使用Java在hdfs中编写文件

Question

我想在HDFS中创建一个文件并在其中写入数据.我用过这段代码:

Configuration config = new Configuration();     
FileSystem fs = FileSystem.get(config); 
Path filenamePath = new Path("input.txt");  
try {
    if (fs.exists(filenamePath)) {
        fs.delete(filenamePath, true);
    }

    FSDataOutputStream fin = fs.create(filenamePath);
    fin.writeUTF("hello");
    fin.close();
}

它会创建文件,但不会在其中写入任何内容.我搜索了很多但没有找到任何东西.我的问题是什么？我是否需要获得HDFS写入权限？

谢谢.

Answer 1

替换@Tariq的asnwer你可以在获取文件系统时传递URI

Configuration configuration = new Configuration();
FileSystem hdfs = FileSystem.get( new URI( "hdfs://localhost:54310" ), configuration );
Path file = new Path("hdfs://localhost:54310/s2013/batch/table.html");
if ( hdfs.exists( file )) { hdfs.delete( file, true ); } 
OutputStream os = hdfs.create( file,
    new Progressable() {
        public void progress() {
            out.println("...bytes written: [ "+bytesWritten+" ]");
        } });
BufferedWriter br = new BufferedWriter( new OutputStreamWriter( os, "UTF-8" ) );
br.write("Hello World");
br.close();
hdfs.close();

Answer 2

将HADOOP_CONF_DIR环境变量定义到Hadoop配置文件夹,或在代码中添加以下2行:

config.addResource(new Path("/HADOOP_HOME/conf/core-site.xml"));
config.addResource(new Path("/HADOOP_HOME/conf/hdfs-site.xml"));

如果您不添加此项,您的客户端将尝试写入本地FS,从而导致权限被拒绝的异常.

Answer 3

请尝试以下方法。

FileSystem fs = path.getFileSystem(conf);
SequenceFile.Writer inputWriter = new SequenceFile.Writer(fs, conf, path, LongWritable.class, MyWritable.class);
inputWriter.append(new LongWritable(uniqueId++), new MyWritable(data));
inputWriter.close();