学步园

    public OfferInfo parseXml(String content) throws NumberFormatException, XMLStreamException {
        if (content == null || content.isEmpty()) {
            return null;
        }
        XMLInputFactory factory = XMLInputFactory.newInstance();
        XMLStreamReader reader = null;
        try {
            reader = factory.createXMLStreamReader(new StringReader(content));
        } catch (XMLStreamException e1) {
            return null;
        }

        if (reader == null) {
            return null;
        }

        OfferInfo offerInfo = new OfferInfo();
        while (reader.hasNext()) {
            int event = 0;
            try {
                event = reader.nextTag();
            } catch (Exception e) {
            }
            switch (event) {
                case XMLStreamConstants.START_ELEMENT:
                    if (reader.getLocalName().equalsIgnoreCase(OFFER_ID)) {
                        offerInfo.setOfferId(Long.parseLong(reader.getElementText()));
                    } else if (reader.getLocalName().equalsIgnoreCase(MEMBER_ID)) {
                        offerInfo.setMemberId(reader.getElementText());
                    } else if (reader.getLocalName().equalsIgnoreCase(ACTION)) {
                        offerInfo.setAction(reader.getElementText());
                    }
                    break;
                case XMLStreamConstants.END_ELEMENT:
                    break;
            }
            //如果已经解析完需要的字段，则跳过剩余xml内容的解析，提高性能
            if(offerInfo.getOfferId() != null && offerInfo.getMemberId() != null && offerInfo.getAction() != null){
                return offerInfo;
            }
        }
        return offerInfo;

    }

这段代码的

  try {
                event = reader.nextTag();
            } catch (Exception e) {
            }

居然能搞出一个死循环，导致cpu跟load飙升，yonggc非常频繁

初步诊断如下：

stax在调用reader的nextTag方法时，因为格式不对，导致抛异常，本来我是只需要xml内容的三个字段，我认为如果是其他字段解析有问题，我直接忽略，所以我没打印日志，也没有跳出xml解析，而是直接解析，因为对nextTag可能不熟悉，我要的功能跟nextTag提供的不匹配，导致抛出异常之后，我又调用了该方法，然后因为nextTag抛出异常之后没有忽略当前有问题的xml内容，导致下次调用时又回到有问题的xml起始位置继续处理，重复抛出异常，这样就成为死循环了。

之前两个多月应用一直没问题，由于没有打印日志所以也扑捉不到当时xml的内容。

这里需要做两个教训：1.打印日志，2调用API时一定要了解API的详细处理过程，避免错误调用API导致问题；3.对于出错时event初始参数可以进行判断是否出错了，进行处理。

从jstack里面打印出来10几个这样的线程信息

"ActiveMQ Session Task" prio=10 tid=0x00000000451b3000 nid=0x7db7 runnable [0x00000000429ff000]
   java.lang.Thread.State: RUNNABLE
	at java.util.Arrays.copyOf(Arrays.java:2882)
	at java.lang.AbstractStringBuilder.expandCapacity(AbstractStringBuilder.java:100)
	at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:390)
	at java.lang.StringBuilder.append(StringBuilder.java:119)
	at javax.xml.stream.XMLStreamException.<init>(XMLStreamException.java:61)
	at com.sun.org.apache.xerces.internal.impl.XMLStreamReaderImpl.next(XMLStreamReaderImpl.java:594)
	at com.sun.org.apache.xerces.internal.impl.XMLStreamReaderImpl.nextTag(XMLStreamReaderImpl.java:1235)
	at com.alibaba.china.industry.brand.napoli.OfferNewReceiverWorker.parseXml(OfferNewReceiverWorker.java:195)

"ActiveMQ Session Task" prio=10 tid=0x0000000046892000 nid=0x7baf runnable [0x0000000040a72000]
   java.lang.Thread.State: RUNNABLE
	at java.lang.StringBuffer.toString(StringBuffer.java:585)
	- locked <0x000000078890bc10> (a java.lang.StringBuffer)
	at java.text.MessageFormat.makeFormat(MessageFormat.java:1337)
	at java.text.MessageFormat.applyPattern(MessageFormat.java:458)
	at java.text.MessageFormat.<init>(MessageFormat.java:350)
	at java.text.MessageFormat.format(MessageFormat.java:811)
	at com.sun.org.apache.xerces.internal.impl.msg.XMLMessageFormatter.formatMessage(XMLMessageFormatter.java:85)
	at com.sun.xml.internal.stream.StaxErrorReporter.reportError(StaxErrorReporter.java:95)
	at com.sun.org.apache.xerces.internal.impl.XMLScanner.reportFatalError(XMLScanner.java:1414)
	at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanCDATASection(XMLDocumentFragmentScannerImpl.java:1690)
	at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2985)
	at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:648)
	at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:140)
	at com.sun.org.apache.xerces.internal.impl.XMLStreamReaderImpl.next(XMLStreamReaderImpl.java:554)
	at com.sun.org.apache.xerces.internal.impl.XMLStreamReaderImpl.nextTag(XMLStreamReaderImpl.java:1235)