ResponseEntity<InputStreamResource> 返回两个服务方法

Question

我有两个服务返回两个不同的 ResponseEntity。

public ResponseEntity<InputStreamResource> getA(...) {
return ResponseEntity
            .ok()
            .headers(headers)
            .contentType(MediaType.APPLICATION_PDF)
            .contentLength(out.size())
            .body(new InputStreamResource(bis)); }
public ResponseEntity<InputStreamResource> getB(...) {
return ResponseEntity
            .ok()
            .headers(headers)
            .contentType(MediaType.APPLICATION_PDF)
            .contentLength(out.size())
            .body(new InputStreamResource(bis)); }

每个服务都有一个调用和返回的控制器。

public ResponseEntity<InputStreamResource> getA(...) {
return aService.getA(...) }
public ResponseEntity<InputStreamResource> getB(...) {
return bService.getB(...) }

我正在尝试创建另一个控制器，它同时执行并返回两个服务。

public ResponseEntity<InputStreamResource> getAB(...) {
return aService.getA(...) *and* bService.getB(...) ?????? }

不确定如何将两个 ResponseEntities 返回合并为一个。

Answer 1

import org.springframework.core.io.InputStreamResource;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import com.itextpdf.text.Document;
import com.itextpdf.text.PageSize;
import com.itextpdf.text.pdf.PdfCopy;
import com.itextpdf.text.pdf.PdfReader;

@RestController
public class ReportController {
private static final Logger LOGGER = ...

@Autowired
private ReportManager manager;

@GetMapping("/reportcard/students")
public ResponseEntity<InputStreamResource> getStudentReportCard(parameters...) throws ServiceException {
    List<InputStream> studentReportList = manager.getStudentReports(parameters.... );
            
    HttpHeaders headers = getHeaders(Constants.STUDENTS_REPORT_CARD);

    Document document = new Document(PageSize.LETTER);
    ByteArrayOutputStream outputStream = null;

    try {
        outputStream = new ByteArrayOutputStream();
        PdfCopy copy = new PdfCopy(document, outputStream);

        document.open();

        for (InputStream file : studentReportList) {
            copy.addDocument(new PdfReader(file)); // writes directly to the output stream
        }
        outputStream.flush();
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        if (document.isOpen()) {
            document.close();
        }
        try {
            if (outputStream != null) {
                outputStream.close();
            }
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }
    }

    InputStreamResource inputStreamResource = new InputStreamResource(new ByteArrayInputStream(outputStream.toByteArray()));
    return ResponseEntity.ok().headers(headers).contentType(MediaType.APPLICATION_PDF).body(inputStreamResource);
}

private HttpHeaders getHeaders(String fileName) {
    HttpHeaders headers = new HttpHeaders();
    headers.add("Cache-Control", "no-cache, no-store, must-revalidate");
    headers.add("Pragma", "no-cache");
    headers.add("Expires", "0");
    headers.set("Content-disposition", "attachment; filename=" + fileName);
    return headers;
}


public class ReportManagerImpl implements ReportManager {
private static final Logger LOGGER = ...

@Autowired
private HttpClient httpClient;

@Override
public List<InputStream> getStudentReports(parameters...)
        throws ServiceException {
    
    List<InputStream> studentReportList = new Vector<InputStream>();
    
    List<String> learnersList = //list of students
    
    String reportUrl = //url
        
    for (String learner : learnersList) {
        studentReportList.add(getHttpResponse(reportUrl + learner));
    }
    
    return studentReportList;
}

private InputStream getHttpResponse(String url) throws ServiceException {
    try {
        HttpResponse response = httpClient.execute(new HttpGet(url));
        HttpEntity entity = response.getEntity();

        return entity.getContent();
    } catch (IOException e) {
        throw new ServiceException(e.getMessage());
    }

}

Answer 2

从 Service 方法返回 ResponseEntity 不是一个好主意。

Controller 层应该负责生成 ResponseEntity 对象。那是他的事，不是服务层的事。同样，服务层的职责是根据给定的输入准备某种 DTO 对象，然后控制器将环绕该 DTO 并将其作为响应发送。

所以，我建议在这里做一些结构上的改变。

服务层

public InputStreamResource getA(...) {
  return A 
}
public InputStreamResource getB(...) {
  return B 
}

控制器层

public ResponseEntity<InputStreamResource> getA(...) {
  return new ResponseEntity<>(aService.getA(...) (
}
public ResponseEntity<InputStreamResource> getB(...) {
  return new ResponseEntity<>(bService.getB(...) )
}

合并 2 个流

---

如果您的目标是逐个流式传输 2 个不同的 pdf 文档，那么我认为可以先将内存中的 pdf 文档与您可能使用的任何 pdf 库合并。然后创建一个 InputStreamResource 作为 Response。

但是，如果流可以按顺序运行，那么下面是一个使用 SequenceInputStream 合并 2 个流的工作示例 -

@RequestMapping(
        path = "/sayHello",
        method = RequestMethod.GET,
        produces = MediaType.TEXT_PLAIN_VALUE
)
public ResponseEntity<InputStreamResource> get() {
        byte[] inputBytes1 = "Hello".getBytes();
        // 1st stream has "Hello" text
        ByteArrayInputStream baos1 = new ByteArrayInputStream(inputBytes1);

        byte[] inputBytes2 = "World".getBytes();
        // 2nd stream has "World" text
        ByteArrayInputStream baos2 = new ByteArrayInputStream(inputBytes2);

        // combined stream will have "HelloWorld" text
        SequenceInputStream combinedStream = new SequenceInputStream(baos1, baos2);
        InputStreamResource inputStreamResource = new InputStreamResource(combinedStream);
        return ResponseEntity.ok().body(inputStreamResource);
    }

输出 ->

 curl -X GET  http://localhost:8083/sayHello
 HelloWorld

Answer 3

您可以通过这种方式尝试：

public ResponseEntity<List<InputStreamResource> getAAndB(...) {
    
                  private List<InputStreamResource> result = new ArrayList<>();
                  result.add(aService.getA(...));
                  result.add(bService.getB(...));
           return ResponseEntity.ok().body(result)); }  
    }