ConverterManager.java

/*******************************************************************************
 * Copyright (c) 2014, 2015 IBH SYSTEMS GmbH.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBH SYSTEMS GmbH - initial API and implementation
 *******************************************************************************/
package org.eclipse.packagedrone.utils.converter;

import java.util.Collection;
import java.util.LinkedList;

public class ConverterManager
{
    private final Collection<Converter> converters = new LinkedList<> ();

    private final Collection<DefaultProvider> defaults = new LinkedList<> ();

    public static ConverterManager create ()
    {
        final ConverterManager result = new ConverterManager ();

        result.addConverter ( StringToIntegerConverter.INSTANCE );
        result.addConverter ( StringToBooleanConverter.INSTANCE );
        result.addConverter ( StringToPrimitiveBooleanConverter.INSTANCE );
        result.addConverter ( StringToPrimitiveIntegerConverter.INSTANCE );
        result.addConverter ( StringToPrimitiveLongConverter.INSTANCE );
        result.addConverter ( BooleanToStringConverter.INSTANCE );
        result.addConverter ( IntegerToStringConverter.INSTANCE );
        result.addConverter ( StringToSetConverter.INSTANCE );
        result.addConverter ( StringToJsonConverter.INSTANCE );
        result.addConverter ( JsonToStringConverter.INSTANCE );
        result.addConverter ( LongToStringConverter.INSTANCE );
        result.addConverter ( StringToLongConverter.INSTANCE );

        result.addDefault ( PrimitiveBooleanDefault.INSTANCE );

        return result;
    }

    public ConverterManager ()
    {
    }

    public void addConverter ( final Converter converter )
    {
        this.converters.add ( converter );
    }

    public void addDefault ( final DefaultProvider defaultProvider )
    {
        this.defaults.add ( defaultProvider );
    }

    @SuppressWarnings ( "unchecked" )
    public <T> T convertTo ( final Object value, final Class<T> clazz ) throws Exception
    {
        if ( value == null )
        {
            return getDefault ( clazz );
        }

        if ( clazz.isAssignableFrom ( value.getClass () ) )
        {
            return clazz.cast ( value );
        }

        final Class<?> from = value.getClass ();

        for ( final Converter cvt : this.converters )
        {
            if ( cvt.canConvert ( from, clazz ) )
            {
                final Object o = cvt.convertTo ( value, clazz );
                if ( o == null )
                {
                    return null;
                }

                if ( clazz.isAssignableFrom ( o.getClass () ) )
                {
                    return clazz.cast ( o );
                }
                else if ( clazz.isPrimitive () )
                {
                    return (T)o;
                }
                else
                {
                    throw new ConversionException ( String.format ( "Invalid result type (expected: %s, actual: %s)", clazz.getName (), o.getClass ().getName () ) );
                }
            }
        }
        throw new ConversionException ( String.format ( "Unable to convert %s to %s", value.getClass (), clazz.getName () ) );
    }

    @SuppressWarnings ( "unchecked" )
    private <T> T getDefault ( final Class<T> clazz )
    {
        for ( final DefaultProvider provider : this.defaults )
        {
            if ( provider.providesFor ( clazz ) )
            {
                return (T)provider.defaultValue ();
            }
        }

        // fall back to null
        return null;
    }
}