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The class is very simple and we could easily create unit tests for it to verify that it works as expected. So what we want now is to let Camel invoke this class and its generateFilename with the input parameters and use the output as the filename. Pheeeww is this really possible out-of-the-box in Camel? Yes it is. So lets get on with the show. We have the code that computes the filename, we just need to call it from our route using the Bean language:

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    public void configure() throws Exception {
        from("direct:start")
            // set the filename using the bean language and call the FilenameGenerator class.
            // the 2nd null parameter is optional methodname, to be used to avoid ambiguity.
            // if not provided Camel will try to figure out the best method to invoke, as we
            // only have one method this is very simple
            .setHeader(FileComponent.HEADER_FILE_NAME, BeanLanguage.bean(FilenameGenerator.class, null))
            .to("velocity:MailBody.vm")
            .to("file://target/subfolder");
    }

Notice that we use the bean language where we supply the class with our bean to invoke. Camel will instantiate an instance of the class and invoke the suited method. For completeness and ease of code readability we add the methodname as the 2nd parameter

            .setHeader(FileComponent.HEADER_FILE_NAME, BeanLanguage.bean(FilenameGenerator.class, "generateFilename"))

Then other developers can understand what the parameter is, instead of null.
Notice: The Bean language is far more advanced that what is shown here. We will get back to this in later parts. For now this is a solution we can use.

Now we have a nice solution, but as a sidetrack I want to demonstrate the Camel has other languages out-of-the-box, and that scripting language is a first class citizen in Camel where it etc. can be used in content based routing. However we want it to be used for the filename generation.

Using a script language to set the filename

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import static org.apache.camel.language.ognl.OgnlExpression.ognl;
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    .setHeader(FileComponent.HEADER_FILE_NAME, ognl("'mail-incident-' + request.body.incidentId + '.txt'"))

Notice the import static also applies for all the other languages, such as the Bean language we used previously.

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