How to write a transformer

Your transformer class needs to extend org.mule.transformers.AbstractTransformer and implement two methods (optionally also contain a private static final long serialVersionUID for being serializable, this may throw a warning if not done)
eg.

private static final long serialVersionUID = 1L;

The methods are:

• a no input parameter contructor which registers the source data type to the transformer method (below) and constructs using a call to super();
  • eg. this constructor registers the source transformer input type as a String.

    public StringToStringArray() {
            super();
            this.registerSourceType(String.class);
        }

• the method: doTransform(Object src, String encoding) throws TransformerException
  • eg. this transformer converts a colon delimited string into an ArrayList

    public ArrayList doTransform(Object src, String encoding) throws TransformerException {
            
            StringTokenizer st = new StringTokenizer((String)src, ":");        
            ArrayList<String> stringout = new ArrayList<String>();
            String temp;
            for(int i = 0;st.hasMoreTokens(); i++){
                temp = st.nextToken();            
                stringout.add(temp);  
                
            }
                    
            return stringout;
        }

This method implementation can be set to return any class you want but the return class needs to be registered in the mule configuration - see below.

<transformers>		
	<transformer name="StringToStringArray"
		className="net.customware.enterprise.StringToStringArray"
		returnClass="java.util.ArrayList" />
</transformers>

Your transformer is now setup for use, you can use it by adding a transformers attribute to an enpoint in your mule descriptor. eg.

<mule-descriptor name="CreateRow"
	implementation="net.customware.enterprise.insertData">
	<inbound-router>
	<endpoint address="file:///data/inbound"
		transformers="FileToString StringToStringArray">
		<filter pattern="create.txt"
			className="org.mule.providers.file.filters.FilenameWildcardFilter" />
		<properties>
			<property name="pollingFrequency" value="5000" />
		</properties>
	</endpoint>
	</inbound-router>
	<outbound-router>
		<router	className="org.mule.routing.outbound.MulticastingRouter">
			<endpoint address="stream://System.out" />
		</router>
	</outbound-router>
</mule-descriptor>

This code is an alteration on the SFDC example. The toString() method will be called on the ArrayList to be printed out to System.out.