jakarta.el.Expression Maven / Gradle / Ivy
/*
* Copyright (c) 1997, 2019 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;
import java.io.Serializable;
/**
* Base class for the expression subclasses {@link ValueExpression} and {@link MethodExpression}, implementing
* characteristics common to both.
*
*
* All expressions must implement the equals() and hashCode() methods so that two expressions
* can be compared for equality. They are redefined abstract in this class to force their implementation in subclasses.
*
*
*
* All expressions must also be Serializable so that they can be saved and restored.
*
*
*
* Expressions are also designed to be immutable so that only one instance needs to be created for any
* given expression String / {@link FunctionMapper}. This allows a container to pre-create expressions and not have to
* re-parse them each time they are evaluated.
*
*
* @since Jakarta Server Pages 2.1
*/
public abstract class Expression implements Serializable {
private static final long serialVersionUID = -6663767980471823812L;
/**
* Returns the original String used to create this Expression, unmodified.
*
*
* This is used for debugging purposes but also for the purposes of comparison (e.g. to ensure the expression in a
* configuration file has not changed).
*
*
*
* This method does not provide sufficient information to re-create an expression. Two different expressions can have
* exactly the same expression string but different function mappings. Serialization should be used to save and restore
* the state of an Expression.
*
*
* @return The original expression String.
*/
public abstract String getExpressionString();
// Comparison
/**
* Determines whether the specified object is equal to this Expression.
*
*
* The result is true if and only if the argument is not null, is an Expression
* object that is the of the same type (ValueExpression or MethodExpression), and has an
* identical parsed representation.
*
*
*
* Note that two expressions can be equal if their expression Strings are different. For example,
* ${fn1:foo()} and ${fn2:foo()} are equal if their corresponding FunctionMappers
* mapped fn1:foo and fn2:foo to the same method.
*
*
* @param obj the Object to test for equality.
* @return true if obj equals this Expression; false otherwise.
* @see java.util.Hashtable
* @see java.lang.Object#equals(java.lang.Object)
*/
@Override
public abstract boolean equals(Object obj);
/**
* Returns the hash code for this Expression.
*
*
* See the note in the {@link #equals} method on how two expressions can be equal if their expression Strings are
* different. Recall that if two objects are equal according to the equals(Object) method, then calling the
* hashCode method on each of the two objects must produce the same integer result. Implementations must
* take special note and implement hashCode correctly.
*
*
* @return The hash code for this Expression.
* @see #equals
* @see java.util.Hashtable
* @see java.lang.Object#hashCode()
*/
@Override
public abstract int hashCode();
/**
* Returns whether this expression was created from only literal text.
*
*
* This method must return true if and only if the expression string this expression was created from
* contained no unescaped Jakarta Expression Language delimeters (${...} or #{...}).
*
* @return true if this expression was created from only literal text; false otherwise.
*/
public abstract boolean isLiteralText();
}