Class ExpressionFactory
- Direct Known Subclasses:
ExpressionFactoryImpl
String
into a ValueExpression
or
MethodExpression
instance for later evaluation.
Classes that implement the EL expression language expose their functionality via this abstract class. There is no concrete implementation of this API available in this package. Technologies such as JavaServer Pages and JavaServer Faces provide access to an implementation via factory methods.
The createValueExpression(org.jdesktop.el.ELContext, java.lang.String, java.lang.Class<?>)
method is used to parse expressions
that evaluate to values (both l-values and r-values are supported).
The createMethodExpression(org.jdesktop.el.ELContext, java.lang.String, java.lang.Class<?>, java.lang.Class<?>[])
method is used to parse expressions
that evaluate to a reference to a method on an object.
Unlike previous incarnations of this API, there is no way to parse and evaluate an expression in one single step. The expression needs to first be parsed, and then evaluated.
Resolution of model objects is performed at evaluation time, via the
ELResolver
associated with the ELContext
passed to
the ValueExpression
or MethodExpression
.
The ELContext object also provides access to the FunctionMapper
and VariableMapper
to be used when parsing the expression.
EL function and variable mapping is performed at parse-time, and
the results are
bound to the expression. Therefore, the ELContext
,
FunctionMapper
,
and VariableMapper
are not stored for future use and do not have to be
Serializable
.
The createValueExpression
and
createMethodExpression
methods must be thread-safe. That is,
multiple threads may call these methods on the same
ExpressionFactory
object simultaneously. Implementations
should synchronize access if they depend on transient state.
Implementations should not, however, assume that only one object of
each ExpressionFactory
type will be instantiated; global
caching should therefore be static.
The ExpressionFactory
must be able to handle the following
types of input for the expression
parameter:
- Single expressions using the
${}
delimiter (e.g."${employee.lastName}"
). - Single expressions using the
#{}
delimiter (e.g."#{employee.lastName}"
). - Literal text containing no
${}
or#{}
delimiters (e.g."John Doe"
). - Multiple expressions using the same delimiter (e.g.
"${employee.firstName}${employee.lastName}"
or"#{employee.firstName}#{employee.lastName}"
). - Mixed literal text and expressions using the same delimiter (e.g.
"Name: ${employee.firstName} ${employee.lastName}"
).
The following types of input are illegal and must cause an
ELException
to be thrown:
- Multiple expressions using different delimiters (e.g.
"${employee.firstName}#{employee.lastName}"
). - Mixed literal text and expressions using different delimiters(e.g.
"Name: ${employee.firstName} #{employee.lastName}"
).
- Since:
- JSP 2.1
-
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionabstract Object
coerceToType
(Object obj, Class<?> targetType) Coerces an object to a specific type according to the EL type conversion rules.abstract MethodExpression
createMethodExpression
(ELContext context, String expression, Class<?> expectedReturnType, Class<?>[] expectedParamTypes) Parses an expression into aMethodExpression
for later evaluation.abstract ValueExpression
createValueExpression
(Object instance, Class<?> expectedType) Creates a ValueExpression that wraps an object instance.abstract ValueExpression
createValueExpression
(ELContext context, String expression, Class<?> expectedType) Parses an expression into aValueExpression
for later evaluation.
-
Constructor Details
-
ExpressionFactory
public ExpressionFactory()
-
-
Method Details
-
createValueExpression
public abstract ValueExpression createValueExpression(ELContext context, String expression, Class<?> expectedType) Parses an expression into aValueExpression
for later evaluation. Use this method for expressions that refer to values.This method should perform syntactic validation of the expression. If in doing so it detects errors, it should raise an
ELException
.- Parameters:
context
- The EL context used to parse the expression. TheFunctionMapper
andVariableMapper
stored in the ELContext are used to resolve functions and variables found in the expression. They can benull
, in which case functions or variables are not supported for this expression. The object returned must invoke the same functions and access the same variable mappings regardless of whether the mappings in the providedFunctionMapper
andVariableMapper
instances change between callingExpressionFactory.createValueExpression()
and any method onValueExpression
.Note that within the EL, the ${} and #{} syntaxes are treated identically. This includes the use of VariableMapper and FunctionMapper at expression creation time. Each is invoked if not null, independent of whether the #{} or ${} syntax is used for the expression.
expression
- The expression to parseexpectedType
- The type the result of the expression will be coerced to after evaluation.- Returns:
- The parsed expression
- Throws:
NullPointerException
- Thrown if expectedType is null.ELException
- Thrown if there are syntactical errors in the provided expression.
-
createValueExpression
Creates a ValueExpression that wraps an object instance. This method can be used to pass any object as a ValueExpression. The wrapper ValueExpression is read only, and returns the wrapped object via itsgetValue()
method, optionally coerced.- Parameters:
instance
- The object instance to be wrapped.expectedType
- The type the result of the expression will be coerced to after evaluation. There will be no coercion if it is Object.class,
-
createMethodExpression
public abstract MethodExpression createMethodExpression(ELContext context, String expression, Class<?> expectedReturnType, Class<?>[] expectedParamTypes) Parses an expression into aMethodExpression
for later evaluation. Use this method for expressions that refer to methods.If the expression is a String literal, a
MethodExpression
is created, which when invoked, returns the String literal, coerced to expectedReturnType. An ELException is thrown if expectedReturnType is void or if the coercion of the String literal to the expectedReturnType yields an error (see Section "1.16 Type Conversion").This method should perform syntactic validation of the expression. If in doing so it detects errors, it should raise an
ELException
.- Parameters:
context
- The EL context used to parse the expression. TheFunctionMapper
andVariableMapper
stored in the ELContext are used to resolve functions and variables found in the expression. They can benull
, in which case functions or variables are not supported for this expression. The object returned must invoke the same functions and access the same variable mappings regardless of whether the mappings in the providedFunctionMapper
andVariableMapper
instances change between callingExpressionFactory.createMethodExpression()
and any method onMethodExpression
.Note that within the EL, the ${} and #{} syntaxes are treated identically. This includes the use of VariableMapper and FunctionMapper at expression creation time. Each is invoked if not null, independent of whether the #{} or ${} syntax is used for the expression.
expression
- The expression to parseexpectedReturnType
- The expected return type for the method to be found. After evaluating the expression, theMethodExpression
must check that the return type of the actual method matches this type. Passing in a value ofnull
indicates the caller does not care what the return type is, and the check is disabled.expectedParamTypes
- The expected parameter types for the method to be found. Must be an array with no elements if there are no parameters expected. It is illegal to passnull
.- Returns:
- The parsed expression
- Throws:
ELException
- Thrown if there are syntactical errors in the provided expression.NullPointerException
- if paramTypes isnull
.
-
coerceToType
Coerces an object to a specific type according to the EL type conversion rules.An
ELException
is thrown if an error results from applying the conversion rules.- Parameters:
obj
- The object to coerce.targetType
- The target type for the coercion.- Throws:
ELException
- thrown if an error results from applying the conversion rules.
-