api/src/main/java/jakarta/el/ELResolver.java - third_party/jakartaee/expression-language - Git at Google

 /*
  * Copyright (c) 1997, 2025 Oracle and/or its affiliates and others.
  * All rights reserved.
  * Copyright 2004 The Apache Software Foundation
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package jakarta.el;

 /**
  * Enables customization of variable, property, method call, and type conversion resolution behavior for Jakarta
  * Expression Language expression evaluation.
  *
  * <p>
  * While evaluating an expression, the <code>ELResolver</code> associated with the {@link ELContext} is consulted to do
  * the initial resolution of the first variable of an expression. It is also consulted when a <code>.</code> or
  * <code>[]</code> operator is encountered.
  *
  * <p>
  * For example, in the Jakarta Expression Language expression <code>${employee.lastName}</code>, the
  * <code>ELResolver</code> determines what object <code>employee</code> refers to, and what it means to get the
  * <code>lastName</code> property on that object.
  *
  * <p>
  * Most methods in this class accept a <code>base</code> and <code>property</code> parameter. In the case of variable
  * resolution (e.g. determining what <code>employee</code> refers to in <code>${employee.lastName}</code>), the
  * <code>base</code> parameter will be <code>null</code> and the <code>property</code> parameter will always be of type
  * <code>String</code>. In this case, if the <code>property</code> is not a <code>String</code>, the behavior of the
  * <code>ELResolver</code> is undefined.
  *
  * <p>
  * In the case of property resolution, the <code>base</code> parameter identifies the base object and the
  * <code>property</code> object identifies the property on that base. For example, in the expression
  * <code>${employee.lastName}</code>, <code>base</code> is the result of the variable resolution for
  * <code>employee</code> and <code>property</code> is the string <code>"lastName"</code>. In the expression
  * <code>${y[x]}</code>, <code>base</code> is the result of the variable resolution for <code>y</code> and
  * <code>property</code> is the result of the variable resolution for <code>x</code>.
  *
  * <p>
  * In the case of method call resolution, the <code>base</code> parameter identifies the base object and the
  * <code>method</code> parameter identifies a method on that base. In the case of overloaded methods, the <code>
  * paramTypes</code> parameter can be optionally used to identify a method. The <code>params</code>parameter are the
  * parameters for the method call, and can also be used for resolving overloaded methods when the
  * <code>paramTypes</code> parameter is not specified.
  *
  * <p>
  * In the case of type conversion resolution, the <code>obj</code> parameter identifies the source object and the
  * <code>targetType</code> parameter identifies the target type the source to covert to.
  *
  * <p>
  * Though only a single <code>ELResolver</code> is associated with an <code>ELContext</code>, there are usually multiple
  * resolvers considered for any given variable or property resolution. <code>ELResolver</code>s are combined together
  * using {@link CompositeELResolver}s, to define rich semantics for evaluating an expression.
  * </p>
  *
  * <p>
  * For the {@link #getValue}, {@link #getType}, {@link #setValue}, and {@link #isReadOnly} methods, an
  * <code>ELResolver</code> is not responsible for resolving all possible (base, property) pairs. In fact, most resolvers
  * will only handle a <code>base</code> of a single type. To indicate that a resolver has successfully resolved a
  * particular (base, property) pair, it must set the <code>propertyResolved</code> property of the
  * <code>ELContext</code> to <code>true</code>. If it could not handle the given pair, it must leave this property
  * alone. The caller must ignore the return value of the method if <code>propertyResolved</code> is <code>false</code>.
  *
  * <p>
  * Similarly, for the {@link #convertToType} method an <code>ELResolver</code> must set the
  * <code>propertyResolved</code> to <code>true</code> to indicate that it handles the conversion of the object to the
  * target type.
  *
  * <p>
  * The {@link #getCommonPropertyType} method is primarily designed for design-time
  * tool support, but must handle invocation at runtime as well. The {@link java.beans.Beans#isDesignTime} method can be
  * used to determine if the resolver is being consulted at design-time or runtime.
  *
  * @see CompositeELResolver
  * @see ELContext#getELResolver
  * @since Jakarta Server Pages 2.1
  */
 public abstract class ELResolver {

