HDFS客户端环境准备HDFS的API操作HDFS的I/O流操作

Posted 2022-05-30 爱上口袋的天空

一、HDFS客户端环境准备

1、配置hadoop的环境变量

 

2、创建一个maven的工程

3、导入相应的依赖坐标+日志添加 

<dependencies>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>RELEASE</version>
		</dependency>
		<dependency>
			<groupId>org.apache.logging.log4j</groupId>
			<artifactId>log4j-core</artifactId>
			<version>2.8.2</version>
		</dependency>
		<dependency>
			<groupId>org.apache.hadoop</groupId>
			<artifactId>hadoop-common</artifactId>
			<version>2.7.2</version>
		</dependency>
		<dependency>
			<groupId>org.apache.hadoop</groupId>
			<artifactId>hadoop-client</artifactId>
			<version>2.7.2</version>
		</dependency>
		<dependency>
			<groupId>org.apache.hadoop</groupId>
			<artifactId>hadoop-hdfs</artifactId>
			<version>2.7.2</version>
		</dependency>
		<dependency>
			<groupId>jdk.tools</groupId>
			<artifactId>jdk.tools</artifactId>
			<version>1.8</version>
			<scope>system</scope>
			<systemPath>$JAVA_HOME/lib/tools.jar</systemPath>
		</dependency>
</dependencies>

4、创建log4j.properties文件

log4j.rootLogger=INFO, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] - %m%n
log4j.appender.logfile=org.apache.log4j.FileAppender
log4j.appender.logfile.File=target/spring.log
log4j.appender.logfile.layout=org.apache.log4j.PatternLayout
log4j.appender.logfile.layout.ConversionPattern=%d %p [%c] - %m%n

 5、创建HdfsClient类

package com.kgf.hadoop;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;

public class HdfsClient 

    public static void main(String[] args) throws URISyntaxException, IOException, InterruptedException 

        // 1 获取文件系统
        Configuration configuration = new Configuration();

        FileSystem fs = FileSystem.get(new URI("hdfs://hadoop20:9000"), configuration, "kgf");

        // 2 创建目录
        fs.mkdirs(new Path("/1108/daxian/banzhang"));

        // 3 关闭资源
        fs.close();
    

运行之后的效果：

6、我们也可以换种方式去指定运行时的用户名称 

package com.kgf.hadoop;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;

public class HdfsClient 

    public static void main(String[] args) throws URISyntaxException, IOException, InterruptedException 

        // 1 获取文件系统
        Configuration configuration = new Configuration();

//        FileSystem fs = FileSystem.get(new URI("hdfs://hadoop20:9000"), configuration, "kgf");

        // 配置在集群上运行
         configuration.set("fs.defaultFS", "hdfs://hadoop20:9000");
         FileSystem fs = FileSystem.get(configuration);

        // 2 创建目录
        fs.mkdirs(new Path("/kgf/test"));

        // 3 关闭资源
        fs.close();

        System.out.println("over!");
    

客户端去操作HDFS时，是有一个用户身份的。默认情况下，HDFS客户端API会从JVM中获取一个参数来作为自己的用户身份：-DHADOOP_USER_NAME=kgf，kgf为用户名称。

然后运行结果：

二、HDFS的API操作

1、HDFS文件上传（测试参数优先级）

 /**
     * HDFS文件上传
     * @throws IOException
     * @throws InterruptedException
     * @throws URISyntaxException
     */
    private void testCopyFromLocalFile() throws IOException, InterruptedException, URISyntaxException 
        // 1 获取文件系统
        Configuration configuration = new Configuration();
        configuration.set("dfs.replication", "2");//设置副本数量
        FileSystem fs = FileSystem.get(new URI("hdfs://hadoop20:9000"), configuration, "kgf");

        // 2 上传文件
        fs.copyFromLocalFile(new Path("e:/banzhang.txt"), new Path("/banzhang.txt"));

