转载：https://www.jb51.net/article/101931.htm
背景
在网站开发中，文件上传是很常见的一个功能。相信很多人都会遇到这种情况，想传一个文件上去，然后网页提示“该文件过大”。因为一般情况下，我们都需要对上传的文件大小做限制，防止出现意外的情况。
但是在有些业务场景中，大文件上传又是必须的，比如邮箱附件，或者内部OA等等。
问题
服务端为什么不能直接传大文件？跟php.ini里面的几个配置有关
upload_max_filesize = 2M //PHP最大能接受的文件大小
post_max_size = 8M //PHP能收到的最大POST值'
memory_limit = 128M //内存上限
max_execution_time = 30 //最大执行时间
当然不能简单粗暴的把上面几个值调大，否则服务器内存资源吃光是迟早的问题。
解决思路
好在HTML5开放了新的FILE API，也可以直接操作二进制对象，我们可以直接在浏览器端实现文件切割，按照以前的做法就得用Flash的方案，实现起来会麻烦很多。
JS思路
1.监听上传按钮的onchange事件
2.获取文件的FILE对象
3.把文件的FILE对象进行切割，并且附加到FORMDATA对象中
4.把FORMDATA对象通过AJAX发送到服务器
5.重复3、4步骤，直到文件发送完。
PHP思路
1.建立上传文件夹
2.把文件从上传临时目录移动到上传文件夹
3.所有的文件块上传完成后，进行文件合成
4.删除文件夹
5.返回上传后的文件路径
DEMO代码
前端部分代码
<!doctype html><html lang="en"><head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>Document</title> <style> #progress{ 300px; height: 20px; padding: 0px 0px 0px 5px; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; border-left: 3px solid rgb(108, 226, 108); line-height: 20px; 640px; clear: both; outline: 0px !important; border-radius: 0px !important; border-top: 0px !important; border-right: 0px !important; border-bottom: 0px !important; border-image: initial !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; overflow: visible !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; box-sizing: content-box !important; font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important; min-height: auto !important; color: gray !important;">#f7f7f7; box-shadow:inset 0 1px 2px rgba(0,0,0,0.1); border-radius:4px; background-image:linear-gradient(to bottom,#f5f5f5,#f9f9f9); } #finish{ padding: 0px 0px 0px 5px; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; border-left: 3px solid rgb(108, 226, 108); line-height: 20px; 640px; clear: both; outline: 0px !important; border-radius: 0px !important; border-top: 0px !important; border-right: 0px !important; border-bottom: 0px !important; border-image: initial !important; bottom: auto !important; float: none !important; height: auto !important; left: auto !important; overflow: visible !important; position: static !important; right: auto !important; top: auto !important; vertical-align: baseline !important; box-sizing: content-box !important; font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important; min-height: auto !important; color: gray !important;">#149bdf; background-image:linear-gradient(45deg,rgba(255,255,255,0.15) 25%,transparent 25%,transparent 50%,rgba(255,255,255,0.15) 50%,rgba(255,255,255,0.15) 75%,transparent 75%,transparent); background-size:40px 40px; height: 100%; } form{ margin-top: 50px; } </style></head><body><div id="progress"> <div id="finish" style=" 0%;" progress="0"></div></div><form action="./upload.php"> <input type="file" name="file" id="file"> <input type="button" value="停止" id="stop"></form><script> var fileForm = document.getElementById("file"); var stopBtn = document.getElementById('stop'); var upload = new Upload(); fileForm.onchange = function(){ upload.addFileAndSend(this); } stopBtn.onclick = function(){ this.value = "停止中"; upload.stop(); this.value = "已停止"; } function Upload(){ var xhr = new XMLHttpRequest(); var form_data = new FormData(); const LENGTH = 1024 * 1024; var start = 0; var end = start + LENGTH; var blob; var