MultipartFile是springframe封裝好的一個專門用於檔案上傳的介面，MultipartFile有一下幾個抽象方法（直接copy的原始碼）：

public interface MultipartFile {

	/**
	 * Return the name of the parameter in the multipart form.
	 * @return the name of the parameter (never {@code null} or empty)
	 */
	String getName();

	/**
	 * Return the original filename in the client's filesystem.
	 * <p>This may contain path information depending on the browser used,
	 * but it typically will not with any other than Opera.
	 * @return the original filename, or the empty String if no file
	 * has been chosen in the multipart form, or {@code null}
	 * if not defined or not available
	 */
	String getOriginalFilename();

	/**
	 * Return the content type of the file.
	 * @return the content type, or {@code null} if not defined
	 * (or no file has been chosen in the multipart form)
	 */
	String getContentType();

	/**
	 * Return whether the uploaded file is empty, that is, either no file has
	 * been chosen in the multipart form or the chosen file has no content.
	 */
	boolean isEmpty();

	/**
	 * Return the size of the file in bytes.
	 * @return the size of the file, or 0 if empty
	 */
	long getSize();

	/**
	 * Return the contents of the file as an array of bytes.
	 * @return the contents of the file as bytes, or an empty byte array if empty
	 * @throws IOException in case of access errors (if the temporary store fails)
	 */
	byte[] getBytes() throws IOException;

	/**
	 * Return an InputStream to read the contents of the file from.
	 * The user is responsible for closing the stream.
	 * @return the contents of the file as stream, or an empty stream if empty
	 * @throws IOException in case of access errors (if the temporary store fails)
	 */
	InputStream getInputStream() throws IOException;

	/**
	 * Transfer the received file to the given destination file.
	 * <p>This may either move the file in the filesystem, copy the file in the
	 * filesystem, or save memory-held contents to the destination file.
	 * If the destination file already exists, it will be deleted first.
	 * <p>If the file has been moved in the filesystem, this operation cannot
	 * be invoked again. Therefore, call this method just once to be able to
	 * work with any storage mechanism.
	 * @param dest the destination file
	 * @throws IOException in case of reading or writing errors
	 * @throws IllegalStateException if the file has already been moved
	 * in the filesystem and is not available anymore for another transfer
	 */
	void transferTo(File dest) throws IOException, IllegalStateException;

}
 

看下介面的實現類：

有兩個實現

 commons:

/*
 * Copyright 2002-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.multipart.commons;

import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.Serializable;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItem;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.web.multipart.MultipartFile;

/**
 * MultipartFile implementation for Jakarta Commons FileUpload.
 *
 * @author Trevor D. Cook
 * @author Juergen Hoeller
 * @since 29.09.2003
 * @see CommonsMultipartResolver
 */
@SuppressWarnings("serial")
public class CommonsMultipartFile implements MultipartFile, Serializable {

	protected static final Log logger = LogFactory.getLog(CommonsMultipartFile.class);

	private final FileItem fileItem;

	private final long size;


	/**
	 * Create an instance wrapping the given FileItem.
	 * @param fileItem the FileItem to wrap
	 */
	public CommonsMultipartFile(FileItem fileItem) {
		this.fileItem = fileItem;
		this.size = this.fileItem.getSize();
	}

	/**
	 * Return the underlying {@code org.apache.commons.fileupload.FileItem}
	 * instance. There is hardly any need to access this.
	 */
	public final FileItem getFileItem() {
		return this.fileItem;
	}


	@Override
	public String getName() {
		return this.fileItem.getFieldName();
	}

	@Override
	public String getOriginalFilename() {
		String filename = this.fileItem.getName();
		if (filename == null) {
			// Should never happen.
			return "";
		}
		// check for Unix-style path
		int pos = filename.lastIndexOf("/");
		if (pos == -1) {
			// check for Windows-style path
			pos = filename.lastIndexOf("\\");
		}
		if (pos != -1)  {
			// any sort of path separator found
			return filename.substring(pos + 1);
		}
		else {
			// plain name
			return filename;
		}
	}

	@Override
	public String getContentType() {
		return this.fileItem.getContentType();
	}

	@Override
	public boolean isEmpty() {
		return (this.size == 0);
	}

	@Override
	public long getSize() {
		return this.size;
	}

	@Override
	public byte[] getBytes() {
		if (!isAvailable()) {
			throw new IllegalStateException("File has been moved - cannot be read again");
		}
		byte[] bytes = this.fileItem.get();
		return (bytes != null ? bytes : new byte[0]);
	}

	@Override
	public InputStream getInputStream() throws IOException {
		if (!isAvailable()) {
			throw new IllegalStateException("File has been moved - cannot be read again");
		}
		InputStream inputStream = this.fileItem.getInputStream();
		return (inputStream != null ? inputStream : new ByteArrayInputStream(new byte[0]));
	}

