Java访问Hadoop分布式文件系统HDFS的配置说明

配置文件

m103替换为hdfs服务地址。
要利用Java客户端来存取HDFS上的文件，不得不说的是配置文件hadoop-0.20.2/conf/core-site.xml了，最初我就是在这里吃了大亏，所以我死活连不上HDFS，文件无法创建、读取。

<?xml version="1.0"?><?xml-stylesheet type="text/xsl" href="configuration.xsl"?><configuration><!--- global properties --><property><name>hadoop.tmp.dir</name><value>/home/zhangzk/hadoop</value><description>A base for other temporary directories.</description></property><!-- file system properties --><property><name>fs.default.name</name><value>hdfs://linux-zzk-113:9000</value></property></configuration>

配置项：hadoop.tmp.dir表示命名节点上存放元数据的目录位置，对于数据节点则为该节点上存放文件数据的目录。

配置项：fs.default.name表示命名的IP地址和端口号,缺省值是file:///，对于JavaAPI来讲，连接HDFS必须使用这里的配置的URL地址，对于数据节点来讲，数据节点通过该URL来访问命名节点。

hdfs-site.xml

<?xml version="1.0" encoding="UTF-8"?><!--Autogenerated by Cloudera Manager--><configuration> <property>  <name>dfs.namenode.name.dir</name>  <value>file:///mnt/sdc1/dfs/nn</value> </property> <property>  <name>dfs.namenode.servicerpc-address</name>  <value>m103:8022</value> </property> <property>  <name>dfs.https.address</name>  <value>m103:50470</value> </property> <property>  <name>dfs.https.port</name>  <value>50470</value> </property> <property>  <name>dfs.namenode.http-address</name>  <value>m103:50070</value> </property> <property>  <name>dfs.replication</name>  <value>3</value> </property> <property>  <name>dfs.blocksize</name>  <value>134217728</value> </property> <property>  <name>dfs.client.use.datanode.hostname</name>  <value>false</value> </property> <property>  <name>fs.permissions.umask-mode</name>  <value>022</value> </property> <property>  <name>dfs.namenode.acls.enabled</name>  <value>false</value> </property> <property>  <name>dfs.block.local-path-access.user</name>  <value>cloudera-scm</value> </property> <property>  <name>dfs.client.read.shortcircuit</name>  <value>false</value> </property> <property>  <name>dfs.domain.socket.path</name>  <value>/var/run/hdfs-sockets/dn</value> </property> <property>  <name>dfs.client.read.shortcircuit.skip.checksum</name>  <value>false</value> </property> <property>  <name>dfs.client.domain.socket.data.traffic</name>  <value>false</value> </property> <property>  <name>dfs.datanode.hdfs-blocks-metadata.enabled</name>  <value>true</value> </property> <property>  <name>fs.http.impl</name>  <value>com.scistor.datavision.fs.HTTPFileSystem</value> </property></configuration>

mapred-site.xml

<?xml version="1.0" encoding="UTF-8"?><!--Autogenerated by Cloudera Manager--><configuration> <property>  <name>mapreduce.job.split.metainfo.maxsize</name>  <value>10000000</value> </property> <property>  <name>mapreduce.job.counters.max</name>  <value>120</value> </property> <property>  <name>mapreduce.output.fileoutputformat.compress</name>  <value>true</value> </property> <property>  <name>mapreduce.output.fileoutputformat.compress.type</name>  <value>BLOCK</value> </property> <property>  <name>mapreduce.output.fileoutputformat.compress.codec</name>  <value>org.apache.hadoop.io.compress.SnappyCodec</value> </property> <property>  <name>mapreduce.map.output.compress.codec</name>  <value>org.apache.hadoop.io.compress.SnappyCodec</value> </property> <property>  <name>mapreduce.map.output.compress</name>  <value>true</value> </property> <property>  <name>zlib.compress.level</name>  <value>DEFAULT_COMPRESSION</value> </property> <property>  <name>mapreduce.task.io.sort.factor</name>  <value>64</value> </property> <property>  <name>mapreduce.map.sort.spill.percent</name>  <value>0.8</value> </property> <property>  <name>mapreduce.reduce.shuffle.parallelcopies</name>  <value>10</value> </property> <property>  <name>mapreduce.task.timeout</name>  <value>600000</value> </property> <property>  <name>mapreduce.client.submit.file.replication</name>  <value>1</value> </property> <property>  <name>mapreduce.job.reduces</name>  <value>24</value> </property> <property>  <name>mapreduce.task.io.sort.mb</name>  <value>256</value> </property> <property>  <name>mapreduce.map.speculative</name>  <value>false</value> </property> <property>  <name>mapreduce.reduce.speculative</name>  <value>false</value> </property> <property>  <name>mapreduce.job.reduce.slowstart.completedmaps</name>  <value>0.8</value> </property> <property>  <name>mapreduce.jobhistory.address</name>  <value>m103:10020</value> </property> <property>  <name>mapreduce.jobhistory.webapp.address</name>  <value>m103:19888</value> </property> <property>  <name>mapreduce.jobhistory.webapp.https.address</name>  <value>m103:19890</value> </property> <property>  <name>mapreduce.jobhistory.admin.address</name>  <value>m103:10033</value> </property> <property>  <name>mapreduce.framework.name</name>  <value>yarn</value> </property> <property>  <name>yarn.app.mapreduce.am.staging-dir</name>  <value>/user</value> </property> <property>  <name>mapreduce.am.max-attempts</name>  <value>2</value> </property> <property>  <name>yarn.app.mapreduce.am.resource.mb</name>  <value>2048</value> </property> <property>  <name>yarn.app.mapreduce.am.resource.cpu-vcores</name>  <value>1</value> </property> <property>  <name>mapreduce.job.ubertask.enable</name>  <value>false</value> </property> <property>  <name>yarn.app.mapreduce.am.command-opts</name>  <value>-Djava.net.preferIPv4Stack=true -Xmx1717986918</value> </property> <property>  <name>mapreduce.map.java.opts</name>  <value>-Djava.net.preferIPv4Stack=true -Xmx1717986918</value> </property> <property>  <name>mapreduce.reduce.java.opts</name>  <value>-Djava.net.preferIPv4Stack=true -Xmx2576980378</value> </property> <property>  <name>yarn.app.mapreduce.am.admin.user.env</name>  <value>LD_LIBRARY_PATH=$HADOOP_COMMON_HOME/lib/native:$JAVA_LIBRARY_PATH</value> </property> <property>  <name>mapreduce.map.memory.mb</name>  <value>2048</value> </property> <property>  <name>mapreduce.map.cpu.vcores</name>  <value>1</value> </property> <property>  <name>mapreduce.reduce.memory.mb</name>  <value>3072</value> </property> <property>  <name>mapreduce.reduce.cpu.vcores</name>  <value>1</value> </property> <property>  <name>mapreduce.application.classpath</name>  <value>$HADOOP_MAPRED_HOME/*,$HADOOP_MAPRED_HOME/lib/*,$MR2_CLASSPATH,$CDH_HCAT_HOME/share/hcatalog/*,$CDH_HIVE_HOME/lib/*,/etc/hive/conf,/opt/cloudera/parcels/CDH/lib/udps/*</value> </property> <property>  <name>mapreduce.admin.user.env</name>  <value>LD_LIBRARY_PATH=$HADOOP_COMMON_HOME/lib/native:$JAVA_LIBRARY_PATH</value> </property> <property>  <name>mapreduce.shuffle.max.connections</name>  <value>80</value> </property></configuration>

