两个类，一个HDFS文件操作类，一个是wordcount 词数统计类，都是从网上看来的。上代码：
package mapreduce; import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.BlockLocation;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hdfs.DistributedFileSystem;
import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
import org.apache.hadoop.io.IOUtils;
/**
* file operation on HDFS
* @author liuxingjiaofu
*
*/
public class HDFS_File {
//read the file from HDFS
public void ReadFile(Configuration conf, String FileName){
try{
FileSystem hdfs = FileSystem.get(conf);
FSDataInputStream dis = hdfs.open(new Path(FileName));
IOUtils.copyBytes(dis, System.out, 4096, false);
dis.close();
}catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
//copy the file from HDFS to local
public void GetFile(Configuration conf, String srcFile, String dstFile){
try {
FileSystem hdfs = FileSystem.get(conf);
Path srcPath = new Path(srcFile);
Path dstPath = new Path(dstFile);
hdfs.copyToLocalFile(true,srcPath, dstPath);
}catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
//copy the local file to HDFS
public void PutFile(Configuration conf, String srcFile, String dstFile){
try {
FileSystem hdfs = FileSystem.get(conf);
Path srcPath = new Path(srcFile);
Path dstPath = new Path(dstFile);
hdfs.copyFromLocalFile(srcPath, dstPath);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
//create the new file
public FSDataOutputStream CreateFile(Configuration conf, String FileName){
try {
FileSystem hdfs = FileSystem.get(conf);
Path path = new Path(FileName);
FSDataOutputStream outputStream = hdfs.create(path);
return outputStream;
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
//rename the file name
public boolean ReNameFile(Configuration conf, String srcName, String dstName){
try {
Configuration config = new Configuration();
FileSystem hdfs = FileSystem.get(config);
Path fromPath = new Path(srcName);
Path toPath = new Path(dstName);
boolean isRenamed = hdfs.rename(fromPath, toPath);
return isRenamed;
}catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return false;
}
//delete the file
// tyep = true, delete the directory
// type = false, delete the file
public boolean DelFile(Configuration conf, String FileName, boolean type){
try {
FileSystem hdfs = FileSystem.get(conf);
Path path = new Path(FileName);
boolean isDeleted = hdfs.delete(path, type);
return isDeleted;
}catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return false;
}
//Get HDFS file last modification time
public long GetFileModTime(Configuration conf, String FileName){
try{
FileSystem hdfs = FileSystem.get(conf);
Path path = new Path(FileName);
FileStatus fileStatus = hdfs.getFileStatus(path);
long modificationTime = fileStatus.getModificationTime();
return modificationTime;
}catch(IOException e){
e.printStackTrace();
}
return 0;
}
//check if a file exists in HDFS
public boolean CheckFileExist(Configuration conf, String FileName){
try{
FileSystem hdfs = FileSystem.get(conf);
Path path = new Path(FileName);
boolean isExists = hdfs.exists(path);
return isExists;
}catch(IOException e){
e.printStackTrace();
}
return false;
}
//Get the locations of a file in the HDFS cluster
public List<String []> GetFileBolckHost(Configuration conf, String FileName){
try{
List<String []> list = new ArrayList<String []>();
FileSystem hdfs = FileSystem.get(conf);
Path path = new Path(FileName);
FileStatus fileStatus = hdfs.getFileStatus(path); BlockLocation[] blkLocations = hdfs.getFileBlockLocations(fileStatus, 0, fileStatus.getLen()); int blkCount = blkLocations.length;
for (int i=0; i < blkCount; i++) {
String[] hosts = blkLocations[i].getHosts();
list.add(hosts);
}
return list;
}catch(IOException e){
e.printStackTrace();
}
return null;
}
//Get a list of all the nodes host names in the HDFS cluster
// have no authorization to do this operation