        // 3 关闭资源
        fs.close();
        System.out.println("over");
    

将hdfs-site.xml拷贝到项目的根目录下

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>
<configuration>
    <property>
        <name>dfs.replication</name>
        <value>1</value>
    </property>
</configuration>

执行效果如下：

 可以发现副本数是2：

参数优先级排序：

（1）客户端代码中设置的值 >

（2）ClassPath下的用户自定义配置文件 >

（3）然后是服务器的默认配置

2、HDFS文件下载

/***
     * HDFS文件下载
     * @throws IOException
     * @throws InterruptedException
     * @throws URISyntaxException
     */
    public void testCopyToLocalFile() throws IOException, InterruptedException, URISyntaxException

        // 1 获取文件系统
        Configuration configuration = new Configuration();
        FileSystem fs = FileSystem.get(new URI("hdfs://hadoop20:9000"), configuration, "kgf");

        // 2 执行下载操作
        // boolean delSrc 指是否将原文件删除
        // Path src 指要下载的文件路径
        // Path dst 指将文件下载到的路径
        // boolean useRawLocalFileSystem 是否开启文件校验
        fs.copyToLocalFile(false, new Path("/banzhang.txt"), new Path("e:/banhua.txt"), true);

        // 3 关闭资源
        fs.close();
    

3、HDFS文件夹删除

/***
     * HDFS文件夹删除
     * @throws IOException
     * @throws InterruptedException
     * @throws URISyntaxException
     */
    public void testDelete() throws IOException, InterruptedException, URISyntaxException

        // 1 获取文件系统
        Configuration configuration = new Configuration();
        FileSystem fs = FileSystem.get(new URI("hdfs://hadoop20:9000"), configuration, "kgf");

        // 2 执行删除
        fs.delete(new Path("/1108/"), true);

        // 3 关闭资源
        fs.close();
    

4、HDFS文件名更改

/***
     * HDFS文件名更改
     * @throws IOException
     * @throws InterruptedException
     * @throws URISyntaxException
     */
    public void testRename() throws IOException, InterruptedException, URISyntaxException
        // 1 获取文件系统
        Configuration configuration = new Configuration();
        FileSystem fs = FileSystem.get(new URI("hdfs://hadoop20:9000"), configuration, "kgf");
        // 2 修改文件名称
        fs.rename(new Path("/banzhang.txt"), new Path("/banhua.txt"));
        // 3 关闭资源
        fs.close();
        System.out.println("over!");
    

5、HDFS文件详情查看

/***
     * 查看文件名称、权限、长度、块信息
     * @throws IOException
     * @throws InterruptedException
     * @throws URISyntaxException
     */
    public void testListFiles() throws IOException, InterruptedException, URISyntaxException

        // 1获取文件系统
        Configuration configuration = new Configuration();
        FileSystem fs = FileSystem.get(new URI("hdfs://hadoop20:9000"), configuration, "kgf");

        // 2 获取文件详情
        RemoteIterator<LocatedFileStatus> listFiles = fs.listFiles(new Path("/"), true);

        while(listFiles.hasNext())
            LocatedFileStatus status = listFiles.next();

            // 输出详情
            // 文件名称
            System.out.println(status.getPath().getName());
            // 长度
            System.out.println(status.getLen());
            // 权限
            System.out.println(status.getPermission());
            // 分组
            System.out.println(status.getGroup());

            // 获取存储的块信息
            BlockLocation[] blockLocations = status.getBlockLocations();

            for (BlockLocation blockLocation : blockLocations) 

                // 获取块存储的主机节点
                String[] hosts = blockLocation.getHosts();

                for (String host : hosts) 
                    System.out.println(host);
                
            

            System.out.println("-----------班长的分割线----------");
        

        // 3 关闭资源
        fs.close();
    

