Package jakarta.el

Class ELResolver

    • Field Detail

      • TYPE

        public static final String TYPE
        The attribute name of the named attribute in the FeatureDescriptor that specifies the runtime type of the variable or property.
        See Also:
        Constant Field Values

      • RESOLVABLE_AT_DESIGN_TIME

        public static final String RESOLVABLE_AT_DESIGN_TIME
        The attribute name of the named attribute in the FeatureDescriptor that specifies whether the variable or property can be resolved at runtime.
        See Also:
        Constant Field Values

    • Constructor Detail

      • ELResolver

        public ELResolver()

    • Method Detail

      • getValue

        public abstract Object getValue​(ELContext context,
                                Object base,
                                Object property)
        Attempts to resolve the given property object on the given base object.

        If this resolver handles the given (base, property) pair, the propertyResolved property of the ELContext object must be set to true by the resolver, before returning. If this property is not true after this method is called, the caller should ignore the return value.

        Parameters:
        context - The context of this evaluation.
        base - The base object whose property value is to be returned, or null to resolve a top-level variable.
        property - The property or variable to be resolved.
        Returns:
        If the propertyResolved property of ELContext was set to true, then the result of the variable or property resolution; otherwise undefined.
        Throws:
        NullPointerException - if context is null
        PropertyNotFoundException - if the given (base, property) pair is handled by this ELResolver but the specified variable or property does not exist or is not readable.
        ELException - if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.

      • invoke

        public Object invoke​(ELContext context,
                     Object base,
                     Object method,
                     Class<?>[] paramTypes,
                     Object[] params)
        Attempts to resolve and invoke the given method on the given base object.

        If this resolver handles the given (base, method) pair, the propertyResolved property of the ELContext object must be set to true by the resolver, before returning. If this property is not true after this method is called, the caller should ignore the return value.

        A default implementation is provided that returns null so that existing classes that extend ELResolver can continue to function.

        Parameters:
        context - The context of this evaluation.
        base - The bean on which to invoke the method
        method - The simple name of the method to invoke. Will be coerced to a String.
        paramTypes - An array of Class objects identifying the method's formal parameter types, in declared order. Use an empty array if the method has no parameters. Can be null, in which case the method's formal parameter types are assumed to be unknown.
        params - The parameters to pass to the method, or null if no parameters.
        Returns:
        The result of the method invocation (null if the method has a void return type).
        Throws:
        MethodNotFoundException - if no suitable method can be found.
        ELException - if an exception was thrown while performing (base, method) resolution. The thrown exception must be included as the cause property of this exception, if available. If the exception thrown is an InvocationTargetException, extract its cause and pass it to the ELException constructor.
        Since:
        Jakarta Expression Language 2.2

      • getType

        public abstract Class<?> getType​(ELContext context,
                                 Object base,
                                 Object property)
        For a given base and property, attempts to identify the most general type that is acceptable for an object to be passed as the value parameter in a future call to the setValue(jakarta.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object) method.

        If this resolver handles the given (base, property) pair, the propertyResolved property of the ELContext object must be set to true by the resolver, before returning. If this property is not true after this method is called, the caller should ignore the return value.

        This is not always the same as getValue().getClass(). For example, in the case of an ArrayELResolver, the getType method will return the element type of the array, which might be a superclass of the type of the actual element that is currently in the specified array element.

        If the resolver or the property is read-only, this method must return null.

        Parameters:
        context - The context of this evaluation.
        base - The base object whose property value is to be analyzed, or null to analyze a top-level variable.
        property - The property or variable to return the acceptable type for.
        Returns:
        If the propertyResolved property of ELContext was set to true, the most general acceptable type which must be null if the either the property or the resolver is read-only; otherwise undefined
        Throws:
        PropertyNotFoundException - if the given (base, property) pair is handled by this ELResolver but the specified variable or property does not exist or is not readable.
        ELException - if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.

      • setValue

        public abstract void setValue​(ELContext context,
                              Object base,
                              Object property,
                              Object value)
        Attempts to set the value of the given property object on the given base object.

        If this resolver handles the given (base, property) pair, the propertyResolved property of the ELContext object must be set to true by the resolver, before returning. If this property is not true after this method is called, the caller can safely assume no value has been set.

        Parameters:
        context - The context of this evaluation.
        base - The base object whose property value is to be set, or null to set a top-level variable.
        property - The property or variable to be set.
        value - The value to set the property or variable to.
        Throws:
        NullPointerException - if context is null
        PropertyNotFoundException - if the given (base, property) pair is handled by this ELResolver but the specified variable or property does not exist.
        PropertyNotWritableException - if the given (base, property) pair is handled by this ELResolver but the specified variable or property is not writable.
        ELException - if an exception was thrown while attempting to set the property or variable. The thrown exception must be included as the cause property of this exception, if available.

