java/javax/el/ValueExpression.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 javax.el;

public abstract class ValueExpression extends Expression {

    private static final long serialVersionUID = 8577809572381654673L;

    /**
     * @param context The EL context for this evaluation
     *
     * @return The result of evaluating this value expression
     *
     * @throws NullPointerException
     *              If the supplied context is <code>null</code>
     * @throws PropertyNotFoundException
     *              If a property/variable resolution failed because no match
     *              was found or a match was found but was not readable
     * @throws ELException
     *              Wraps any exception throw whilst resolving a property or
     *              variable
     */
    public abstract Object getValue(ELContext context);

    /**
     * @param context The EL context for this evaluation
     * @param value   The value to set the property to which this value
     *                expression refers
     *
     * @throws NullPointerException
     *              If the supplied context is <code>null</code>
     * @throws PropertyNotFoundException
     *              If a property/variable resolution failed because no match
     *              was found
     * @throws PropertyNotWritableException
     *              If a property/variable resolution failed because a match was
     *              found but was not writable
     * @throws ELException
     *              Wraps any exception throw whilst resolving a property or
     *              variable
     */
    public abstract void setValue(ELContext context, Object value);

    /**
     * @param context The EL context for this evaluation
     *
     * @return <code>true</code> if this expression is read only otherwise
     *         <code>false</code>
     *
     * @throws NullPointerException
     *              If the supplied context is <code>null</code>
     * @throws PropertyNotFoundException
     *              If a property/variable resolution failed because no match
     *              was found or a match was found but was not readable
     * @throws ELException
     *              Wraps any exception throw whilst resolving a property or
     *              variable
     */
    public abstract boolean isReadOnly(ELContext context);

    /**
     * @param context The EL context for this evaluation
     *
     * @return The type of the result of this value expression
     *
     * @throws NullPointerException
     *              If the supplied context is <code>null</code>
     * @throws PropertyNotFoundException
     *              If a property/variable resolution failed because no match
     *              was found or a match was found but was not readable
     * @throws ELException
     *              Wraps any exception throw whilst resolving a property or
     *              variable
     */
    public abstract Class<?> getType(ELContext context);

    public abstract Class<?> getExpectedType();

    /**
     * @param context The EL context for this evaluation
     *
     * @return This default implementation always returns <code>null</code>
     *
     * @since EL 2.2
     */
    public ValueReference getValueReference(ELContext context) {
        // Expected to be over-ridden by implementation
        context.notifyBeforeEvaluation(getExpressionString());
        context.notifyAfterEvaluation(getExpressionString());
        return null;
    }
}