效果(将目录下的文件都递归查询出来了)：

D:\\jdk1.8.0_51\\bin\\java.exe -Dvisualvm.id=1345450326278400 -javaagent:D:\\JetBrains\\idea20190303\\lib\\idea_rt.jar=1048:D:\\JetBrains\\idea20190303\\bin -Dfile.encoding=UTF-8 -classpath D:\\jdk1.8.0_51\\jre\\lib\\charsets.jar;D:\\jdk1.8.0_51\\jre\\lib\\deploy.jar;D:\\jdk1.8.0_51\\jre\\lib\\ext\\access-bridge-64.jar;D:\\jdk1.8.0_51\\jre\\lib\\ext\\cldrdata.jar;D:\\jdk1.8.0_51\\jre\\lib\\ext\\dnsns.jar;D:\\jdk1.8.0_51\\jre\\lib\\ext\\jaccess.jar;D:\\jdk1.8.0_51\\jre\\lib\\ext\\jfxrt.jar;D:\\jdk1.8.0_51\\jre\\lib\\ext\\localedata.jar;D:\\jdk1.8.0_51\\jre\\lib\\ext\\nashorn.jar;D:\\jdk1.8.0_51\\jre\\lib\\ext\\sunec.jar;D:\\jdk1.8.0_51\\jre\\lib\\ext\\sunjce_provider.jar;D:\\jdk1.8.0_51\\jre\\lib\\ext\\sunmscapi.jar;D:\\jdk1.8.0_51\\jre\\lib\\ext\\sunpkcs11.jar;D:\\jdk1.8.0_51\\jre\\lib\\ext\\zipfs.jar;D:\\jdk1.8.0_51\\jre\\lib\\javaws.jar;D:\\jdk1.8.0_51\\jre\\lib\\jce.jar;D:\\jdk1.8.0_51\\jre\\lib\\jfr.jar;D:\\jdk1.8.0_51\\jre\\lib\\jfxswt.jar;D:\\jdk1.8.0_51\\jre\\lib\\jsse.jar;D:\\jdk1.8.0_51\\jre\\lib\\management-agent.jar;D:\\jdk1.8.0_51\\jre\\lib\\plugin.jar;D:\\jdk1.8.0_51\\jre\\lib\\resources.jar;D:\\jdk1.8.0_51\\jre\\lib\\rt.jar;E:\\WorkSpace\\hadoop-demo\\java-hadoop-demo\\target\\classes;D:\\software\\maven\\repository\\junit\\junit\\4.13.2\\junit-4.13.2.jar;D:\\software\\maven\\repository\\org\\hamcrest\\hamcrest-core\\1.3\\hamcrest-core-1.3.jar;D:\\software\\maven\\repository\\org\\apache\\logging\\log4j\\log4j-core\\2.8.2\\log4j-core-2.8.2.jar;D:\\software\\maven\\repository\\org\\apache\\logging\\log4j\\log4j-api\\2.8.2\\log4j-api-2.8.2.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-common\\2.7.2\\hadoop-common-2.7.2.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-annotations\\2.7.2\\hadoop-annotations-2.7.2.jar;D:\\software\\maven\\repository\\com\\google\\guava\\guava\\11.0.2\\guava-11.0.2.jar;D:\\software\\maven\\repository\\commons-cli\\commons-cli\\1.2\\commons-cli-1.2.jar;D:\\software\\maven\\repository\\org\\apache\\commons\\commons-math3\\3.1.1\\commons-math3-3.1.1.jar;D:\\software\\maven\\repository\\xmlenc\\xmlenc\\0.52\\xmlenc-0.52.jar;D:\\software\\maven\\repository\\commons-httpclient\\commons-httpclient\\3.1\\commons-httpclient-3.1.jar;D:\\software\\maven\\repository\\commons-codec\\commons-codec\\1.4\\commons-codec-1.4.jar;D:\\software\\maven\\repository\\commons-io\\commons-io\\2.4\\commons-io-2.4.jar;D:\\software\\maven\\repository\\commons-net\\commons-net\\3.1\\commons-net-3.1.jar;D:\\software\\maven\\repository\\commons-collections\\commons-collections\\3.2.2\\commons-collections-3.2.2.jar;D:\\software\\maven\\repository\\javax\\servlet\\servlet-api\\2.5\\servlet-api-2.5.jar;D:\\software\\maven\\repository\\org\\mortbay\\jetty\\jetty\\6.1.26\\jetty-6.1.26.jar;D:\\software\\maven\\repository\\org\\mortbay\\jetty\\jetty-util\\6.1.26\\jetty-util-6.1.26.jar;D:\\software\\maven\\repository\\javax\\servlet\\jsp\\jsp-api\\2.1\\jsp-api-2.1.jar;D:\\software\\maven\\repository\\com\\sun\\jersey\\jersey-core\\1.9\\jersey-core-1.9.jar;D:\\software\\maven\\repository\\com\\sun\\jersey\\jersey-json\\1.9\\jersey-json-1.9.jar;D:\\software\\maven\\repository\\org\\codehaus\\jettison\\jettison\\1.1\\jettison-1.1.jar;D:\\software\\maven