Package org.apache.hadoop.mapred.join

Class Parser

java.lang.Object

org.apache.hadoop.mapred.join.Parser

@Public
@Evolving
public class Parser
extends Object

Very simple shift-reduce parser for join expressions. This should be sufficient for the user extension permitted now, but ought to be replaced with a parser generator if more complex grammars are supported. In particular, this "shift-reduce" parser has no states. Each set of formals requires a different internal node type, which is responsible for interpreting the list of tokens it receives. This is sufficient for the current grammar, but it has several annoying properties that might inhibit extension. In particular, parenthesis are always function calls; an algebraic or filter grammar would not only require a node type, but must also work around the internals of this parser. For most other cases, adding classes to the hierarchy- particularly by extending JoinRecordReader and MultiFilterRecordReader- is fairly straightforward. One need only override the relevant method(s) (usually only CompositeRecordReader.combine(java.lang.Object[], org.apache.hadoop.mapred.join.TupleWritable)) and include a property to map its value to an identifier in the parser.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	Parser.Node
static class	Parser.NodeToken
static class	Parser.NumToken
static class	Parser.StrToken
static class	Parser.Token	Tagged-union type for tokens from the join expression.
static enum	Parser.TType

Constructor Summary

Constructors

Constructor	Description
Parser()

Method Summary

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

Parser

public Parser()