alvinalexander.com | career | drupal | java | mac | mysql | perl | scala | uml | unix  

What this is

This file is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Other links

The source code

/*
 * Copyright 1999-2004 The Apache Software 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.
 */
package org.apache.commons.jxpath.util;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Arrays;

import org.apache.commons.jxpath.ExpressionContext;
import org.apache.commons.jxpath.JXPathException;

/**
 * Method lookup utilities, which find static and non-static methods as well
 * as constructors based on a name and list of parameters.
 *
 * @author Dmitri Plotnikov
 * @version $Revision: 1.7 $ $Date: 2004/02/29 14:17:43 $
 */
public class MethodLookupUtils {

    private static final int NO_MATCH = 0;
    private static final int APPROXIMATE_MATCH = 1;
    private static final int EXACT_MATCH = 2;
    private static final Object[] EMPTY_ARRAY = new Object[0];

     public static Constructor lookupConstructor(
        Class targetClass,
        Object[] parameters) 
     {
        boolean tryExact = true;
        int count = parameters == null ? 0 : parameters.length;
        Class types[] = new Class[count];
        for (int i = 0; i < count; i++) {
            Object param = parameters[i];
            if (param != null) {
                types[i] = param.getClass();
            }
            else {
                types[i] = null;
                tryExact = false;
            }
        }

        Constructor constructor = null;

        if (tryExact) {
            // First - without type conversion
            try {
                constructor = targetClass.getConstructor(types);
                if (constructor != null) {
                    return constructor;
                }
            }
            catch (NoSuchMethodException ex) {
                // Ignore
            }
        }

        int currentMatch = 0;
        boolean ambiguous = false;

        // Then - with type conversion
        Constructor[] constructors = targetClass.getConstructors();
        for (int i = 0; i < constructors.length; i++) {
            int match =
                matchParameterTypes(
                    constructors[i].getParameterTypes(),
                    parameters);
            if (match != NO_MATCH) {
                if (match > currentMatch) {
                    constructor = constructors[i];
                    currentMatch = match;
                    ambiguous = false;
                }
                else if (match == currentMatch) {
                    ambiguous = true;
                }
            }
        }
        if (ambiguous) {
            throw new JXPathException(
                "Ambigous constructor " + Arrays.asList(parameters));
        }
        return constructor;
    }

    public static Method lookupStaticMethod(
        Class targetClass,
        String name,
        Object[] parameters) 
    {
        boolean tryExact = true;
        int count = parameters == null ? 0 : parameters.length;
        Class types[] = new Class[count];
        for (int i = 0; i < count; i++) {
            Object param = parameters[i];
            if (param != null) {
                types[i] = param.getClass();
            }
            else {
                types[i] = null;
                tryExact = false;
            }
        }

        Method method = null;

        if (tryExact) {
            // First - without type conversion
            try {
                method = targetClass.getMethod(name, types);
                if (method != null
                    && Modifier.isStatic(method.getModifiers())) {
                    return method;
                }
            }
            catch (NoSuchMethodException ex) {
                // Ignore
            }
        }

        int currentMatch = 0;
        boolean ambiguous = false;

        // Then - with type conversion
        Method[] methods = targetClass.getMethods();
        for (int i = 0; i < methods.length; i++) {
            if (Modifier.isStatic(methods[i].getModifiers())
                && methods[i].getName().equals(name)) {
                int match =
                    matchParameterTypes(
                        methods[i].getParameterTypes(),
                        parameters);
                if (match != NO_MATCH) {
                    if (match > currentMatch) {
                        method = methods[i];
                        currentMatch = match;
                        ambiguous = false;
                    }
                    else if (match == currentMatch) {
                        ambiguous = true;
                    }
                }
            }
        }
        if (ambiguous) {
            throw new JXPathException("Ambigous method call: " + name);
        }
        return method;
    }

    public static Method lookupMethod(
        Class targetClass,
        String name,
        Object[] parameters) 
    {
        if (parameters == null
            || parameters.length < 1
            || parameters[0] == null) {
            return null;
        }

        if (matchType(targetClass, parameters[0]) == NO_MATCH) {
            return null;
        }

        targetClass = TypeUtils.convert(parameters[0], targetClass).getClass();

        boolean tryExact = true;
        int count = parameters.length - 1;
        Class types[] = new Class[count];
        Object arguments[] = new Object[count];
        for (int i = 0; i < count; i++) {
            Object param = parameters[i + 1];
            arguments[i] = param;
            if (param != null) {
                types[i] = param.getClass();
            }
            else {
                types[i] = null;
                tryExact = false;
            }
        }

        Method method = null;

        if (tryExact) {
            // First - without type conversion
            try {
                method = targetClass.getMethod(name, types);
                if (method != null
                    && !Modifier.isStatic(method.getModifiers())) {
                    return method;
                }
            }
            catch (NoSuchMethodException ex) {
                // Ignore
            }
        }

        int currentMatch = 0;
        boolean ambiguous = false;

        // Then - with type conversion
        Method[] methods = targetClass.getMethods();
        for (int i = 0; i < methods.length; i++) {
            if (!Modifier.isStatic(methods[i].getModifiers())
                && methods[i].getName().equals(name)) {
                int match =
                    matchParameterTypes(
                        methods[i].getParameterTypes(),
                        arguments);
                if (match != NO_MATCH) {
                    if (match > currentMatch) {
                        method = methods[i];
                        currentMatch = match;
                        ambiguous = false;
                    }
                    else if (match == currentMatch) {
                        ambiguous = true;
                    }
                }
            }
        }
        if (ambiguous) {
            throw new JXPathException("Ambigous method call: " + name);
        }
        return method;
    }

    private static int matchParameterTypes(
        Class types[],
        Object parameters[]) 
    {
        int pi = 0;
        if (types.length >= 1
            && ExpressionContext.class.isAssignableFrom(types[0])) {
            pi++;
        }
        int length = parameters == null ? 0 : parameters.length;
        if (types.length != length + pi) {
            return NO_MATCH;
        }
        int totalMatch = EXACT_MATCH;
        for (int i = 0; i < length; i++) {
            int match = matchType(types[i + pi], parameters[i]);
            if (match == NO_MATCH) {
                return NO_MATCH;
            }
            if (match < totalMatch) {
                totalMatch = match;
            }
        }
        return totalMatch;
    }

    private static int matchType(Class expected, Object object) {
        if (object == null) {
            return APPROXIMATE_MATCH;
        }

        Class actual = object.getClass();

        if (expected.equals(actual)) {
            return EXACT_MATCH;
        }
        if (expected.isAssignableFrom(actual)) {
            return EXACT_MATCH;
        }

        if (TypeUtils.canConvert(object, expected)) {
            return APPROXIMATE_MATCH;
        }

        return NO_MATCH;
    }
}
... this post is sponsored by my books ...

#1 New Release!

FP Best Seller

 

new blog posts

 

Copyright 1998-2021 Alvin Alexander, alvinalexander.com
All Rights Reserved.

A percentage of advertising revenue from
pages under the /java/jwarehouse URI on this website is
paid back to open source projects.