public String[] GetAllNodeName(Configuration conf){
try{
FileSystem fs = FileSystem.get(conf);
DistributedFileSystem hdfs = (DistributedFileSystem) fs;
DatanodeInfo[] dataNodeStats = hdfs.getDataNodeStats();
String[] names = new String[dataNodeStats.length];
for (int i = 0; i < dataNodeStats.length; i++) {
names[i] = dataNodeStats[i].getHostName();
}
return names;
}catch(IOException e){
System.out.println("error!!!!");
e.printStackTrace();
}
return null;
}
}
wordcount.java:
package mapreduce; import java.io.IOException;
import java.util.StringTokenizer; import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text; import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat; public class mywordcount {
public static class wordcountMapper extends
Mapper<LongWritable, Text, Text, IntWritable>{
private final static IntWritable one = new IntWritable(1);
private Text word = new Text();
public void map(LongWritable key, Text value, Context context)throws IOException, InterruptedException{
String line = value.toString();
StringTokenizer itr = new StringTokenizer(line);
while(itr.hasMoreElements()){
word.set(itr.nextToken());
context.write(word, one);
}
}
}
public static class wordcountReducer extends
Reducer<Text, IntWritable, Text, IntWritable>{
public void reduce(Text key, Iterable<IntWritable>values, Context context)throws IOException, InterruptedException{
int sum = 0;
for (IntWritable str : values){
sum += str.get();
}
context.write(key, new IntWritable(sum));
}
}
/**
* 2 args, the file you want to count words from and the directory you want to save the result
* @param args /home/hadooper/testmp/testtext /home/hadooper/testmp/testresult
* @throws Exception
*/
public static void main(String args[])throws Exception{
//首先定义两个临时文件夹，这里可以使用随机函数+文件名，这样重名的几率就很小。
String dstFile = "temp_src";
String srcFile = "temp_dst";
//这里生成文件操作对象。
HDFS_File file = new HDFS_File(); Configuration conf = new Configuration();
// must!!! config the fs.default.name be the same to the value in core-site.xml
conf.set("fs.default.name","hdfs://node1");
conf.set("mapred.job.tracker","node1:54311"); //从本地上传文件到HDFS,可以是文件也可以是目录
file.PutFile(conf, args[0], dstFile); System.out.println("up ok");
Job job = new Job(conf, "mywordcount");
job.setJarByClass(mywordcount.class); job.setInputFormatClass(TextInputFormat.class); job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class); job.setMapperClass(wordcountMapper.class);
job.setReducerClass(wordcountReducer.class);
job.setCombinerClass(wordcountReducer.class);
//注意这里的输入输出都应该是在HDFS下的文件或目录
FileInputFormat.setInputPaths(job, new Path(dstFile));
FileOutputFormat.setOutputPath(job, new Path(srcFile));
//开始运行
job.waitForCompletion(true);
//从HDFS取回文件保存至本地
file.GetFile(conf, srcFile, args[1]);
System.out.println("down the result ok!");
//删除临时文件或目录
file.DelFile(conf, dstFile, true);
file.DelFile(conf, srcFile, true);
System.out.println("delete file on hdfs ok!");
}
}
期间，遇到几个错误：
1.HDFS版本问题--Call to node1/172.*.*.*:8020 failed on local exception: java.io.EOFException
main() {……
Configuration conf = new Configuration();
conf.set("fs.default.name","hdfs://node1");//与conf/core-site里的值对应，必须
HDFS_File file = new HDFS_File();
//print all the node name
String[] host_name = file.GetAllNodeName(conf);
……}
public String[] GetAllNodeName(Configuration conf){
try{
// Configuration config = new Configuration();
FileSystem fs = FileSystem.get(conf);
DistributedFileSystem hdfs = (DistributedFileSystem) fs;
DatanodeInfo[] dataNodeStats = hdfs.getDataNodeStats();
String[] names = new String[dataNodeStats.length];
for (int i = 0; i < dataNodeStats.length; i++) {
names[i] = dataNodeStats[i].getHostName();
}
return names;
}catch(IOException e){
System.out.println("eeeeeeeeeeeeeeeeeeeerror!!!!");
e.printStackTrace();
}
return null;
}
异常：
eeeeeeeeeeeeeeeeeeeerror!!!!