blob_num = 1; var is_stop = 0 //对外方法，传入文件对象 this.addFileAndSend = function(that){ var file = that.files[0]; blob = cutFile(file); sendFile(blob,file); blob_num += 1; } //停止文件上传 this.stop = function(){ xhr.abort(); is_stop = 1; } //切割文件 function cutFile(file){ var file_blob = file.slice(start,end); start = end; end = start + LENGTH; return file_blob; }; //发送文件 function sendFile(blob,file){ var total_blob_num = Math.ceil(file.size / LENGTH); form_data.append('file',blob); form_data.append('blob_num',blob_num); form_data.append('total_blob_num',total_blob_num); form_data.append('file_name',file.name); xhr.open('POST','./upload.php',false); xhr.onreadystatechange = function () { var progress; var progressObj = document.getElementById('finish'); if(total_blob_num == 1){ progress = '100%'; }else{ progress = Math.min(100,(blob_num/total_blob_num)* 100 ) +'%'; } progressObj.style.width = progress; var t = setTimeout(function(){ if(start < file.size && is_stop === 0){ blob = cutFile(file); sendFile(blob,file); blob_num += 1; }else{ setTimeout(t); } },1000); } xhr.send(form_data); } }</script></body></html>PHP部分代码
<?phpclass Upload{ private $filepath = './upload'; //上传目录 private $tmpPath; //PHP文件临时目录 private $blobNum; //第几个文件块 private $totalBlobNum; //文件块总数 private $fileName; //文件名 public function __construct($tmpPath,$blobNum,$totalBlobNum,$fileName){ $this->tmpPath = $tmpPath; $this->blobNum = $blobNum; $this->totalBlobNum = $totalBlobNum; $this->fileName = $fileName; $this->moveFile(); $this->fileMerge(); } //判断是否是最后一块，如果是则进行文件合成并且删除文件块 private function fileMerge(){ if($this->blobNum == $this->totalBlobNum){ $blob = ''; for($i=1; $i<= $this->totalBlobNum; $i++){ $blob .= file_get_contents($this->filepath.'/'. $this->fileName.'__'.$i); } file_put_contents($this->filepath.'/'. $this->fileName,$blob); $this->deleteFileBlob(); } } //删除文件块 private function deleteFileBlob(){ for($i=1; $i<= $this->totalBlobNum; $i++){ @unlink($this->filepath.'/'. $this->fileName.'__'.$i); } } //移动文件 private function moveFile(){ $this->touchDir(); $filename = $this->filepath.'/'. $this->fileName.'__'.$this->blobNum; move_uploaded_file($this->tmpPath,$filename); } //API返回数据 public function apiReturn(){ if($this->blobNum == $this->totalBlobNum){ if(file_exists($this->filepath.'/'. $this->fileName)){ $data['code'] = 2; $data['msg'] = 'success'; $data['file_path'] = 'http://'.$_SERVER['HTTP_HOST'].dirname($_SERVER['DOCUMENT_URI']).str_replace('.','',$this->filepath).'/'. $this->fileName; } }else{ if(file_exists($this->filepath.'/'. $this->fileName.'__'.$this->blobNum)){ $data['code'] = 1; $data['msg'] = 'waiting for all'; $data['file_path'] = ''; } } header('Content-type: application/json'); echo json_encode($data); } //建立上传文件夹 private function touchDir(){ if(!file_exists($this->filepath)){ return mkdir($this->filepath); } }}//实例化并获取系统变量传参$upload = new Upload($_FILES['file']['tmp_name'],$_POST['blob_num'],$_POST['total_blob_num'],$_POST['file_name']);//调用方法，返回结果$upload->apiReturn();存在的问题
这只是一个简单的DEMO，有很多地方需要改进，比如上传的文件夹与临时文件放在一起，用户中途取消也没有发请求进行清理，容易造成文件冗余。JS采用的是同步模型，文件需要一块一块按顺序上传，会导致整个浏览器在上传的过程中出于堵塞的状态，按了按钮可能需要几秒钟才能反应过来，用户体验不好。真正需要产品化的时候就要综合考虑多种情况，当然作为一个示例，引导大家了解分块上传的思路还是不错的。
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。