      • isReadOnly

        public abstract boolean isReadOnly​(ELContext context,
                                   Object base,
                                   Object property)
        For a given base and property, attempts to determine whether a call to setValue(jakarta.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object) will always fail.

        If this resolver handles the given (base, property) pair, the propertyResolved property of the ELContext object must be set to true by the resolver, before returning. If this property is not true after this method is called, the caller should ignore the return value.

        Parameters:
        context - The context of this evaluation.
        base - The base object whose property value is to be analyzed, or null to analyze a top-level variable.
        property - The property or variable to return the read-only status for.
        Returns:
        If the propertyResolved property of ELContext was set to true, then true if the property is read-only or false if not; otherwise undefined.
        Throws:
        NullPointerException - if context is null
        PropertyNotFoundException - if the given (base, property) pair is handled by this ELResolver but the specified variable or property does not exist.
        ELException - if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.

      • getFeatureDescriptors

        @Deprecated(forRemoval=true,
            since="5.0")
public Iterator<FeatureDescriptor> getFeatureDescriptors​(ELContext context,
                                                         Object base)
        Deprecated, for removal: This API element is subject to removal in a future version.
        This method will be removed without replacement in EL 6.0
        Returns information about the set of variables or properties that can be resolved for the given base object. One use for this method is to assist tools in auto-completion.

        If the base parameter is null, the resolver must enumerate the list of top-level variables it can resolve.

        The Iterator returned must contain zero or more instances of FeatureDescriptor, in no guaranteed order. In the case of primitive types such as int, the value null must be returned. This is to prevent the useless iteration through all possible primitive values. A return value of null indicates that this resolver does not handle the given base object or that the results are too complex to represent with this method and the getCommonPropertyType(jakarta.el.ELContext, java.lang.Object) method should be used instead.

        Each FeatureDescriptor will contain information about a single variable or property. In addition to the standard properties, the FeatureDescriptor must have two named attributes (as set by the setValue method):

        • TYPE - The value of this named attribute must be an instance of java.lang.Class and specify the runtime type of the variable or property.
        • RESOLVABLE_AT_DESIGN_TIME - The value of this named attribute must be an instance of java.lang.Boolean and indicates whether it is safe to attempt to resolve this property at design-time. For instance, it may be unsafe to attempt a resolution at design time if the ELResolver needs access to a resource that is only available at runtime and no acceptable simulated value can be provided.

        The caller should be aware that the Iterator returned might iterate through a very large or even infinitely large set of properties. Care should be taken by the caller to not get stuck in an infinite loop.

        This is a "best-effort" list. Not all ELResolvers will return completely accurate results, but all must be callable at both design-time and runtime (i.e. whether or not Beans.isDesignTime() returns true), without causing errors.

        The propertyResolved property of the ELContext is not relevant to this method. The results of all ELResolvers are concatenated in the case of composite resolvers.

        The default implementation in ELResolver returns null. Sub-classes may wish to over-ride this method.

        Parameters:
        context - The context of this evaluation.
        base - The base object whose set of valid properties is to be enumerated, or null to enumerate the set of top-level variables that this resolver can evaluate.
        Returns:
        An Iterator containing zero or more (possibly infinitely more) FeatureDescriptor objects, or null if this resolver does not handle the given base object or that the results are too complex to represent with this method
        See Also:
        FeatureDescriptor

      • getCommonPropertyType

        public abstract Class<?> getCommonPropertyType​(ELContext context,
                                               Object base)
        Returns the most general type that this resolver accepts for the property argument, given a base object. One use for this method is to assist tools in auto-completion.

        This assists tools in auto-completion and also provides a way to express that the resolver accepts a primitive value, such as an integer index into an array. For example, the ArrayELResolver will accept any int as a property, so the return value would be Integer.class.

        Parameters:
        context - The context of this evaluation.
        base - The base object to return the most general property type for, or null to enumerate the set of top-level variables that this resolver can evaluate.
        Returns:
        null if this ELResolver does not know how to handle the given base object; otherwise Object.class if any type of property is accepted; otherwise the most general property type accepted for the given base.

      • convertToType

        public <T> T convertToType​(ELContext context,
                           Object obj,
                           Class<T> targetType)
        Converts an object to a specific type.

        An ELException is thrown if an error occurs during the conversion.

        Parameters:
        context - The context of this evaluation.
        obj - The object to convert.
        targetType - The target type for the conversion.
        Returns:
        object converted to targetType
        Throws:
        ELException - thrown if errors occur.