java8中的ByteArrayOutputStream异常处理

Question

private void logSoapMessage(SOAPMessage soapMessage, String type) {
        ByteArrayOutputStream bout = null;
        try {
            bout = new ByteArrayOutputStream();
            soapMessage.writeTo(bout);
            logger.info("The " + type + " is " + bout.toString("UTF-8"));
        } catch (IOException e) {
            logger.debug("Exception while logging soap message " + e);
        }
    }

Is above code can give resource leak error?

Answer 1

Is above code can give resource leak error?

No it isn't / doesn't.

A ByteArrayOutputStream doesn't have any resources ¹ that can leak.

However, an unsophisticated static checker might mistakenly flag your code as a potential resource leak. You could either mark this as a "false positive" in the appropriate way, or just close the stream anyway. The following is the best way to do the latter for Java 7 and later:

    try (ByteArrayOutputStream bout = new ByteArrayOutputStream()) {
        soapMessage.writeTo(bout);
        logger.info("The " + type + " is " + bout.toString("UTF-8"));
    } catch (IOException e) {
        logger.debug("Exception while logging soap message " + e);
    }

---

^{1 - Resources refers to things like file descriptors that are obtained from the operating system, and are only available in limited numbers. If these resources are not managed properly by a Java application, there is a risk that the application will run out of them. It is conventional for an object that holds a resource to implement AutoClosable and provide a close() method that releases the resources.}

Answer 2

Its because you're not closing the resource when you're done with it.

Java 7 introduced the try-with-resource function:

private void logSoapMessage(SOAPMessage soapMessage, String type) {
  try (ByteArrayOutputStream bout = new ByteArrayOutputStream()){
    soapMessage.writeTo(bout);
    logger.info("The " + type + " is " + bout.toString("UTF-8"));
  } catch (IOException e) {
    logger.debug("Exception while logging soap message " + e);
  }
}

Which will automatically close the ByteArrayOutputStream even if it throws an exception.

The old way prior to java 7 you'd have to write it this way:

private void logSoapMessage(SOAPMessage soapMessage, String type) {
  ByteArrayOutputStream bout = null;
  try {
    bout = new ByteArrayOutputStream();
    soapMessage.writeTo(bout);
    logger.info("The " + type + " is " + bout.toString("UTF-8"));
  } catch (IOException e) {
    logger.debug("Exception while logging soap message " + e);
  } finally {
    if (bout != null) bout.close();
  }
}

To make sure the resource was closed prior to exiting the method and not get a resource leak.

Here is some info about the try-with-resource: https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html