hadoop的hdfs，下载文件

1、首先启动hadoop

start-all.sh

2、建立maven工程

2.1 编辑pom.xml文件

 1 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 2   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 3   <modelVersion>4.0.0</modelVersion>
 4 
 5   <groupId>com.js</groupId>
 6   <artifactId>ss</artifactId>
 7   <version>0.0.1-SNAPSHOT</version>
 8   <packaging>jar</packaging>
 9 
10   <name>ss</name>
11   <url>http://maven.apache.org</url>
12 
13   <properties>
14     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
15     <!-- 定義一個變量 -->
16     <hadoop.version>3.1.1</hadoop.version>
17   </properties>
18  
19   <dependencies>
20     <dependency>
21       <groupId>junit</groupId>
22       <artifactId>junit</artifactId>
23       <version>3.8.1</version>
24       <scope>test</scope>
25     </dependency>
26      
27     <!-- JDK依賴 -->
28     <dependency>
29         <groupId>jdk.tools</groupId>
30         <artifactId>jdk.tools</artifactId>
31         <version>1.8</version>
32         <scope>system</scope>
33         <systemPath>${JAVA_HOME}/lib/tools.jar</systemPath>
34     </dependency>
35      
36     <!-- hadoop start -->
37      
38       <dependency>
39           <groupId>org.apache.hadoop</groupId>
40           <artifactId>hadoop-hdfs</artifactId>
41           <version>${hadoop.version}</version>
42       </dependency>
43      
44       <dependency> 
45           <groupId>org.apache.hadoop</groupId> 
46           <artifactId>hadoop-client</artifactId> 
47           <version>${hadoop.version}</version> 
48       </dependency>
49      
50       <dependency>
51           <groupId>org.apache.hadoop</groupId>
52           <artifactId>hadoop-common</artifactId>
53           <version>${hadoop.version}</version>
54       </dependency>
55        
56      <!-- hadoop end -->
57  </dependencies>
58  
59 </project>

2.2 新建一个类文件

 1 package com.js;
 2 
 3 import java.io.FileOutputStream;
 4 import java.io.IOException;
 5 import java.net.URI;
 6 import java.net.URISyntaxException;
 7 
 8 import org.apache.hadoop.conf.Configuration;
 9 import org.apache.hadoop.fs.FSDataInputStream;
10 import org.apache.hadoop.fs.FileSystem;
11 import org.apache.hadoop.fs.Path;
12 import org.apache.hadoop.io.IOUtils;
13 
14 /**
15  * Hello world!
16  *
17  */
18 public class App 
19 {
20     public static void main( String[] args ) throws IOException, InterruptedException, URISyntaxException {
21         System.out.println( "Hello World!" );
22         System.out.println("hello world");
23 
24         
25         Configuration conf = new Configuration();
26         // 设置hadoop的文件系统格式
27         conf.set("fs.defaultFS", "hdfs://localhost:9000");
28         
29         FileSystem fs = FileSystem.get(conf);
30         
31         Path src = new Path("/wordcount/input");
32         FSDataInputStream in = fs.open(src);
33         
34         FileOutputStream os = new FileOutputStream("./out");
35         IOUtils.copyBytes(in, os, conf, true);
36         
37     }
38 }

在当前目录下,会出现out文件