mac 上运行cassandra出现的java.net.MalformedURLException: Local host name unknown: java.net.UnknownHostException: : : unknown error错误解决方法
运行： ./bin/cassandra
得到输出结果：
objc[1881]: Class JavaLaunchHelper is implemented in both /Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/bin/java and /Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/jre/lib/libinstrument.dylib. One of the two will be used. Which one is undefined.
CompilerOracle: inline org/apache/cassandra/db/AbstractNativeCell.compareTo (Lorg/apache/cassandra/db/composites/Composite;)I
CompilerOracle: inline org/apache/cassandra/db/composites/AbstractSimpleCellNameType.compareUnsigned (Lorg/apache/cassandra/db/composites/Composite;Lorg/apache/cassandra/db/composites/Composite;)I
CompilerOracle: inline org/apache/cassandra/utils/ByteBufferUtil.compare (Ljava/nio/ByteBuffer;[B)I
CompilerOracle: inline org/apache/cassandra/utils/ByteBufferUtil.compare ([BLjava/nio/ByteBuffer;)I
CompilerOracle: inline org/apache/cassandra/utils/ByteBufferUtil.compareUnsigned (Ljava/nio/ByteBuffer;Ljava/nio/ByteBuffer;)I
CompilerOracle: inline org/apache/cassandra/utils/FastByteOperations$UnsafeOperations.compareTo (Ljava/lang/Object;JILjava/lang/Object;JI)I
CompilerOracle: inline org/apache/cassandra/utils/FastByteOperations$UnsafeOperations.compareTo (Ljava/lang/Object;JILjava/nio/ByteBuffer;)I
CompilerOracle: inline org/apache/cassandra/utils/FastByteOperations$UnsafeOperations.compareTo (Ljava/nio/ByteBuffer;Ljava/nio/ByteBuffer;)I
CompilerOracle: inline org/apache/cassandra/db/composites/AbstractSimpleCellNameType.compareUnsigned (Lorg/apache/cassandra/db/composites/Composite;Lorg/apache/cassandra/db/composites/Composite;)I
CompilerOracle: inline org/apache/cassandra/utils/ByteBufferUtil.compare (Ljava/nio/ByteBuffer;[B)I
CompilerOracle: inline org/apache/cassandra/utils/ByteBufferUtil.compare ([BLjava/nio/ByteBuffer;)I
CompilerOracle: inline org/apache/cassandra/utils/ByteBufferUtil.compareUnsigned (Ljava/nio/ByteBuffer;Ljava/nio/ByteBuffer;)I
CompilerOracle: inline org/apache/cassandra/utils/FastByteOperations$UnsafeOperations.compareTo (Ljava/lang/Object;JILjava/lang/Object;JI)I
CompilerOracle: inline org/apache/cassandra/utils/FastByteOperations$UnsafeOperations.compareTo (Ljava/lang/Object;JILjava/nio/ByteBuffer;)I
CompilerOracle: inline org/apache/cassandra/utils/FastByteOperations$UnsafeOperations.compareTo (Ljava/nio/ByteBuffer;Ljava/nio/ByteBuffer;)I
错误: 代理抛出异常错误: java.net.MalformedURLException: Local host name unknown: java.net.UnknownHostException: : : unknown error
初期总以为第一个错误导致的问题：
objc[1881]: Class JavaLaunchHelper is implemented in both /Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/bin/java and /Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/jre/lib/libinstrument.dylib. One of the two will be used. Which one is undefined.
然后搜寻stackoverflow， 说是mac上java7的一个漏洞，然后就更换了java8，统一了jre 和 jdk的版本到上面的1.8.0 update 25.
结果还是一样。
然后，我只要把原因转移到最后的MalformedURLException上，自己查看了hosts， 发现完全正常，实在无法子，今天又到另外的一台mac上安装了相同版本的java，启动cassandra，完全正常，唯独就是我自己的mac 不行。
无意中发现了一个方法, 参见附录一中的URL链接：
使用 scutils —get HostName 命令查看当前的hostname ， 尽然是空。
然后使用 scutils —set HostName localhost ， 之后重新启动cassandra， 完全正常了。
参考：
【1】： http://biomedicalontologies.com/2012/11/14/fixing-java-net-local-host-name-unknown-error-on-mac-os-x/