读取连接中文件流和页面展示base64编码的文件

• 背景需求
• • 从接口处获取base64编码的字节流
  • • 依赖
    • java 代码
  • 前端展示
  • • pdf
    • 图片

背景需求

我需要展示一个pdf 文件在页面上，但是我一直没办法将 pdf的下载链接用预览方式展示出来，于是打算讨个巧，直接给前端页面发送 Base64 编码的字符串，用来展示pdf文件。而正好我们的文件也有一个获取流的接口。于是，变出现了这篇文章。

从接口处获取base64编码的字节流

依赖

                     org.apache.hadoop             hadoop-common             3.4.0          

java 代码

1. 直接从 URL 获取流

    public static String downloadFile3(String UrlFilePath, String localFilePath) {         URL url = null;         HttpURLConnection httpUrl = null;         try {             url = new URL(UrlFilePath);             httpUrl = (HttpURLConnection) url.openConnection();             // 设置请求方式，默认是GET             // httpUrl.setRequestMethod("POST");             httpUrl.connect();             try (BufferedInputStream bis = new BufferedInputStream(httpUrl.getInputStream())) {                 byte[] bytes = IOUtils.toByteArray(bis);                 String base64String = Base64.getEncoder().encodeToString(bytes);                  // Write the BASE64 encoded string to the file                 try (BufferedWriter writer = new BufferedWriter(new FileWriter(localFilePath))) {                     writer.write(base64String);                 }                 return base64String;             }         } catch (Exception e) {             e.printStackTrace();         }         return "";     } 

2. 发送 GET 请求 获取流

/**      * @param url 远程文件路径      * @return base64 编码字符串      */     public static String byGet(String url) {         // 创建Httpclient对象         CloseableHttpClient httpclient = HttpClientBuilder.create().build();         RequestConfig requestConfig = RequestConfig.custom().setConnectTimeout(30000).setConnectionRequestTimeout(30000).setSocketTimeout(30000).build();          String resultString = "";         CloseableHttpResponse response = null;         try {             URIBuilder builder = new URIBuilder(url);             URI uri = builder.build();             // 创建http GET请求             HttpGet httpGet = new HttpGet(uri);             httpGet.setConfig(requestConfig);             httpGet.addHeader("Content-type", "application/json; charset=utf-8");              // 执行请求             response = httpclient.execute(httpGet);               // 判断返回状态是否为200             if (response.getStatusLine().getStatusCode() == 200) {                 InputStream inputStream = response.getEntity().getContent();                 byte[] bytes = IOUtils.toByteArray(inputStream);                 BASE64Encoder encoder = new BASE64Encoder();                 resultString = encoder.encode(bytes);                 return resultString;             }         } catch (Exception e) {          } finally {             try {                 if (response != null) {                     response.close();                 }                 httpclient.close();             } catch (IOException e) {                 e.printStackTrace();             }         }         return "";     } 

前端展示

pdf

        function viewPdf (content) {              const blob = this.base64ToBlob(content)             if (window.navigator && window.navigator.msSaveOrOpenBlob) {                 window.navigator.msSaveOrOpenBlob(blob)             } else {                 const fileURL = URL.createObjectURL(blob)                 window.open(fileURL)             }         }         function base64ToBlob (code) {             code = code.replace(/[\n\r]/g, '')             const raw = window.atob(code)             const rawLength = raw.length             const uInt8Array = new Uint8Array(rawLength)             for (let i = 0; i < rawLength; ++i) {                 uInt8Array[i] = raw.charCodeAt(i)             }             return new Blob([uInt8Array], { type: 'application/pdf' })         } 

图片

let ImgURL ="\"; 

将拼接好的 ImgURL 拼接即可