基于Spring MVC的Web应用开发(4) - FileUpload

于 2013-02-24 13:20:00 发布
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分类专栏： SpringMVC 文章标签： mvc spring springmvc
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本文链接：https://blog.youkuaiyun.com/yimeng528/article/details/84394389
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本文介绍如何使用SpringMVC实现文件上传功能，包括配置视图解析器、处理上传请求及解析上传文件。

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上一篇文章介绍了Spring MVC如何处理静态资源文件，本文讲解如何使用Spring MVC做文件上传，附带深入一下Spring MVC的ModelAndView。增加一个Controller，叫FileUploadController：

Java代码 复制代码 收藏代码
  1. package org.springframework.samples.mvc.fileupload;
  3. import org.springframework.stereotype.Controller;
  4. import org.springframework.web.bind.annotation.RequestMapping;
  5. import org.springframework.web.bind.annotation.RequestMethod;
  7. @Controller
  8. @RequestMapping("/fileupload")
  9. publicclass FileUploadController {
  11. @RequestMapping(method=RequestMethod.GET)
  12. publicvoid fileUploadForm() {
  13. }
  15. } 
package org.springframework.samples.mvc.fileupload;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
@RequestMapping("/fileupload")
public class FileUploadController {

	@RequestMapping(method=RequestMethod.GET)
	public void fileUploadForm() {
	}

}

这个类和HelloWorld中的Controller类就有点差别了，首先类名上加入了@RequestMapping注解，这样在做HandlerMapping时，SpringMVC会将类名和方法名的@RequestMapping连接起来，而本例方法名前并没有具体路径（当然也可以写），因此最终映射的URL还是"/fileupload"，另外一点就是在方法级@RequestMapping的注解增加了一个RequestMothod.GET，意思是只有以GET方式提交的"/fileupload"URL请求才会进入fileUploadForm()方法，其实根据HTTP协议，HTTP支持一系列提交方法（GET，POST，PUT，DELETE），同一个URL都可以使用这几种提交方式，事实上SpringMVC正是通过将同一个URL的不同提交方法对应到不同的方法上达到RESTful。

访问http://localhost:8080/web/fileupload，后台报错：

Java代码 复制代码 收藏代码
  1. 2012-03-2019:12:44.557:WARN::/web/fileupload
  2. javax.servlet.ServletException: Circular view path [fileupload]: would dispatch back to the current handler URL [/web/fileupload] again. Check your ViewResolver setup! (Hint: This may be the result of an unspecified view, due to default view name generation.)
  3. at org.springframework.web.servlet.view.InternalResourceView.prepareForRendering(InternalResourceView.java:292)
  4. ... 
2012-03-20 19:12:44.557:WARN::/web/fileupload
javax.servlet.ServletException: Circular view path [fileupload]: would dispatch back to the current handler URL [/web/fileupload] again. Check your ViewResolver setup! (Hint: This may be the result of an unspecified view, due to default view name generation.)
	at org.springframework.web.servlet.view.InternalResourceView.prepareForRendering(InternalResourceView.java:292)
...

正如Hint中指出的，没有指定一个View，大家可能会有疑问，HelloWorld中不是可以将结果返回到浏览器么？注意HelloWorld中的@ResponseBody跟View没有任何关系，HelloWorld中其实也是返回了一个ModelAndView，但这个View为null，并且在返回前，已经将结果通过HttpServletResponse发送给浏览器了。
那么怎么指定一个View呢？通常我们会想到一个默认的View，即如果没有写特殊的View，所有的结果都将转到这个默认的View上，最后将这个View推到浏览器展示。在servlet-context.xml中增加一个配置：

Xml代码 复制代码 收藏代码
  1. <!-- Resolves views selected for rendering by @Controllers to .jsp resources in the /WEB-INF/views directory -->
  2. <beans:beanclass="org.springframework.web.servlet.view.InternalResourceViewResolver">
  3. <beans:propertyname="prefix"value="/WEB-INF/views/"/>
  4. <beans:propertyname="suffix"value=".jsp"/>
  5. </beans:bean>
	<!-- 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>

