impl/src/main/java/org/apache/myfaces/taglib/core/DelegateConverter.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.myfaces.taglib.core;

import javax.el.ELContext;
import javax.el.ValueExpression;
import javax.faces.component.StateHolder;
import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.convert.Converter;
import javax.faces.convert.ConverterException;

/**
 * This class is used in conjunction with ConverterImplTag. 
 * 
 * When a tag like this is in a jsp page:
 * <code>
 * &lt;f:converter binding="#{mybean}"/&gt;
 *  
 *  or
 *  
 * &lt;f:converter converterId="#{'anyid'}" binding="#{mybean}"/&gt;
 * </code>
 * The value of mybean could be already on the context, so this
 * converter avoid creating a new variable and use the previous one.
 * 
 * @author Leonardo Uribe (latest modification by $Author$)
 * @version $Revision$ $Date$ 
 */
public class DelegateConverter implements Converter, StateHolder
{

    private ValueExpression _converterId;
    private ValueExpression _binding;
    private String _converterIdString = null;
    
    public DelegateConverter()
    {
        
    }
    
    public DelegateConverter(ValueExpression id, ValueExpression binding, String converterIdString)
    {
        super();
        _converterId = id;
        _binding = binding;
        _converterIdString = converterIdString;
    }

    @Override
    public boolean isTransient()
    {
        return false;
    }

    @Override
    public void restoreState(FacesContext facesContext, Object state)
    {
        Object[] values = (Object[]) state;
        _converterId = (ValueExpression) values[0];
        _binding = (ValueExpression) values[1];
        _converterIdString = (String) values[2];
    }

    @Override
    public Object saveState(FacesContext facesContext)
    {
        Object[] values = new Object[3];
        values[0] = _converterId;
        values[1] = _binding;
        values[2] = _converterIdString;
        return values;
    }

    @Override
    public void setTransient(boolean arg0)
    {
        // Do nothing        
    }

    @Override
    public Object getAsObject(FacesContext facesContext, UIComponent component, String value)
    {
        return _getDelegate().getAsObject(facesContext, component, value);
    }

    @Override
    public String getAsString(FacesContext facesContext, UIComponent component, Object value)
    {
        return _getDelegate().getAsString(facesContext, component, value);
    }

    private Converter _getDelegate()
    {
        return _createConverter();
    }

    private Converter _createConverter()
    {
        Converter converter = null;

        FacesContext facesContext = FacesContext.getCurrentInstance();
        ELContext elContext = facesContext.getELContext();

        // try to create the converter from the binding expression first, and then from
        // the converterId
        if (_binding != null)
        {
            try
            {
                converter = (Converter) _binding.getValue(elContext);

                if (converter != null)
                {
                    return converter;
                }
            }
            catch (Exception e)
            {
                throw new ConverterException("Exception creating converter using binding", e);
            }
        }

        if ((_converterId != null) || (_converterIdString != null))
        {
            try
            {
                if (null != _converterIdString)
                {
                    converter = facesContext.getApplication().createConverter(_converterIdString);
                }
                else
                {
                    String converterId = (String) _converterId.getValue(elContext);
                    converter = facesContext.getApplication().createConverter(converterId);
                }

                // with binding no converter was created, set its value with the converter
                // created using the converterId
                if (converter != null && _binding != null)
                {
                    _binding.setValue(elContext, converter);
                }
            }
            catch (Exception e)
            {
                throw new ConverterException("Exception creating converter with converterId: " + _converterId, e);
            }
        }
        
        if (converter == null)
        {
            throw new IllegalStateException("Could not create converter. Please specify a valid converterId" +
                    " or a non-null binding.");
        }

        return converter;
    }

}