	@Override
	public void transferTo(File dest) throws IOException, IllegalStateException {
		if (!isAvailable()) {
			throw new IllegalStateException("File has already been moved - cannot be transferred again");
		}

		if (dest.exists() && !dest.delete()) {
			throw new IOException(
					"Destination file [" + dest.getAbsolutePath() + "] already exists and could not be deleted");
		}

		try {
			this.fileItem.write(dest);
			if (logger.isDebugEnabled()) {
				String action = "transferred";
				if (!this.fileItem.isInMemory()) {
					action = isAvailable() ? "copied" : "moved";
				}
				logger.debug("Multipart file '" + getName() + "' with original filename [" +
						getOriginalFilename() + "], stored " + getStorageDescription() + ": " +
						action + " to [" + dest.getAbsolutePath() + "]");
			}
		}
		catch (FileUploadException ex) {
			throw new IllegalStateException(ex.getMessage());
		}
		catch (IOException ex) {
			throw ex;
		}
		catch (Exception ex) {
			logger.error("Could not transfer to file", ex);
			throw new IOException("Could not transfer to file: " + ex.getMessage());
		}
	}

	/**
	 * Determine whether the multipart content is still available.
	 * If a temporary file has been moved, the content is no longer available.
	 */
	protected boolean isAvailable() {
		// If in memory, it's available.
		if (this.fileItem.isInMemory()) {
			return true;
		}
		// Check actual existence of temporary file.
		if (this.fileItem instanceof DiskFileItem) {
			return ((DiskFileItem) this.fileItem).getStoreLocation().exists();
		}
		// Check whether current file size is different than original one.
		return (this.fileItem.getSize() == this.size);
	}

	/**
	 * Return a description for the storage location of the multipart content.
	 * Tries to be as specific as possible: mentions the file location in case
	 * of a temporary file.
	 */
	public String getStorageDescription() {
		if (this.fileItem.isInMemory()) {
			return "in memory";
		}
		else if (this.fileItem instanceof DiskFileItem) {
			return "at [" + ((DiskFileItem) this.fileItem).getStoreLocation().getAbsolutePath() + "]";
		}
		else {
			return "on disk";
		}
	}

}
 

standard:

/*
 * Copyright 2002-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.multipart.support;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.Part;

import org.springframework.http.HttpHeaders;
import org.springframework.util.FileCopyUtils;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.web.multipart.MultipartException;
import org.springframework.web.multipart.MultipartFile;

/**
 * Spring MultipartHttpServletRequest adapter, wrapping a Servlet 3.0 HttpServletRequest
 * and its Part objects. Parameters get exposed through the native request's getParameter
 * methods - without any custom processing on our side.
 *
 * @author Juergen Hoeller
 * @since 3.1
 */
public class StandardMultipartHttpServletRequest extends AbstractMultipartHttpServletRequest {

	private static final String CONTENT_DISPOSITION = "content-disposition";

	private static final String FILENAME_KEY = "filename=";

	private Set<String> multipartParameterNames;


	/**
	 * Create a new StandardMultipartHttpServletRequest wrapper for the given request,
	 * immediately parsing the multipart content.
	 * @param request the servlet request to wrap
	 * @throws MultipartException if parsing failed
	 */
	public StandardMultipartHttpServletRequest(HttpServletRequest request) throws MultipartException {
		this(request, false);
	}

	/**
	 * Create a new StandardMultipartHttpServletRequest wrapper for the given request.
	 * @param request the servlet request to wrap
	 * @param lazyParsing whether multipart parsing should be triggered lazily on
	 * first access of multipart files or parameters
	 * @throws MultipartException if an immediate parsing attempt failed
	 */
	public StandardMultipartHttpServletRequest(HttpServletRequest request, boolean lazyParsing) throws MultipartException {
		super(request);
		if (!lazyParsing) {
			parseRequest(request);
		}
	}


	private void parseRequest(HttpServletRequest request) {
		try {
			Collection<Part> parts = request.getParts();
			this.multipartParameterNames = new LinkedHashSet<String>(parts.size());
			MultiValueMap<String, MultipartFile> files = new LinkedMultiValueMap<String, MultipartFile>(parts.size());
			for (Part part : parts) {
				String filename = extractFilename(part.getHeader(CONTENT_DISPOSITION));
				if (filename != null) {
					files.add(part.getName(), new StandardMultipartFile(part, filename));
				}
				else {
					this.multipartParameterNames.add(part.getName());
				}
			}
			setMultipartFiles(files);
		}
		catch (Exception ex) {
			throw new MultipartException("Could not parse multipart servlet request", ex);
		}
	}

	private String extractFilename(String contentDisposition) {
		if (contentDisposition == null) {
			return null;
		}
		// TODO: can only handle the typical case at the moment
		int startIndex = contentDisposition.indexOf(FILENAME_KEY);
		if (startIndex == -1) {
			return null;
		}
		String filename = contentDisposition.substring(startIndex + FILENAME_KEY.length());
		if (filename.startsWith("\"")) {
			int endIndex = filename.indexOf("\"", 1);
			if (endIndex != -1) {
				return filename.substring(1, endIndex);
			}
		}
		else {
			int endIndex = filename.indexOf(";");
			if (endIndex != -1) {
				return filename.substring(0, endIndex);
			}
		}
		return filename;
	}