配置了一个Bean，对应的类为InternalResourceViewResolver，并设置了prefix属性为"/WEB-INF/views"，suffix属性为".jsp"，这个类为视图解析器（view resolver），支持InternalResourceView（比如Servlet和JSP）及其子类如JstlView，默认的是InternalResourceView，如果有JSTL API存在的话，就是JstlView。

现在有一个默认的View了，这个View将view名字解析到/WEB-INF/views/目录下对应的jsp文件。
哪里有view名字？当带有@RequestMapping的方法返回void时，@RequestMapping映射的URL路径即view名字。

所以当使用GET方式访问http://localhost:8080/web/fileupload时，最终会找WEB-INF/views/目录下有没有fileupload.jsp文件，有则将此jsp文件显示在浏览器上，没有则报如下错误：

Java代码 复制代码 收藏代码
  1. ERROR: PWC6117: File &quot;/Users/stephansun/Documents/workspace/samples/samples-web/src/main/webapp/WEB-INF/views/fileupload.jsp&quot; not found 
ERROR: PWC6117: File &quot;/Users/stephansun/Documents/workspace/samples/samples-web/src/main/webapp/WEB-INF/views/fileupload.jsp&quot; not found

fileUploadForm.jsp文件为：

Html代码 复制代码 收藏代码
  1. <%@ taglib uri="http://java.sun.com/jsp/jstl/core"prefix="c" %>
  2. <html>
  3. <head>
  4. <title>fileupload | mvc-showcase</title>
  5. <linkhref="<c:url value="/resources/form.css" />" rel="stylesheet"type="text/css"/>
  6. <scripttype="text/javascript"src="<c:url value="/resources/jquery/1.6/jquery.js" />"></script>
  7. <scripttype="text/javascript"src="<c:url value="/resources/jqueryform/2.8/jquery.form.js" />"></script>
  8. </head>
  9. <body>
  10. <divid="fileuploadContent">
  11. <h2>File Upload</h2>
  12. <p>
  13. See the <code>org.springframework.samples.mvc.fileupload</code> package for the @Controller code
  14. </p>
  15. <formid="fileuploadForm"action="fileupload"method="POST"enctype="multipart/form-data"class="cleanform">
  16. <divclass="header">
  17. <h2>Form</h2>
  18. <c:iftest="${not empty message}">
  19. <divid="message"class="success">${message}</div>
  20. </c:if>
  21. </div>
  22. <labelfor="file">File</label>
  23. <inputid="file"type="file"name="file"/>
  24. <p><buttontype="submit">Upload</button></p>
  25. </form>
  26. </div>
  27. </body>
  28. </html>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<html>
<head>
	<title>fileupload | mvc-showcase</title>
	<link href="<c:url value="/resources/form.css" />" rel="stylesheet"  type="text/css" />		
	<script type="text/javascript" src="<c:url value="/resources/jquery/1.6/jquery.js" />"></script>
	<script type="text/javascript" src="<c:url value="/resources/jqueryform/2.8/jquery.form.js" />"></script>	
</head>
<body>
	<div id="fileuploadContent">
		<h2>File Upload</h2>
		<p>
			See the <code>org.springframework.samples.mvc.fileupload</code> package for the @Controller code	
		</p>
		<form id="fileuploadForm" action="fileupload" method="POST" enctype="multipart/form-data" class="cleanform">
			<div class="header">
		  		<h2>Form</h2>
		  		<c:if test="${not empty message}">
					<div id="message" class="success">${message}</div>	  		
		  		</c:if>
			</div>
			<label for="file">File</label>
			<input id="file" type="file" name="file" />
			<p><button type="submit">Upload</button></p>		
		</form>	
	</div>
</body>
</html>

