html页面中展示pdf文件

由于最近安卓app开发中遇到WebView不支持pdf文件的预览，所以在h5页面中使用pdf.js来实现预览。

PDF.js可在官网下载地址：http://mozilla.github.io/pdf.js/

以下代码可以直接在服务器端运行，查看效果（需要注意一下几点）

下载jquery.min.js文件
下载pdf.js文件
下载pdf.worker.js(demo.html页面无需引入，因为在pdf.js文件中已经引入了)
任意pdf文件（比如demo中的1212.pdf）,js代码中的url就是需要预览的pdf地址，可以是本地pdf文件，可以是在线的，也可以是pdf文件流
demo.html页面必须放在服务器端才能预览pdf
pdf.js默认不显示电子签章(数字签名），解决办法：在pdf.worker.js中找到如下代码并注释掉

pdf.js旧版本

if (this.data.fieldType === 'Sig') {
    warn('unimplemented annotation type: Widget signature');
    return false;
}

pdf.js新版本v1.10.88

if (data.fieldType === 'Sig') {
    _this2.setFlags(_util.AnnotationFlag.HIDDEN);
 }

demo.html文件如下：

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0 user-scalable=yes" />
  <meta name="hotcss" content="initial-dpr=1;max-width=0;design-width=720">
  <title>pdf预览</title>
  <link rel="stylesheet" href="https://cdn.staticfile.org/font-awesome/4.7.0/css/font-awesome.css">
  <link rel="stylesheet" href="http://cdn.bootcss.com/bootstrap/3.3.5/css/bootstrap.min.css">
  <link rel="icon" href="data:;base64,=">
  <script src="./jquery.min.js"></script>
  <script src="./pdf.js"></script>
  <style type="text/css">
  .close-pdf{position:fixed; top:20px; right:20px; color:#1d69b3; }
  button{width:40px; border:none; background: none; color:#1d69b3; font-size: 20px; outline: none;}
  .control{
      position: fixed;
      bottom: 20px;
      left: 50%;
      margin-left: -140px;
  }
  .control span{color:#1d69b3; font-size: 16px; line-height: 30px;}
</style>
</head>
<body>
  <a href="javascript:;" onclick="history.go(-1)" class="close-pdf"> <i class="glyphicon glyphicon-remove"></i></a>
  <div class="">
      <canvas id="the-canvas" style="width: 100%;height: 95%;"></canvas>
  </div>
  <div class="control">
      <button id="first"><i class="fa fa-angle-double-left"></i></button>
      &nbsp; &nbsp;
      <button id="prev"><i class="fa fa-angle-left"></i></button>
      &nbsp; &nbsp;
      <span><span id="page_num"></span> / <span id="page_count"></span></span>
      &nbsp; &nbsp;
      <button id="next"><i class="fa fa-angle-right"></i></button>
      &nbsp; &nbsp;
      <button id="final"><i class="fa fa-angle-double-right"></i></button>
  </div>
</body>
<script>
    var url = '1212.pdf'
    var pdfDoc = null,
    pageNum = 1,
    pageRendering = false,
    pageNumPending = null,
    scale = 2.5,   //调节预览文件的清晰度
    canvas = document.getElementById('the-canvas'),
    ctx = canvas.getContext('2d');

    /**
        * Get page info from document, resize canvas accordingly, and render page.
        * @param num Page number.
        */
    function renderPage(num) {
        pageRendering = true;
        // Using promise to fetch the page
        pdfDoc.getPage(num).then(function(page) {
            var viewport = page.getViewport(scale);
            canvas.height = viewport.height;
            canvas.width = viewport.width;

            // Render PDF page into canvas context
            var renderContext = {
                canvasContext: ctx,
                viewport: viewport
            };
            var renderTask = page.render(renderContext);

            // Wait for rendering to finish
            renderTask.promise.then(function() {
                pageRendering = false;
                if (pageNumPending !== null) {
                    // New page rendering is pending
                    renderPage(pageNumPending);
                    pageNumPending = null;
                }
            });
        });

        // Update page counters
        document.getElementById('page_num').textContent = num;
    }

    /**
        * If another page rendering in progress, waits until the rendering is
        * finised. Otherwise, executes rendering immediately.
        */
    function queueRenderPage(num) {
        if (pageRendering) {
            pageNumPending = num;
        } else {
            renderPage(num);
        }
    }

    /**
        * Displays previous page.
        */
    function onPrevPage() {
        if (pageNum <= 1) {
            return;
        }
        pageNum--;
        queueRenderPage(pageNum);
    }
    document.getElementById('prev').addEventListener('click', onPrevPage);

    /**
        * Displays next page.
        */
    function onNextPage() {
        if (pageNum >= pdfDoc.numPages) {
            return;
        }
        pageNum++;
        queueRenderPage(pageNum);
    }
    document.getElementById('next').addEventListener('click', onNextPage);

    /**
        * Displays first page.
        */
    function onFirstPage() {
        if (pageNum <= 1) {
            return;
        }
        pageNum=1;
        queueRenderPage(pageNum);
    }
    document.getElementById('first').addEventListener('click', onFirstPage);

    /**
        * Displays final page.
        */
    function onFinalPage() {
        if (pageNum >= pdfDoc.numPages) {
            return;
        }
        pageNum=pdfDoc.numPages;
        queueRenderPage(pageNum);
    }
    document.getElementById('final').addEventListener('click', onFinalPage);

    /**
        * Asynchronously downloads PDF.
        */
    PDFJS.getDocument(url).then(function(pdfDoc_) {
        pdfDoc = pdfDoc_;
        document.getElementById('page_count').textContent = pdfDoc.numPages;

        // Initial/first page rendering
        renderPage(pageNum);
    });
</script>
</html>