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A Java library for parsing command line options
There is a newer version: 6.0-alpha-3
/*
 The MIT License

 Copyright (c) 2004-2015 Paul R. Holser, Jr.

 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the
 "Software"), to deal in the Software without restriction, including
 without limitation the rights to use, copy, modify, merge, publish,
 distribute, sublicense, and/or sell copies of the Software, and to
 permit persons to whom the Software is furnished to do so, subject to
 the following conditions:

 The above copyright notice and this permission notice shall be
 included in all copies or substantial portions of the Software.

 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

package joptsimple.internal;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import static java.lang.reflect.Modifier.*;

import joptsimple.ValueConverter;

import static joptsimple.internal.Classes.*;

/**
 * Helper methods for reflection.
 *
 * @author Paul Holser
 */
public final class Reflection {
    private Reflection() {
        throw new UnsupportedOperationException();
    }

    /**
     * Finds an appropriate value converter for the given class.
     *
     * @param  a constraint on the class object to introspect
     * @param clazz class to introspect on
     * @return a converter method or constructor
     */
    public static  ValueConverter findConverter( Class clazz ) {
        Class maybeWrapper = wrapperOf( clazz );

        ValueConverter valueOf = valueOfConverter( maybeWrapper );
        if ( valueOf != null )
            return valueOf;

        ValueConverter constructor = constructorConverter( maybeWrapper );
        if ( constructor != null )
            return constructor;

        throw new IllegalArgumentException( clazz + " is not a value type" );
    }

    private static  ValueConverter valueOfConverter( Class clazz ) {
        try {
            Method valueOf = clazz.getMethod( "valueOf", String.class );
            if ( meetsConverterRequirements( valueOf, clazz ) )
                return new MethodInvokingValueConverter<>( valueOf, clazz );

            return null;
        } catch ( NoSuchMethodException ignored ) {
            return null;
        }
    }

    private static  ValueConverter constructorConverter( Class clazz ) {
        try {
            return new ConstructorInvokingValueConverter<>( clazz.getConstructor( String.class ) );
        } catch ( NoSuchMethodException ignored ) {
            return null;
        }
    }

    /**
     * Invokes the given constructor with the given arguments.
     *
     * @param  constraint on the type of the objects yielded by the constructor
     * @param constructor constructor to invoke
     * @param args arguments to hand to the constructor
     * @return the result of invoking the constructor
     * @throws ReflectionException in lieu of the gaggle of reflection-related exceptions
     */
    public static  T instantiate( Constructor constructor, Object... args ) {
        try {
            return constructor.newInstance( args );
        } catch ( Exception ex ) {
            throw reflectionException( ex );
        }
    }

    /**
     * Invokes the given static method with the given arguments.
     *
     * @param method method to invoke
     * @param args arguments to hand to the method
     * @return the result of invoking the method
     * @throws ReflectionException in lieu of the gaggle of reflection-related exceptions
     */
    public static Object invoke( Method method, Object... args ) {
        try {
            return method.invoke( null, args );
        } catch ( Exception ex ) {
            throw reflectionException( ex );
        }
    }

    @SuppressWarnings( "unchecked" )
    public static  V convertWith( ValueConverter converter, String raw ) {
        return converter == null ? (V) raw : converter.convert( raw );
    }

    private static boolean meetsConverterRequirements( Method method, Class expectedReturnType ) {
        int modifiers = method.getModifiers();
        return isPublic( modifiers ) && isStatic( modifiers ) && expectedReturnType.equals( method.getReturnType() );
    }

    private static RuntimeException reflectionException( Exception ex ) {
        if ( ex instanceof IllegalArgumentException )
            return new ReflectionException( ex );
        if ( ex instanceof InvocationTargetException )
            return new ReflectionException( ex.getCause() );
        if ( ex instanceof RuntimeException )
            return (RuntimeException) ex;

        return new ReflectionException( ex );
    }
}