pdf格式文件预览，使用pdf.js

Java做pdf预览，我使用pdf.js进行的预览
pdf.js：http://mozilla.github.io/pdf.js/

参考了：http://mozilla.github.io/pdf.js/examples/
在文档中有两种方式，一种是pdf文件直接进行预览，另外一种是base64格式进行预览的。
我文件存储的地方是阿里云的oss，所以文件地址是一个链接。pdf.js预览文件直接给链接地址，会出现跨域等问题，所以我采用了base64进行pdf文件的预览，废话不多说代码如下：
1.首先需要引入jar包：
<dependency>
<groupId>org.apache.pdfbox</groupId>
<artifactId>fontbox</artifactId>
<version>2.0.1</version>
</dependency>
<dependency>
<groupId>org.apache.pdfbox</groupId>
<artifactId>pdfbox</artifactId>
<version>2.0.1</version>
</dependency>

2.读取pdf文件的链接地址，转换为base64格式输出。
import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;

/**
 * Created by gf on 2017/12/28.
 */
public class Demo04 {

    static BASE64Encoder encoder = new sun.misc.BASE64Encoder();
    static BASE64Decoder decoder = new sun.misc.BASE64Decoder();

    /**
     *  将PDF转换成base64编码
     *  1.使用BufferedInputStream和FileInputStream从File指定的文件中读取内容；
     *  2.然后建立写入到ByteArrayOutputStream底层输出流对象的缓冲输出流BufferedOutputStream
     *  3.底层输出流转换成字节数组，然后由BASE64Encoder的对象对流进行编码
     * */
    static String getPDFBinary(File file) {
        FileInputStream fin =null;
        BufferedInputStream bin =null;
        ByteArrayOutputStream baos = null;
        BufferedOutputStream bout =null;
        try {
            //建立读取文件的文件输出流
            fin = new FileInputStream(file);
            //在文件输出流上安装节点流（更大效率读取）
            bin = new BufferedInputStream(fin);
            // 创建一个新的 byte 数组输出流，它具有指定大小的缓冲区容量
            baos = new ByteArrayOutputStream();
            //创建一个新的缓冲输出流，以将数据写入指定的底层输出流
            bout = new BufferedOutputStream(baos);
            byte[] buffer = new byte[1024];
            int len = bin.read(buffer);
            while(len != -1){
                bout.write(buffer, 0, len);
                len = bin.read(buffer);
            }
            //刷新此输出流并强制写出所有缓冲的输出字节，必须这行代码，否则有可能有问题
            bout.flush();
            byte[] bytes = baos.toByteArray();
            //sun公司的API
            return encoder.encodeBuffer(bytes).trim();
            //apache公司的API
            //return Base64.encodeBase64String(bytes);

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally{
            try {
                fin.close();
                bin.close();
                //关闭 ByteArrayOutputStream 无效。此类中的方法在关闭此流后仍可被调用，而不会产生任何 IOException
                //baos.close();
                bout.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    /**
     * 将base64编码转换成PDF
     * @param base64sString
     * 1.使用BASE64Decoder对编码的字符串解码成字节数组
     *  2.使用底层输入流ByteArrayInputStream对象从字节数组中获取数据；
     *  3.建立从底层输入流中读取数据的BufferedInputStream缓冲输出流对象；
     *  4.使用BufferedOutputStream和FileOutputSteam输出数据到指定的文件中
     */
    static void base64StringToPDF(String base64sString){
        BufferedInputStream bin = null;
        FileOutputStream fout = null;
        BufferedOutputStream bout = null;
        try {
            //将base64编码的字符串解码成字节数组
            byte[] bytes = decoder.decodeBuffer(base64sString);
            //apache公司的API
            //byte[] bytes = Base64.decodeBase64(base64sString);
            //创建一个将bytes作为其缓冲区的ByteArrayInputStream对象
            ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
            //创建从底层输入流中读取数据的缓冲输入流对象
            bin = new BufferedInputStream(bais);
            //指定输出的文件
            File file = new File("d:/test.pdf");
            //创建到指定文件的输出流
            fout  = new FileOutputStream(file);
            //为文件输出流对接缓冲输出流对象
            bout = new BufferedOutputStream(fout);

            byte[] buffers = new byte[1024];
            int len = bin.read(buffers);
            while(len != -1){
                bout.write(buffers, 0, len);
                len = bin.read(buffers);
            }
            //刷新此输出流并强制写出所有缓冲的输出字节，必须这行代码，否则有可能有问题
            bout.flush();

        } catch (IOException e) {
            e.printStackTrace();
        }finally{
            try {
                bin.close();
                fout.close();
                bout.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    //url生成base64
    static String urlToPdf(String u) throws Exception {
        URL url = new URL(u);
        HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();// 打开URL