	@Override
	protected void initializeMultipart() {
		parseRequest(getRequest());
	}

	@Override
	public Enumeration<String> getParameterNames() {
		if (this.multipartParameterNames == null) {
			initializeMultipart();
		}
		if (this.multipartParameterNames.isEmpty()) {
			return super.getParameterNames();
		}

		// Servlet 3.0 getParameterNames() not guaranteed to include multipart form items
		// (e.g. on WebLogic 12) -> need to merge them here to be on the safe side
		Set<String> paramNames = new LinkedHashSet<String>();
		Enumeration<String> paramEnum = super.getParameterNames();
		while (paramEnum.hasMoreElements()) {
			paramNames.add(paramEnum.nextElement());
		}
		paramNames.addAll(this.multipartParameterNames);
		return Collections.enumeration(paramNames);
	}

	@Override
	public Map<String, String[]> getParameterMap() {
		if (this.multipartParameterNames == null) {
			initializeMultipart();
		}
		if (this.multipartParameterNames.isEmpty()) {
			return super.getParameterMap();
		}

		// Servlet 3.0 getParameterMap() not guaranteed to include multipart form items
		// (e.g. on WebLogic 12) -> need to merge them here to be on the safe side
		Map<String, String[]> paramMap = new LinkedHashMap<String, String[]>();
		paramMap.putAll(super.getParameterMap());
		for (String paramName : this.multipartParameterNames) {
			if (!paramMap.containsKey(paramName)) {
				paramMap.put(paramName, getParameterValues(paramName));
			}
		}
		return paramMap;
	}

	@Override
	public String getMultipartContentType(String paramOrFileName) {
		try {
			Part part = getPart(paramOrFileName);
			return (part != null ? part.getContentType() : null);
		}
		catch (Exception ex) {
			throw new MultipartException("Could not access multipart servlet request", ex);
		}
	}

	@Override
	public HttpHeaders getMultipartHeaders(String paramOrFileName) {
		try {
			Part part = getPart(paramOrFileName);
			if (part != null) {
				HttpHeaders headers = new HttpHeaders();
				for (String headerName : part.getHeaderNames()) {
					headers.put(headerName, new ArrayList<String>(part.getHeaders(headerName)));
				}
				return headers;
			}
			else {
				return null;
			}
		}
		catch (Exception ex) {
			throw new MultipartException("Could not access multipart servlet request", ex);
		}
	}


	/**
	 * Spring MultipartFile adapter, wrapping a Servlet 3.0 Part object.
	 */
	private static class StandardMultipartFile implements MultipartFile {

		private final Part part;

		private final String filename;

		public StandardMultipartFile(Part part, String filename) {
			this.part = part;
			this.filename = filename;
		}

		@Override
		public String getName() {
			return this.part.getName();
		}

		@Override
		public String getOriginalFilename() {
			return this.filename;
		}

		@Override
		public String getContentType() {
			return this.part.getContentType();
		}

		@Override
		public boolean isEmpty() {
			return (this.part.getSize() == 0);
		}

		@Override
		public long getSize() {
			return this.part.getSize();
		}

		@Override
		public byte[] getBytes() throws IOException {
			return FileCopyUtils.copyToByteArray(this.part.getInputStream());
		}

		@Override
		public InputStream getInputStream() throws IOException {
			return this.part.getInputStream();
		}

		@Override
		public void transferTo(File dest) throws IOException, IllegalStateException {
			this.part.write(dest.getPath());
		}
	}

}
 

只看上面的方法，感覺有點抽象，做一個案例試一下：

案例（上傳圖片）：

        //這裡用到了getOriginalFilename()方法，為了獲取檔名
String fileName=uploadFile.getOriginalFilename();
		String fileType=fileName.substring(fileName.lastIndexOf("."));
        if (! fileType.matches("^.(jpg|png|tif)$")) {
         //這裡的error=1時，表示操作不正常
			result.setError(1);
			return result;
		}  

try {
              //這裡用到了getInputStream()方法，為了將檔案轉換成流
              //判斷是否檔案為惡意檔案
			BufferedImage bufferedImage=ImageIO.read(uploadFile.getInputStream());
			int height=bufferedImage.getHeight();
			int width=bufferedImage.getWidth();
			if (width==0||height==0) {
           //這裡的error=1時，表示操作不正常
				result.setError(1);
				return result;
			}	
			//這裡用到了transferTo()方法，進行寫盤操作
            //這裡的path需要自己設定，這裡我就沒有寫，只是隨便寫的path代表路徑
			uploadFile.transferTo(path);
			return result;
		} catch (IOException e) {
			e.printStackTrace();
		}