maven-javadoc-plugin 出现错误Unsupported major.minor version 51.0

[INFO] --- maven-javadoc-plugin:3.0.0:jar (attach-javadocs) @ eii-frame-sms ---
[WARNING] Error injecting: org.apache.maven.plugins.javadoc.JavadocJar
java.lang.TypeNotPresentException: Type org.apache.maven.plugins.javadoc.JavadocJar not present
at org.eclipse.sisu.space.URLClassSpace.loadClass(URLClassSpace.java:115)
at org.eclipse.sisu.space.NamedClass.load(NamedClass.java:46)
at org.eclipse.sisu.space.AbstractDeferredClass.get(AbstractDeferredClass.java:48)
at com.google.inject.internal.ProviderInternalFactory.provision(ProviderInternalFactory.java:86)
at com.google.inject.internal.InternalFactoryToInitializableAdapter.provision(InternalFactoryToInitializableAdapter.java:55)
at com.google.inject.internal.ProviderInternalFactory$1.call(ProviderInternalFactory.java:70)
at com.google.inject.internal.ProvisionListenerStackCallback$Provision.provision(ProvisionListenerStackCallback.java:100)
at org.eclipse.sisu.plexus.PlexusLifecycleManager.onProvision(PlexusLifecycleManager.java:133)
at com.google.inject.internal.ProvisionListenerStackCallback$Provision.provision(ProvisionListenerStackCallback.java:109)
at com.google.inject.internal.ProvisionListenerStackCallback.provision(ProvisionListenerStackCallback.java:55)
at com.google.inject.internal.ProviderInternalFactory.circularGet(ProviderInternalFactory.java:68)
at com.google.inject.internal.InternalFactoryToInitializableAdapter.get(InternalFactoryToInitializableAdapter.java:47)
at com.google.inject.internal.InjectorImpl$2$1.call(InjectorImpl.java:997)
at com.google.inject.internal.InjectorImpl.callInContext(InjectorImpl.java:1047)
at com.google.inject.internal.InjectorImpl$2.get(InjectorImpl.java:993)
at com.google.inject.Scopes$1$1.get(Scopes.java:59)
at org.eclipse.sisu.inject.LazyBeanEntry.getValue(LazyBeanEntry.java:82)
at org.eclipse.sisu.plexus.LazyPlexusBean.getValue(LazyPlexusBean.java:51)
at org.codehaus.plexus.DefaultPlexusContainer.lookup(DefaultPlexusContainer.java:260)
at org.codehaus.plexus.DefaultPlexusContainer.lookup(DefaultPlexusContainer.java:252)
at org.apache.maven.plugin.internal.DefaultMavenPluginManager.getConfiguredMojo(DefaultMavenPluginManager.java:462)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:119)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:80)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:120)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:347)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:154)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:582)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:214)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:158)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
at org.codehaus.classworlds.Launcher.main(Launcher.java:46)
Caused by: java.lang.UnsupportedClassVersionError: org/apache/maven/plugins/javadoc/JavadocJar : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClassFromSelf(ClassRealm.java:389)
at org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy.loadClass(SelfFirstStrategy.java:42)
at org.codehaus.plexus.classworlds.realm.ClassRealm.unsynchronizedLoadClass(ClassRealm.java:259)
at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:242)
at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:227)
at org.eclipse.sisu.space.URLClassSpace.loadClass(URLClassSpace.java:107)
... 42 more
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.967 s
[INFO] Finished at: 2018-01-12T11:16:46+08:00
[INFO] Final Memory: 15M/216M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-javadoc-plugin:3.0.0:jar (attach-javadocs) on project eii-frame-sms: Execution attach-javadocs of goal org.apache.maven.plugins:maven-javadoc-plugin:3.0.0:jar failed: Unable to load the mojo 'jar' in the plugin 'org.apache.maven.plugins:maven-javadoc-plugin:3.0.0' due to an API incompatibility: org.codehaus.plexus.component.repository.exception.ComponentLookupException: org/apache/maven/plugins/javadoc/JavadocJar : Unsupported major.minor version 51.0
[ERROR] -----------------------------------------------------

项目的java compiler设置的是jdk1.6。但在run as ->Run Configuations 中，也默认选择了jdk6，必须选择如下方式：