JexlPropertyGet.java

/*
* Copyright 2016 Nabarun Mondal
* 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 com.noga.njexl.lang.introspection;

/**
 * Interface for getting values that appear to be properties.
 * Ex.
 * <code>
 * ${foo.bar}
 * </code>
 * @since 1.0
 */
public interface JexlPropertyGet {
    /**
     * Method used to get the property value of an object.
     * 
     * @param obj the object to get the property value from.
     * @return the property value.
     * @throws Exception on any error.
     */
    Object invoke(Object obj) throws Exception;

    /**
     * Attempts to reuse this JexlPropertyGet, checking that it is compatible with
     * the actual set of arguments.
     * @param obj the object to invoke the property get upon
     * @param key the property key to get
     * @return the result of the method invocation that should be checked by tryFailed to determine if it succeeded
     * or failed.
     */
    Object tryInvoke(Object obj, Object key);

    /**
     * Checks whether a tryInvoke failed or not.
     * @param rval the value returned by tryInvoke
     * @return true if tryInvoke failed, false otherwise
     */
    boolean tryFailed(Object rval);

    /**
     * Specifies if this JexlPropertyGet is cacheable and able to be reused for
     * this class of object it was returned for.
     *
     * @return true if can be reused for this class, false if not
     */
    boolean isCacheable();
}