So implementieren Sie das Hoch- und Herunterladen von HDFS-Dateien in Java

1、pom.xml配置

<!--配置-->
<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <hadoop.version>3.1.3</hadoop.version>
</properties>
<!--依赖库-->
<dependencies>
    <dependency>
        <groupId>org.apache.hadoop</groupId>
          <artifactId>hadoop-common</artifactId>
          <version>${hadoop.version}</version>
    </dependency>
    <dependency>
         <groupId>org.apache.hadoop</groupId>
          <artifactId>hadoop-mapreduce-client-core</artifactId>
          <version>${hadoop.version}</version>
    </dependency>
</dependencies>

2、创建与删除

//导包
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import java.io.IOException;
public static void main( String[] args ){
    //初始化hadoop文件系统的configration对象
    Configuration conf = new Configuration();
    //将hadoop的configration信息传入
    conf.set("fs.defaultFS","hdfs://192.168.50.102:9000");
    //初始化Hadoop文件系统的句柄
    FileSystem fs=null;
    try {
        //配置Hadoop的文件句柄信息
        fs=FileSystem.get(conf);
        //定义Hadoop的文件路径
        final String PATH="/test/kb16/hadoop/ratings.csv";
        //初始化Hadoop的路径信息
        Path path = new Path(PATH);
        //如果文件路径存在就删除
        if (fs.exists(path)) {
            System.out.println("DELETE "+fs.delete(path, true));
        }else{
            //如果文件路径不存在就创建
            System.out.println("CREATE "+fs.create(path));
        }
    } catch (IOException e) {
        e.printStackTrace();
    }finally {
        //结束的时候，句柄还没有释放就进行释放
        if (fs!=null) {
            try {
                fs.close() ;
            }catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

3、文件上传

//导包
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import java.io.File;
import java.io.IOException;
public static void main(String[] args) {
    //定义本地上传文件路径
    final String formPath="E:\\ratings.csv";
    //本地文件不存在就报错，并强制让程序终止
    if (!new File(formPath).exists()) {
        System.out.println(formPath +"doesn't exits");
        return;
    }
    //初始化hadoop文件系统的configration对象
    Configuration conf = new Configuration();
    //将hadoop的configration信息传入
    conf.set("fs.defaultFS","hdfs://192.168.50.102:9000");
    //初始化Hadoop文件系统的句柄
    FileSystem fs=null;
    try {
        //将config信息传入
        fs=FileSystem.get(conf);
        //定义上传到HDFS的路径
        final String toPath="/test/kb16/hive";
        //初始化路径
        Path to =new Path(toPath);
        //如果文件路径存在不执行，如果文件路径不存在就尝试创建，如果创建失败就跳过
          if (!fs.exists(to)&& !fs.mkdirs(to)) {
            System.out.println(toPath +"doesn't exit and can't be created");
            return;
        }
        //初始化上传文件路径
        Path from=new Path(formPath);
        //利用方法将本地文件复制到HDFS中
        fs.copyFromLocalFile(from, to);
        System.out.println("succeed in copying from "+formPath+" to "+toPath);
    } catch (IOException e) {
        e.printStackTrace();
        System.out.println("FAILURE");
    }finally{
        //如果结束Hadoop文件系统句柄没有关闭，利用方法进行句柄释放
        if (null!=fs) {
            try {
                fs.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

4、文件下载

//导包
import com.google.inject.internal.cglib.core.$LocalVariablesSorter;
import com.google.inject.internal.cglib.proxy.$Factory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import java.io.File;
import java.io.IOException;
public class Download {
    public static void main(String[] args) {
        //定义文件下载路径
        final String toPath = "C:\\Users\\Jialin\\Desktop";
        //获取路径
        File to = new File(toPath);
        //如果路存在或者文件路径不存在但是创建成功就不执行if方法
        if (!to.exists()&&!to.mkdirs()) {
            System.err.println(toPath + "doesn't exist and can't be created");
            return;
        }
        //初始化hadoop文件系统的configration对象
        Configuration config = new Configuration();
        //将hadoop的configration信息传入
        config.set("fs.defaultFS", "hdfs://192.168.50.102:9000");
        //初始化Hadoop文件系统的句柄
        FileSystem fs = null;
        try {
            //将config信息传入
            fs = FileSystem.get(config);
            //定义下载文件路径
            final String fromPath = "/test/kb16/hive/ratings.csv";
            //获取路径信息
            Path from = new Path(fromPath);
            //如果指定下载文件不存在就退出
            if (!fs.exists(from)) {
                System.err.println(toPath + "doesn't exist ");
                return;
            }
            //获取文件下载路径信息
            Path _to = new Path(toPath);
            //利用方法将Hadoop文件下载到本地
            fs.copyToLocalFile(from,_to);
            System.out.println("succeed in downloading from "+fromPath+" to"+toPath);
        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("FAILURE");
        } finally {
            //如果结束Hadoop文件系统句柄没有关闭，利用方法进行句柄释放
            if (null != fs)
                try {
                    fs.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
        }
    }
}

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