Class ExpressionFactory
- java.lang.Object
-
- org.jdesktop.el.ExpressionFactory
-
- Direct Known Subclasses:
ExpressionFactoryImpl
public abstract class ExpressionFactory extends java.lang.Object
Parses aString
into aValueExpression
orMethodExpression
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). ThecreateMethodExpression(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 theELContext
passed to theValueExpression
orMethodExpression
.The ELContext object also provides access to the
FunctionMapper
andVariableMapper
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, theELContext
,FunctionMapper
, andVariableMapper
are not stored for future use and do not have to beSerializable
.The
createValueExpression
andcreateMethodExpression
methods must be thread-safe. That is, multiple threads may call these methods on the sameExpressionFactory
object simultaneously. Implementations should synchronize access if they depend on transient state. Implementations should not, however, assume that only one object of eachExpressionFactory
type will be instantiated; global caching should therefore be static.The
ExpressionFactory
must be able to handle the following types of input for theexpression
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 Constructor Description ExpressionFactory()
-
Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description abstract java.lang.Object
coerceToType(java.lang.Object obj, java.lang.Class<?> targetType)
Coerces an object to a specific type according to the EL type conversion rules.abstract MethodExpression
createMethodExpression(ELContext context, java.lang.String expression, java.lang.Class<?> expectedReturnType, java.lang.Class<?>[] expectedParamTypes)
Parses an expression into aMethodExpression
for later evaluation.abstract ValueExpression
createValueExpression(java.lang.Object instance, java.lang.Class<?> expectedType)
Creates a ValueExpression that wraps an object instance.abstract ValueExpression
createValueExpression(ELContext context, java.lang.String expression, java.lang.Class<?> expectedType)
Parses an expression into aValueExpression
for later evaluation.
-
-
-
Method Detail
-
createValueExpression
public abstract ValueExpression createValueExpression(ELContext context, java.lang.String expression, java.lang.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:
java.lang.NullPointerException
- Thrown if expectedType is null.ELException
- Thrown if there are syntactical errors in the provided expression.
-
createValueExpression
public abstract ValueExpression createValueExpression(java.lang.Object instance, java.lang.Class<?> expectedType)
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, java.lang.String expression, java.lang.Class<?> expectedReturnType, java.lang.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.java.lang.NullPointerException
- if paramTypes isnull
.
-
coerceToType
public abstract java.lang.Object coerceToType(java.lang.Object obj, java.lang.Class<?> targetType)
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.
-
-