java多个pdf合并为一个pdf，并通过feign下载

1.首先pom文件添加依赖，操作pdf文件工具类

        
            org.apache.pdfbox
            pdfbox
            2.0.21
        

2.pdf合并操作

public ResponseEntity mergePdf(MultipartFile[] files) {
        //pdf合并工具类
        PDFMergerUtility mergePdf = new PDFMergerUtility();
        //合并pdf生成的文件名
        String filename = "d:/"+new Date().getTime()+".pdf";
        for (MultipartFile multipartFile : files) {
            try {
                byte[] bytes = multipartFile.getBytes();
                InputStream in = new ByteArrayInputStream(bytes);
                mergePdf.addSource(in); // 合并pdf
            } catch (IOException e) {
                throw new BaseException("Error merging pdf files- " + filename, e);
            }
        }
        try {
            // 设置合并生成pdf文件名称及路径
            mergePdf.setDestinationFileName(filename);
            mergePdf.mergeDocuments(MemoryUsageSetting.setupMainMemoryOnly());
        } catch (IOException e) {
            e.printStackTrace();
        }
        return exportFile(new File(filename), filename);
    }

注意：在feign之间传输二进制流时，返回值必须为 ResponseEntity 类型，所以封装了个私有方法，如下：

private ResponseEntity exportFile(File file, String filename) {

        HttpHeaders headers = new HttpHeaders();
        ResponseEntity entity = null;
        InputStream in=null;
        try {
            in=new FileInputStream(file);
            byte[] bytes = new byte[in.available()];
            filename = URLEncoder.encode(filename, "utf-8");
            in.read(bytes);
            headers.add("Content-Disposition", "attachment;filename="+filename);
            entity = new ResponseEntity<>(bytes, headers, HttpStatus.OK);
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            if(in!=null) {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return entity;
    }

注意：feign层代码接收类型 必须为 feign.Response

    Response mergePdf(@RequestPart("file") MultipartFile[] file);

3.消费层 controller代码：

public void mergePdf(@RequestPart("file") MultipartFile[] file, HttpServletResponse response){
        InputStream inputStream = null;
        OutputStream outputStream = null;
        try {
        	// 调用feign层代码获取Response 
            Response responseEntity = orderService.mergePdf(file);
            // Response 获取响应体
            Response.Body body = responseEntity.body();
            // 通过响应体来获取 一个输入流
            inputStream = body.asInputStream();
            BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);
            // 设置http 响应头信息等
            response.setContentType("multipart.form-data");
            response.setHeader("Content-Disposition", responseEntity.headers().get("Content-Disposition").toString().replace("[","").replace("]",""));

            outputStream = new BufferedOutputStream(response.getOutputStream());
            int length = 0;
            byte[] temp = new byte[1024 * 10];
            while ((length = bufferedInputStream.read(temp)) != -1) {
            	// 输出二进制流
                outputStream.write(temp, 0, length);
            }
            outputStream.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (outputStream != null) {
                try {
                    outputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

最后调用接口，可以发现浏览器响应一个 blob 协议地址，最终由前端处理为二进制文件