JavaScript 二进制转文件

菜的黑人牙膏

发布于 2019-01-21 16:21:52

3.9K0

发布于 2019-01-21 16:21:52

文章被收录于专栏：前端学习归纳总结前端学习归纳总结

关于在javascript下，如何将二进制转换成相应的文件并下载。

首先，我们需要得到二进制的数据以及相应的文件格式，没有相应的格式也可以，可以通过二进制来判断，但相对会麻烦很多，所以建议可以要求后端提供文件的名字来得到相应的文件格式。

http://blog.csdn.net/sdomain/article/details/4636197 这是一个二进制判断文件类型的博客有兴趣可以看看

首先我们拿到了二进制的数据。在这里，我拿到的是一个对象two_object.

/*
* 提示：该行代码过长，系统自动注释不进行高亮。一键复制会移除系统注释 
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*/

这是一张png的图片。他的MIME类型是 image/png MIME类型参考

拿到了相应的MIME类型和二进制数据后，就可以开始转换文件了，先把对象转成数组，

在这里我们需要了解一下 ArrayBuffer和 Unit8Array等数组类型，我们最终需要得到一个ArrayBuffer类型的二进制数组。

这里不能使用普通数组的原因是我们接下来需要将二进制数组转成Blob对象，而Blob构造函数明确要求：

传入的第一个参数array 是一个由ArrayBuffer, ArrayBufferView, Blob, DOMString 等对象构成的 Array ，或者其他类似对象的混合体，它将会被放进 Blob.

相关代码：

// 首先将对象转换成普通数组 得到长度
var cacheArr = new Array();
    for (let i in two_obj){
        cacheArr[i] = two_obj[i];
    }
    var len = cacheArr.length;
// 构造ArrayBuffer 并通过Uint8Array的实例来对其修改 将普通的数组转成ArrayBuffer数组
    var buffer = new ArrayBuffer(len);
    var arr = new Uint8Array(buffer);

    for (var i = 0;i<len;i++){
        arr[i] = cacheArr[i];
    }

第一步完成后，下一步就是真正的转换了，首先把得到的二进制数组转成相应的Blob对象，然后由window.URL.createObjectURL将该对象转成一个链接，然后就可以通过创建一个a标签来下载相应的文件啦。

下载完成后记得用window.URL.revokeObjectURL释放这个链接。

相关代码：

       var data = new Blob([arr],{type:"image/png"});
        var downloadUrl = window.URL.createObjectURL(data);
        var result=document.getElementById("result");    
        var anchor = document.createElement("a");
        anchor.href = downloadUrl;
        anchor.download = "fsdfds.png";
        anchor.click();
        window.URL.revokeObjectURL(data);

总结一下，具体的思路就是：

1.将二进制转成ArrayBuffer数组，方便Blob使用，

2.将得到的Blob对象，利用window.URL.createObjectURL()来创建一个链接指向它。

3.创建A标签元素 download属性指向该链接，通过点击来下载它。

4.释放创建的链接。

最后放上例子代码：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title></title>
    
</head>
<body>
<script type="text/javascript">  
  
</script>  
    <input type="button" value="下载文件" onclick="readAsBinaryString()" /> 
<div id="result" name="result"></div> 
</body>
</html>
<script type="text/javascript">
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