HDFS 的 API 操作

先配置好Windows环境

然后导入 Maven 依赖

     <dependencies>
          <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-common</artifactId>
            <version>2.7.5</version>
        </dependency>
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-client</artifactId>
            <version>2.7.5</version>
        </dependency>
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-hdfs</artifactId>
            <version>2.7.5</version>
        </dependency>
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-mapreduce-client-core</artifactId>
            <version>2.7.5</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>RELEASE</version>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <encoding>UTF-8</encoding>
                    <!--    <verbal>true</verbal>-->
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.4.3</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <minimizeJar>true</minimizeJar>
                        </configuration>
                    </execution>
                </executions>
            </plugin>

        </plugins>
    </build>

使用url方式访问数据

@Test
public void demo1()throws  Exception{
    //第一步：注册hdfs 的url
    URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory());

    //获取文件输入流
    InputStream inputStream  = new URL("hdfs://node01:8020/a.txt").openStream();
    //获取文件输出流
    FileOutputStream outputStream = new FileOutputStream(new File("D:\\hello.txt"));

    //实现文件的拷贝
    IOUtils.copy(inputStream, outputStream);

    //关闭流
    IOUtils.closeQuietly(inputStream);
    IOUtils.closeQuietly(outputStream);
}

**使用**文件系统方式访问数据

 获取 FileSystem 的几种方式

* 第一种方式
```java
@Test
public void getFileSystem1() throws IOException {
    Configuration configuration = new Configuration();
    //指定我们使用的文件系统类型:
    configuration.set("fs.defaultFS", "hdfs://node01:8020/");

    //获取指定的文件系统
    FileSystem fileSystem = FileSystem.get(configuration);
    System.out.println(fileSystem.toString());

}
```

* 第二种方式
```java
@Test
public void getFileSystem2() throws  Exception{
    FileSystem fileSystem = FileSystem.get(new URI("hdfs://node01:8020"), new       Configuration());
    System.out.println("fileSystem:"+fileSystem);
}
```

* 第三种方式
```java
@Test
public void getFileSystem3() throws  Exception{
    Configuration configuration = new Configuration();
    configuration.set("fs.defaultFS", "hdfs://node01:8020");
    FileSystem fileSystem = FileSystem.newInstance(configuration);
    System.out.println(fileSystem.toString());
}
```

* 第四种方式
```java
//@Test
public void getFileSystem4() throws  Exception{
    FileSystem fileSystem = FileSystem.newInstance(new URI("hdfs://node01:8020") ,new Configuration());
    System.out.println(fileSystem.toString());
}
```

 遍历 HDFS 中所有文件

* 使用 API 遍历
```java
@Test
public void listMyFiles()throws Exception{
    //获取fileSystem类
    FileSystem fileSystem = FileSystem.get(new URI("hdfs://node01:8020"), new Configuration());
    //获取RemoteIterator 得到所有的文件或者文件夹，第一个参数指定遍历的路径，第二个参数表示是否要递归遍历
    RemoteIterator<LocatedFileStatus> locatedFileStatusRemoteIterator = fileSystem.listFiles(new Path("/"), true);
    while (locatedFileStatusRemoteIterator.hasNext()){
        LocatedFileStatus next = locatedFileStatusRemoteIterator.next();
        System.out.println(next.getPath().toString());
    }
    fileSystem.close();
}
```

创建文件夹

```java
@Test
public void mkdirs() throws  Exception{
    FileSystem fileSystem = FileSystem.get(new URI("hdfs://node01:8020"), new Configuration());
    boolean mkdirs = fileSystem.mkdirs(new Path("/hello/mydir/test"));
    fileSystem.close();
}
```

下载文件

```java
@Test
public void getFileToLocal()throws  Exception{
    FileSystem fileSystem = FileSystem.get(new URI("hdfs://node01:8020"), new Configuration());
    FSDataInputStream inputStream = fileSystem.open(new Path("/timer.txt"));
    FileOutputStream  outputStream = new FileOutputStream(new File("e:\\timer.txt"));
    IOUtils.copy(inputStream,outputStream );
    IOUtils.closeQuietly(inputStream);
    IOUtils.closeQuietly(outputStream);
    fileSystem.close();
}
```

文件上传

```java
@Test
public void putData() throws  Exception{
    FileSystem fileSystem = FileSystem.get(new URI("hdfs://node01:8020"), new Configuration());
    fileSystem.copyFromLocalFile(new Path("file:///c:\\install.log"),new Path("/hello/mydir/test"));
    fileSystem.close();
}
```