Package com.randomnoun.common.jexl.eval

Class Evaluator

java.lang.Object

com.randomnoun.common.jexl.visitor.GJDepthFirst<Object,EvalContext>

com.randomnoun.common.jexl.eval.Evaluator

All Implemented Interfaces:

GJVisitor<Object,EvalContext>

Direct Known Subclasses:

SqlGenerator

public class Evaluator
extends GJDepthFirst<Object,EvalContext>

This class traverses (and evaluates) an expression AST graph. It traverses the AST in depth-first order (by extending the ObjectDepthFirst visitor class generated by jtb). This class implements the 'Visitor' design pattern.

Each visit() method in this class takes two parameters, the first being the node being visited, and the second contains an EvalContext object containing the variables and functions which can be referenced within the expression. The visitor (i.e. this class) is then passed to it's children nodes using the nodes' accept() method (generated by jtb).

Variables can be any wrappered primitive type (e.g. Long, Integer, ...), although mathematical evaluation (+, -, /, etc) are currently only implemented for Doubles and Longs.

This class can be considered thread-safe, since it holds no instance-wide state. (All methods that require access to a EvalContext have it passed in through a method parameter). i.e. many threads may use the same Evaluator instance to evaluate different expressions.

NB: In the javadocs below, "lhs" refers to the left-hand-side value of any binary operation, and "rhs" refers to the right-hand-side value; e.g. in "3 + 4", the lhs is "3", the rhs is "4" and the op is "+".

Author:

knoxg

Constructor Summary

Constructors

Constructor	Description
Evaluator()

Method Summary

Modifier and Type	Method	Description
Object	coerceType(Object a, Object b)	Coerce parameter 'b' into a compatible type of parameter 'a', to be used in a binary math op.
Object	mathOp(Object a, Object b, String op, com.randomnoun.common.jexl.eval.Evaluator.BinaryOp longOp, com.randomnoun.common.jexl.eval.Evaluator.BinaryOp doubleOp)	Binary math operation.
Object	visit(AdditiveExpression n, EvalContext context)	Evaluate a AdditiveExpression node.
Object	visit(ArgumentList n, EvalContext context)	Evaluate a ArgumentList node.
Object	visit(Arguments n, EvalContext context)	Evaluates an Arguments node
Object	visit(BooleanLiteral n, EvalContext context)	Evaluate a BooleanLiteral node.
Object	visit(ConditionalAndExpression n, EvalContext context)	Evaluate a ConditionalAndExpression node.
Object	visit(EqualityExpression n, EvalContext context)	Evaluate a EqualityExpression node.
Object	visit(Expression n, EvalContext context)	Evaluate an Expression node.
Object	visit(FunctionCall n, EvalContext context)	Evaluate a FunctionCall node.
Object	visit(Literal n, EvalContext context)	Evaluate a Literal node.
Object	visit(MultiplicativeExpression n, EvalContext context)	Evaluate a MultiplicativeExpression node.
Object	visit(Name n, EvalContext context)	Evaluate a Name node.
Object	visit(NodeToken n, EvalContext context)	This is never executed (we do not evaluate tokens)
Object	visit(NullLiteral n, EvalContext context)	Evaluate a NullLiteral node.
Object	visit(PrimaryExpression n, EvalContext context)	Evaluate a PrimaryExpression node.
Object	visit(RelationalExpression n, EvalContext context)	Evaluate a RelationalExpression node.
Object	visit(TopLevelExpression n, EvalContext context)	Evaluate a TopLevelExpression node.
Object	visit(UnaryExpression n, EvalContext context)	Evaluate a UnaryExpression node.

Methods inherited from class com.randomnoun.common.jexl.visitor.GJDepthFirst

visit, visit, visit, visit

Methods inherited from class java.lang.Object

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

Constructor Details

Evaluator

public Evaluator()

Method Details

coerceType

public Object coerceType(Object a,
 Object b)

Coerce parameter 'b' into a compatible type of parameter 'a', to be used in a binary math op. If 'b' can't be coerced into 'a', then throw an EvalException.

Parameters:

a - First binary op parameter (the type of which we are casting to)

b - Second binary op parameter (the value we are casting)

Returns:

The value of 'b', coerced to be the same type of value 'a'

mathOp

public Object mathOp(Object a,
 Object b,
 String op,
 com.randomnoun.common.jexl.eval.Evaluator.BinaryOp longOp,
 com.randomnoun.common.jexl.eval.Evaluator.BinaryOp doubleOp)

Binary math operation. Takes two parameters, the name of the op (only used in exception text), and BinaryOp classes for all supported types. (We only support math operations on Longs and Doubles at the moment, should be easy to add new types if required). If we were aiming for completeness, I'd implement Short, Int, Byte, Char, BigInteger and BigDecimal.

