利用JavaAPI访问HDFS的文件
1、重读配置文件core-site.xml
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。
2、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(); } } 注意：对于append操作，从hadoop-0.21版本开始就不支持了，关于Append的操作可以参考Javaeye上的一篇文档。
http://dongyajun.javaeye.com/blog/643391
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