Object
Optimization
Description of optimizations or simplifications to attempt on filters and expressions.
Optimizations can include the following changes:
- Application of some logical identities such as
NOT(NOT(A)) == A
. - Application of logical short circuits such as
A & FALSE == FALSE
. - Immediate evaluation of expressions where all parameters are literal values.
- The type of the
Feature
instances to be filtered.
Usage in multi-threads context
This class is not thread-safe. A new instance shall be created for each thread applying optimizations. Example:Filter<R> filter = ...;
filter = new Optimization().apply(filter);
How optimizations are applied
Optimizations are specific to each expression and filter type. For optimizations to happen, classes must implement theOptimization.OnExpression
or Optimization.OnFilter
interface.
The apply(Filter)
and apply(Expression)
methods in this Optimization
class merely
delegate to the methods defined in above-cited interfaces, with safety guards against infinite recursivity.
Behavioral changes
Optimized filters shall produce the same results than non-optimized filters. However side-effects may differ, in particular regarding exceptions that may be thrown. For example if a filter testsA & B
and if Optimization
determines that the B
condition will always evaluate to false
, then the A
condition will never be tested.
If that condition had side-effects or threw an exception,
those effects will disappear in the optimized filter.- Since:
- 1.1
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Nested Class Summary
Modifier and TypeClassDescriptionstatic interface
Expression that can be optimized.static interface
Filter that can be optimized. -
Constructor Summary
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Method Summary
Modifier and TypeMethodDescription<R,
V> Expression <R, ? extends V> apply
(Expression<R, V> expression) Optimizes or simplifies the given expression.<R> Filter
<R> Optimizes or simplifies the given filter.applyAndDecompose
(Filter<R> filter) Optimizes or simplifies the given filter and returns it as a list ofAND
operands.Returns the type of feature instances to be filtered, ornull
if unknown.static <R,
V> Expression <R, V> literal
(V value) Creates a constant, literal value that can be used in expressions.static Set
<FunctionProperty> properties
(Expression<?, ?> expression) Returns the manner in which values are computed from resources given to the specified expression.static Set
<FunctionProperty> properties
(Filter<?> filter) Returns the manner in which values are computed from resources given to the specified filter.void
Sets the type of feature instances to be filtered.
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Constructor Details
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Optimization
public Optimization()Creates a new instance.
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Method Details
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getFeatureType
Returns the type of feature instances to be filtered, ornull
if unknown. This is the last value specified by a call tosetFeatureType(DefaultFeatureType)
. The default value isnull
.- Returns:
- the type of feature instances to be filtered, or
null
if unknown.
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setFeatureType
Sets the type of feature instances to be filtered. If this type is known in advance, specifying it may allow to compute more specificObjectConverter
s or to apply some geometry reprojection in advance.- Parameters:
type
- the type of feature instances to be filtered, ornull
if unknown.
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apply
Optimizes or simplifies the given filter. If the given instance implements theOptimization.OnFilter
interface, then itsoptimize(this)
method is invoked. Otherwise this method returns the given filter as-is.- Type Parameters:
R
- the type of resources (e.g.Feature
) used as inputs.- Parameters:
filter
- the filter to optimize, ornull
.- Returns:
- the optimized filter, or
null
if the given filter was null. May befilter
if no optimization or simplification has been applied. - Throws:
IllegalArgumentException
- if the given filter is already in process of being optimized (i.e. there is a recursive call toapply(…)
for the same filter).
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apply
Optimizes or simplifies the given expression. If the given instance implements theOptimization.OnExpression
interface, then itsoptimize(this)
method is invoked. Otherwise this method returns the given expression as-is.- Type Parameters:
R
- the type of resources (e.g.Feature
) used as inputs.V
- the type of values computed by the expression.- Parameters:
expression
- the expression to optimize, ornull
.- Returns:
- the optimized expression, or
null
if the given expression was null. May beexpression
if no optimization or simplification has been applied. - Throws:
IllegalArgumentException
- if the given expression is already in process of being optimized (i.e. there is a recursive call toapply(…)
for the same expression).
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applyAndDecompose
Optimizes or simplifies the given filter and returns it as a list ofAND
operands. If such list cannot be built, then this method returns the optimized filter in a singleton list.Use case
This method tries to transform a filter into aF₀ AND F₁ AND F₂ AND F₃ AND ...
sequence. This transformation is useful when some operands can be handled by the storage engine (for example a SQL database) and other operands cannot. For example, when reading features from a relational database, the implementation may choose to express the F₁ and F₃ operands as SQL statements and apply the other operands in Java code.- Type Parameters:
R
- the type of resources (e.g.Feature
) used as inputs.- Parameters:
filter
- the filter to decompose.- Returns:
- a sequence of
AND
operands, or an empty list if the given filter was null. - Throws:
ClassCastException
- if a filter declares theAND
,OR
orNOT
type without implementing theLogicalOperator
interface.
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properties
Returns the manner in which values are computed from resources given to the specified filter. This set of properties may determine which optimizations are allowed. The values of particular interest are:FunctionProperty.VOLATILE
if the computed value changes each time that the filter is evaluated, even if the resource to evaluate stay the same immutable instance.
- Parameters:
filter
- the filter for which to query function properties.- Returns:
- the manners in which values are computed from resources.
- Since:
- 1.4
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properties
Returns the manner in which values are computed from resources given to the specified expression. This set of properties may determine which optimizations are allowed. The values of particular interest are:FunctionProperty.INJECTIVE
if the computed value is unique for each resource instance (e.g. identifiers).FunctionProperty.VOLATILE
if the computed value changes each time that the expression is evaluated, even if the resource to evaluate stay the same immutable instance.FunctionProperty.isConstant(Set)
if the expression returns a constant value.
- Parameters:
expression
- the expression for which to query function properties.- Returns:
- the manners in which values are computed from resources.
- Since:
- 1.4
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literal
Creates a constant, literal value that can be used in expressions. This is a helper methods for optimizations which simplified an expression to a constant value.- Type Parameters:
R
- the type of resources used as inputs.V
- the type of the value of the literal.- Parameters:
value
- the literal value. May benull
.- Returns:
- a literal for the given value.
- See Also:
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