Windows平台下安装Eclipse插件,开发Hadoop应用
2017-03-09 16:01
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安装插件
将hadoop安装包hadoop\contrib\eclipse-plugin\hadoop-0.20.2-eclipse-plugin.jar拷贝到eclipse的插件目录plugins下。需要注意的是插件版本(及后面开发导入的所有jar包)与运行的hadoop一致,否则可能会出现EOFException异常。
重启eclipse,打开windows->open perspective->other->map/reduce 可以看到map/reduce开发视图。
设置连接参数
打开windows->show view->other-> map/reduce Locations视图,在点击大象后弹出的对话框(General tab)进行参数的添加:参数说明如下:
Location name:任意
map/reduce master:与mapred-site.xml里面mapred.job.tracker设置一致。
DFS master:与core-site.xml里fs.default.name设置一致。
User name: 服务器上运行hadoop服务的用户名。
然后是打开“Advanced parameters”设置面板,修改相应参数。上面的参数填写以后,也会反映到这里相应的参数,主要关注下面几个参数:
fs.defualt.name:与core-site.xml里fs.default.name设置一致。
mapred.job.tracker:与mapred-site.xml里面mapred.job.tracker设置一致。
dfs.replication:与hdfs-site.xml里面的dfs.replication一致。
hadoop.tmp.dir:与core-site.xml里hadoop.tmp.dir设置一致。
hadoop.job.ugi:并不是设置用户名与密码。是用户与组名,所以这里填写hadoop,hadoop。
说明:第一次设置的时候可能是没有hadoop.job.ugi和dfs.replication参数的,不要紧,确认保存。打开Project Explorer中DFS Locations目录,应该可以年看到文件系统中的结构了。但是在/hadoop/mapred/system下却没有查看权限,如下图:
而且删除文件的时候也会报错:
这个原因是我使用地本用户Administrator(我是用管理员用户登陆来地windows系统的)进行远程hadoop系统操作,没有权限。
此时再打开“Advanced parameters”设置面板,应该可以看到hadoop.job.ugi了,这个参数默认是本地操作系统的用户名,如果不幸与远程hadoop用户不一致,那就要改过来了,将hadoop加在第一个,并用逗号分隔。如:
保存配置后,重新启动eclipse。/hadoop/mapred/system下就一目了然了,删除文件也OK。
运行hadoop程序
首先将hadoop安装包下面的所有jar包都导到eclipse工程里。然后建立一个类:DFSOperator.java,该类写了四个基本方法:创建文件,删除文件,把文件内容读为字符串,将字符串写入文件。同时有个main函数,可以修改测试:package com.kingdee.hadoop; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.FSDataOutputStream; import org.apache.hadoop.fs.FileSystem; import org.apache.hadoop.fs.Path; /** * * The utilities to operate file on hadoop hdfs. * * @author luolihui 2011-07-18 * */ public class DFSOperator { private static final String ROOT_PATH = "hdfs:///"; private static final int BUFFER_SIZE = 4096; /** * construct. */ public DFSOperator(){} /** * Create a file on hdfs.The root path is /.<br> * for example: DFSOperator.createFile("/lory/test1.txt", true); * @param path the file name to open * @param overwrite if a file with this name already exists, then if true, the file will be * @return true if delete is successful else IOException. * @throws IOException */ public static boolean createFile(String path, boolean overwrite) throws IOException { //String uri = "hdfs://192.168.1.100:9000"; //FileSystem fs1 = FileSystem.get(URI.create(uri), conf); Configuration conf = new Configuration(); FileSystem fs = FileSystem.get(conf); Path f = new Path(ROOT_PATH + path); fs.create(f, overwrite); fs.close(); return true; } /** * Delete a file on hdfs.The root path is /. <br> * for example: DFSOperator.deleteFile("/user/hadoop/output", true); * @param path the path to delete * @param recursive if path is a directory and set to true, the directory is deleted else throws an exception. In case of a file the recursive can be set to either true or false. * @return true if delete is successful else IOException. * @throws IOException */ public static boolean deleteFile(String path, boolean recursive) throws IOException { //String uri = "hdfs://192.168.1.100:9000"; //FileSystem fs1 = FileSystem.get(URI.create(uri), conf); Configuration conf = new Configuration(); FileSystem fs = FileSystem.get(conf); Path f = new Path(ROOT_PATH + path); fs.delete(f, recursive); fs.close(); return true; } /** * Read a file to string on hadoop hdfs. From stream to string. <br> * for example: System.out.println(DFSOperator.readDFSFileToString("/user/hadoop/input/test3.txt")); * @param path the path to read * @return true if read is successful else IOException. * @throws IOException */ public static String readDFSFileToString(String path) throws IOException { Configuration conf = new Configuration(); FileSystem fs = FileSystem.get(conf); Path f = new Path(ROOT_PATH + path); InputStream in = null; String str = null; StringBuilder sb = new StringBuilder(BUFFER_SIZE); if (fs.exists(f)) { in = fs.open(f); BufferedReader bf = new BufferedReader(new InputStreamReader(in)); while ((str = bf.readLine()) != null) { sb.append(str); sb.append("\n"); } in.close(); bf.close(); fs.close(); return sb.toString(); } else { return null; } } /** * Write string to a hadoop hdfs file. <br> * for example: DFSOperator.writeStringToDFSFile("/lory/test1.txt", "You are a bad man.