上传页面正确显示后，我们需要一个方法处理上传请求，processUpload，现在FileUploadController看起来是这样的：

Java代码 复制代码 收藏代码
  1. package org.springframework.samples.mvc.fileupload;
  3. import java.io.IOException;
  5. import org.springframework.stereotype.Controller;
  6. import org.springframework.ui.Model;
  7. import org.springframework.web.bind.annotation.RequestMapping;
  8. import org.springframework.web.bind.annotation.RequestMethod;
  9. import org.springframework.web.bind.annotation.RequestParam;
  10. import org.springframework.web.multipart.MultipartFile;
  12. @Controller
  13. @RequestMapping("/fileupload")
  14. publicclass FileUploadController {
  16. @RequestMapping(method=RequestMethod.GET)
  17. publicvoid fileUploadForm() {
  18. }
  20. @RequestMapping(method=RequestMethod.POST)
  21. publicvoid processUpload(@RequestParam MultipartFile file, Model model) throws IOException {
  22. model.addAttribute("message", "File '" + file.getOriginalFilename() + "' uploaded successfully");
  23. }
  25. } 
package org.springframework.samples.mvc.fileupload;

import java.io.IOException;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
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.multipart.MultipartFile;

@Controller
@RequestMapping("/fileupload")
public class FileUploadController {

	@RequestMapping(method=RequestMethod.GET)
	public void fileUploadForm() {
	}

	@RequestMapping(method=RequestMethod.POST)
	public void processUpload(@RequestParam MultipartFile file, Model model) throws IOException {
		model.addAttribute("message", "File '" + file.getOriginalFilename() + "' uploaded successfully");
	}
	
}

这里出现了一个新注解@RequestParam，先看一下JSP页面的代码片段：

Html代码 复制代码 收藏代码
  1. <inputid="file"type="file"name="file"/>
<input id="file" type="file" name="file" />

input框提交的参数名就是file，@RequestParam注解自动将POST提交的参数中名为file的封装到一个MultipartFile类中，一切都在开发人员眼皮底下做好了，大大减少了开发人员的代码量。现在我们在上传页面选择一个文件上传，后台报错，看报错日志：

Java代码 复制代码 收藏代码
  1. java.lang.IllegalArgumentException: Expected MultipartHttpServletRequest: is a MultipartResolver configured?
  2. at org.springframework.util.Assert.notNull(Assert.java:112) 
java.lang.IllegalArgumentException: Expected MultipartHttpServletRequest: is a MultipartResolver configured?
	at org.springframework.util.Assert.notNull(Assert.java:112)

说"是不是没配置MultipartResolver？"，恩，还没有配，所有在servlet-context.xml中加上这么一段配置：

Xml代码 复制代码 收藏代码
  1. <!-- Only needed because we require fileupload in the org.springframework.samples.mvc.fileupload package -->
  2. <beans:beanid="multipartResolver"class="org.springframework.web.multipart.commons.CommonsMultipartResolver"/>
<!-- Only needed because we require fileupload in the org.springframework.samples.mvc.fileupload package -->
	<beans:bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver" />

这个Bean也是一个视图解析器（view resolver）。

完整的XML：

Xml代码 复制代码 收藏代码
  1. <?xmlversion="1.0"encoding="UTF-8"?>
  2. <beans:beansxmlns="http://www.springframework.org/schema/mvc"
  3. xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  4. xmlns:beans="http://www.springframework.org/schema/beans"
  5. xmlns:context="http://www.springframework.org/schema/context"
  6. xmlns:mvc="http://www.springframework.org/schema/mvc"
  7. xsi:schemaLocation="
  8. http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.1.xsd
  9. http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
  10. http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd">
  12. <!-- DispatcherServlet Context: defines this servlet's request-processing infrastructure -->
  14. <!-- Handles HTTP GET requests for /resources/** by efficiently serving up static resources in the ${webappRoot}/resources/ directory -->
  15. <resourcesmapping="/resources/**"location="/resources/"/>
  17. <!-- Imports user-defined @Controller beans that process client requests -->
  18. <beans:importresource="controllers.xml"/>
  20. <!-- You have to add this because you had a <resources/> declare -->
  21. <mvc:annotation-driven/>
  23. <!-- Resolves views selected for rendering by @Controllers to .jsp resources in the /WEB-INF/views directory -->
  24. <beans:beanclass="org.springframework.web.servlet.view.InternalResourceViewResolver">
  25. <beans:propertyname="prefix"value="/WEB-INF/views/"/>
  26. <beans:propertyname="suffix"value=".jsp"/>
  27. </beans:bean>
  29. <!-- Only needed because we require fileupload in the org.springframework.samples.mvc.fileupload package -->
  30. <beans:beanid="multipartResolver"class="org.springframework.web.multipart.commons.CommonsMultipartResolver"/>
  32. </beans:beans>
<?xml version="1.0" encoding="UTF-8"?>
<beans:beans xmlns="http://www.springframework.org/schema/mvc"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:beans="http://www.springframework.org/schema/beans"
	xmlns:context="http://www.springframework.org/schema/context"
	xmlns:mvc="http://www.springframework.org/schema/mvc"
	xsi:schemaLocation="
        http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.1.xsd
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd">