     /**
      * Attempts to resolve the given <code>property</code> object on the given <code>base</code> object.
      *
      * <p>
      * If this resolver handles the given (base, property) pair, the <code>propertyResolved</code> property of the
      * <code>ELContext</code> object must be set to <code>true</code> by the resolver, before returning. If this property is
      * not <code>true</code> after this method is called, the caller should ignore the return value.
      * </p>
      *
      * @param context The context of this evaluation.
      * @param base The base object whose property value is to be returned, or <code>null</code> to resolve a top-level
      * variable.
      * @param property The property or variable to be resolved.
      *
      * @return If the <code>propertyResolved</code> property of <code>ELContext</code> was set to <code>true</code>, then
      * the result of the variable or property resolution; otherwise undefined.
      *
      * @throws NullPointerException if context is <code>null</code>
      * @throws PropertyNotFoundException if the given (base, property) pair is handled by this <code>ELResolver</code> but
      * the specified variable or property does not exist or is not readable.
      * @throws 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.
      */
     public abstract Object getValue(ELContext context, Object base, Object property);

     /**
      * Attempts to resolve and invoke the given <code>method</code> on the given <code>base</code> object.
      *
      * <p>
      * If this resolver handles the given (base, method) pair, the <code>propertyResolved</code> property of the
      * <code>ELContext</code> object must be set to <code>true</code> by the resolver, before returning. If this property is
      * not <code>true</code> after this method is called, the caller should ignore the return value.
      *
      * <p>
      * A default implementation is provided that returns null so that existing classes that extend ELResolver can continue
      * to function.
      *
      * @param context The context of this evaluation.
      * @param base The bean on which to invoke the method
      * @param method The simple name of the method to invoke. Will be coerced to a <code>String</code>.
      * @param 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 <code>null</code>, in which case the method's formal parameter
      * types are assumed to be unknown.
      * @param params The parameters to pass to the method, or <code>null</code> if no parameters.
      *
      * @return The result of the method invocation (<code>null</code> if the method has a <code>void</code> return type).
      *
      * @throws MethodNotFoundException if no suitable method can be found.
      * @throws 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
      * <code>InvocationTargetException</code>, extract its <code>cause</code> and pass it to the <code>ELException</code>
      * constructor.
      *
      * @since Jakarta Expression Language 2.2
      */
     public Object invoke(ELContext context, Object base, Object method, Class<?>[] paramTypes, Object[] params) {
         return null;
     }

     /**
      * For a given <code>base</code> and <code>property</code>, attempts to identify the most general type that is
      * acceptable for an object to be passed as the <code>value</code> parameter in a future call to the {@link #setValue}
      * method.
      *
      * <p>
      * If this resolver handles the given (base, property) pair, the <code>propertyResolved</code> property of the
      * <code>ELContext</code> object must be set to <code>true</code> by the resolver, before returning. If this property is
      * not <code>true</code> after this method is called, the caller should ignore the return value.
      * </p>
      *
      * <p>
      * This is not always the same as <code>getValue().getClass()</code>. For example, in the case of an
      * {@link ArrayELResolver}, the <code>getType</code> 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.
      * </p>
      *
      * <p>
      * If the resolver or the property is read-only, this method must return {@code null}.
      * </p>
      *
      * @param context The context of this evaluation.
      * @param base The base object whose property value is to be analyzed, or <code>null</code> to analyze a top-level
      * variable.
      * @param property The property or variable to return the acceptable type for.
      * @return If the <code>propertyResolved</code> property of <code>ELContext</code> was set to <code>true</code>,
      * the most general acceptable type which must be {@code 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 <code>ELResolver</code> but
      * the specified variable or property does not exist or is not readable.
      * @throws 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.
      */
     public abstract Class<?> getType(ELContext context, Object base, Object property);

