MutipartFile是spring里面定义的接口，它封装了用户在上传图片时所包含的所有信息，但是有些时候我们要将file转换成MutipartFile，才能在保持原有代码逻辑的情况下方便代码的调整，但是file不能直接转换成MutipartFile，现在就要教大家如何将file转换成MutipartFile。
如果要转换，要用到的包是spring-test
maven:
<properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><spring.version>4.2.5.RELEASE</spring.version></properties><dependencies><dependency><groupId>org.springframework</groupId><artifactId>spring-test</artifactId><version>${spring.version}</version><scope>test</scope></dependency></dependencies> 或者
<properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><spring.version>4.2.5.RELEASE</spring.version></properties><dependencies><dependency><groupId>org.springframework</groupId><artifactId>spring-test</artifactId><version>${spring.version}</version><scope>test</scope></dependency></dependencies> maven配置好了之后，要用到一个非常重要的类MockMultipartFile
他是继承MultipartFile接口来模拟MultipartFile。当然具体的实现要自己看源码，我们要讲的是如何file转换成MultipartFile。
转换的方式很简单，就是创建MockMultipartFile的构造函数。
具体的有四个构造函数
-MockMultipartFile(String name, byte[] content)
-MockMultipartFile(String name, InputStream contentStream)
-MockMultipartFile(String name, String originalFilename, String contentType, byte[] content)
-MockMultipartFile(String name, String originalFilename, String contentType, InputStream contentStream)
*name文件名
*originalFilename原文件名
*contentStream输入流
*content byte数组
例子：
MultipartFile multipartFile = new MockMultipartFile(file.getName(), inputStream);
下面贴上我在应用上面的截取的具体代码片段：
要求：把url里的图片导入到本地。
WebFileUtils.java
import java.io.BufferedOutputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream; import java.net.HttpURLConnection; import java.net.URL; import org.springframework.stereotype.Service; @Service("webFileUtils") public class WebFileUtils { private static final org.slf4j.Logger logger = org.slf4j.LoggerFactory.getLogger(WebFileUtils.class); /** * 根据url拿取file * * @param url * @param suffix * 文件后缀名 * */ public static File createFileByUrl(String url, String suffix) { byte[] byteFile = getImageFromNetByUrl(url); if (byteFile != null) { File file = getFileFromBytes(byteFile, suffix); return file; } else { logger.info("生成文件失败！"); return null; } } /** * 根据地址获得数据的字节流 * * @param strUrl * 网络连接地址 * @return */ private static byte[] getImageFromNetByUrl(String strUrl) { try { URL url = new URL(strUrl); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setRequestMethod("GET"); conn.setConnectTimeout(5 * 1000); InputStream inStream = conn.getInputStream();// 通过输入流获取图片数据 byte[] btImg = readInputStream(inStream);// 得到图片的二进制数据 return btImg; } catch (Exception e) { e.printStackTrace(); } return null; } /** * 从输入流中获取数据 * * @param inStream * 输入流 * @return * @throws Exception */ private static byte[] readInputStream(InputStream inStream) throws Exception { ByteArrayOutputStream outStream = new ByteArrayOutputStream(); byte[] buffer = new byte[1024]; int len = 0; while ((len = inStream.read(buffer)) != -1) { outStream.write(buffer, 0, len); } inStream.close(); return outStream.toByteArray(); } // 创建临时文件 private static File getFileFromBytes(byte[] b, String suffix) { BufferedOutputStream stream = null; File file = null; try { file = File.createTempFile("pattern", "." + suffix); System.out.println("临时文件位置："+file.getCanonicalPath()); FileOutputStream fstream = new FileOutputStream(file); stream = new BufferedOutputStream(fstream); stream.write(b); } catch (Exception e) { e.printStackTrace(); } finally { if (stream != null) { try { stream.close(); } catch (IOException e) { e.printStackTrace(); } } } return file; } public static void main(String[] args) { WebFileUtils.createFileByUrl("https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1508327007250&di=b7be3e44999983ec75ba54537287ff13&imgtype=0&src=http%3A%2F%2Fb.hiphotos.baidu.com%2Fimage%2Fpic%2Fitem%2Faa64034f78f0f736ce4ff5720055b319ebc4130b.jpg","jpg"); } }
ImgUploadServiceImpl.java
public MultipartFile createImg(String url){try {// File转换成MutipartFileFile file = WebFileUtils.createFileByUrl(url, "jpg");FileInputStream inputStream = new FileInputStream(file);MultipartFile multipartFile = new MockMultipartFile(file.getName(), inputStream);//注意这里面填啥，MultipartFile里面对应的参数就有啥，比如我只填了name，则//MultipartFile.getName()只能拿到name参数，但是originalFilename是空。return multipartFile; } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); return null; } } 以上是我做项目中对file转MultipartFile的分享。
api链接：https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/mock/web/MockMultipartFile.html
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