\nReally!\n"); * @param path the file where the string to write in. * @param string the context to write in a file. * @return true if write is successful else IOException. * @throws IOException */ public static boolean writeStringToDFSFile(String path, String string) throws IOException { Configuration conf = new Configuration(); FileSystem fs = FileSystem.get(conf); FSDataOutputStream os = null; Path f = new Path(ROOT_PATH + path); os = fs.create(f,true); os.writeBytes(string); os.close(); fs.close(); return true; } public static void main(String[] args) { try { DFSOperator.createFile("/lory/test1.txt", true); DFSOperator.deleteFile("/dfs_operator.txt", true); DFSOperator.writeStringToDFSFile("/lory/test1.txt", "You are a bad man.\nReally?\n"); System.out.println(DFSOperator.readDFSFileToString("/lory/test1.txt")); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } System.out.println("===end==="); } }
然后Run As->Run on Hadoop->Choose an exitsing server from the list below->finish.
结果很简单(那个警告不管):
11/07/16 18:44:32 WARN conf.Configuration: DEPRECATED: hadoop-site.xml found in the classpath. Usage of hadoop-site.xml is deprecated. Instead use core-site.xml, mapred-site.xml and hdfs-site.xml to override properties of core-default.xml, mapred-default.xml and hdfs-default.xml respectively You are a bad man. Really? ===end===
也可以运行hadoop自带的WorkCount程序,找到其源代码导进来,然后设置输入输出参数,然后同样“Run on hadoop”。具体步骤不再示范。
每“Run on hadoop”都会在workspace.metadata.plugins\org.apache.hadoop.eclipse下生成临时jar包。不过第一次需要Run on hadoop,以后只需要点击那运行的绿色按钮了。
错误及处理
安全模式问题
我在eclipse上删除DFS上的文件夹时,出现下面错误:错误提示说得也比较明示,是NameNode在安全模式中,其解决方案也一并给出。类似的运行hadoop程序时,有时候会报以下错误:
org.apache.hadoop.dfs.SafeModeException: Cannot delete /user/hadoop/input. Name node is in safe mode
解除安全模式:
bin/hadoop dfsadmin -safemode leave
用户可以通过dfsadmin -safemode value 来操作安全模式,参数value的说明如下:
enter - 进入安全模式
leave - 强制NameNode离开安全模式
get - 返回安全模式是否开启的信息
wait - 等待,一直到安全模式结束。
开发时报错Permission denied
org.apache.hadoop.security.AccessControlException: org.apache.hadoop.security.AccessControlException: Permission denied: user=Administrator, access=WRITE, inode="test1.txt":hadoop:supergroup:rw-r--r-- at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at org.apache.hadoop.ipc.RemoteException.instantiateException(RemoteException.java:96) at org.apache.hadoop.ipc.RemoteException.unwrapRemoteException(RemoteException.java:58) at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.<init>(DFSClient.java:2710) at org.apache.hadoop.hdfs.DFSClient.create(DFSClient.java:492) at org.apache.hadoop.hdfs.DistributedFileSystem.create(DistributedFileSystem.java:195) at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:484) at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:465) at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:372) at com.kingdee.hadoop.DFSOperator.createFile(DFSOperator.java:46) at com.kingdee.hadoop.DFSOperator.main(DFSOperator.java:134)
解决方法是,在“Advanced parameters”设置面板,设置hadoop.job.ugi参数,将hadoop用户加上去。
变为:
然后重新在运行中”Run on hadoop”。另一方法是改变要操作的文件的权限。
Permission denied: user=Administrator, access=WRITE, inode="test1.txt":hadoop:supergroup:rw-r--r--
上面的意思是:test1.txt文件的访问权限是rw-r--r--,归属组是supergroup,归属用户是hadoop,现在使用Administrator用户对test1.txt文件进行WRITE方式访问,被拒绝了。所以可以改变下test1.txt文件的访问权限:
$ hadoop fs –chmod 777 /lory/test1.txt $ hadoop fs –chmod 777 /lory #或者上一级文件夹
当然使用-chown命令也可以。
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