java.io.IOException: Call to node1/172.10.39.250:8020 failed on local exception: java.io.EOFException
at org.apache.hadoop.ipc.Client.wrapException(Client.java:775)
at org.apache.hadoop.ipc.Client.call(Client.java:743)
at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:220)
at $Proxy0.getProtocolVersion(Unknown Source)
at org.apache.hadoop.ipc.RPC.getProxy(RPC.java:359)
at org.apache.hadoop.hdfs.DFSClient.createRPCNamenode(DFSClient.java:112)
at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:213)
at org.apache.hadoop.hdfs.DFSClient.<init>(DFSClient.java:176)
at org.apache.hadoop.hdfs.DistributedFileSystem.initialize(DistributedFileSystem.java:82)
at org.apache.hadoop.fs.FileSystem.createFileSystem(FileSystem.java:1378)
at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:66)
at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:1390)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:196)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:95)
at mapreduce.HDFS_File.GetAllNodeName(HDFS_File.java:151)
at mapreduce.File_Operation.main(File_Operation.java:15)
Caused by: java.io.EOFException
at java.io.DataInputStream.readInt(DataInputStream.java:392)
at org.apache.hadoop.ipc.Client$Connection.receiveResponse(Client.java:501)
at org.apache.hadoop.ipc.Client$Connection.run(Client.java:446)
Exception in thread "main" java.lang.NullPointerException
at mapreduce.File_Operation.main(File_Operation.java:16)
原因：版本问题，确保java中的jar包跟hadoop集群的jar包是相同版本的
2.HDFS权限问题
org.apache.hadoop.security.AccessControlException: org.apache.hadoop.security.AccessControlException: Permission denied: user=hadooper, access=WRITE, inode="/user":root:supergroup:drwxr-xr-x
解决方案之
（1 added this entry to conf/hdfs-site.xml
<property>
<name>dfs.permissions</name>
<value>false</value>
</property>
（2.放开 要写入目录 hadoop 目录的权限 ， 命令如下 ：$ hadoop fs -chmod 777 /user/
我用的是第2种方案
3.HDFS 2011-12-20 17:00:32 org.apache.hadoop.util.NativeCodeLoader <clinit>
警告: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
在Hadoop的配置文件core-site.xml中可以设置是否使用本地库：
<property>
<name>hadoop.native.lib</name>
<value>true</value>
<description>Should native hadoop libraries, if present, be used.</description>
</property>
Hadoop默认的配置为启用本地库。
另外，可以在环境变量中设置使用本地库的位置：
export JAVA_LIBRARY_PATH=/path/to/hadoop-native-libs
有的时候也会发现Hadoop自带的本地库无法使用，这种情况下就需要自己去编译本地库了。在$HADOOP_HOME目录下，使用如下命令即可：
ant compile-native
编译完成后，可以在$HADOOP_HOME/build/native目录下找到相应的文件，然后指定文件的路径或者移动编译好的文件到默认目录下即可
我试了下，那个是64位的，我电脑是32位的，没有源代码，编译不了，那只好一段段程序的试，找出哪段代码出了这个警告，我的是
try {
FileSystem hdfs = FileSystem.get(conf);
Path srcPath = new Path(srcFile);
Path dstPath = new Path(dstFile);
hdfs.copyToLocalFile(true,srcPath, dstPath);//定位到此句
}catch (IOException e) {
到了此步，便只能如此了，为什么呢，java不是跨平台的吗
4.MR-jar包缺失
ClassNotFoundException: org.codehaus.jackson.map.JsonMappingException
NoClassDefFoundError: org/apache/commons/httpclient/HttpMethod
添加jar包到java工程中
jackson-core-asl-1.5.2.jar
jackson-mapper-asl-1.5.2.jar
commons-httpclient-3.0.1.jar
我是不习惯将所有Jar包都加到工程里，觉得这样很容易便加多了，浪费时空。
完成第一次mapreduce，不错！
5.远程的JOB挂掉了，居然还能运行成功，发现是mapred.job.tracker属性没设，默认在local下运行，其值在namenode的mapred-site.xml中看
conf.set("mapred.job.tracker","node1:54311");
配置完了，运行可以初始化，但是找不到mapper类：
信息: Task Id : attempt_201112221123_0010_m_000000_0, Status : FAILED
java.lang.RuntimeException: java.lang.ClassNotFoundException: mapreduce.mywordcount$wordcountMapper
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:996)
at org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:212)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:611)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:325)
at org.apache.hadoop.mapred.Child$4.run(Child.java:270)
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:1127)
at org.apache.hadoop.mapred.Child.main(Child.java:264)
将程序打成jar包放到hadoop集群的jobtracker上可用，正常，结果也正确，但是在客户端运行却报上述错误，暂时还没解决。
总结
1.远程操作HDFS文件以及远程提交MR任务，必须配置的两项（其他暂时还没发现）：
conf.set("fs.default.name","hdfs://node1");//与conf/core-site.xml里的值对应，必须
conf.set("mapred.job.tracker","node1:54311");//mapred-site.xml
2.耐心分析问题，解决问题