\\repository\\com\\sun\\xml\\bind\\jaxb-impl\\2.2.3-1\\jaxb-impl-2.2.3-1.jar;D:\\software\\maven\\repository\\javax\\xml\\bind\\jaxb-api\\2.2.2\\jaxb-api-2.2.2.jar;D:\\software\\maven\\repository\\javax\\xml\\stream\\stax-api\\1.0-2\\stax-api-1.0-2.jar;D:\\software\\maven\\repository\\javax\\activation\\activation\\1.1\\activation-1.1.jar;D:\\software\\maven\\repository\\org\\codehaus\\jackson\\jackson-jaxrs\\1.8.3\\jackson-jaxrs-1.8.3.jar;D:\\software\\maven\\repository\\org\\codehaus\\jackson\\jackson-xc\\1.8.3\\jackson-xc-1.8.3.jar;D:\\software\\maven\\repository\\com\\sun\\jersey\\jersey-server\\1.9\\jersey-server-1.9.jar;D:\\software\\maven\\repository\\asm\\asm\\3.1\\asm-3.1.jar;D:\\software\\maven\\repository\\commons-logging\\commons-logging\\1.1.3\\commons-logging-1.1.3.jar;D:\\software\\maven\\repository\\log4j\\log4j\\1.2.17\\log4j-1.2.17.jar;D:\\software\\maven\\repository\\net\\java\\dev\\jets3t\\jets3t\\0.9.0\\jets3t-0.9.0.jar;D:\\software\\maven\\repository\\org\\apache\\httpcomponents\\httpclient\\4.1.2\\httpclient-4.1.2.jar;D:\\software\\maven\\repository\\org\\apache\\httpcomponents\\httpcore\\4.1.2\\httpcore-4.1.2.jar;D:\\software\\maven\\repository\\com\\jamesmurty\\utils\\java-xmlbuilder\\0.4\\java-xmlbuilder-0.4.jar;D:\\software\\maven\\repository\\commons-lang\\commons-lang\\2.6\\commons-lang-2.6.jar;D:\\software\\maven\\repository\\commons-configuration\\commons-configuration\\1.6\\commons-configuration-1.6.jar;D:\\software\\maven\\repository\\commons-digester\\commons-digester\\1.8\\commons-digester-1.8.jar;D:\\software\\maven\\repository\\commons-beanutils\\commons-beanutils\\1.7.0\\commons-beanutils-1.7.0.jar;D:\\software\\maven\\repository\\commons-beanutils\\commons-beanutils-core\\1.8.0\\commons-beanutils-core-1.8.0.jar;D:\\software\\maven\\repository\\org\\slf4j\\slf4j-api\\1.7.10\\slf4j-api-1.7.10.jar;D:\\software\\maven\\repository\\org\\slf4j\\slf4j-log4j12\\1.7.10\\slf4j-log4j12-1.7.10.jar;D:\\software\\maven\\repository\\org\\codehaus\\jackson\\jackson-core-asl\\1.9.13\\jackson-core-asl-1.9.13.jar;D:\\software\\maven\\repository\\org\\codehaus\\jackson\\jackson-mapper-asl\\1.9.13\\jackson-mapper-asl-1.9.13.jar;D:\\software\\maven\\repository\\org\\apache\\avro\\avro\\1.7.4\\avro-1.7.4.jar;D:\\software\\maven\\repository\\com\\thoughtworks\\paranamer\\paranamer\\2.3\\paranamer-2.3.jar;D:\\software\\maven\\repository\\org\\xerial\\snappy\\snappy-java\\1.0.4.1\\snappy-java-1.0.4.1.jar;D:\\software\\maven\\repository\\com\\google\\protobuf\\protobuf-java\\2.5.0\\protobuf-java-2.5.0.jar;D:\\software\\maven\\repository\\com\\google\\code\\gson\\gson\\2.2.4\\gson-2.2.4.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-auth\\2.7.2\\hadoop-auth-2.7.2.jar;D:\\software\\maven\\repository\\org\\apache\\directory\\server\\apacheds-kerberos-codec\\2.0.0-M15\\apacheds-kerberos-codec-2.0.0-M15.jar;D:\\software\\maven\\repository\\org\\apache\\directory\\server\\apacheds-i18n\\2.0.0-M15\\apacheds-i18n-2.0.0-M15.jar;D:\\software\\maven\\repository\\org\\apache\\directory\\api\\api-asn1-api\\1.0.0-M20\\api-asn1-api-1.0.0-M20.jar;D:\\software\\maven\\repository\\org\\apache\\directory\\api\\api-util\\1.0.0-M20\\api-util-1.0.0-M20.jar;D:\\software\\maven\\repository