Get and format yesterday's date in Camel's expression language

Well, not directly. The date: object in the simple language can only grab the current time (or some time value you have placed inside a header - which you could do in java or similar.

But you could also do like this. Create a class:

public class YesterdayBean{
    public String getYesterday(){
        Calendar cal = Calendar.getInstance();
        DateFormat dateFormat = new SimpleDateFormat("dd-MM-yyyy");
        cal.add(Calendar.DATE, -1); 
        return dateFormat.format(cal.getTime());  
    }
}

Wire it to your Camel (or spring, if you use that) registry as a bean. If you are unsure how to do that, lookup registry and the "using" section of bean.

Let's say you named the bean "yesterday" in the registry, with spring:

<bean id="yesterday" class="some.package.YesterdayBean"/>

then just use it with the file component.

.to("file:fo/bar?fileName=${bean:yesterday}")

If this is just one single place you need it, and you are using Java DSL, you could also just pre-create the date with a java processor and place it in a header.

Like this:

from("file:somewhere")
        .process(new Processor(){
            public void process(Exchange ex){
                Calendar cal = Calendar.getInstance();
                cal.add(Calendar.DATE, -1); 
                ex.getIn().setHeader("yesterday",cal.getTime());
            }
        })
       .to("file:target?fileName=${date:header.yesterday:dd-MM-yyyy}");
}

I was curious about this and sought out some help from the camel mailing list. You can in fact do what you're asking with inline scripts, such as groovy. See here.

I got this to work for me:

<camelContext id="contextname">
    <route id="routename">
        <from uri="file://\temp\?fileName=#myGroovyExp" />
        <split>
            <tokenize token="(?=MSH\|)" regex="true" />
            <to uri="bean:filePickupByDateTest?method=test" />
        </split>
    </route>
</camelContext>

<spring:bean id="myGroovyExp" class="org.apache.camel.model.language.GroovyExpression">
    <spring:constructor-arg index="0" value="new Date().previous().format('MMddyy') + 'pa'" />
</spring:bean>

Where my file names are yesterday: MMddyypa

You would just need to change your script body to:

new Date().previous().format('dd-MM-yyyy')

You need camel-groovy (or whatever script lang you use) on your path of course.