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The Commons Jexl library is an implementation of the JSTL Expression Language with extensions.
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/*
 * 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 org.apache.commons.jexl2.internal;
import java.lang.reflect.InvocationTargetException;

/**
 * Specialized executor to get a property from an object.
 * @since 2.0
 */
public final class PropertyGetExecutor extends AbstractExecutor.Get {
    /** A static signature for method(). */
    private static final Object[] EMPTY_PARAMS = {};
    /** The property. */
    private final String property;
    
    /**
     * Creates an instance by attempting discovery of the get method.
     * @param is the introspector
     * @param clazz the class to introspect
     * @param identifier the property to get
     */
    public PropertyGetExecutor(Introspector is, Class clazz, String identifier) {
        super(clazz, discover(is, clazz, identifier));
        property = identifier;
    }

    /** {@inheritDoc} */
    @Override
    public Object getTargetProperty() {
        return property;
    }
    
    /** {@inheritDoc} */
    @Override
    public Object execute(Object o)
        throws IllegalAccessException, InvocationTargetException {
        return method == null ? null : method.invoke(o, (Object[]) null);
    }

    /** {@inheritDoc} */
    @Override
    public Object tryExecute(Object o, Object identifier) {
        if (o != null && method !=  null
            && property.equals(identifier)
            && objectClass.equals(o.getClass())) {
            try {
                return method.invoke(o, (Object[]) null);
            } catch (InvocationTargetException xinvoke) {
                return TRY_FAILED; // fail
            } catch (IllegalAccessException xill) {
                return TRY_FAILED;// fail
            }
        }
        return TRY_FAILED;
    }

    /**
     * Discovers the method for a {@link PropertyGet}.
     * The method to be found should be named "get{P,p}property.
     *@param is the introspector
     *@param clazz the class to find the get method from
     *@param property the property name to find
     *@return the method if found, null otherwise
     */
    static java.lang.reflect.Method discover(Introspector is,
            final Class clazz, String property) {
        return discoverGet(is, "get", clazz, property);
    }


    /**
     * Base method for boolean & object property get.
     * @param is the introspector
     * @param which "is" or "get" for boolean or object
     * @param clazz The class being examined.
     * @param property The property being addressed.
     * @return The {get,is}{p,P}roperty method if one exists, null otherwise.
     */
    static java.lang.reflect.Method discoverGet(Introspector is,
            String which, Class clazz, String property) {
        //  this is gross and linear, but it keeps it straightforward.
        java.lang.reflect.Method method = null;
        final int start = which.length(); // "get" or "is" so 3 or 2 for char case switch
        // start with get
        StringBuilder sb = new StringBuilder(which);
        sb.append(property);
        // uppercase nth char
        char c = sb.charAt(start);
        sb.setCharAt(start, Character.toUpperCase(c));
        method = is.getMethod(clazz, sb.toString(), EMPTY_PARAMS);
        //lowercase nth char
        if (method == null) {
            sb.setCharAt(start, Character.toLowerCase(c));
            method = is.getMethod(clazz, sb.toString(), EMPTY_PARAMS);
        }
        return method;
    }
}