </beans:property>
    <beans:property name="hibernateProperties">
        <beans:value>
           hibernate.dialect=org.hibernate.dialect.MySQLDialect
          hibernate.hbm2ddl.auto=validate
        </beans:value>
      </beans:property>
    </beans:bean>

  <!-- Hibernate Transaction Manager -->
  <beans:bean id="transactionManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager">
    <beans:property name="sessionFactory" ref="mySessionFactory"/>
  </beans:bean>

  <!-- Activates annotation based transaction management -->
  <tx:annotation-driven transaction-manager="transactionManager"/>


</beans:beans>

Web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">





    <!-- The definition of the Root Spring Container shared by all Servlets and Filters -->
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/spring/root-context.xml</param-value>
    </context-param>

    <!-- Creates the Spring Container shared by all Servlets and Filters -->
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

    <!-- Processes application requests -->
    <servlet>
        <servlet-name>appServlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/spring/appServlet/servlet-context.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>appServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

</web-app>

- Roman

Answer 1

这里是一个可直接使用的图片上传/下载控制器，完全符合此目的：

1. 首先，我们需要通过一个简单的表单（admin.jsp）上传图片：

 <form method="POST" action="uploadFile" enctype="multipart/form-data">
    File to upload: <input type="file" name="file" >
    <br />
    Name: <input type="text" name="name" >
    <br />
    <br />
    <input type="submit" value="Upload">
</form>
<c:if test="${not empty message}">
    ${message} <!-- here would be a message with a result of processing -->
</c:if>

现在我们需要一个控制器，它可以将图片上传至服务器，并且在jsp页面上展示它们：

package com.pizza.controllers;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.servlet.ModelAndView;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.file.Files;

@Controller
public class FileUploadController {

    private static final String PIZZA_IMAGES = "pizzaImages";
    private static final String TOMCAT_HOME_PROPERTY = "catalina.home";
    private static final String TOMCAT_HOME_PATH = System.getProperty(TOMCAT_HOME_PROPERTY);
    private static final String PIZZA_IMAGES_PATH = TOMCAT_HOME_PATH + File.separator + PIZZA_IMAGES;

    private static final File PIZZA_IMAGES_DIR = new File(PIZZA_IMAGES_PATH);
    private static final String PIZZA_IMAGES_DIR_ABSOLUTE_PATH = PIZZA_IMAGES_DIR.getAbsolutePath() + File.separator;

    private static final String FAILED_UPLOAD_MESSAGE = "You failed to upload [%s] because the file because %s";
    private static final String SUCCESS_UPLOAD_MESSAGE = "You successfully uploaded file = [%s]";

    @RequestMapping(value = "/uploadFile", method = RequestMethod.POST)
    public ModelAndView uploadFileHandler(@RequestParam("name") String name,
                                      @RequestParam("file") MultipartFile file) {
        ModelAndView modelAndView = new ModelAndView("admin");

        if (file.isEmpty()) {
            modelAndView.addObject("message", String.format(FAILED_UPLOAD_MESSAGE, name, "file is empty"));
        } else {
            createPizzaImagesDirIfNeeded();
            modelAndView.addObject("message", createImage(name, file));
        }

        return modelAndView;
    }

    private void createPizzaImagesDirIfNeeded() {
        if (!PIZZA_IMAGES_DIR.exists()) {
            PIZZA_IMAGES_DIR.mkdirs();
        }
    }

    private String createImage(String name, MultipartFile file) {
        try {
            File image = new File(PIZZA_IMAGES_DIR_ABSOLUTE_PATH + name);
            BufferedOutputStream stream = new BufferedOutputStream(new FileOutputStream(image));
            stream.write(file.getBytes());
            stream.close();

            return String.format(SUCCESS_UPLOAD_MESSAGE, name);
        } catch (Exception e) {
            return String.format(FAILED_UPLOAD_MESSAGE, name, e.getMessage());
        }
    }

    @RequestMapping(value = "/image/{imageName}")
    @ResponseBody
    public byte[] getImage(@PathVariable(value = "imageName") String imageName) throws IOException {
        createPizzaImagesDirIfNeeded();

        File serverFile = new File(PIZZA_IMAGES_DIR_ABSOLUTE_PATH + imageName + ".jpg");

        return Files.readAllBytes(serverFile.toPath());
    }

}

2. 现在让我们来测试上传功能。选择一张图片并指定一个名称（包括扩展名）。稍后（在单击上传按钮后），此图像将出现在{Tomcat.dir}/pizzaImages文件夹中：

4. 让我们检查图像显示功能。为此，我们只需要在需要显示图像的位置中包含一个 <img>标记（这就是Spring MVC的工作原理）：

   <img src="/image/11" />

附言，你看，这很简单。

- Lord Nighton

Answer 2

您需要将文件保存到外部文件夹中。

例如，我创建一个目录，如/home/webappFolder/，并在其中创建其他子目录。例如，存储上传数据的存储库目录..我放置我的jasper报告文件的报告子目录..等等

/home/webappFolder/repo
/home/webappFolder/report
/home/webappFolder/logs

根据您在问题中发布的xml，可以看到：

<!-- Handles HTTP GET requests for /resources/** by efficiently serving up static resources in the ${webappRoot}/resources directory -->

在资源中，您提供了 静态 资源。

- gipinani

---

谢谢您的回答。但是，从/home/webappFolder/repo提供文件的最佳实践是什么？我假设它们默认情况下不可访问？ - Roman

它们默认情况下不可访问。您可以将正确的文件流式传输到 HttpServletResponse，直接写入用户。您只能流式传输特定用户可以访问的文件。我还将该文件夹映射为 NFS，以便将其保留在我们的备份存储下。 - gipinani

Answer 3

我经常遇到这样的问题，这取决于我的项目基础。例如，如果这是一个在Netbeans中使用Maven的项目，并且您的上传文件放在目标目录中，那么下一次执行"clean & build"时它们就会消失。

如果您将它们放在src/main/webapps/resources中，根据IDE中的设置，它们可能在重部署之前不可用/被删除，因为应用程序运行在目标目录中。

再次强调，这完全取决于您的设置、IDE、目录结构等。我认为这与Spring MVC没有太大关系。

- Russell Shingleton

Answer 4

请查看此指南：https://github.com/jdmr/fileUpload，它解释了如何将文件上传到“外部”文件夹并提供文件服务。在这里查看控制器类： https://github.com/jdmr/fileUpload/blob/master/src/main/java/org/davidmendoza/fileUpload/web/ImageController.java

- Yarix