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Spring4 MVC文件下载实例

这篇文章将向您展示如何使用Spring MVC4执行文件下载，我们将看到应用程序从文件系统内部以及外部文件下载文件。

本教程的主要亮点：

下载文件是相当简单的，涉及以下步骤。

创建一个InputStream到文件用于下载。
查找MIME类型下载文件的内容。
–可以是application/pdf, text/html,application/xml,image/png等等。
将内容类型与上述发现的MIME类型响应（HttpServletResponse）。
response.setContentType(mimeType);
针对以上找到MIME类型设置内容长度。
response.setContentLength(file.getLength());//length in bytes
为响应设置内容处理标头。
response.setHeader(“Content-Disposition”, “attachment; filename=” + fileName); //随着“附件”文件将下载。可能会显示一个“另存为”基于浏览器的设置对话框。
response.setHeader(“Content-Disposition”, “inline; filename=” + fileName);//通过“内联”浏览器将尝试显示内容到浏览器中（图片，PDF，文本，...）。对于其他内容类型，文件将直接下载。
从InputStream中复制字节响应到 OutputStream。
一旦复制完成后，关闭输入输出流。

完整实施例在下面讨论。

使用到以下技术：

Spring 4.2.0.RELEASE
Bootstrap v3.3.2
Maven 3
JDK 1.7
Tomcat 8.0.21
Eclipse JUNO Service Release 2

现在让我们开始

项目结构

在pom.xml中声明依赖关系

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.yiibai.springmvc</groupId>
  <artifactId>Spring4MVCFileDownloadExample</artifactId>
  <packaging>war</packaging>
  <version>1.0.0</version>
  <name>Spring4MVCFileDownloadExample Maven Webapp</name>
 
     <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.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>Spring4MVCFileDownloadExample</warName>
						<failOnMissingWebXml>false</failOnMissingWebXml>
					</configuration>
				</plugin>
			</plugins>
		</pluginManagement>

		<finalName>Spring4MVCFileDownloadExample</finalName>
	</build>
</project>

创建控制器

package com.yiibai.springmvc.controller;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLConnection;
import java.nio.charset.Charset;

import javax.servlet.http.HttpServletResponse;

import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.util.FileCopyUtils;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
public class FileDownloadController {
	
	private static final String INTERNAL_FILE="irregular-verbs-list.pdf";
	private static final String EXTERNAL_FILE_PATH="C:/mytemp/SpringMVCHibernateManyToManyCRUDExample.zip";
	

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

	/*
	 * Download a file from 
	 *   - inside project, located in resources folder.
	 *   - outside project, located in File system somewhere. 
	 */
	@RequestMapping(value="/download/{type}", method = RequestMethod.GET)
	public void downloadFile(HttpServletResponse response, @PathVariable("type") String type) throws IOException {
	
		File file = null;
		
		if(type.equalsIgnoreCase("internal")){
			ClassLoader classloader = Thread.currentThread().getContextClassLoader();
			file = new File(classloader.getResource(INTERNAL_FILE).getFile());
		}else{
			file = new File(EXTERNAL_FILE_PATH);
		}
		
		if(!file.exists()){
			String errorMessage = "Sorry. The file you are looking for does not exist";
			System.out.println(errorMessage);
			OutputStream outputStream = response.getOutputStream();
			outputStream.write(errorMessage.getBytes(Charset.forName("UTF-8")));
			outputStream.close();
			return;
		}
		
		String mimeType= URLConnection.guessContentTypeFromName(file.getName());
		if(mimeType==null){
			System.out.println("mimetype is not detectable, will take default");
			mimeType = "application/octet-stream";
		}
		
		System.out.println("mimetype : "+mimeType);
		
        response.setContentType(mimeType);
        
        /* "Content-Disposition : inline" will show viewable types [like images/text/pdf/anything viewable by browser] right on browser 
            while others(zip e.g) will be directly downloaded [may provide save as popup, based on your browser setting.]*/
        response.setHeader("Content-Disposition", String.format("inline; filename="" + file.getName() +"""));

        
        /* "Content-Disposition : attachment" will be directly download, may provide save as popup, based on your browser setting*/
        //response.setHeader("Content-Disposition", String.format("attachment; filename="%s"", file.getName()));
        
        response.setContentLength((int)file.length());

		InputStream inputStream = new BufferedInputStream(new FileInputStream(file));

        //Copy bytes from source to destination(outputstream in this example), closes both streams.
        FileCopyUtils.copy(inputStream, response.getOutputStream());
	}

}

该控制器包括两个文件。一个文件是内部应用（内部资源），和其他文件位于外部的应用程序的文件系统。您的项目一定要改变外部文件的路径。仅用于演示的目的，我们已在路径一个额外的路径变量（内部/外部）。我们正在使用Spring FileCopyUtils工具类流从源复制到目的地。

配置

package com.yiibai.springmvc.configuration;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
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{

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

}

初始化

package com.yiibai.springmvc.configuration;

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[] { "/" };
    }
 
 }

添加视图

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

<head>
	<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
	<title>Spring 4 MVC File Download Example</title>
	<link href="<c:url value='/static/css/bootstrap.css' />"  rel="stylesheet"></link>
	<link href="<c:url value='/static/css/app.css' />" rel="stylesheet"></link>
</head>
<body>
	<div class="form-container">
		<h1>Welcome to FileDownloader Example</h1>
		
		Click on below links to see FileDownload in action.<br/><br/>
		
		
		<a href="<c:url value='/download/internal' />">Download This File (located inside project)</a>  
		<br/>
		<a href="<c:url value='/download/external' />">Download This File (located outside project, on file system)</a>
		
	</div> 
</body>
</html>