Class Parser

  extended by org.apache.hadoop.mapred.join.Parser

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
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 class Parser.TType
Constructor Summary
Method Summary
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail


public Parser()

Copyright © 2009 The Apache Software Foundation