AbstractStringBuilder.ensureCapacityInternal在風暴之錘得到NullPointerException異常

Question

在線系統，風暴博爾特獲得NullPointerException異常，但我認爲我行61前檢查;偶爾會得到NullPointerException;

import ***.KeyUtils; 
import ***.redis.PipelineHelper; 
import ***.redis.PipelinedCacheClusterClient; 
import **.redis.R2mClusterClient; 
import org.apache.commons.lang3.StringUtils; 
import org.apache.storm.task.OutputCollector; 
import org.apache.storm.task.TopologyContext; 
import org.apache.storm.topology.IRichBolt; 
import org.apache.storm.topology.OutputFieldsDeclarer; 
import org.apache.storm.tuple.Tuple; 
import org.slf4j.Logger; 
import org.slf4j.LoggerFactory; 
import org.springframework.context.ApplicationContext; 
import org.springframework.context.support.ClassPathXmlApplicationContext; 

import java.util.Map; 

/** 
* RedisBolt batch operate 
*/ 
public class RedisBolt implements IRichBolt { 
    static final long serialVersionUID = 737015318988609460L; 
    private static ApplicationContext applicationContext; 
    private static long logEmitNumber = 0; 
    private static StringBuffer totalCmds = new StringBuffer(); 
    private Logger logger = LoggerFactory.getLogger(getClass()); 
    private OutputCollector _collector; 
    private R2mClusterClient r2mClusterClient; 

    @Override 
    public void prepare(Map map, TopologyContext topologyContext, OutputCollector outputCollector) { 
     _collector = outputCollector; 
     if (applicationContext == null) { 
      applicationContext = new ClassPathXmlApplicationContext("spring/spring-config-redisbolt.xml"); 
     } 
     if (r2mClusterClient == null) { 
      r2mClusterClient = (R2mClusterClient) applicationContext.getBean("r2mClusterClient"); 
     } 


    } 

    @Override 
    public void execute(Tuple tuple) { 
     String log = tuple.getString(0); 
     String lastCommands = tuple.getString(1); 

     try { 
      //log count 
      if (StringUtils.isNotEmpty(log)) { 
       logEmitNumber++; 
      } 

      if (StringUtils.isNotEmpty(lastCommands)) { 
       if(totalCmds==null){ 
        totalCmds = new StringBuffer(); 
       } 
       totalCmds.append(lastCommands);//line 61 
      } 

      //日誌數量控制 
      int numberLimit = 1; 
      String flow_log_limit = r2mClusterClient.get(KeyUtils.KEY_PIPELINE_LIMIT); 
      if (StringUtils.isNotEmpty(flow_log_limit)) { 
       try { 
        numberLimit = Integer.parseInt(flow_log_limit); 
       } catch (Exception e) { 
        numberLimit = 1; 
        logger.error("error", e); 
       } 
      } 

      if (logEmitNumber >= numberLimit) { 
       StringBuffer _totalCmds = new StringBuffer(totalCmds); 
       try { 
        //pipeline submit 
        PipelinedCacheClusterClient pip = r2mClusterClient.pipelined(); 
        String[] commandArray = _totalCmds.toString().split(KeyUtils.REDIS_CMD_SPILT); 
        PipelineHelper.cmd(pip, commandArray); 
        pip.sync(); 
        pip.close(); 
        totalCmds = new StringBuffer(); 
       } catch (Exception e) { 
        logger.error("error", e); 
       } 

       logEmitNumber = 0; 
      } 
     } catch (Exception e) { 
      logger.error(new StringBuffer("====RedisBolt error for log=[ ").append(log).append("] \n commands=[").append(lastCommands).append("]").toString(), e); 
      _collector.reportError(e); 
      _collector.fail(tuple); 
     } 

     _collector.ack(tuple); 
    } 

    @Override 
    public void cleanup() { 

    } 

    @Override 
    public void declareOutputFields(OutputFieldsDeclarer outputFieldsDeclarer) { 
    } 

    @Override 
    public Map<String, Object> getComponentConfiguration() { 
     return null; 
    } 

} 

異常信息：

顯示java.lang.NullPointerException在java.lang.AbstractStringBuilder.ensureCapacityInternal（AbstractStringBuilder.java:113）在java.lang.AbstractStringBuilder.append（AbstractStringBuilder.java:415）在java.lang.StringBuffer.append（StringBuffer.java:237）在com.jd.jr.dataeye.storm.bolt.RedisBolt.execute（RedisBolt.java:61）在org.apache.storm.daemon.executor $ fn__5044 $ tuple_action_fn__5046.invoke（executor.clj：727）在org.apache.storm.daemon.executor $ mk_task_receiver $ fn__4965.invoke（executor.clj：459）在org.apache.storm.disruptor $ clojure_handler $ reify__4480.onEvent（否決。 clj：40）at org.apache.storm.utils.DisruptorQueue.consumeBatchToCursor（D isruptorQueue.java:472）在org.apache.storm.utils.DisruptorQueue.consumeBatchWhenAvailable（DisruptorQueue.java:451）在org.apache.storm.disruptor $ consume_batch_when_available.invoke（disruptor.clj：在org.apache.storm 73） .daemon.executor $ fn__5044 $ fn__5057 $ fn__5110.invoke（executor.clj：846）在org.apache.storm.util $ async_loop $ fn__557.invoke（util.clj：484）在clojure.lang.AFn.run（AFN的.java：22）在java.lang.Thread.run（Thread.java:745）

任何人都可以給我一些建議，以找到原因。

Answer 1

這真的很奇怪的事情發生。請閱讀兩個課程的代碼。

https://github.com/openjdk-mirror/jdk7u-jdk/blob/master/src/share/classes/java/lang/AbstractStringBuilder.java

https://github.com/openjdk-mirror/jdk7u-jdk/blob/master/src/share/classes/java/lang/StringBuffer.java

AbstractStringBuilder具有構造與無參數不分配字段「值」，這使得訪問「值」字段是NPE。 StringBuffer中的任何構造函數都使用該構造函數。因此，在序列化/反序列化中可能會出現一些奇怪的事情，並且不幸的是AbstractStringBuilder中的'value'字段爲空。

也許在prepare（）中初始化totalCmds會更好，還需要考慮螺栓之間的同步（線程安全性）。 prepare（）可以稱爲每個螺栓實例，因此字段是線程安全的，但類字段不是線程安全的。

Answer 2

我想我可能會發現問題;

關鍵的一點是

「的StringBuffer _totalCmds =新的StringBuffer（totalCmds）;」和 「totalCmds.append（lastCommands）; //線61」

當新目的，這需要藪步驟：

（1）分配內存，並返回參考

（2）初始化

如果在（1）之後和（2）之前追加，則StringBuffer.java擴展AbstractStringBuilder。java的

/** 
* The value is used for character storage. 
*/ 
char[] value; 

值沒有被初始化，那麼這將讓空：

@Override 
public synchronized void ensureCapacity(int minimumCapacity) { 
    if (minimumCapacity > value.length) { 
     expandCapacity(minimumCapacity); 
    } 
} 

這個印跡有另外一個問題，一些數據的多線程環境