php web development - Upload and download folder

The core principle:

The core of the project is to upload the file block. Front and rear end to high level of cooperation, the two sides agreed need better data in order to complete large file segment, we focus on in the project to solve the following problems.

* How fragmentation;

* How to synthesize a file;

* Interrupted which slice from the beginning.

How points, using powerful js library to ease our work, have been able to block the wheels on large files on the market, although the nature of the programmer has forced me to re-create the wheel. However, because of the relationship as well as working time, I can only give up the. Finally, I chose Baidu's WebUploader to achieve the desired front-end.

How close, before closing, we must first solve a problem, how do we distinguish the file block belongs. At the beginning, I was using a front-end to generate a unique uuid do sign documents, put on each slice request. But later, when do I give up the second pass, using Md5 to maintain block and file relationships.

Merge file server in question, and record blocking, and in this respect the industry has actually given a good solution. Referring Thunder, you will find that each download time, there will be two files, a file body, another file is a temporary file, temporary file stores the state of each block corresponding byte position.

These are the need to make close contact with front and rear ends, the front end of a fixed size need to file fragmentation, and fragmentation to bring the request number and size. After successful transmission request reaches the front end of the background, according to the server only needs to request data slice number and slice each block size (segment size is fixed and the same) is calculated start position, and the read segment data file, writing into the file.

In order to facilitate the development, I will end service business logic follows divided into initialization, block processing, and the like uploaded file.

The server-side business logic module follows

Functional Analysis:

Folder generating module

After the folder is uploaded by the server scan code is as follows

分块上传，分块处理逻辑应该是最简单的逻辑了，up6已经将文件进行了分块，并且对每个分块数据进行了标识，这些标识包括文件块的索引，大小，偏移，文件MD5，文件块MD5（需要开启）等信息，服务端在接收这些信息后便可以非常方便的进行处理了。比如将块数据保存到分布式存储系统中

分块上传可以说是我们整个项目的基础，像断点续传、暂停这些都是需要用到分块。

分块这块相对来说比较简单。前端是采用了webuploader，分块等基础功能已经封装起来，使用方便。

借助webUpload提供给我们的文件API,前端就显得异常简单。

前台HTML模板

分则必合。把大文件分片了，但是分片了就没有原本文件功能，所以我们要把分片合成为原本的文件。我们只需要把分片按原本位置写入到文件中去。因为前面原理那一部我们已经讲到了，我们知道分块大小和分块序号，我就可以知道该分块在文件中的起始位置。所以这里使用RandomAccessFile是明智的，RandomAccessFile能在文件里面前后移动。但是在andomAccessFile的绝大多数功能，已经被JDK1.4的NIO的“内存映射文件(memory-mapped files)”取代了。我在该项目中分别写了使用RandomAccessFile与MappedByteBuffer来合成文件。分别对应的方法是uploadFileRandomAccessFile和uploadFileByMappedByteBuffer。两个方法代码如下。

秒传功能

服务端逻辑

秒传功能，相信大家都体现过了，网盘上传的时候，发现上传的文件秒传了。其实原理稍微有研究过的同学应该知道，其实就是检验文件MD5，记录下上传到系统的文件的MD5,在一个文件上传前先获取文件内容MD5值或者部分取值MD5，然后在匹配系统上的数据。

Breakpoint-http实现秒传原理，客户端选择文件之后，点击上传的时候触发获取文件MD5值，获取MD5后调用系统一个接口（/index/checkFileMd5），查询该MD5是否已经存在（我在该项目中用redis来存储数据，用文件MD5值来作key，value是文件存储的地址。）接口返回检查状态，然后再进行下一步的操作。相信大家看代码就能明白了。

嗯，前端的MD5取值也是用了webuploader自带的功能，这还是个不错的工具。