Improve PigContext code by using Factory Pattern
------------------------------------------------
Key: PIG-70
URL: https://issues.apache.org/jira/browse/PIG-70
Project: Pig
Issue Type: Improvement
Components: impl
Affects Versions: 0.1.0
Reporter: Benjamin Francisoud
Even if the PigContext code is still quite small at the moment, for an outsider
(me) it's already hard to understand :(
If I understand correctly the PigContext purpose (on a Object Oriented point of
view) is to hold various configuration objects like JobConf, JobClient,
JobSubmissionProtocol...
The initialization code mainly use the ExecType parameter but can also use
quite complex code like: doHod(), initProperties(), connect()...
(btw, the connect() method is actually doing 2 things: initializing some var
and trying to connect, it initialization code should be move somewhere else)
It is the perfect case to apply the [Factory
Pattern|http://en.wikipedia.org/wiki/Factory_method_pattern] , you can also see
[Replace Constructor with Factory
Method|http://www.refactoring.com/catalog/replaceConstructorWithFactoryMethod.html]
for more details.
My proposal is to create a new PigContextFactory class, to old the
initialization code make to PigContext and PigContextFactory 200 lines classes
instead of one big 500 lines of code class.
PigContext would hold some getter and setter and methods related to
instantiate/run "functions"
The new API would be:
h4. PigContextFactory .java
{code:java}
public class PigContextFactory {
public static PigContext getInstance(ExecType execType) {...}
}
{code}
h4. PigContext.java
{code:java}
public class PigContext implements Serializable, FunctionInstantiator {
public String getJobName(){...}
public JobSubmissionProtocol getJobTracker() {...}
public JobConf getConf() {...}
public static Object instantiateFuncFromSpec(String funcSpec) throws
IOException{...}
public Object instantiateFuncFromAlias(String alias) throws IOException
{...}
public void registerFunction(String function, String functionSpec) {...}
}
{code}
h4. Client code
{code:java}
PigContext context = PigContextFactory.getInstance(ExecType.MAPREDUCE);
{code}
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