Java后端返回PDF预览给前端

前端要预览服务器PDF 可直接将要blob流返回给前端 即可用浏览器自带pdf预览功能打开，现有两种方式

方式1 返回blob流给前端 代码如下       

1. @PostMapping(value = "/preview")
2. @ResponseBody
3. public void showPdf(HttpServletResponse response) {
4. try {
5. File file = new File("filePath");
6. OutputStream out = null;
7. try (BufferedInputStream br = new BufferedInputStream(new FileInputStream(file));
8. ) {
9. byte[] bs = new byte[1024];
10. int len;
11. response.reset(); // 非常重要
12. URL u = new URL("file:///" + "filePath");
13. String contentType = u.openConnection().getContentType();
14. response.setContentType(contentType);
15. response.setHeader("Content-Disposition", "inline;filename="
16. + "preview.pdf");
17. out = response.getOutputStream();
18. while ((len = br.read(bs)) > 0) {
19. out.write(bs, 0, len);
20. }
21. out.flush();
22. out.close();
23. }
24. } catch (Exception e) {
25. e.printStackTrace();
26. }
27. }

此时 前端解析可直接拿返回的文件流 例子如下

1. let blob = this.response;
2. const binaryData = [];
3. binaryData.push(blob);
4. const url = window.URL.createObjectURL(new Blob(binaryData, { type: 'application/pdf' }));
5. window.open(url);

但有的时候 不想返回文件流 可把文件返回为base64 （注意 base64可能超长）此时代码修改如下

1. File file = new File("filePath");
2. OutputStream out = null;
3. try (BufferedInputStream br = new BufferedInputStream(new FileInputStream(file));
4. ByteArrayOutputStream outStream = new ByteArrayOutputStream();
5. ) {
6. int len;
7. URL u = new URL("file:///" + "filePath");
8. String contentType = u.openConnection().getContentType();
9. byte[] buffer = new byte[1024];
10. //每次读取的字符串长度，如果为-1，代表全部读取完毕
11. //使用输入流从buffer里把数据读取出来
12. while ((len = br.read(buffer)) != -1) {
13. //用输出流往buffer里写入数据，中间参数代表从哪个位置开始读，len代表读取的长度
14. outStream.write(buffer, 0, len);
15. }
16. // 对字节数组Base64编码
17. Base64Encoder base64 = new Base64Encoder();
18. String base64Str = replaceEnter(base64.encode(outStream.toByteArray()));
21. }
22. } catch (Exception e) {
23. }

前端修改如下

1. let base64 = resBase64.data.base64;
2. base64 = base64.replace(/[\n\r]/g, '')
3. const raw = window.atob(base64)
4. const rawLength = raw.length
5. const uInt8Array = new Uint8Array(rawLength)
6. for (let i = 0; i < rawLength; ++i) {
7. uInt8Array[i] = raw.charCodeAt(i)
8. }
9. const url = window.URL.createObjectURL(new Blob([uInt8Array], { type: resBase64.data.contentType }));
10. window.open(url);