     /**
      * Attempts to set the value of the given <code>property</code> object on the given <code>base</code> object.
      *
      * <p>
      * If this resolver handles the given (base, property) pair, the <code>propertyResolved</code> property of the
      * <code>ELContext</code> object must be set to <code>true</code> by the resolver, before returning. If this property is
      * not <code>true</code> after this method is called, the caller can safely assume no value has been set.
      * </p>
      *
      * @param context The context of this evaluation.
      * @param base The base object whose property value is to be set, or <code>null</code> to set a top-level variable.
      * @param property The property or variable to be set.
      * @param value The value to set the property or variable to.
      * @throws NullPointerException if context is <code>null</code>
      * @throws PropertyNotFoundException if the given (base, property) pair is handled by this <code>ELResolver</code> but
      * the specified variable or property does not exist.
      * @throws PropertyNotWritableException if the given (base, property) pair is handled by this <code>ELResolver</code>
      * but the specified variable or property is not writable.
      * @throws 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.
      */
     public abstract void setValue(ELContext context, Object base, Object property, Object value);

     /**
      * For a given <code>base</code> and <code>property</code>, attempts to determine whether a call to {@link #setValue}
      * will always fail.
      *
      * <p>
      * If this resolver handles the given (base, property) pair, the <code>propertyResolved</code> property of the
      * <code>ELContext</code> object must be set to <code>true</code> by the resolver, before returning. If this property is
      * not <code>true</code> after this method is called, the caller should ignore the return value.
      * </p>
      *
      * @param context The context of this evaluation.
      * @param base The base object whose property value is to be analyzed, or <code>null</code> to analyze a top-level
      * variable.
      * @param property The property or variable to return the read-only status for.
      * @return If the <code>propertyResolved</code> property of <code>ELContext</code> was set to <code>true</code>, then
      * <code>true</code> if the property is read-only or <code>false</code> if not; otherwise undefined.
      * @throws NullPointerException if context is <code>null</code>
      * @throws PropertyNotFoundException if the given (base, property) pair is handled by this <code>ELResolver</code> but
      * the specified variable or property does not exist.
      * @throws 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.
      */
     public abstract boolean isReadOnly(ELContext context, Object base, Object property);

     /**
      * Returns the most general type that this resolver accepts for the <code>property</code> argument, given a
      * <code>base</code> object. One use for this method is to assist tools in auto-completion.
      *
      * <p>
      * 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 {@link ArrayELResolver} will accept any <code>int</code> as
      * a <code>property</code>, so the return value would be <code>Integer.class</code>.
      * </p>
      *
      * @param context The context of this evaluation.
      * @param base The base object to return the most general property type for, or <code>null</code> to enumerate the set
      * of top-level variables that this resolver can evaluate.
      * @return <code>null</code> if this <code>ELResolver</code> does not know how to handle the given <code>base</code>
      * object; otherwise <code>Object.class</code> if any type of <code>property</code> is accepted; otherwise the most
      * general <code>property</code> type accepted for the given <code>base</code>.
      */
     public abstract Class<?> getCommonPropertyType(ELContext context, Object base);

     /**
      * Converts an object to a specific type.
      *
      * <p>
      * An <code>ELException</code> is thrown if an error occurs during the conversion.
      * </p>
      *
      * @param <T> The target type for the conversion
      * @param context The context of this evaluation.
      * @param obj The object to convert.
      * @param targetType The target type for the conversion.
      * @return object converted to <code>targetType</code>
      * @throws ELException thrown if errors occur.
      */
     public <T> T convertToType(ELContext context, Object obj, Class<T> targetType) {
         return null;
     }

     /**
      * This class is used as a key for {@link ELContext#getContext(Class)}. The key references a context object that if
      * present and set to {@code Boolean#TRUE}, indicates that the identifier being resolved is a single, stand-alone
      * identifier. This allows {@link ELResolver} instances - and in particular
      * {@code jakarta.servlet.jsp.el.ImportELResolver} - to optimise the resolution of the identifier and avoid
      * unnecessary and expensive class loader lookups.
      * <p>
      * The EL implementation is required to set this key with the value {@code Boolean#TRUE} when resolving a single,
      * stand-alone identifier.
      *
      * @since Jakarta Expression Language 6.1
      */
     public static class StandaloneIdentifierMarker {

         private StandaloneIdentifierMarker() {
             // Non-public default constructor as there is no need to create instances of this class.
         }
     }
 }
	/*
	* Copyright (c) 1997, 2025 Oracle and/or its affiliates and others.
	* All rights reserved.
	* Copyright 2004 The Apache Software Foundation
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	package jakarta.el;

