这是Bootstrap 3,4,5的解决方案。

要制作一个看起来像按钮的功能文件输入控件，你只需要HTML:

HTML

<label class="btn btn-default">
    Browse <input type="file" hidden>
</label>

这适用于所有现代浏览器，包括IE9+。如果你也需要对旧IE的支持，请使用下面所示的遗留方法。

这种技术依赖于HTML5的隐藏属性。Bootstrap 4使用以下CSS在不支持的浏览器中填充此特性。如果使用Bootstrap 3，则可能需要添加。

[hidden] {
  display: none !important;
}

旧IE的遗留方法

如果您需要IE8及以下版本的支持，请使用以下HTML/CSS:

HTML

<span class="btn btn-default btn-file">
    Browse <input type="file">
</span>

CSS

.btn-file {
    position: relative;
    overflow: hidden;
}
.btn-file input[type=file] {
    position: absolute;
    top: 0;
    right: 0;
    min-width: 100%;
    min-height: 100%;
    font-size: 100px;
    text-align: right;
    filter: alpha(opacity=0);
    opacity: 0;
    outline: none;
    background: white;
    cursor: inherit;
    display: block;
}

注意，当你点击<label>时，旧的IE不会触发文件输入，所以CSS“膨胀”做了一些事情来解决这个问题:

使文件输入的跨度为周围<span>的全宽/高 使文件输入不可见

反馈和额外阅读

我已经发布了关于这个方法的更多细节，以及如何向用户显示选中了多少文件的示例:

https://www.abeautifulsite.net/posts/whipping-file-inputs-into-shape-with-bootstrap-3/

不需要花哨的东西:

HTML:

<form method="post" action="/api/admin/image" enctype="multipart/form-data">
    <input type="hidden" name="url" value="<%= boxes[i].url %>" />
    <input class="image-file-chosen" type="text" />
    <br />
    <input class="btn image-file-button" value="Choose Image" />
    <input class="image-file hide" type="file" name="image"/> <!-- Hidden -->
    <br />
    <br />
    <input class="btn" type="submit" name="image" value="Upload" />
    <br />
</form>

JS:

$('.image-file-button').each(function() {
      $(this).off('click').on('click', function() {
           $(this).siblings('.image-file').trigger('click');
      });
});
$('.image-file').each(function() {
      $(this).change(function () {
           $(this).siblings('.image-file-chosen').val(this.files[0].name);
      });
});

注意:所讨论的三个表单元素必须是彼此的兄弟元素(。Image-file-chosen， .image-file-button， .image-file)

设置上传按钮的样式很麻烦，因为它设置的是输入的样式而不是按钮的样式。

但是你可以用这个技巧:

http://www.quirksmode.org/dom/inputfile.html

简介:

Take a normal <input type="file"> and put it in an element with position: relative. To this same parent element, add a normal <input> and an image, which have the correct styles. Position these elements absolutely, so that they occupy the same place as the <input type="file">. Set the z-index of the <input type="file"> to 2 so that it lies on top of the styled input/image. Finally, set the opacity of the <input type="file"> to 0. The <input type="file"> now becomes effectively invisible, and the styles input/image shines through, but you can still click on the "Browse" button. If the button is positioned on top of the image, the user appears to click on the image and gets the normal file selection window. (Note that you can't use visibility: hidden, because a truly invisible element is unclickable, too, and we need the to remain clickable)

这是另一个技巧，它不是最好的解决方案，但它只是给你一个选择

HTML代码:

<button clss="btn btn-primary" id="btn_upload">Choose File</button>
<input id="fileupload" class="hide" type="file" name="files[]">

Javascript:

$("#btn_upload").click(function(e){
e.preventDefault();
$("#fileupload").trigger('click');
});

从上面的其他文章中得到一些灵感，这里有一个完整的解决方案，它结合了一个看起来像表单控制字段的输入组插件，用于一个干净的文件输入小部件，其中包括到当前文件的链接。

.input-file { position: relative; margin: 60px 60px 0 } /* Remove margin, it is just for stackoverflow viewing */ .input-file .input-group-addon { border: 0px; padding: 0px; } .input-file .input-group-addon .btn { border-radius: 0 4px 4px 0 } .input-file .input-group-addon input { cursor: pointer; position:absolute; width: 72px; z-index:2;top:0;right:0;filter: alpha(opacity=0);-ms-filter:"progid:DXImageTransform.Microsoft.Alpha(Opacity=0)";opacity:0; background-color:transparent; color:transparent; } <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.1/css/bootstrap.min.css"> <div class="input-group input-file"> <div class="form-control"> <a href="/path/to/your/current_file_name.pdf" target="_blank">current_file_name.pdf</a> </div> <span class="input-group-addon"> <a class='btn btn-primary' href='javascript:;'> Browse <input type="file" name="field_name" onchange="$(this).parent().parent().parent().find('.form-control').html($(this).val());"> </a> </span> </div>

我已经创建了一个自定义上传按钮，只接受图像，这可以根据您的要求修改。

希望这能有所帮助!!：）

(已使用的Bootstrap框架)

代码笔链接

HTML

<center>
 <br />
 <br />
 <span class="head">Upload Button Re-Imagined</span>
 <br />
 <br />
 <div class="fileUpload blue-btn btn width100">
   <span>Upload your Organizations logo</span>
   <input type="file" class="uploadlogo" />
 </div>
</center>

CSS

 .head {
   font-size: 25px;
   font-weight: 200;
 }

 .blue-btn:hover,
 .blue-btn:active,
 .blue-btn:focus,
 .blue-btn {
   background: transparent;
   border: solid 1px #27a9e0;
   border-radius: 3px;
   color: #27a9e0;
   font-size: 16px;
   margin-bottom: 20px;
   outline: none !important;
   padding: 10px 20px;
 }

 .fileUpload {
   position: relative;
   overflow: hidden;
   height: 43px;
   margin-top: 0;
 }

 .fileUpload input.uploadlogo {
   position: absolute;
   top: 0;
   right: 0;
   margin: 0;
   padding: 0;
   font-size: 20px;
   cursor: pointer;
   opacity: 0;
   filter: alpha(opacity=0);
   width: 100%;
   height: 42px;
 }


 /*Chrome fix*/

 input::-webkit-file-upload-button {
   cursor: pointer !important;
 }

JS

// You can modify the upload files to pdf's, docs etc
//Currently it will upload only images
$(document).ready(function($) {

  // Upload btn
  $(".uploadlogo").change(function() {
    readURL(this);
  });

  function readURL(input) {
    var url = input.value;
    var ext = url.substring(url.lastIndexOf('.') + 1).toLowerCase();
    if (input.files && input.files[0] && (ext == "png" || ext == "jpeg" || ext == "jpg" || ext == "gif" || ext == "svg")) {
      var path = $('.uploadlogo').val();
      var filename = path.replace(/^.*\\/, "");
      $('.fileUpload span').html('Uploaded logo : ' + filename);
      // console.log(filename);
    } else {
      $(".uploadlogo").val("");
      $('.fileUpload span').html('Only Images Are Allowed!');
    }
  }
});