hadoop DistributedCache returns null - hadoop

Question

i'm using hadoop DistributedCache,but i got some troubles.
my hadoop is in pseudo-distributed mode.
from here we can see in pseudo-distributed mode we use
DistributedCache.getLocalCache(xx) to retrive cached file.
first i put my file into DistributedCache:
DistributedCache.addCacheFile(new Path(
"hdfs://localhost:8022/user/administrator/myfile").toUri(),
job.getConfiguration());
then retrieve in mapper setup(),but DistributedCache.getLocalCache returns null.i can see my cached file through
System.out.println("Cache: "+context.getConfiguration().get("mapred.cache.files"));
and it print out:
hdfs://localhost:8022/user/administrator/myfile
here is my Pseudocode:
public static class JoinMapper{
#Override
protected void setup(Context context){
Path[] cacheFiles = DistributedCache.getLocalCacheFiles(context
.getConfiguration());
System.out.println("Cache
:"+context.getConfiguration().get("mapred.cache.files"));
Path cacheFile;
if (cacheFiles != null) {}
}
}
xx....
public static void main(String[] args){
Job job = new Job(conf, "Join Test");
DistributedCache.addCacheFile(new Path("hdfs://localhost:8022/user/administrator/myfile").toUri(),
job.getConfiguration());}
sorry about poor Typesetting.anyone help please....
btw,i can get uris using
URI[] uris = DistributedCache.getCacheFiles(context
.getConfiguration());
uris returns :
hdfs://localhost:8022/user/administrator/myfile
when i try to read from uri,error with file not found exception.

Answer 1

The Distributed Cache will copy your files from HDFS to the local file system of all TaskTracker.
How are u reading the file? If the file is in HDFS u will have to get HDFS FileSystem, otherwise it is going to use the default (probably the local one). So to read the file in HDFS try:
FileSystem fs = FileSystem.get(new Path("hdfs://localhost:8022/user/administrator/myfile").toUri(), new Configuration());
Path path = new Path (url);
BufferedReader br = new BufferedReader(new InputStreamReader(fs.open(path)));