com.twitter.elephantbird.pig.piggybank.GenericInvoker Maven / Gradle / Ivy
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* to you under the Apache License, Version 2.0 (the
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* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
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*/
package com.twitter.elephantbird.pig.piggybank;
import java.io.IOException;
import org.apache.pig.EvalFunc;
import org.apache.pig.backend.executionengine.ExecException;
import org.apache.pig.data.DataType;
import org.apache.pig.data.Tuple;
import org.apache.pig.impl.logicalLayer.FrontendException;
import org.apache.pig.impl.logicalLayer.schema.Schema;
import org.apache.pig.impl.logicalLayer.schema.Schema.FieldSchema;
/**
* The generic Invoker class does all the common grunt work of setting up an invoker.
* Class-specific non-generic extensions of this class are needed for Pig to know what type
* of return to expect from exec, and to find the appropriate classes through reflection.
* All they have to do is implement the constructors that call into super(). Note that the
* no-parameter constructor is required, if seemingly nonsensical, for Pig to do its work.
*
* The Invoker family of udfs understand the following class names (all case-independent):
*
String
* Long
* Float
* Double
* Int
*
* Invokers can also work with array arguments, represented in Pig as DataBags of single-tuple
* elements. Simply refer to string[], for example.
*
* This UDF allows one to dynamically invoke Java methods that return a T
*
* Usage of the Invoker family of UDFs (adjust as appropriate):
*
*
* {@code
* -- invoking a static method
* DEFINE StringToLong InvokeForLong('java.lang.Long.valueOf', 'String')
* longs = FOREACH strings GENERATE StringToLong(some_chararray);
*
* -- invoking a method on an object
* DEFINE StringConcat InvokeForString('java.lang.String.concat', 'String String', 'false')
* concatenations = FOREACH strings GENERATE StringConcat(str1, str2);
* }
*
*
* The first argument to the constructor is the full path to desired method.
* The second argument is a list of classes of the method parameters.
* If the method is not static, the first element in this list is the object to invoke the method on.
* The second argument is optional (a no-argument static method is assumed if it is not supplied).
* The third argument is the keyword "static" (or "true") to signify that the method is static.
* The third argument is optional, and true by default.
*
* @param
*/
public abstract class GenericInvoker extends EvalFunc {
private Invoker invoker_;
public GenericInvoker() {}
public GenericInvoker(String fullName)
throws ClassNotFoundException, FrontendException, SecurityException, NoSuchMethodException {
invoker_ = new Invoker(fullName, "");
}
public GenericInvoker(String fullName, String paramSpecsStr)
throws ClassNotFoundException, FrontendException, SecurityException, NoSuchMethodException {
invoker_ = new Invoker(fullName, paramSpecsStr);
}
public GenericInvoker(String fullName, String paramSpecsStr, String isStatic)
throws ClassNotFoundException, FrontendException, SecurityException, NoSuchMethodException {
invoker_ = new Invoker(fullName, paramSpecsStr, isStatic);
}
@Override
public T exec(Tuple input) throws IOException {
if (invoker_ == null) {
throw new ExecException("exec() attempted on an unitialized invoker. " +
"Invokers must be constructed with the method to invoke, and parameter signature to same.");
}
return invoker_.invoke(input);
}
@Override
public Schema outputSchema(Schema input) {
if (invoker_ == null) return null;
FieldSchema fs = new FieldSchema(null, DataType.findType(invoker_.getReturnType()));
return new Schema(fs);
}
}