Package org.geotools.api.filter.expression

package org.geotools.api.filter.expression
An expression is a combination of one or more elements that evaluate to single Object value.

The following is adapted from Filter encoding specifications:

An expression can be formed using the elements: Add, Subtract, Multiply, Divide, PropertyName, Literal and Function. They all belong to the substitution group expression which means that any of them can be used wherever an expression is called for. In addition, the combinations of these elements are themselves expressions and can be used wherever an expression is called for.

Arithmetic operators

The elements defined in this package are used to encode the fundamental arithmetic operations of addition, subtraction, multiplication and division. Arithmetic operators are binary operators meaning that they accept two arguments and evaluate to a single result.

Literals

A literal value is any part of a statement or expression that is to be used exactly as it is specified, rather than as a variable or other element. The Literal element is used to encode literal scalar and geometric values.

Functions

A function is a named procedure that performs a distinct computation. A function may accept zero or more arguments as input and generates a single result. A function is composed of the name of the function, encoded using the attribute name, and zero or more arguments contained within the Function element. The arguments themselves are expressions.

Data Access

Data access is acomplished by means of PropertyName expressions. These Expressions are independent of the data being queried and form the foundation of a, very simple, general query language offering independence specific bindings to Feature, Metadata and Record data structures.

Filter Encodings

At the time of this writing the Filter API has standard encodings for XML (Filter 1.0 and Filter 1.1) and Text (a BNF form is provided in the Catalog 2.0.1 specification above). You should be warned that not all content can be expressed in all encodings, please refer to the javadocs for specific limitations.

  • Class
    Description
    Add
    Encodes the operation of addition.
    BinaryExpression
    Abstract base class for the various filter expressions that compute some value from two input values.
    Divide
    Encodes the operation of division where the first argument is divided by the second argument.
    Expression
    Interface for all the OGC Filter elements that compute values.
    ExpressionVisitor
    Visitor with visit methods to be called by Expression.accept(...).
    Function
    Instances of this class represent a function call into some implementation-specific function.
    InternalFunction
    Special Function type indicating that that the function is to be executed exclusively at run-time, and does not participate in the SPI (Service Provider Interface) lookup mechanism (i.e. cannot be created using a FilterFactory).
    Literal
    Instances of this interface provide a constant, literal value that can be used in expressions.
    Multiply
    Encodes the operation of multiplication.
    NilExpression
    Placeholder class used to represent a NIL expression, evaluates to null.
    PropertyName
    Expression class whose value is computed by retrieving the value indicated by the provided name.
    SimplifiableFunction
    Implemented by functions that can turn themselves into a simpler, more efficient expression, when certain conditions are met.
    Subtract
    Encodes the operation of subtraction where the second argument is subtracted from the first.
    VolatileFunction
    Marker interface indicating that that the function return value can change during a single data access operation even if the argument values provided to it remain constant