HDFS API hello world

代碼：

public class HdfsAPI {public static void main(String[] args) throws IOException {put("input/test.txt", "/user/xuefeng/test.txt");//get("output/test.txt", "/user/xuefeng/test.txt");//delete("/user/xuefeng/test.txt");}public static boolean put(String localPath, String hdfsPath)throws IOException {Configuration conf = new Configuration();FileSystem hdfs = FileSystem.get(conf);Path src = new Path(localPath);Path dst = new Path(hdfsPath);hdfs.copyFromLocalFile(src, dst);hdfs.close();return true;}public static boolean get(String localPath, String hdfsPath)throws IOException {Configuration conf = new Configuration();FileSystem hdfs = FileSystem.get(conf);Path dst = new Path(localPath);Path src = new Path(hdfsPath);hdfs.copyToLocalFile(src, dst);hdfs.close();return true;}public static boolean delete(String hdfsPath) throws IOException {Configuration conf = new Configuration();FileSystem hdfs = FileSystem.get(conf);Path path = new Path(hdfsPath);boolean deleted = hdfs.delete(path, true);hdfs.close();return deleted;}}

遇到問題：

1. 

12/07/11 20:35:25 INFO ipc.Client: Retrying connect to server: 192.168.1.102/192.168.1.102:9000. Already tried 8 time(s).12/07/11 20:35:27 INFO ipc.Client: Retrying connect to server: 192.168.1.102/192.168.1.102:9000. Already tried 9 time(s).Exception in thread "main" java.net.ConnectException: Call to 192.168.1.102/192.168.1.102:9000 failed on connection exception: java.net.ConnectException: Connection refused: no further informationat org.apache.hadoop.ipc.Client.wrapException(Client.java:1095)at org.apache.hadoop.ipc.Client.call(Client.java:1071)at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:225)at $Proxy1.getProtocolVersion(Unknown Source)at org.apache.hadoop.ipc.RPC.getProxy(RPC.java:396)at org.apache.hadoop.ipc.RPC.getProxy(RPC.java:379)at org.apache.hadoop.hdfs.DFSClient.createRPCNamenode(DFSClient.java:119)at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:238)at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:203)at org.apache.hadoop.hdfs.DistributedFileSystem.initialize(DistributedFileSystem.java:89)at org.apache.hadoop.fs.FileSystem.createFileSystem(FileSystem.java:1386)at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:66)at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:1404)at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:254)at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:123)at org.apache.hadoop.examples.HdfsAPI.put(HdfsAPI.java:22)at org.apache.hadoop.examples.HdfsAPI.main(HdfsAPI.java:14)Caused by: java.net.ConnectException: Connection refused: no further informationat sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)at sun.nio.ch.SocketChannelImpl.finishConnect(Unknown Source)at org.apache.hadoop.net.SocketIOWithTimeout.connect(SocketIOWithTimeout.java:206)at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:489)at org.apache.hadoop.ipc.Client$Connection.setupConnection(Client.java:434)at org.apache.hadoop.ipc.Client$Connection.setupIOstreams(Client.java:560)at org.apache.hadoop.ipc.Client$Connection.access$2000(Client.java:184)at org.apache.hadoop.ipc.Client.getConnection(Client.java:1202)at org.apache.hadoop.ipc.Client.call(Client.java:1046)... 15 more

借鑒 http://www.hadoopor.com/viewthread.php?action=printable&tid=853 

root@test:/work/hadoop/hadoop-1.0.2# lsof -i :9000COMMAND   PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAMEjava    11783 root   65u  IPv6  32454      0t0  TCP test:9000 (LISTEN)java    11783 root   85u  IPv6  33634      0t0  TCP test:9000->test:46187 (ESTABLISHED)java    11986 root   83u  IPv6  33633      0t0  TCP test:46187->test:9000 (ESTABLISHED)

發現hadoop使用的是IPv6。。。。

在%HADOOP_HOME%\conf\hadoop-env.sh中，添加

export HADOOP_OPTS=-Djava.net.preferIPv4Stack=true

後，問題沒了。

2.

put() 的時候，報錯：

Exception in thread "main" org.apache.hadoop.ipc.RemoteException: org.apache.hadoop.hdfs.server.namenode.SafeModeException: Cannot create file/user/xuefeng/test.txt. Name node is in safe mode.The ratio of reported blocks 0.0000 has not reached the threshold 0.9990. Safe mode will be turned off automatically.at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startFileInternal(FSNamesystem.java:1220)at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startFile(FSNamesystem.java:1188)at org.apache.hadoop.hdfs.server.namenode.NameNode.create(NameNode.java:628)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.apache.hadoop.ipc.RPC$Server.call(RPC.java:563)at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1388)at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1384)at java.security.AccessController.doPrivileged(Native Method)at javax.security.auth.Subject.doAs(Subject.java:396)at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1093)at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1382)

借鑒 http://shutiao2008.iteye.com/blog/318950

bin/hadoop dfsadmin -safemode leave #關閉safe mode

OK。