	/**
	* Enables customization of variable, property, method call, and type conversion resolution behavior for Jakarta
	* Expression Language expression evaluation.
	*
	* <p>
	* While evaluating an expression, the <code>ELResolver</code> associated with the {@link ELContext} is consulted to do
	* the initial resolution of the first variable of an expression. It is also consulted when a <code>.</code> or
	* <code>[]</code> operator is encountered.
	*
	* <p>
	* For example, in the Jakarta Expression Language expression <code>${employee.lastName}</code>, the
	* <code>ELResolver</code> determines what object <code>employee</code> refers to, and what it means to get the
	* <code>lastName</code> property on that object.
	*
	* <p>
	* Most methods in this class accept a <code>base</code> and <code>property</code> parameter. In the case of variable
	* resolution (e.g. determining what <code>employee</code> refers to in <code>${employee.lastName}</code>), the
	* <code>base</code> parameter will be <code>null</code> and the <code>property</code> parameter will always be of type
	* <code>String</code>. In this case, if the <code>property</code> is not a <code>String</code>, the behavior of the
	* <code>ELResolver</code> is undefined.
	*
	* <p>
	* In the case of property resolution, the <code>base</code> parameter identifies the base object and the
	* <code>property</code> object identifies the property on that base. For example, in the expression
	* <code>${employee.lastName}</code>, <code>base</code> is the result of the variable resolution for
	* <code>employee</code> and <code>property</code> is the string <code>"lastName"</code>. In the expression
	* <code>${y[x]}</code>, <code>base</code> is the result of the variable resolution for <code>y</code> and
	* <code>property</code> is the result of the variable resolution for <code>x</code>.
	*
	* <p>
	* In the case of method call resolution, the <code>base</code> parameter identifies the base object and the
	* <code>method</code> parameter identifies a method on that base. In the case of overloaded methods, the <code>
	* paramTypes</code> parameter can be optionally used to identify a method. The <code>params</code>parameter are the
	* parameters for the method call, and can also be used for resolving overloaded methods when the
	* <code>paramTypes</code> parameter is not specified.
	*
	* <p>
	* In the case of type conversion resolution, the <code>obj</code> parameter identifies the source object and the
	* <code>targetType</code> parameter identifies the target type the source to covert to.
	*
	* <p>
	* Though only a single <code>ELResolver</code> is associated with an <code>ELContext</code>, there are usually multiple
	* resolvers considered for any given variable or property resolution. <code>ELResolver</code>s are combined together
	* using {@link CompositeELResolver}s, to define rich semantics for evaluating an expression.
	* </p>
	*
	* <p>
	* For the {@link #getValue}, {@link #getType}, {@link #setValue}, and {@link #isReadOnly} methods, an
	* <code>ELResolver</code> is not responsible for resolving all possible (base, property) pairs. In fact, most resolvers
	* will only handle a <code>base</code> of a single type. To indicate that a resolver has successfully resolved a
	* particular (base, property) pair, it must set the <code>propertyResolved</code> property of the
	* <code>ELContext</code> to <code>true</code>. If it could not handle the given pair, it must leave this property
	* alone. The caller must ignore the return value of the method if <code>propertyResolved</code> is <code>false</code>.
	*
	* <p>
	* Similarly, for the {@link #convertToType} method an <code>ELResolver</code> must set the
	* <code>propertyResolved</code> to <code>true</code> to indicate that it handles the conversion of the object to the
	* target type.
	*
	* <p>
	* The {@link #getCommonPropertyType} method is primarily designed for design-time
	* tool support, but must handle invocation at runtime as well. The {@link java.beans.Beans#isDesignTime} method can be
	* used to determine if the resolver is being consulted at design-time or runtime.
	*
	* @see CompositeELResolver
	* @see ELContext#getELResolver
	* @since Jakarta Server Pages 2.1
	*/
	public abstract class ELResolver {

