Hadoop学习二(java api调用操作HDFS)

上一篇文章记录了在Ubuntu虚拟机上启动了hadoop

这篇文章在windows机器上通过java api方式调用操作hdfs，在使用过程中也遇到了一些问题，这里简单介绍一下。

工具：.IntellJ IDEA

首先创建了一个maven项目，pom.xml文件中引入了 hadoop-common 包

<!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-common --><dependency>  <groupId>org.apache.hadoop</groupId>  <artifactId>hadoop-common</artifactId>  <version>2.7.1</version></dependency><!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-mapreduce-client-core --><dependency>  <groupId>org.apache.hadoop</groupId>  <artifactId>hadoop-mapreduce-client-core</artifactId>  <version>2.7.1</version></dependency>

我测试了下从hdfs上下载文件，过程如下：

在linux的hadoop服务器上面创建了一个文件，文件名是newrt （就是把jdk下面的rt.jar上传到了hdfs）

在windows本地创建一个class--->HDFSTest，代码如下

import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.IOUtils;import java.io.FileOutputStream;import java.io.InputStream;import java.io.OutputStream;import java.net.URI;/** * Created by lixintang on 2017/4/17. */public class HDFSTest {    public static void main(String[] args) throws Exception{               Configuration conf = new Configuration();        FileSystem fs = FileSystem.get(URI.create("hdfs://192.168.56.101:9000"), conf);        InputStream in = fs.open(new Path("/newrt"));        OutputStream out = new FileOutputStream("D:/hadoop/hdfs/rt.jar");        IOUtils.copyBytes(in, out, 4096, true);    }}

运行报出如下问题：

1    [main] DEBUG org.apache.hadoop.util.Shell  - Failed to detect a valid hadoop home directory

java.io.IOException: HADOOP_HOME or hadoop.home.dir are not set.
at org.apache.hadoop.util.Shell.checkHadoopHome(Shell.java:303)
at org.apache.hadoop.util.Shell.<clinit>(Shell.java:328)
at org.apache.hadoop.util.StringUtils.<clinit>(StringUtils.java:80)
at org.apache.hadoop.fs.FileSystem$Cache$Key.<init>(FileSystem.java:2807)
at org.apache.hadoop.fs.FileSystem$Cache$Key.<init>(FileSystem.java:2802)
at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:2668)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:371)
at com.xintangli.bigdata.hadooptest.hdfs.HDFSTest.main(HDFSTest.java:21)
6    [main] ERROR org.apache.hadoop.util.Shell  - Failed to locate the winutils binary in the hadoop binary path
java.io.IOException: Could not locate executable null\bin\winutils.exe in the Hadoop binaries.
at org.apache.hadoop.util.Shell.getQualifiedBinPath(Shell.java:356)
at org.apache.hadoop.util.Shell.getWinUtilsPath(Shell.java:371)
at org.apache.hadoop.util.Shell.<clinit>(Shell.java:364)
at org.apache.hadoop.util.StringUtils.<clinit>(StringUtils.java:80)
at org.apache.hadoop.fs.FileSystem$Cache$Key.<init>(FileSystem.java:2807)
at org.apache.hadoop.fs.FileSystem$Cache$Key.<init>(FileSystem.java:2802)
at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:2668)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:371)
at com.xintangli.bigdata.hadooptest.hdfs.HDFSTest.main(HDFSTest.java:21)

看错误信息是HADOOP_HOME没有配置

可以在调用之前设置 hadoop.home.dir(这里是设置本地的hadoop目录)

System.setProperty("hadoop.home.dir", "D:\\soft\\dev_soft\\database\\hadoop\\hadoop-2.7.1");

public class HDFSTest {    public static void main(String[] args) throws Exception{        System.setProperty("hadoop.home.dir", "D:\\soft\\dev_soft\\database\\hadoop\\hadoop-2.7.1");        Configuration conf = new Configuration();        FileSystem fs = FileSystem.get(URI.create("hdfs://192.168.56.101:9000"), conf);        InputStream in = fs.open(new Path("/newrt"));        OutputStream out = new FileOutputStream("D:/hadoop/hdfs/rt.jar");        IOUtils.copyBytes(in, out, 4096, true);    }}

之后运行报错：

No FileSystem for scheme: hdfs

经过查资料发现是没有引入hadoop-hdfs包导致的，pom文件内容如下

<dependency>  <groupId>org.apache.hadoop</groupId>  <artifactId>hadoop-hdfs</artifactId>  <version>2.7.1</version></dependency>

设置好后，可正常运行，并下载了newrt文件保存到本地为rt.jar