Write a file in hdfs with Java

问题

I want to create a file in HDFS and write data in that. I used this code:

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();
}

It creates the file, but it does't write anything in it. I searched a lot but didn't find anything. What is my problem? Do I need any permission to write in HDFS?

Thanks.

回答1:

an alternative to @Tariq's asnwer you could pass the URI when getting the filesystem

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();

回答2:

Either define the HADOOP_CONF_DIR environment variable to your Hadoop configuration folder or add the following 2 lines in your code :

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

If you don't add this, your client will try to write to the local FS, hence resulting into the permission denied exception.

回答3:

Please try the below approach.

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();

来源：https://stackoverflow.com/questions/16000840/write-a-file-in-hdfs-with-java

标签

java

Hadoop

HDFS