如何使用StreamingResponseBody并尝试使用资源？

Question

我想动态地创建一个Excel表并将其返回给客户端。为了保存一些内存，我想使用StreamingResponseBody作为返回类型。我还使用try-with-resources自动关闭workbook。这是密码。

@RestController
public class ExcelController {

  @GetMapping("/hello")
  public ResponseEntity<StreamingResponseBody> excel() throws IOException {
    try (var workbook = new XSSFWorkbook();) {
      workbook.createSheet("hello world");
      return ResponseEntity.ok()
          .contentType(MediaType.parseMediaType("application/vnd.ms-excel"))
          .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=data.xlsx")
          .body(workbook::write);
    }
  }
}

不幸的是，这不起作用，我得到了以下错误消息。

Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception

java.io.IOException: Cannot write data, document seems to have been closed already
        at org.apache.poi.ooxml.POIXMLDocument.write(POIXMLDocument.java:215) ~[poi-ooxml-5.1.0.jar:5.1.0]
        at org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBodyReturnValueHandler$StreamingResponseBodyTask.call(StreamingResponseBodyReturnValueHandler.java:111) ~[spring-webmvc-5.3.13.jar:5.3.13]
        at org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBodyReturnValueHandler$StreamingResponseBodyTask.call(StreamingResponseBodyReturnValueHandler.java:98) ~[spring-webmvc-5.3.13.jar:5.3.13]
        at org.springframework.web.context.request.async.WebAsyncManager.lambda$startCallableProcessing$4(WebAsyncManager.java:337) ~[spring-web-5.3.13.jar:5.3.13]
        at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539) ~[na:na]
        at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) ~[na:na]
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136) ~[na:na]
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635) ~[na:na]
        at java.base/java.lang.Thread.run(Thread.java:833) ~[na:na]

我已经尝试过使用我的自定义TaskExecutor，正如StreamingResponseBody所描述的那样，但这并没有真正的帮助。最后，我找到了一个可行的解决方案，但我想知道为什么第一个解决方案(包括try-with-resources和方法引用)不能工作。

@RestController
public class ExcelController {

  @GetMapping("/hello")
  public ResponseEntity<StreamingResponseBody> excel() throws IOException {
    var workbook = new XSSFWorkbook();
    workbook.createSheet("hello world");
    return ResponseEntity.ok()
        .contentType(MediaType.parseMediaType("application/vnd.ms-excel"))
        .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=data.xlsx")
        .body(
            out -> {
              workbook.write(out);
              workbook.close();
            });
  }
}

我非常感谢你的帮助！谢谢

Answer 1

因为StreamingResponseBody工作异步，而且由于您的试用资源在该部分之外，所以资源可能已经关闭(我怀疑99.9%的情况下？)。来修复StreamingResponseBody中的所有内容。

return ResponseEntity.ok()
    .contentType(MediaType.parseMediaType("application/vnd.ms-excel"))
    .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=data.xlsx")
    .body(
        out -> {
          try (var workbook = new XSSFWorkbook()) {
            workbook.createSheet("hello world");
            workbook.write(out);
          }
      });
}

为了使它更具可读性(以及我不喜欢多行lambda这一事实)，您当然也可以将代码移到方法中，并从lambda调用它。

private void writeWorkbook(OutputStream out) {
  try (var workbook = new XSSFWorkbook()) {
    workbook.createSheet("hello world");
    workbook.write(out);
  }
}

return ResponseEntity.ok()
    .contentType(MediaType.parseMediaType("application/vnd.ms-excel"))
    .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=data.xlsx")
    .body( this::writeWorkbook);
}

这将在适当的时间打开(并关闭) Workbook。