	/**
	* Attempts to resolve the given <code>property</code> object on the given <code>base</code> object.
	*
	* <p>
	* If this resolver handles the given (base, property) pair, the <code>propertyResolved</code> property of the
	* <code>ELContext</code> object must be set to <code>true</code> by the resolver, before returning. If this property is
	* not <code>true</code> after this method is called, the caller should ignore the return value.
	* </p>
	*
	* @param context The context of this evaluation.
	* @param base The base object whose property value is to be returned, or <code>null</code> to resolve a top-level
	* variable.
	* @param property The property or variable to be resolved.
	*
	* @return If the <code>propertyResolved</code> property of <code>ELContext</code> was set to <code>true</code>, then
	* the result of the variable or property resolution; otherwise undefined.
	*
	* @throws NullPointerException if context is <code>null</code>
	* @throws PropertyNotFoundException if the given (base, property) pair is handled by this <code>ELResolver</code> but
	* the specified variable or property does not exist or is not readable.
	* @throws 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.
	*/
	public abstract Object getValue(ELContext context, Object base, Object property);

	/**
	* Attempts to resolve and invoke the given <code>method</code> on the given <code>base</code> object.
	*
	* <p>
	* If this resolver handles the given (base, method) pair, the <code>propertyResolved</code> property of the
	* <code>ELContext</code> object must be set to <code>true</code> by the resolver, before returning. If this property is
	* not <code>true</code> after this method is called, the caller should ignore the return value.
	*
	* <p>
	* A default implementation is provided that returns null so that existing classes that extend ELResolver can continue
	* to function.
	*
	* @param context The context of this evaluation.
	* @param base The bean on which to invoke the method
	* @param method The simple name of the method to invoke. Will be coerced to a <code>String</code>.
	* @param 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 <code>null</code>, in which case the method's formal parameter
	* types are assumed to be unknown.
	* @param params The parameters to pass to the method, or <code>null</code> if no parameters.
	*
	* @return The result of the method invocation (<code>null</code> if the method has a <code>void</code> return type).
	*
	* @throws MethodNotFoundException if no suitable method can be found.
	* @throws 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
	* <code>InvocationTargetException</code>, extract its <code>cause</code> and pass it to the <code>ELException</code>
	* constructor.
	*
	* @since Jakarta Expression Language 2.2
	*/
	public Object invoke(ELContext context, Object base, Object method, Class<?>[] paramTypes, Object[] params) {
	return null;
	}

	/**
	* For a given <code>base</code> and <code>property</code>, attempts to identify the most general type that is
	* acceptable for an object to be passed as the <code>value</code> parameter in a future call to the {@link #setValue}
	* method.
	*
	* <p>
	* If this resolver handles the given (base, property) pair, the <code>propertyResolved</code> property of the
	* <code>ELContext</code> object must be set to <code>true</code> by the resolver, before returning. If this property is
	* not <code>true</code> after this method is called, the caller should ignore the return value.
	* </p>
	*
	* <p>
	* This is not always the same as <code>getValue().getClass()</code>. For example, in the case of an
	* {@link ArrayELResolver}, the <code>getType</code> 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.
	* </p>
	*
	* <p>
	* If the resolver or the property is read-only, this method must return {@code null}.
	* </p>
	*
	* @param context The context of this evaluation.
	* @param base The base object whose property value is to be analyzed, or <code>null</code> to analyze a top-level
	* variable.
	* @param property The property or variable to return the acceptable type for.
	* @return If the <code>propertyResolved</code> property of <code>ELContext</code> was set to <code>true</code>,
	* the most general acceptable type which must be {@code 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 <code>ELResolver</code> but
	* the specified variable or property does not exist or is not readable.
	* @throws 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.
	*/
	public abstract Class<?> getType(ELContext context, Object base, Object property);

