org.codehaus.plexus.util.introspection.ReflectionValueExtractor Maven / Gradle / Ivy

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package org.codehaus.plexus.util.introspection;

/*
 * Copyright The 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 java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.List;
import java.util.WeakHashMap;
import java.util.Map;
import java.util.StringTokenizer;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.codehaus.plexus.util.StringUtils;

/**
 * Using simple dotted expressions to extract the values from an Object instance,
 * For example we might want to extract a value like: project.build.sourceDirectory
 *
 * The implementation supports indexed, nested and mapped properties similar to the JSP way.
 *
 * @author Jason van Zyl 
 * @author Vincent Siveton
 * @version $Id: ReflectionValueExtractor.java 8010 2009-01-07 12:59:50Z vsiveton $
 * @see http://struts.apache.org/1.x/struts-taglib/indexedprops.html
 */
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 classMaps = new WeakHashMap();

    /**
     * Indexed properties pattern, ie (\\w+)\\[(\\d+)\\]
     */
    private static final Pattern INDEXED_PROPS = Pattern.compile( "(\\w+)\\[(\\d+)\\]" );

    /**
     * Indexed properties pattern, ie (\\w+)\\((.+)\\)
     */
    private static final Pattern MAPPED_PROPS = Pattern.compile( "(\\w+)\\((.+)\\)" );

    private ReflectionValueExtractor()
    {
    }

    /**
     * The implementation supports indexed, nested and mapped properties.
     *
     * 
     * nested properties should be defined by a dot, i.e. "user.address.street"
     * indexed properties (java.util.List or array instance) should be contains (\\w+)\\[(\\d+)\\]
     * pattern, i.e. "user.addresses[1].street"
     * mapped properties should be contains (\\w+)\\((.+)\\) pattern, i.e. "user.addresses(myAddress).street"
     * 
     *
     * @param expression not null expression
     * @param root not null object
     * @return the object defined by the expression
     * @throws Exception if any
     */
    public static Object evaluate( String expression, Object root )
        throws Exception
    {
        return evaluate( expression, root, true );
    }

    /**
     * The implementation supports indexed, nested and mapped properties.
     *
     * 
     * nested properties should be defined by a dot, i.e. "user.address.street"
     * indexed properties (java.util.List or array instance) should be contains (\\w+)\\[(\\d+)\\]
     * pattern, i.e. "user.addresses[1].street"
     * mapped properties should be contains (\\w+)\\((.+)\\) pattern, i.e. "user.addresses(myAddress).street"
     * 
     *
     * @param expression not null expression
     * @param root not null object
     * @return the object defined by the expression
     * @throws Exception if any
     */
    // 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() )
        {
            // if we have nothing, stop now
            if ( value == null )
            {
                return null;
            }

            String token = parser.nextToken();

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

            Method method;
            Object[] localParams = OBJECT_ARGS;

            // do we have an indexed property?
            Matcher matcher = INDEXED_PROPS.matcher( token );
            if ( matcher.find() )
            {
                String methodBase = StringUtils.capitalizeFirstLetter( matcher.group( 1 ) );
                String methodName = "get" + methodBase;
                method = classMap.findMethod( methodName, CLASS_ARGS );
                value = method.invoke( value, OBJECT_ARGS );
                classMap = getClassMap( value.getClass() );

                if ( classMap.getCachedClass().isArray() )
                {
                    value = Arrays.asList( (Object[]) value );
                    classMap = getClassMap( value.getClass() );
                }

                if ( value instanceof List )
                {
                    // use get method on List interface
                    localParams = new Object[1];
                    localParams[0] = Integer.valueOf( matcher.group( 2 ) );
                    method = classMap.findMethod( "get", localParams );
                }
                else
                {
                    throw new Exception( "The token '" + token
                        + "' refers to a java.util.List or an array, but the value seems is an instance of '"
                        + value.getClass() + "'." );
                }
            }
            else
            {
                // do we have a mapped property?
                matcher = MAPPED_PROPS.matcher( token );
                if ( matcher.find() )
                {
                    String methodBase = StringUtils.capitalizeFirstLetter( matcher.group( 1 ) );
                    String methodName = "get" + methodBase;
                    method = classMap.findMethod( methodName, CLASS_ARGS );
                    value = method.invoke( value, OBJECT_ARGS );
                    classMap = getClassMap( value.getClass() );

                    if ( value instanceof Map )
                    {
                        // use get method on List interface
                        localParams = new Object[1];
                        localParams[0] = matcher.group( 2 );
                        method = classMap.findMethod( "get", localParams );
                    }
                    else
                    {
                        throw new Exception( "The token '" + token
                            + "' refers to a java.util.Map, but the value seems is an instance of '"
                            + value.getClass() + "'." );
                    }
                }
                else
                {
                    String methodBase = StringUtils.capitalizeFirstLetter( token );
                    String methodName = "get" + methodBase;
                    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;
            }

            try
            {
                value = method.invoke( value, localParams );
            }
            catch ( InvocationTargetException e )
            {
                // catch array index issues gracefully, otherwise release
                if ( e.getCause() instanceof IndexOutOfBoundsException )
                {
                    return null;
                }

                throw e;
            }
        }

        return value;
    }

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

        if ( classMap == null )
        {
            classMap = new ClassMap( clazz );

            classMaps.put( clazz, classMap );
        }

        return classMap;
    }
}