Java 批处理作业期间，我面临空指针

我有一个批处理作业，它处理从源到目标的数据。偶尔，我会在作业触发后立即看到NPE，它运行良好，直到完成。看起来第96行抛出了错误，但我不知道为什么会在作业触发时抛出？我认为这条线是错误的根源

Node node = nodeList.item( 0 ).getAttributes().getNamedItem(DCDirectProcessorConstants.Tag_Response_Status);

Java代码

InputSource source = new InputSource();
            source.setCharacterStream(new StringReader(response));
            Document document = builder.parse(source);

            XPath xpath = XPathFactory.newInstance().newXPath();
            NodeList nodeList = document.getElementsByTagName(DCDirectProcessorConstants.Tag_Response_getValue);
            Node node = nodeList.item( 0 ).getAttributes().getNamedItem(DCDirectProcessorConstants.Tag_Response_Status);

            RatingSessionTO responseTO = XMLProcessingUtil.processResponseData(
                    ratingSessionTO, response, migrationConfig, data.toString());

            /*DataMigrationDao dao  = null;
                if( migrationConfig.isOneTimeMigration() ){

                    dao = (DataMigrationDao) appContext.getBean("oneTimeMigrationDao");
                }else{
                    dao = (DataMigrationDao) appContext.getBean("dailyMigrationDao");
                }
             */

            //This flow is explicitly for Catchup
            if("1".equals(catchUp)){

                if(kafkaFailure){
                    postMessageToKafka(responseTO,catchUp,dao);

                }
                else if(raterFailure){
                    //Handle rater failure
                    int ID = dao.getExternalID(responseTO);
                    if(ID != 0){
                        responseTO.setExternalID(ID);
                    }
                    migrateMessageToRaterInfo(responseTO,dao,catchUp);

                }
                else{       //Handle XML_Sessions failure

                    try{
                        if(dao.verifySessionID(responseTO) == 0){   
                            // Defect 76093 
                            if (node == null || DCDirectProcessorConstants.Status_Failure.equalsIgnoreCase(node.getTextContent())) {
                                logger.error("Retry failure.Source id already present in catchup "+ ratingSessionTO.getSrcId());
                            } else {
                                dao.migrateData(responseTO);
                                postMessageToKafka(responseTO, catchUp, dao);
                                migrateMessageToRaterInfo(responseTO, dao, catchUp);
                            }
                        } else{
                            logger.error("Source id already present in archive "+ratingSessionTO.getSrcId()+" Updating status to 'C'");
                            dao.updateCatchupCompletion(ratingSessionTO.getSrcId());
                        }
                    }
                    catch(Exception e){
                        logger.error("Catchup failed for "+ratingSessionTO.getSrcId()+" Status remains 'P'");
                    }
                }
            }

堆栈跟踪

java.lang.NullPointerException

在com.mercuryinsurance.r3.util.MigrationExecutorThread.run（MigrationExecutorThread.java:96）[migration.jar:？] 位于java.util.concurrent.ThreadPoolExecutor.runWorker（ThreadPoolExecutor.java:1142）[？：1.8.066] 在java.util.concurrent.ThreadPoolExecutor$Worker.run（ThreadPoolExecutor.java:617）[？：1.8.066]

---

在java.lang.Thread.run（Thread.java:745）[？：1.8.0_66]

来自

NodeList.item（）的java文档：

返回集合中的索引第X项。如果索引大于或等于列表中的节点数，则返回null


要防止出现
NullPointerException
，您应该在访问元素之前检查节点列表的长度：

NodeList nodeList = document.getElementsByTagName(DCDirectProcessorConstants.Tag_Response_getValue);
if(nodeList.getLength() > 0) {
  Node node = nodeList.item( 0 ).getAttributes().getNamedItem(DCDirectProcessorConstants.Tag_Response_Status);
  ...
} else {
  // handle the case no node found
}

尽管出现了
NullpointerException
，但您的代码并没有说明为什么作业仍然运行良好，但我猜在您发布的代码段周围有一些
try/catch
可以处理和记录异常