我正在尝试让 UDF 在 pig 中运行，但是我遇到了一些问题，即当我尝试运行 pig 脚本时，它会出错，说不能用值“null”实例化 mathPow，如果有任何机构可以提供帮助，那就太好了。
谢谢
猪脚本如下：
REGISTER MathPower.jar
A = load ‘input’ using PigStorage(‘,’);
C = foreach A generate $0 as x, $1 as z;
B = foreach A generate powUDF.mathUDF(x, z);
dump B;
输入文件包含：2,3 4,5
java如下，没有添加任何外部库，我只是按照教程进行的。我正在使用 java 1.6 版和 eclipse：
package powUDF;
import java.io.IOException;
import org.apache.pig.EvalFunc;
import org.apache.pig.data.Tuple;
import org.apache.commons.logging.Log;
import org.apache.*;
public class mathUDF extends EvalFunc<Long> {
/**
* A simple UDF that takes a value and raises it to the power of a second
* value. It can be used in a Pig Latin script as Pow(x, y), where x and y
* are both expected to be ints.
*/
public Long exec(Tuple input) throws IOException {
try {
/* Rather than give you explicit arguments, UDFs are always handed
* a tuple. The UDF must know the arguments it expects and pull
* them out of the tuple. These next two lines get the first and
* second fields out of the input tuple that was handed in. Since
* Tuple.get returns Objects, we must cast them to Integers. If
* the case fails, an exception will be thrown.
*/
int base = (Integer)input.get(0);
int exponent = (Integer)input.get(1);
long result = 1;
/* Probably not the most efficient method...*/
for (int i = 0; i < exponent; i++) {
long preresult = result;
result *= base;
if (preresult > result) {
// We overflowed. Give a warning, but do not throw an
// exception.
warn("Overflow!", PigWarning.TOO_LARGE_FOR_INT);
// Returning null will indicate to Pig that we failed but
// we want to continue execution.
return null;
}
}
return result;
} catch (Exception e) {
// Throwing an exception will cause the task to fail.
throw new IOException("Something bad happened!", e);
}
} }
堆栈跟踪是
Pig Stack Trace
错误 1200：无法使用参数“null”实例化“powUDF2.mathUDF”
Failed to parse: could not instantiate 'powUDF2.mathUDF' with arguments 'null'
at org.apache.pig.parser.QueryParserDriver.parse(QueryParserDriver.java:193)
at org.apache.pig.PigServer$Graph.validateQuery(PigServer.java:1571)
at org.apache.pig.PigServer$Graph.registerQuery(PigServer.java:1544)
at org.apache.pig.PigServer.registerQuery(PigServer.java:516)
at org.apache.pig.tools.grunt.GruntParser.processPig(GruntParser.java:991)
at org.apache.pig.tools.pigscript.parser.PigScriptParser.parse(PigScriptParser.java:412)
at org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:194)
at org.apache.pig.tools.grunt.GruntParser.parseStopOnError(GruntParser.java:170)
at org.apache.pig.tools.grunt.Grunt.run(Grunt.java:69)
at org.apache.pig.Main.run(Main.java:538)
at org.apache.pig.Main.main(Main.java:157)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.util.RunJar.main(RunJar.java:160)
Caused by: java.lang.RuntimeException: could not instantiate 'powUDF2.mathUDF' with arguments 'null'
at org.apache.pig.impl.PigContext.instantiateFuncFromSpec(PigContext.java:618)
at org.apache.pig.newplan.logical.expression.UserFuncExpression.getFieldSchema(UserFuncExpression.java:193)
at org.apache.pig.newplan.logical.optimizer.FieldSchemaResetter.execute(SchemaResetter.java:264)
at org.apache.pig.newplan.logical.expression.AllSameExpressionVisitor.visit(AllSameExpressionVisitor.java:143)
at org.apache.pig.newplan.logical.expression.UserFuncExpression.accept(UserFuncExpression.java:88)
at org.apache.pig.newplan.ReverseDependencyOrderWalker.walk(ReverseDependencyOrderWalker.java:70)
at org.apache.pig.newplan.PlanVisitor.visit(PlanVisitor.java:52)
at org.apache.pig.newplan.logical.optimizer.SchemaResetter.visitAll(SchemaResetter.java:67)
at org.apache.pig.newplan.logical.optimizer.SchemaResetter.visit(SchemaResetter.java:122)
at org.apache.pig.newplan.logical.relational.LOGenerate.accept(LOGenerate.java:246)
at org.apache.pig.newplan.DependencyOrderWalker.walk(DependencyOrderWalker.java:75)
at org.apache.pig.newplan.logical.optimizer.SchemaResetter.visit(SchemaResetter.java:114)
at org.apache.pig.newplan.logical.relational.LOForEach.accept(LOForEach.java:76)
at org.apache.pig.newplan.DependencyOrderWalker.walk(DependencyOrderWalker.java:75)
at org.apache.pig.newplan.PlanVisitor.visit(PlanVisitor.java:52)
at org.apache.pig.parser.LogicalPlanBuilder.expandAndResetVisitor(LogicalPlanBuilder.java:392)
at org.apache.pig.parser.LogicalPlanBuilder.buildForeachOp(LogicalPlanBuilder.java:924)
at org.apache.pig.parser.LogicalPlanGenerator.foreach_clause(LogicalPlanGenerator.java:14195)
at org.apache.pig.parser.LogicalPlanGenerator.op_clause(LogicalPlanGenerator.java:1623)
at org.apache.pig.parser.LogicalPlanGenerator.general_statement(LogicalPlanGenerator.java:799)
at org.apache.pig.parser.LogicalPlanGenerator.statement(LogicalPlanGenerator.java:517)
at org.apache.pig.parser.LogicalPlanGenerator.query(LogicalPlanGenerator.java:392)
at org.apache.pig.parser.QueryParserDriver.parse(QueryParserDriver.java:184)
... 15 more
Caused by: java.lang.Error: Unresolved compilation problems:
The type org.apache.commons.logging.Log cannot be resolved. It is indirectly referenced from required .class files
The import org.apache.commons.logging.Log cannot be resolved
The type org.apache.hadoop.io.WritableComparable cannot be resolved. It is indirectly referenced from required .class files
PigWarning cannot be resolved to a variable
at powUDF2.mathUDF.<init>(mathUDF.java:1)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at java.lang.Class.newInstance0(Class.java:355)
at java.lang.Class.newInstance(Class.java:308)
at org.apache.pig.impl.PigContext.instantiateFuncFromSpec(PigContext.java:588)
... 37 more
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