Hadoop URL中读取数据出错:unknown protocol: hdfs

在尝试从Hadoop的hdfs URL读取数据时遇到'unknown protocol: hdfs'的错误。根据《Hadoop权威指南》,需要在Java中设置URLStreamHandlerFactory来识别hdfs协议。解决方案是在代码中添加一个静态执行块,通过FsUrlStreamHandlerFactory注册hdfs协议。执行此操作后,代码能够成功运行,不再报错。

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今天在学习如何从hadoop中读取数据时,写了一个简单的方法,测试时,却报以下错误:

154835_1JUC_1434710.png

以下是读取hadoop中文件并写入本地磁盘的代码:

package hdfs;

import java.io.BufferedReader;
import java.io.FileWriter;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import org.apache.hadoop.io.IOUtils;

public class HDFS {
		public static void main(String[] args) throws Exception {
		InputStream inputStream = n
root@job-da8abcdd-9948-4878-9d20-371dceb00ee1-master-0:/home# start-dfs.sh Starting namenodes on [master] /opt/hadoop/hadoop/bin/hdfs: 26: function: not found /opt/hadoop/hadoop/bin/hdfs: 28: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 29: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 30: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 31: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 32: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 33: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 35: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 36: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 37: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 38: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 39: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 40: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 41: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 42: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 43: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 44: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 45: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 46: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 47: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 48: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 49: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 50: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 51: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 52: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 53: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 54: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 55: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 56: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 57: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 58: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 59: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 60: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 61: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 62: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 63: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 64: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 65: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 66: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 67: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 68: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 69: hadoop_generate_usage: not found /opt/hadoop/hadoop/bin/hdfs: 77: function: not found /opt/hadoop/hadoop/bin/hdfs: 218: hadoop_validate_classname: not found /opt/hadoop/hadoop/bin/hdfs: 219: hadoop_exit_with_usage: not found /opt/hadoop/hadoop/bin/hdfs: 226: [[: not found /opt/hadoop/hadoop/bin/hdfs: 235: [[: not found ERROR: Cannot execute /opt/hadoop/hadoop/bin/../libexec/hdfs-config.sh. Starting datanodes /opt/hadoop/hadoop/bin/hdfs: 26: function: not found /opt/hadoop/hadoop/bin/hdfs: 28: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 29: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 30: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 31: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 32: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 33: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 35: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 36: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 37: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 38: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 39: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 40: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 41: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 42: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 43: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 44: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 45: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 46: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 47: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 48: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 49: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 50: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 51: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 52: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 53: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 54: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 55: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 56: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 57: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 58: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 59: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 60: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 61: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 62: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 63: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 64: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 65: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 66: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 67: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 68: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 69: hadoop_generate_usage: not found /opt/hadoop/hadoop/bin/hdfs: 77: function: not found /opt/hadoop/hadoop/bin/hdfs: 218: hadoop_validate_classname: not found /opt/hadoop/hadoop/bin/hdfs: 219: hadoop_exit_with_usage: not found /opt/hadoop/hadoop/bin/hdfs: 226: [[: not found /opt/hadoop/hadoop/bin/hdfs: 235: [[: not found ERROR: Cannot execute /opt/hadoop/hadoop/bin/../libexec/hdfs-config.sh. Starting secondary namenodes [job-da8abcdd-9948-4878-9d20-371dceb00ee1-master-0] /opt/hadoop/hadoop/bin/hdfs: 26: function: not found /opt/hadoop/hadoop/bin/hdfs: 28: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 29: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 30: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 31: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 32: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 33: hadoop_add_option: not found /opt/hadoop/hadoop/bin/hdfs: 35: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 36: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 37: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 38: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 39: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 40: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 41: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 42: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 43: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 44: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 45: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 46: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 47: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 48: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 49: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 50: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 51: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 52: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 53: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 54: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 55: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 56: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 57: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 58: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 59: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 60: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 61: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 62: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 63: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 64: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 65: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 66: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 67: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 68: hadoop_add_subcommand: not found /opt/hadoop/hadoop/bin/hdfs: 69: hadoop_generate_usage: not found /opt/hadoop/hadoop/bin/hdfs: 77: function: not found /opt/hadoop/hadoop/bin/hdfs: 218: hadoop_validate_classname: not found /opt/hadoop/hadoop/bin/hdfs: 219: hadoop_exit_with_usage: not found /opt/hadoop/hadoop/bin/hdfs: 226: [[: not found /opt/hadoop/hadoop/bin/hdfs: 235: [[: not found ERROR: Cannot execute /opt/hadoop/hadoop/bin/../libexec/hdfs-config.sh.
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07-11
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