        BASE64Encoder encoder = new BASE64Encoder();
        BufferedInputStream bin =null;
        ByteArrayOutputStream baos = null;
        BufferedOutputStream bout =null;
        try {
            bin = new BufferedInputStream(urlConnection.getInputStream());
            baos = new ByteArrayOutputStream();
            bout = new BufferedOutputStream(baos);
            byte[] buffer = new byte[1024];
            int len = bin.read(buffer);
            while(len != -1){
                bout.write(buffer, 0, len);
                len = bin.read(buffer);
            }
            //刷新此输出流并强制写出所有缓冲的输出字节
            bout.flush();
            byte[] bytes = baos.toByteArray();
            return encoder.encodeBuffer(bytes).trim();

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally{
            try {
                bin.close();
                bout.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    public static void main(String[] args) throws Exception {
        String base64 = urlToPdf("https://fjstest.oss-cn-hangzhou.aliyuncs.com/Attachment/1514016668340.pdf");
        base64StringToPDF(base64);
    }
}

3.在前端，参考了pdf.js中例子：
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <script type="text/javascript" src="js/jquery-1.11.1.min.js"></script>
    <script src="//mozilla.github.io/pdf.js/build/pdf.js"></script>
    <title>Title</title>
    <script>
        function showPdf() {
            var pdfData = atob(
  'JVBERi0xLjcKCjEgMCBvYmogICUgZW50cnkgcG9pbnQKPDwKICAvVHlwZSAvQ2F0YWxvZwog' +
  'IC9QYWdlcyAyIDAgUgo+PgplbmRvYmoKCjIgMCBvYmoKPDwKICAvVHlwZSAvUGFnZXMKICAv' +
  'TWVkaWFCb3ggWyAwIDAgMjAwIDIwMCBdCiAgL0NvdW50IDEKICAvS2lkcyBbIDMgMCBSIF0K' +
  'Pj4KZW5kb2JqCgozIDAgb2JqCjw8CiAgL1R5cGUgL1BhZ2UKICAvUGFyZW50IDIgMCBSCiAg' +
  'L1Jlc291cmNlcyA8PAogICAgL0ZvbnQgPDwKICAgICAgL0YxIDQgMCBSIAogICAgPj4KICA+' +
  'PgogIC9Db250ZW50cyA1IDAgUgo+PgplbmRvYmoKCjQgMCBvYmoKPDwKICAvVHlwZSAvRm9u' +
  'dAogIC9TdWJ0eXBlIC9UeXBlMQogIC9CYXNlRm9udCAvVGltZXMtUm9tYW4KPj4KZW5kb2Jq' +
  'Cgo1IDAgb2JqICAlIHBhZ2UgY29udGVudAo8PAogIC9MZW5ndGggNDQKPj4Kc3RyZWFtCkJU' +
  'CjcwIDUwIFRECi9GMSAxMiBUZgooSGVsbG8sIHdvcmxkISkgVGoKRVQKZW5kc3RyZWFtCmVu' +
  'ZG9iagoKeHJlZgowIDYKMDAwMDAwMDAwMCA2NTUzNSBmIAowMDAwMDAwMDEwIDAwMDAwIG4g' +
  'CjAwMDAwMDAwNzkgMDAwMDAgbiAKMDAwMDAwMDE3MyAwMDAwMCBuIAowMDAwMDAwMzAxIDAw' +
  'MDAwIG4gCjAwMDAwMDAzODAgMDAwMDAgbiAKdHJhaWxlcgo8PAogIC9TaXplIDYKICAvUm9v' +
  'dCAxIDAgUgo+PgpzdGFydHhyZWYKNDkyCiUlRU9G');
            PDFJS.workerSrc = '//mozilla.github.io/pdf.js/build/pdf.worker.js';
            var loadingTask = PDFJS.getDocument({data: pdfData});
            loadingTask.promise.then(function(pdf) {
                // Fetch the first page
                var pageNumber = pdf.numPages;
                pdf.getPage(pageNumber).then(function(page) {

                    var scale = 0.6;
                    var viewport = page.getViewport(scale);

                    // Prepare canvas using PDF page dimensions
                    var canvas = document.getElementById('the-canvas');
                    var context = canvas.getContext('2d');
                    canvas.height = viewport.height;
                    canvas.width = viewport.width;

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

                    });
                });
            }, function (reason) {
                // PDF loading error
                console.error(reason);
            });

            PDFJS.getDocument({data: pdfData}).then(function(pdfDoc_) {
                pdfDoc = pdfDoc_;
                document.getElementById('page_count').textContent = pdfDoc.numPages;

                renderPage(pageNum);
            });
        }
    </script>
</head>
<body>
    <h1>pdf预览</h1>
    <a href="javascript:void(0)" target="_blank" onclick="showPdf();">显示pdf文档</a>
    <canvas id="the-canvas"></canvas>
</body>
</html>
这样就可以进行预览了，文件可以进行分页具体参考：http://mozilla.github.io/pdf.js/examples/，中的第三个例子。
新手小白，欢迎各位指正。