The rhs of the expression is coerced into the type of the lhs.

Parameters:

a - lhs parameter

b - rhs parameter

op - name of op

longOp - operation to perform if lhs is Long

doubleOp - operation to perform if lhs in Double

Returns:

the evaluated result of the op

visit

public Object visit(TopLevelExpression n,
 EvalContext context)

Evaluate a TopLevelExpression node. The PRE text in this javadoc corresponds to the javacc expansion of this node; e.g. in expression.jj, the rule for TopLevelExpression is

 void TopLevelExpression():
 {}
 {
   Expression() 
 }
 

jtb then creates two fields in the TopLevelExpression object, "expression" (containing the Expression() node) and "nodeToken" (containing the EOF token). This is documented in the form below (this is included for all jtb-generated visit methods):

 expression -> Expression()
 nodeToken -> <EOF>
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(Expression n,
 EvalContext context)

Evaluate an Expression node.

 conditionalAndExpression -> ConditionalAndExpression()
 nodeListOptional -> ( "||" ConditionalAndExpression() )*
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(ConditionalAndExpression n,
 EvalContext context)

Evaluate a ConditionalAndExpression node.

 equalityExpression -> EqualityExpression()
 nodeListOptional -> ( "invalid input: '&'invalid input: '&'" EqualityExpression() )*
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(EqualityExpression n,
 EvalContext context)

Evaluate a EqualityExpression node.

 relationalExpression -> RelationalExpression()
 nodeListOptional -> ( ( "==" | "!=" ) RelationalExpression() )*
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(RelationalExpression n,
 EvalContext context)

Evaluate a RelationalExpression node.

 additiveExpression -> AdditiveExpression()
 nodeListOptional -> ( ( "<" | ">" | "<=" | ">=" ) AdditiveExpression() )*
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(AdditiveExpression n,
 EvalContext context)

Evaluate a AdditiveExpression node.

 multiplicativeExpression -> MultiplicativeExpression()
 nodeListOptional -> ( ( "+" | "-" ) MultiplicativeExpression() )*
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(MultiplicativeExpression n,
 EvalContext context)

Evaluate a MultiplicativeExpression node.

 unaryExpression -> UnaryExpression()
 nodeListOptional -> ( ( "*" | "/" | "%" ) UnaryExpression() )*
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(UnaryExpression n,
 EvalContext context)

Evaluate a UnaryExpression node.

 nodeChoice -> ( "~" | "!" | "-" ) UnaryExpression()
       | PrimaryExpression()
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(PrimaryExpression n,
 EvalContext context)

Evaluate a PrimaryExpression node.

 nodeChoice -> FunctionCall()
       | Name()
       | Literal()
       | "(" Expression() ")"
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(Name n,
 EvalContext context)

Evaluate a Name node.

 nodeToken -> <IDENTIFIER>
 nodeListOptional -> ( "." <IDENTIFIER> )*
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(FunctionCall n,
 EvalContext context)

Evaluate a FunctionCall node.

 nodeToken -> <IDENTIFIER>
 arguments -> Arguments()
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(Arguments n,
 EvalContext context)

Evaluates an Arguments node

 nodeToken -> "("
 nodeOptional -> [ ArgumentList() ]
 nodeToken1 -> ")"
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(ArgumentList n,
 EvalContext context)

Evaluate a ArgumentList node.

 expression -> Expression()
 nodeListOptional -> ( "," Expression() )*
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(Literal n,
 EvalContext context)

Evaluate a Literal node.

 nodeChoice -> <INTEGER_LITERAL>
       | <FLOATING_POINT_LITERAL>
       | <CHARACTER_LITERAL>
       | <STRING_LITERAL>
       | BooleanLiteral()
       | NullLiteral()
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(BooleanLiteral n,
 EvalContext context)

Evaluate a BooleanLiteral node.

 nodeChoice -> "true"
       | "false"
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(NullLiteral n,
 EvalContext context)

Evaluate a NullLiteral node.

 nodeToken -> "null"
 

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>

visit

public Object visit(NodeToken n,
 EvalContext context)

This is never executed (we do not evaluate tokens)

Specified by:

visit in interface GJVisitor<Object,EvalContext>

Overrides:

visit in class GJDepthFirst<Object,EvalContext>