The simple language provides various elementary expressions that return different parts of a message exchange. For example, the expression, simple("header.timeOfDay"), would return the contents of a header called timeOfDay from the incoming message.

You can use the simple language to define string expressions, based on the variables provided. For example, you can use a variable of the form, in.header.HeaderName, to obtain the value of the HeaderName header, as follows:

simple("in.header.foo")

You can embed simple variables in a string expression, but in this case you must enclose the variables in ${ } (when you reference a variable on its own, the enclosing braces are optional)—for example:

simple("Received a message from ${in.header.user} on $(date:in.header.date:yyyyMMdd}.")

As well as providing variables that access all of the different parts of an exchange (see Table 17.1), the simple language also provides special variables for formatting dates, date:command:pattern, and for calling bean methods, bean:beanRef. For example, you can use the date and the bean variables as follows:

simple("Todays date is ${date:now:yyyyMMdd}")
simple("The order type is ${bean:orderService?method=getOrderType}")

The Object Graph Navigation Language (OGNL) is a notation for invoking bean methods in a chain-like fashion. If a message body contains a Java bean, you can easily access its bean properties using OGNL notation. For example, if the message body is a Java object with a getAddress() accessor, you can access the Address object and the Address object's properties as follows:

simple("${body.address}")
simple("${body.address.street}")
simple("${body.address.zip}")
simple("${body.address.city}")

Where the notation, ${body.address.street}, is shorthand for ${body.getAddress.getStreet}.

You can use the null-safe operator, ?., to avoid encountering null-pointer exceptions, in case the body does not have an address. For example:

simple("${body?.address?.street}")

If the body is a java.util.Map type, you can look up a value in the map with the key, foo, using the following notation:

simple("${body[foo]?.name}")

You can also use square brackets notation, [k], to access the elements of a list. For example:

simple("${body.address.lines[0]}")
simple("${body.address.lines[1]}")
simple("${body.address.lines[2]}")

The last keyword returns the index of the last element of a list. For example, you can access the second last element of a list, as follows:

simple("${body.address.lines[last-1]}")