\\org\\apache\\curator\\curator-framework\\2.7.1\\curator-framework-2.7.1.jar;D:\\software\\maven\\repository\\com\\jcraft\\jsch\\0.1.42\\jsch-0.1.42.jar;D:\\software\\maven\\repository\\org\\apache\\curator\\curator-client\\2.7.1\\curator-client-2.7.1.jar;D:\\software\\maven\\repository\\org\\apache\\curator\\curator-recipes\\2.7.1\\curator-recipes-2.7.1.jar;D:\\software\\maven\\repository\\com\\google\\code\\findbugs\\jsr305\\3.0.0\\jsr305-3.0.0.jar;D:\\software\\maven\\repository\\org\\apache\\htrace\\htrace-core\\3.1.0-incubating\\htrace-core-3.1.0-incubating.jar;D:\\software\\maven\\repository\\org\\apache\\zookeeper\\zookeeper\\3.4.6\\zookeeper-3.4.6.jar;D:\\software\\maven\\repository\\org\\apache\\commons\\commons-compress\\1.4.1\\commons-compress-1.4.1.jar;D:\\software\\maven\\repository\\org\\tukaani\\xz\\1.0\\xz-1.0.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-client\\2.7.2\\hadoop-client-2.7.2.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-mapreduce-client-app\\2.7.2\\hadoop-mapreduce-client-app-2.7.2.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-mapreduce-client-common\\2.7.2\\hadoop-mapreduce-client-common-2.7.2.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-yarn-client\\2.7.2\\hadoop-yarn-client-2.7.2.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-yarn-server-common\\2.7.2\\hadoop-yarn-server-common-2.7.2.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-mapreduce-client-shuffle\\2.7.2\\hadoop-mapreduce-client-shuffle-2.7.2.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-yarn-api\\2.7.2\\hadoop-yarn-api-2.7.2.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-mapreduce-client-core\\2.7.2\\hadoop-mapreduce-client-core-2.7.2.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-yarn-common\\2.7.2\\hadoop-yarn-common-2.7.2.jar;D:\\software\\maven\\repository\\com\\sun\\jersey\\jersey-client\\1.9\\jersey-client-1.9.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-mapreduce-client-jobclient\\2.7.2\\hadoop-mapreduce-client-jobclient-2.7.2.jar;D:\\software\\maven\\repository\\org\\apache\\hadoop\\hadoop-hdfs\\2.7.2\\hadoop-hdfs-2.7.2.jar;D:\\software\\maven\\repository\\commons-daemon\\commons-daemon\\1.0.13\\commons-daemon-1.0.13.jar;D:\\software\\maven\\repository\\io\\netty\\netty\\3.6.2.Final\\netty-3.6.2.Final.jar;D:\\software\\maven\\repository\\io\\netty\\netty-all\\4.0.23.Final\\netty-all-4.0.23.Final.jar;D:\\software\\maven\\repository\\xerces\\xercesImpl\\2.9.1\\xercesImpl-2.9.1.jar;D:\\software\\maven\\repository\\xml-apis\\xml-apis\\1.3.04\\xml-apis-1.3.04.jar;D:\\software\\maven\\repository\\org\\fusesource\\leveldbjni\\leveldbjni-all\\1.8\\leveldbjni-all-1.8.jar com.kgf.hadoop.HdfsApiClient
README.txt
1366
rw-r--r--
supergroup
hadoop20
hadoop22
hadoop21
-----------班长的分割线----------
banhua.txt
15
rw-r--r--
supergroup
hadoop22
hadoop21
-----------班长的分割线----------
kongming.txt
14
rw-rw-rw-
kgf
hadoop20
hadoop22
hadoop21
-----------班长的分割线----------
zhuge.txt
14
rw-r--r--
supergroup
hadoop20
hadoop22
hadoop21
-----------班长的分割线----------
wc.input
46
rw-r--r--
supergroup
hadoop20
hadoop22
hadoop21
-----------班长的分割线----------
zaiyiqi.txt
28
rw-r--r--
supergroup
hadoop20
hadoop22
hadoop21
-----------班长的分割线----------

