Database Reference
In-Depth Information
System
.
exit
(
exitCode
);
}
}
We make
ConfigurationPrinter
a subclass of
Configured
, which is an imple-
mentation of the
Configurable
interface. All implementations of
Tool
need to imple-
ment
Configurable
(since
Tool
extends it), and subclassing
Configured
is often
the easiest way to achieve this. The
run()
method obtains the
Configuration
using
Configurable
's
getConf()
method and then iterates over it, printing each property
to standard output.
The static block makes sure that the HDFS, YARN, and MapReduce configurations are
picked up, in addition to the core ones (which
Configuration
knows about already).
ConfigurationPrinter
's
main()
method does not invoke its own
run()
method
directly. Instead, we call
ToolRunner
's static
run()
method, which takes care of cre-
ating a
Configuration
object for the
Tool
before calling its
run()
method.
ToolRunner
also uses a
GenericOptionsParser
to pick up any standard options
specified on the command line and to set them on the
Configuration
instance. We
can see the effect of picking up the properties specified in
conf/hadoop-localhost.xml
by
running the following commands:
%
mvn compile
%
export HADOOP_CLASSPATH=target/classes/
%
hadoop ConfigurationPrinter -conf conf/hadoop-localhost.xml \
| grep yarn.resourcemanager.address=
yarn.resourcemanager.address=localhost:8032