	/**
	* Attempts to set the value of the given <code>property</code> object on the given <code>base</code> object.
	*
	* <p>
	* If this resolver handles the given (base, property) pair, the <code>propertyResolved</code> property of the
	* <code>ELContext</code> object must be set to <code>true</code> by the resolver, before returning. If this property is
	* not <code>true</code> after this method is called, the caller can safely assume no value has been set.
	* </p>
	*
	* @param context The context of this evaluation.
	* @param base The base object whose property value is to be set, or <code>null</code> to set a top-level variable.
	* @param property The property or variable to be set.
	* @param value The value to set the property or variable to.
	* @throws NullPointerException if context is <code>null</code>
	* @throws PropertyNotFoundException if the given (base, property) pair is handled by this <code>ELResolver</code> but
	* the specified variable or property does not exist.
	* @throws PropertyNotWritableException if the given (base, property) pair is handled by this <code>ELResolver</code>
	* but the specified variable or property is not writable.
	* @throws 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.
	*/
	public abstract void setValue(ELContext context, Object base, Object property, Object value);

	/**
	* For a given <code>base</code> and <code>property</code>, attempts to determine whether a call to {@link #setValue}
	* will always fail.
	*
	* <p>
	* If this resolver handles the given (base, property) pair, the <code>propertyResolved</code> property of the
	* <code>ELContext</code> object must be set to <code>true</code> by the resolver, before returning. If this property is
	* not <code>true</code> after this method is called, the caller should ignore the return value.
	* </p>
	*
	* @param context The context of this evaluation.
	* @param base The base object whose property value is to be analyzed, or <code>null</code> to analyze a top-level
	* variable.
	* @param property The property or variable to return the read-only status for.
	* @return If the <code>propertyResolved</code> property of <code>ELContext</code> was set to <code>true</code>, then
	* <code>true</code> if the property is read-only or <code>false</code> if not; otherwise undefined.
	* @throws NullPointerException if context is <code>null</code>
	* @throws PropertyNotFoundException if the given (base, property) pair is handled by this <code>ELResolver</code> but
	* the specified variable or property does not exist.
	* @throws 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.
	*/
	public abstract boolean isReadOnly(ELContext context, Object base, Object property);

	/**
	* Returns the most general type that this resolver accepts for the <code>property</code> argument, given a
	* <code>base</code> object. One use for this method is to assist tools in auto-completion.
	*
	* <p>
	* 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 {@link ArrayELResolver} will accept any <code>int</code> as
	* a <code>property</code>, so the return value would be <code>Integer.class</code>.
	* </p>
	*
	* @param context The context of this evaluation.
	* @param base The base object to return the most general property type for, or <code>null</code> to enumerate the set
	* of top-level variables that this resolver can evaluate.
	* @return <code>null</code> if this <code>ELResolver</code> does not know how to handle the given <code>base</code>
	* object; otherwise <code>Object.class</code> if any type of <code>property</code> is accepted; otherwise the most
	* general <code>property</code> type accepted for the given <code>base</code>.
	*/
	public abstract Class<?> getCommonPropertyType(ELContext context, Object base);

	/**
	* Converts an object to a specific type.
	*
	* <p>
	* An <code>ELException</code> is thrown if an error occurs during the conversion.
	* </p>
	*
	* @param <T> The target type for the conversion
	* @param context The context of this evaluation.
	* @param obj The object to convert.
	* @param targetType The target type for the conversion.
	* @return object converted to <code>targetType</code>
	* @throws ELException thrown if errors occur.
	*/
	public <T> T convertToType(ELContext context, Object obj, Class<T> targetType) {
	return null;
	}

	/**
	* This class is used as a key for {@link ELContext#getContext(Class)}. The key references a context object that if
	* present and set to {@code Boolean#TRUE}, indicates that the identifier being resolved is a single, stand-alone
	* identifier. This allows {@link ELResolver} instances - and in particular
	* {@code jakarta.servlet.jsp.el.ImportELResolver} - to optimise the resolution of the identifier and avoid
	* unnecessary and expensive class loader lookups.
	* <p>
	* The EL implementation is required to set this key with the value {@code Boolean#TRUE} when resolving a single,
	* stand-alone identifier.
	*
	* @since Jakarta Expression Language 6.1
	*/
	public static class StandaloneIdentifierMarker {

	private StandaloneIdentifierMarker() {
	// Non-public default constructor as there is no need to create instances of this class.
	}
	}
	}