Process finished with exit code 0

6、HDFS文件和文件夹判断

/***
     * HDFS文件和文件夹判断
     * @throws IOException
     * @throws InterruptedException
     * @throws URISyntaxException
     */
    public void testListStatus() throws IOException, InterruptedException, URISyntaxException

        // 1 获取文件配置信息
        Configuration configuration = new Configuration();
        FileSystem fs = FileSystem.get(new URI("hdfs://hadoop20:9000"), configuration, "kgf");

        // 2 判断是文件还是文件夹
        FileStatus[] listStatus = fs.listStatus(new Path("/"));

        for (FileStatus fileStatus : listStatus) 

            // 如果是文件
            if (fileStatus.isFile()) 
                System.out.println("f:"+fileStatus.getPath().getName());
            else 
                System.out.println("d:"+fileStatus.getPath().getName());
            
        

        // 3 关闭资源
        fs.close();
        System.out.println("over");
    

效果输出：

f:README.txt
f:banhua.txt
d:kgf
d:sanguo
d:user
over

三、HDFS的I/O流操作

1、把本地e盘上的banhua.txt文件上传到HDFS根目录

 /***
     * 把本地e盘上的banhua.txt文件上传到HDFS根目录
     * @throws IOException
     * @throws InterruptedException
     * @throws URISyntaxException
     */
    public void putFileToHDFS() throws IOException, InterruptedException, URISyntaxException 

        // 1 获取文件系统
        Configuration configuration = new Configuration();
        FileSystem fs = FileSystem.get(new URI("hdfs://hadoop20:9000"), configuration, "kgf");

        // 2 创建输入流
        FileInputStream fis = new FileInputStream(new File("e:/banhua.txt"));

