题目：查看Java帮助手册或其它资料，用“java.net.URL”和“org.apache.hadoop.fs.FsURLStreamHandlerFactory”编程完成输出HDFS中指定文件的文本到终端中。
java代码：
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.Path;
public class MyFSDataInputStream extends FSDataInputStream {
private static final int BUFFER_SIZE = 4096;
private byte[] buffer;
private int pos;
private int end;
private boolean eof;
public MyFSDataInputStream(FileSystem fs, Path file) throws IOException {
super(fs.open(file));
buffer = new byte[BUFFER_SIZE];
pos = 0;
end = 0;
eof = false;
}
public String readNextLine() throws IOException {
StringBuilder sb = new StringBuilder();
int b = -1;
boolean found = false;
while (!eof && !found) {
if (pos >= end) {
fillBuffer();
}
if (end == -1) {
eof = true;
}
while (pos < end) {
b = buffer[pos++];
if (b == '\r' || b == '\n') {
found = true;
break;
}
sb.append((char) b);
}
}
if (sb.length() == 0 && eof) {
return "";
} else {
return sb.toString();
}
}
private void fillBuffer() throws IOException {
end = in.read(buffer);
pos = 0;
}
public static void main(String[] args) throws IOException {
if (args.length < 1) {
System.err.println("Usage: MyFSDataInputStream
System.exit(1);
}
String filePath = args[0];
Configuration conf = new Configuration();
Path path = new Path(filePath);
FileSystem fs = FileSystem.get(path.toUri(), conf);
MyFSDataInputStream in = new MyFSDataInputStream(fs, path);
String line;
while ((line = in.readNextLine()) != null) {
System.out.println(line);
}
in.close();
}
}
命令：
1. start-dfs.sh
2. vim file.txt
3. hadoop fs -mkdir /user/hadoop/input
4. hadoop fs -put /root/file.txt /user/hadoop/input
5. cd /usr/local/hadoop/share
6. ls
7. vim ReadHdfsFileFromURL.java
8. ls
9. javac -classpath /usr/local/hadoop/share/hadoop/common/hadoop-common-2.7.4.jar ReadHdfsFileFromURL.java
10. ls
11. HADOOP_CLASSPATH=. hadoop ReadHdfsFileFromURL
结果：
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