【HDFS API编程】从本地拷贝文件，从本地拷贝大文件，拷贝HDFS文件到本地

接着之前继续API操作的学习

CopyFromLocalFile: 顾名思义，从本地文件拷贝

/**
 * 使用Java API操作HDFS文件系统
 * 关键点:
 * 1)create Configuration
 * 2)get FileSystem
 * 3)...It's your HDFS API operation.
 */
public class HDFSApp {

    public static final String HDFS_PATH = "hdfs://hadoop000:8020";
    FileSystem fileSystem = null;
    Configuration configuration = null;

    @Before
    public void setUp() throws Exception{
        System.out.println("setUp-----------");
        configuration = new Configuration();
        configuration.set("dfs.replication","1");

        /*
         * 构造一个访问制定HDFS系统的客户端对象
         * 第一个参数：HDFS的URI
         * 第二个参数：客户端制定的配置参数
         * 第三个参数：客户端的身份，说白了就是用户名
         */
        fileSystem = FileSystem.get(new URI(HDFS_PATH),configuration,"hadoop");
    }

    /*
     * 拷贝本地文件到HDFS文件系统
     */
    @Test
    public void copyFromLocalFile() throws Exception{
        Path src = new Path("/home/hadoop/t.txt");
        Path dst = new Path("/hdfsapi/test/");
        fileSystem.copyFromLocalFile(src,dst);
    }
　　@After
    public void tearDown(){
        configuration = null;
        fileSystem = null;
        System.out.println("----------tearDown------");
    }
}

方法怎么用？还是那句 哪里不会Ctrl点哪里。

点进CopyFromLocalFile方法源码得知方法需要两个参数：本地文件的Path，和目标文件的Path，无返回值。

我们运行该测试类后进入终端使用-ls查看/hdfsapi/test目录下包含了刚刚copy进来的t.txt文件，测试成功。

[hadoop@hadoop000 ~]$ hadoop fs -ls /hdfsapi/test
Found 3 items
-rw-r--r--   3 hadoop supergroup         14 2019-04-19 16:31 /hdfsapi/test/a.txt
-rw-r--r--   1 hadoop supergroup         28 2019-04-19 16:50 /hdfsapi/test/c.txt
-rw-r--r--   1 hadoop supergroup       2732 2019-04-20 19:51 /hdfsapi/test/t.txt

如果我们需要从本地拷贝一个大文件，文件越大需要等待的时间自然越长，这么漫长的等待且毫无显示严重影响用户体验。

所以在上传大文件的时候可以添加上传进度条，在fileSystem下有个create方法带有进度条的功能：

/**
   * Create an FSDataOutputStream at the indicated Path with write-progress
   * reporting.
   * Files are overwritten by default.
   * @param f the file to create
   * @param progress to report progress
*在具有写入进度的指定路径上创建fsdataoutputstream。
*默认情况下会覆盖文件。
*@参数 f 要创建的文件
*@参数 progress 报告进度
*/ 
  public FSDataOutputStream create(Path f, Progressable progress) 
      throws IOException {
    return create(f, true, 
                  getConf().getInt("io.file.buffer.size", 4096),
                  getDefaultReplication(f),
                  getDefaultBlockSize(f), progress);
  }

运行测试类，能看到打印显示，虽然全是点看起来比较抽象，但是比什么都没有到怀疑死机还是要好点儿。

setUp-----------
log4j:WARN No appenders could be found for logger (org.apache.hadoop.metrics2.lib.MutableMetricsFactory).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
...................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................----------tearDown------

Process finished with exit code 0
........................

我们打开终端-ls查看，上传成功。

[hadoop@hadoop000 software]$ hadoop fs -ls /hdfsapi/test
Found 4 items
-rw-r--r--   3 hadoop supergroup         14 2019-04-19 16:31 /hdfsapi/test/a.txt
-rw-r--r--   1 hadoop supergroup         28 2019-04-19 16:50 /hdfsapi/test/c.txt
-rw-r--r--   1 hadoop supergroup  181367942 2019-04-20 20:10 /hdfsapi/test/jdk.zip
-rw-r--r--   1 hadoop supergroup       2732 2019-04-20 19:51 /hdfsapi/test/t.txt

能上传那就自然会问：怎么下载？直接上代码，和上面类似就不多介绍了。

    /**
     * 拷贝HDFS文件到本地：下载
     * @throws Exception
     */
    @Test
    public void copyToLocalFile() throws Exception{
        Path src = new Path("/hdfsapi/test/t.txt");
        Path dst = new Path("/home/hadoop/app");
        fileSystem.copyToLocalFile(src,dst);
    }