        // 3 获取输出流
        FSDataOutputStream fos = fs.create(new Path("/banhua2.txt"));

        // 4 流对拷
        IOUtils.copyBytes(fis, fos, configuration);

        // 5 关闭资源
        IOUtils.closeStream(fos);
        IOUtils.closeStream(fis);
        fs.close();
        System.out.println("over!");
    

2、从HDFS上下载banhua.txt文件到本地e盘上

 /***
     * 从HDFS上下载banhua.txt文件到本地e盘上
     * @throws IOException
     * @throws InterruptedException
     * @throws URISyntaxException
     */
    public void getFileFromHDFS() throws IOException, InterruptedException, URISyntaxException

        // 1 获取文件系统
        Configuration configuration = new Configuration();
        FileSystem fs = FileSystem.get(new URI("hdfs://hadoop20:9000"), configuration, "kgf");

        // 2 获取输入流
        FSDataInputStream fis = fs.open(new Path("/banhua.txt"));

        // 3 获取输出流
        FileOutputStream fos = new FileOutputStream(new File("e:/banhua3.txt"));

        // 4 流的对拷
        IOUtils.copyBytes(fis, fos, configuration);

        // 5 关闭资源
        IOUtils.closeStream(fos);
        IOUtils.closeStream(fis);
        fs.close();
        System.out.println("over");
    

3、分块读取HDFS上的大文件，比如根目录下的/hadoop-2.7.2.tar.gz

 下载第一块block0(1024*1024*128=134217728=128M):

 /**
     * 下载第一块
     * @throws IOException
     * @throws InterruptedException
     * @throws URISyntaxException
     */
    public void readFileSeek1() throws IOException, InterruptedException, URISyntaxException

        // 1 获取文件系统
        Configuration configuration = new Configuration();
        FileSystem fs = FileSystem.get(new URI("hdfs://hadoop20:9000"), configuration, "kgf");

        // 2 获取输入流
        FSDataInputStream fis = fs.open(new Path("/hadoop-2.7.2.tar.gz"));

        // 3 创建输出流
        FileOutputStream fos = new FileOutputStream(new File("e:/hadoop-2.7.2.tar.gz.part1"));

        // 4 流的拷贝
        byte[] buf = new byte[1024];

        for(int i =0 ; i < 1024 * 128; i++)//计算下载第一块1024*1024*128=134217728
            fis.read(buf);
            fos.write(buf);
        
        // 5关闭资源
        IOUtils.closeStream(fis);
        IOUtils.closeStream(fos);
        fs.close();
    

 下载剩余的第二块block1

 /***
     * 下载第二块
     * @throws IOException
     * @throws InterruptedException
     * @throws URISyntaxException
     */
    public void readFileSeek2() throws IOException, InterruptedException, URISyntaxException

        // 1 获取文件系统
        Configuration configuration = new Configuration();
        FileSystem fs = FileSystem.get(new URI("hdfs://hadoop20:9000"), configuration, "kgf");

        // 2 打开输入流
        FSDataInputStream fis = fs.open(new Path("/hadoop-2.7.2.tar.gz"));

        // 3 定位输入数据位置
        fis.seek(1024*1024*128);

        // 4 创建输出流
        FileOutputStream fos = new FileOutputStream(new File("e:/hadoop-2.7.2.tar.gz.part2"));

        // 5 流的对拷
        IOUtils.copyBytes(fis, fos, configuration);

        // 6 关闭资源
        IOUtils.closeStream(fis);
        IOUtils.closeStream(fos);
    

合并文件：

在Window命令窗口中进入到目录E:\\，然后执行如下命令，对数据进行合并

type hadoop-2.7.2.tar.gz.part2 >> hadoop-2.7.2.tar.gz.part1

合并完成后，将hadoop-2.7.2.tar.gz.part1重新命名为hadoop-2.7.2.tar.gz。解压发现该tar包非常完整。