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{ width: 300px; height: 20px; background-color:#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{ background-color: #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="width: 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>
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