hadoop 2.7.4：java.lang.UnsupportedClassVersionError: org/apache/hadoop/mapreduce/lib/output/Sequence

STARTUP_MSG:   java = 1.7.0_79
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17/10/02 15:32:29 INFO namenode.NameNode: registered UNIX signal handlers for [TERM, HUP, INT]
17/10/02 15:32:29 INFO namenode.NameNode: createNameNode [-format]
17/10/02 15:32:30 ERROR namenode.NameNode: Failed to start namenode.
java.lang.UnsupportedClassVersionError: org/apache/hadoop/mapreduce/lib/output/SequenceFileAsBinaryOutputFormat : Unsupported major.minor version 52.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
at org.apache.hadoop.mapreduce.util.ConfigUtil.addDeprecatedKeys(ConfigUtil.java:54)
at org.apache.hadoop.mapreduce.util.ConfigUtil.loadResources(ConfigUtil.java:42)
at org.apache.hadoop.mapred.JobConf.<clinit>(JobConf.java:119)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:274)
at org.apache.hadoop.conf.Configuration.getClassByNameOrNull(Configuration.java:2134)
at org.apache.hadoop.util.ReflectionUtils.setJobConf(ReflectionUtils.java:95)
at org.apache.hadoop.util.ReflectionUtils.setConf(ReflectionUtils.java:78)
at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:136)
at org.apache.hadoop.security.Groups.<init>(Groups.java:79)
at org.apache.hadoop.security.Groups.<init>(Groups.java:74)
at org.apache.hadoop.security.Groups.getUserToGroupsMappingService(Groups.java:303)
at org.apache.hadoop.security.UserGroupInformation.initialize(UserGroupInformation.java:285)
at org.apache.hadoop.security.UserGroupInformation.ensureInitialized(UserGroupInformation.java:262)
at org.apache.hadoop.security.UserGroupInformation.isAuthenticationMethodEnabled(UserGroupInformation.java:339)
at org.apache.hadoop.security.UserGroupInformation.isSecurityEnabled(UserGroupInformation.java:333)
at org.apache.hadoop.hdfs.server.namenode.NameNode.format(NameNode.java:968)
at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1441)
at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1566)
17/10/02 15:32:30 INFO util.ExitUtil: Exiting with status 1
17/10/02 15:32:30 INFO namenode.NameNode: SHUTDOWN_MSG:
/************************************************************

hadoop 2.7.4  命令：hdfs namenode -format   //格式化文件系统报错：java.lang.UnsupportedClassVersionError: org/apache/hadoop/mapreduce/lib/output/SequenceFileAsBinaryOutputFormat : Unsupported major.minor version 52.0很明显，高版本的class文件，用在了低版本的jvm上，jdk7 的 version 是51，所以需要换成jdk8。但根据官网的说法 jdk1.7 应该是支持 2.x.y 的。有点坑。