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Implementation of JSON transformers for Mule
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/*
 * Copyright (c) MuleSoft, Inc.  All rights reserved.  http://www.mulesoft.com
 * The software in this package is published under the terms of the CPAL v1.0
 * license, a copy of which has been included with this distribution in the
 * LICENSE.txt file.
 */
package org.mule.module.json.transformers;

import org.mule.api.MuleMessage;
import org.mule.api.lifecycle.InitialisationException;
import org.mule.api.transformer.TransformerException;
import org.mule.module.json.filters.IsJsonFilter;
import org.mule.transformer.types.DataTypeFactory;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import java.io.IOException;
import java.io.StringWriter;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Converts a java object to a JSON encoded object that can be consumed by other languages such as
 * Javascript or Ruby.
 * 
 * The returnClass for this transformer is always java.lang.String, there is no need to set this.
 */
public class ObjectToJson extends AbstractJsonTransformer
{
    /**
     * logger used by this class
     */
    protected transient final Log logger = LogFactory.getLog(ObjectToJson.class);

    private Map, Class> serializationMixins = new HashMap, Class>();

    protected Class sourceClass;

    private boolean handleException = false;

    private IsJsonFilter isJsonFilter = new IsJsonFilter();

    public ObjectToJson()
    {
        this.setReturnDataType(DataTypeFactory.JSON_STRING);
    }

    @Override
    public void initialise() throws InitialisationException
    {
        super.initialise();

        //restrict the handled types
        if (getSourceClass() != null)
        {
            sourceTypes.clear();
            registerSourceType(DataTypeFactory.create(getSourceClass()));
        }

        //Add shared mixins first
        for (Map.Entry, Class> entry : getMixins().entrySet())
        {
            getMapper().getSerializationConfig().addMixInAnnotations(entry.getKey(), entry.getValue());
        }

        for (Map.Entry, Class> entry : serializationMixins.entrySet())
        {
            getMapper().getSerializationConfig().addMixInAnnotations(entry.getKey(), entry.getValue());
        }
    }

    @Override
    public Object transformMessage(MuleMessage message, String outputEncoding) throws TransformerException
    {
        Object src = message.getPayload();
        if (src instanceof String && isJsonFilter.accept(src))
        {
            //Nothing to transform
            return src;
        }

        // Checks if there's an exception
        if (message.getExceptionPayload() != null && this.isHandleException())
        {
            if (logger.isDebugEnabled())
            {
                logger.debug("Found exception with null payload");
            }
            src = this.getException(message.getExceptionPayload().getException());
        }

        StringWriter writer = new StringWriter();
        try
        {
            getMapper().writeValue(writer, src);
        }
        catch (IOException e)
        {
            throw new TransformerException(this, e);
        }
        
        if (returnType.getType().equals(byte[].class))
        {
            try
            {
                return writer.toString().getBytes(outputEncoding);
            }
            catch (UnsupportedEncodingException uee)
            {
                throw new TransformerException(this, uee);
            }
        }
        else
        {
            return writer.toString();
        }
    }

    /**
     * The reason of having this is because the original exception object is way too
     * complex and it breaks JSON-lib.
     */
    private Exception getException(Throwable t)
    {
        Exception returnValue = null;
        List causeStack = new ArrayList();

        for (Throwable tempCause = t; tempCause != null; tempCause = tempCause.getCause())
        {
            causeStack.add(tempCause);
        }

        for (int i = causeStack.size() - 1; i >= 0; i--)
        {
            Throwable tempCause = causeStack.get(i);

            // There is no cause at the very root
            if (i == causeStack.size())
            {
                returnValue = new Exception(tempCause.getMessage());
                returnValue.setStackTrace(tempCause.getStackTrace());
            }
            else
            {
                returnValue = new Exception(tempCause.getMessage(), returnValue);
                returnValue.setStackTrace(tempCause.getStackTrace());
            }
        }

        return returnValue;
    }

    public boolean isHandleException()
    {
        return this.handleException;
    }

    public void setHandleException(boolean handleException)
    {
        this.handleException = handleException;
    }

    public Class getSourceClass()
    {
        return sourceClass;
    }

    public void setSourceClass(Class sourceClass)
    {
        this.sourceClass = sourceClass;
    }

    public Map, Class> getSerializationMixins()
    {
        return serializationMixins;
    }

    public void setSerializationMixins(Map, Class> serializationMixins)
    {
        this.serializationMixins = serializationMixins;
    }
}