Class ExpressionFactory
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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.static ExpressionFactory
Creates a new instance of aExpressionFactory
.static ExpressionFactory
newInstance
(Properties properties) Create a new instance of aExpressionFactory
, with optional properties.
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Constructor Details
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ExpressionFactory
public ExpressionFactory()
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Method Details
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newInstance
Creates a new instance of aExpressionFactory
. This method uses the following ordered lookup procedure to determine theExpressionFactory
implementation class to load:- Use the Services API (as detailed in the JAR specification).
If a resource with the name of
META-INF/services/javax.el.ExpressionFactory
exists, then its first line, if present, is used as the UTF-8 encoded name of the implementation class. - Use the properties file "lib/el.properties" in the JRE directory.
If this file exists and it is readable by the
java.util.Properties.load(InputStream)
method, and it contains an entry whose key is "javax.el.ExpressionFactory", then the value of that entry is used as the name of the implementation class. - Use the
javax.el.ExpressionFactory
system property. If a system property with this name is defined, then its value is used as the name of the implementation class. - Use a platform default implementation.
- Use the Services API (as detailed in the JAR specification).
If a resource with the name of
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newInstance
Create a new instance of a
ExpressionFactory
, with optional properties. This method uses the same lookup procedure as the one used innewInstance()
.If the argument
properties
is not null, and if the implementation contains a constructor with a single parameter of typejava.util.Properties
, then the constructor is used to create the instance.Properties are optional and can be ignored by an implementation.
The name of a property should start with "javax.el."
The following are some suggested names for properties.
- javax.el.cacheSize
- Parameters:
properties
- Properties passed to the implementation. If null, then no properties.
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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.
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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,- Throws:
NullPointerException
- Thrown if expectedType is null.
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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
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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.
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