	<!-- DispatcherServlet Context: defines this servlet's request-processing infrastructure -->
	
	<!-- Handles HTTP GET requests for /resources/** by efficiently serving up static resources in the ${webappRoot}/resources/ directory -->
	<resources mapping="/resources/**" location="/resources/" />
	
	<!-- Imports user-defined @Controller beans that process client requests -->
	<beans:import resource="controllers.xml" />
	
	<!-- You have to add this because you had a <resources/> declare -->
	<mvc:annotation-driven/>
	
	<!-- 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>
	
	<!-- Only needed because we require fileupload in the org.springframework.samples.mvc.fileupload package -->
	<beans:bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver" />
	
</beans:beans>

然后再次上传文件，页面显示：

Xml代码 复制代码 收藏代码
  1. File 'a.js' uploaded successfully 
File 'a.js' uploaded successfully

上传成功，最后我们分析一下FileUploadController中的processUpload方法：

Java代码 复制代码 收藏代码
  1. @RequestMapping(method=RequestMethod.POST)
  2. publicvoid processUpload(@RequestParam MultipartFile file, Model model) throws IOException {
  3. model.addAttribute("message", "File '" + file.getOriginalFilename() + "' uploaded successfully");
  4. } 
@RequestMapping(method=RequestMethod.POST)
	public void processUpload(@RequestParam MultipartFile file, Model model) throws IOException {
		model.addAttribute("message", "File '" + file.getOriginalFilename() + "' uploaded successfully");
	}

Model就是MVC模式中的M，Model层封装了要传递给View层显示的值。

最后更新一下pom.xml文件，添加两个依赖：

Xml代码 复制代码 收藏代码
  1. <!-- File Upload -->
  2. <dependency>
  3. <groupId>commons-fileupload</groupId>
  4. <artifactId>commons-fileupload</artifactId>
  5. <version>1.2.2</version>
  6. </dependency>
  7. <dependency>
  8. <groupId>commons-io</groupId>
  9. <artifactId>commons-io</artifactId>
  10. <version>2.0.1</version>
  11. </dependency>
	
	<!-- File Upload -->
	<dependency>
		<groupId>commons-fileupload</groupId>
		<artifactId>commons-fileupload</artifactId>
		<version>1.2.2</version>
	</dependency>	
	<dependency>
		<groupId>commons-io</groupId>
		<artifactId>commons-io</artifactId>
		<version>2.0.1</version>
	</dependency>

好像前面写的代码根本没有涉及到这两个jar包啊，为什么要引入？

之前我写道

@RequestParam注解自动将POST提交的参数中名为file的封装到一个MultipartFile类中，一切都在开发人员眼皮底下做好了，大大减少了开发人员的代码量。

底层真正由谁来做的呢？我们加入了multipartResolver这个Bean，它对应的类为

org.springframework.web.multipart.commons.CommonsMultipartResolver，

看看这个类的源代码，import中赫然写着：

Java代码 复制代码 收藏代码
  1. import org.apache.commons.fileupload.FileItem;
  2. import org.apache.commons.fileupload.FileItemFactory;
  3. import org.apache.commons.fileupload.FileUpload;
  4. import org.apache.commons.fileupload.FileUploadBase;
  5. import org.apache.commons.fileupload.FileUploadException;
  6. import org.apache.commons.fileupload.servlet.ServletFileUpload; 
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.FileUpload;
import org.apache.commons.fileupload.FileUploadBase;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

因此SpringMVC封装了commons-fileupload上传组件，真正起上传作用的还是commons-fileupload-1.2.2.jar这个jar包里面的类。

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