在进行本机实践时遇到的错误具体见这篇博客：flume复制和多路复用简单示例（监控日志文件对接hdfs、kafka、本地文件系统）
错误如下：
19/09/17 03:59:34 ERROR hdfs.HDFSEventSink: process failed
java.lang.NullPointerException: Expected timestamp in the Flume event headers, but it was nullat com.google.common.base.Preconditions.checkNotNull(Preconditions.java:204)at org.apache.flume.formatter.output.BucketPath.replaceShorthand(BucketPath.java:256)at org.apache.flume.formatter.output.BucketPath.escapeString(BucketPath.java:465)at org.apache.flume.sink.hdfs.HDFSEventSink.process(HDFSEventSink.java:368)at org.apache.flume.sink.DefaultSinkProcessor.process(DefaultSinkProcessor.java:67)at org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:145)at java.lang.Thread.run(Thread.java:748)
19/09/17 03:59:34 ERROR flume.SinkRunner: Unable to deliver event. Exception follows.
org.apache.flume.EventDeliveryException: java.lang.NullPointerException: Expected timestamp in the Flume event headers, but it was nullat org.apache.flume.sink.hdfs.HDFSEventSink.process(HDFSEventSink.java:451)at org.apache.flume.sink.DefaultSinkProcessor.process(DefaultSinkProcessor.java:67)at org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:145)at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException: Expected timestamp in the Flume event headers, but it was nullat com.google.common.base.Preconditions.checkNotNull(Preconditions.java:204)at org.apache.flume.formatter.output.BucketPath.replaceShorthand(BucketPath.java:256)at org.apache.flume.formatter.output.BucketPath.escapeString(BucketPath.java:465)at org.apache.flume.sink.hdfs.HDFSEventSink.process(HDFSEventSink.java:368)... 3 more
提取关键信息：
org.apache.flume.EventDeliveryException: java.lang.NullPointerException: Expected timestamp in the Flume event headers, but it was null
时间戳的问题，参考这篇博客：https://www.cnblogs.com/mingfengshan/p/6853615.html
原因是因为写入到hfds时使用到了时间戳来区分目录结构，flume的消息组件event在接受到之后在header中没有发现时间戳参数，导致该错误发生，有三种方法可以解决这个错误；
1、agent1.sources.source1.interceptors = t1
agent1.sources.source1.interceptors.t1.type = timestamp 为source添加拦截，每条event头中加入时间戳；（效率会慢一些）
2、agent1.sinks.sink1.hdfs.useLocalTimeStamp = true 为sink指定该参数为true （如果客户端和flume集群时间不一致数据时间会不准确）
3、在向source发送event时，将时间戳参数添加到event的header中即可，header是一个map，添加时mapkey为timestamp(推荐使用)
我直接就是在对应配置文件上添加了（采用上述第二种方法）：
#using local timestamp
a2.sinks.k1.hdfs.useLocalTimeStamp = true
问题解决
第三中方法就是自定义拦截器了手动在代码里添加时间戳了。
网上有说是flume的一个bug，详见https://issues.apache.org/jira/browse/FLUME-1419