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AttachmentDTO

/**
* 文件流传输基础类
*/
public class AttachmentDTO implements Serializable {
	private static final long serialVersionUID = -5616353779779592228L;
	// 文件名称
	private String name;
	// 文件格式
	private String fileExt;
	// 文件流
	private byte[] fileBytes;
	// 文件存储路径
	private String path;
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getFileExt() {
		return fileExt;
	}
	public void setFileExt(String fileExt) {
		this.fileExt = fileExt;
	}
	public byte[] getFileBytes() {
		return fileBytes;
	}
	public void setFileBytes(byte[] fileBytes) {
		this.fileBytes = fileBytes;
	}
	public String getPath() {
		return path;
	}
	public void setPath(String path) {
		this.path = path;
	}
}

CommonController

@Controller
public class CommonController {
	@Resource
	private CommonProvider commonProvider;
	
	@RequestMapping(value = "")
	public void getFileByName(@RequestParam("file") String fileName, HttpServletRequest request, HttpServletResponse response)
			throws IOException {
		AttachmentDTO attachment = commonProvider.getFileByName(fileName);
		// 判断文件是否存在
		if (attachment == null) {
			throw new BusinessException("目标文件不存在fileName:" + fileName);
		}
		try {
			response.setContentType("application/x-download");
			response.setContentLength((int) attachment.getFileBytes().length);
			response.setHeader("Content-Disposition", "attachment; filename=\"" + attachment.getName() + "\"");
			FileCopyUtils.copy(attachment.getFileBytes(), response.getOutputStream());
		} catch (Exception e) {
			throw new BusinessException("目标文件读取发生异常fileName:" + fileName, e);
		}
	}
}

CommonProvider

/**
* 根据文件名获取byte流
*/
public AttachmentDTO getFileBytesByName(String fileName) {
	AttachmentDTO atta = new AttachmentDTO();
	File file = getFileByName(fileName);
	atta.setFileBytes(FileCopyUtils.copyToByteArray(file));
	atta.setName(file.getName());
	atta.setPath(file.getName());
	atta.setFileExt(FilenameUtils.getExtension(file.getName()));
	
	return atta;
}
private File getFileByName(String fileName){
	String path = ...  // 这里面是服务里文件存储目录,File.separator文件目录分隔符
	File file = new File(path + fileName);
	return file;
}