org.codehaus.plexus.interpolation.reflection.ReflectionValueExtractor Maven / Gradle / Ivy

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package org.codehaus.plexus.interpolation.reflection;

/*
 * Copyright 2001-2006 Codehaus 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.
 */

import org.codehaus.plexus.interpolation.util.StringUtils;

import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.lang.reflect.Method;
import java.util.Map;
import java.util.StringTokenizer;
import java.util.WeakHashMap;

/**
 * NOTE: This class was copied from plexus-utils, to allow this library
 * to stand completely self-contained.
 * 

 * Using simple dotted expressions extract the values from a MavenProject
 * instance, For example we might want to extract a value like:
 * project.build.sourceDirectory
 *
 * @author Jason van Zyl 
 * @version $Id$
 */
public class ReflectionValueExtractor
{
    private static final Class[] CLASS_ARGS = new Class[0];

    private static final Object[] OBJECT_ARGS = new Object[0];

    /**
     * Use a WeakHashMap here, so the keys (Class objects) can be garbage collected.
     * This approach prevents permgen space overflows due to retention of discarded
     * classloaders.
     */
    private static final Map, WeakReference> classMaps = new WeakHashMap, WeakReference>();

    private ReflectionValueExtractor()
    {
    }

    public static Object evaluate( String expression, Object root )
        throws Exception
    {
        return evaluate( expression, root, true );
    }

    // TODO: don't throw Exception
    public static Object evaluate( String expression, Object root, boolean trimRootToken )
        throws Exception
    {
        // if the root token refers to the supplied root object parameter, remove it.
        if ( trimRootToken )
        {
            expression = expression.substring( expression.indexOf( '.' ) + 1 );
        }

        Object value = root;

        // ----------------------------------------------------------------------
        // Walk the dots and retrieve the ultimate value desired from the
        // MavenProject instance.
        // ----------------------------------------------------------------------

        StringTokenizer parser = new StringTokenizer( expression, "." );

        while ( parser.hasMoreTokens() )
        {
            String token = parser.nextToken();

            if ( value == null )
            {
                return null;
            }

            ClassMap classMap = getClassMap( value.getClass() );

            String methodBase = StringUtils.capitalizeFirstLetter( token );

            String methodName = "get" + methodBase;

            Method method = classMap.findMethod( methodName, CLASS_ARGS );

            if ( method == null )
            {
                // perhaps this is a boolean property??
                methodName = "is" + methodBase;

                method = classMap.findMethod( methodName, CLASS_ARGS );
            }

            if ( method == null )
            {
                return null;
            }

            value = method.invoke( value, OBJECT_ARGS );
        }

        return value;
    }

    private static ClassMap getClassMap( Class clazz )
    {
        WeakReference ref = classMaps.get( clazz);

        ClassMap classMap;

        if ( ref == null || (classMap = ref.get()) == null )
        {
            classMap = new ClassMap( clazz );

            classMaps.put( clazz, new WeakReference(classMap) );
        }

        return classMap;
    }
}