基于Spring MVC的Web应用开发(4) - FileUpload

企业开发 2018-05-12 20:51:08 阅读次数: 2

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。

猜你喜欢

转载自zxb1985.iteye.com/blog/1813953
今日推荐
基于大语言模型的开源知识库问答系统 MaxKB GitHub Star 数量突破 5,000 个！
美国拟限制 AI 大模型出口中国和俄罗斯
苹果将与 OpenAI 达成协议，将 ChatGPT 应用于 iPhone
openKylin 社区生态委员会第六次会议圆满召开
阿里云正式发布通义千问 2.5
Python 3.13 发布首个 Beta：实验性自由线程模式和 JIT、改进交互式解释器
Stack Overflow 拿我的代码去训练 AI 大模型，还封了我的账号
Pop!_OS 的 COSMIC 桌面完成 App Store 上架工作
报告：Django 仍然是 74% 开发者的首选
《2024 年一季度互联网投融资运行情况》研究报告
15 年前上了“FFmpeg 耻辱柱”，今天他还得谢谢咱——腾讯QQPlayer一雪前耻？
TIOBE 5 月榜单：Fortran “复活”进入 Top 10
周排行
BPM为企业带来的实际利益
好程序员web前端分享css常用属性缩写
Java文件下载（excel）
css样式的动态添加及显示和隐藏等零碎用法
axios全局配置以及拦截器
使用Logstash来实时同步MySQL和log日志数据到ES
C++获取当前时间（年月日、时分秒、毫秒）
Odoo产品分析 (四) -- 工具板块(11) -- 网站即时聊天(1)
Java环境配置正确，但是java、javac、java -version均返回“不是内部或外部命令，也不是可运行的程序或批处理文件”？
01 官网下载各种CentOS教程（超详细版）
每日归档
更多
2024-05-14(0)
2024-05-13(18)
2024-05-12(0)
2024-05-11(38)
2024-05-10(38)
2024-05-09(35)
2024-05-08(42)
2024-05-07(14)
2024-05-06(40)
2024-05-05(0)

代码天地 © 2018 codetd.com

境外服务器   最新电视剧2022