启动Spark时（CDH版本较常见），报如下错误：
19/02/20 00:20:33 INFO StandaloneRestServer: Started REST server for submitting applications on port 6066
Exception in thread "dispatcher-event-loop-1" java.lang.NoClassDefFoundError: com/fasterxml/jackson/databind/Module
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at org.apache.spark.util.Utils$.classForName(Utils.scala:177)
at org.apache.spark.metrics.MetricsSystem$$anonfun$registerSinks$1.apply(MetricsSystem.scala:196)
at org.apache.spark.metrics.MetricsSystem$$anonfun$registerSinks$1.apply(MetricsSystem.scala:192)
at scala.collection.mutable.HashMap$$anonfun$foreach$1.apply(HashMap.scala:98)
at scala.collection.mutable.HashMap$$anonfun$foreach$1.apply(HashMap.scala:98)
at scala.collection.mutable.HashTable$class.foreachEntry(HashTable.scala:226)
at scala.collection.mutable.HashMap.foreachEntry(HashMap.scala:39)
at scala.collection.mutable.HashMap.foreach(HashMap.scala:98)
at org.apache.spark.metrics.MetricsSystem.registerSinks(MetricsSystem.scala:192)
at org.apache.spark.metrics.MetricsSystem.start(MetricsSystem.scala:100)
at org.apache.spark.deploy.master.Master.onStart(Master.scala:160)
at org.apache.spark.rpc.netty.Inbox$$anonfun$process$1.apply$mcV$sp(Inbox.scala:121)
at org.apache.spark.rpc.netty.Inbox.safelyCall(Inbox.scala:204)
at org.apache.spark.rpc.netty.Inbox.process(Inbox.scala:100)
at org.apache.spark.rpc.netty.Dispatcher$MessageLoop.run(Dispatcher.scala:217)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.ClassNotFoundException: com.fasterxml.jackson.databind.Module
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 20 more
原因是CDH版本jar缺少。。
解决办法：
使用maven或者去jar仓库下载对应的三个json的jar包：
Maven依赖：
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.4.4</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-core</artifactId>
<version>2.4.4</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-annotations</artifactId>
<version>2.4.4</version>
</dependency>
下载完成后去对应本地仓库目录将jar文件添加到hadoop/share/hadoop/common/下。顺便再spark的lib下也添加一下，反正没啥影响，添加完就可以启动成功了。。。