利用JavaAPI来访问HDFS的文件与目录

package com.demo.hdfs;import java.io.BufferedInputStream;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.net.URI;import org.apache.hadoop.conf.Configuration;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.io.IOUtils;import org.apache.hadoop.util.Progressable;/** * @author zhangzk *  */public class FileCopyToHdfs { public static void main(String[] args) throws Exception { try {  //uploadToHdfs();    //deleteFromHdfs();  //getDirectoryFromHdfs();  appendToHdfs();  readFromHdfs(); } catch (Exception e) {  // TODO Auto-generated catch block  e.printStackTrace(); } finally {  System.out.println("SUCCESS"); } } /**上传文件到HDFS上去*/ private static void uploadToHdfs() throws FileNotFoundException,IOException { String localSrc = "d://qq.txt"; String dst = "hdfs://192.168.0.113:9000/user/zhangzk/qq.txt"; InputStream in = new BufferedInputStream(new FileInputStream(localSrc)); Configuration conf = new Configuration();  FileSystem fs = FileSystem.get(URI.create(dst), conf); OutputStream out = fs.create(new Path(dst), new Progressable() {  public void progress() {  System.out.print(".");  } }); IOUtils.copyBytes(in, out, 4096, true); } /**从HDFS上读取文件*/ private static void readFromHdfs() throws FileNotFoundException,IOException { String dst = "hdfs://192.168.0.113:9000/user/zhangzk/qq.txt";  Configuration conf = new Configuration();  FileSystem fs = FileSystem.get(URI.create(dst), conf); FSDataInputStream hdfsInStream = fs.open(new Path(dst));  OutputStream out = new FileOutputStream("d:/qq-hdfs.txt");  byte[] ioBuffer = new byte[1024]; int readLen = hdfsInStream.read(ioBuffer); while(-1 != readLen){ out.write(ioBuffer, 0, readLen);  readLen = hdfsInStream.read(ioBuffer); } out.close(); hdfsInStream.close(); fs.close(); }  /**以append方式将内容添加到HDFS上文件的末尾;注意：文件更新，需要在hdfs-site.xml中添<property><name>dfs.append.support</name><value>true</value></property>*/ private static void appendToHdfs() throws FileNotFoundException,IOException { String dst = "hdfs://192.168.0.113:9000/user/zhangzk/qq.txt";  Configuration conf = new Configuration();  FileSystem fs = FileSystem.get(URI.create(dst), conf);  FSDataOutputStream out = fs.append(new Path(dst)); int readLen = "zhangzk add by hdfs java api".getBytes().length; while(-1 != readLen){ out.write("zhangzk add by hdfs java api".getBytes(), 0, readLen); } out.close(); fs.close(); }  /**从HDFS上删除文件*/ private static void deleteFromHdfs() throws FileNotFoundException,IOException { String dst = "hdfs://192.168.0.113:9000/user/zhangzk/qq-bak.txt";  Configuration conf = new Configuration();  FileSystem fs = FileSystem.get(URI.create(dst), conf); fs.deleteOnExit(new Path(dst)); fs.close(); }  /**遍历HDFS上的文件和目录*/ private static void getDirectoryFromHdfs() throws FileNotFoundException,IOException { String dst = "hdfs://192.168.0.113:9000/user/zhangzk";  Configuration conf = new Configuration();  FileSystem fs = FileSystem.get(URI.create(dst), conf); FileStatus fileList[] = fs.listStatus(new Path(dst)); int size = fileList.length; for(int i = 0; i < size; i++){ System.out.println("name:" + fileList[i].getPath().getName() + "/t/tsize:" + fileList[i].getLen()); } fs.close(); } }