Page edited by Claus Ibsen

Simple _expression_ Language

The Simple _expression_ Language is a really simple language you can use. Its primarily intended for being a really small and simple language for testing without requiring any new dependencies or knowledge of XPath; so its ideal for testing in camel-core. However for real world use cases you are generally recommended to choose a more expressive and powerful language such as:

Bean Language
EL
OGNL
one of the supported Scripting Languages

The simple language uses ${body} placeholders for complex expressions where the _expression_ contains constant literals. The ${ } placeholders can be omitted if the _expression_ is only the token itself.

To get the body of the in message: "body", or "in.body" or "${body}".

A complex _expression_ must use ${ } placeholders, such as: "Hello ${in.header.name} how are you?".

You can have multiple tokens in the same _expression_: "Hello ${in.header.name} this is ${in.header.me} speaking".
However you can not nest tokens (i.e. having another ${ } placeholder in an existing, is not allowed).

File language is now merged with Simple language

From Camel 2.2 onwards, the File Language is now merged with Simple language which means you can use all the file syntax directly within the simple language.

Variables

Variable	Type	Description
id	String	the input message id
body	Object	the input body
in.body	Object	the input body
out.body	Object	the output body
header.foo	Object	refer to the input foo header
headers.foo	Object	refer to the input foo header
in.header.foo	Object	refer to the input foo header
in.headers.foo	Object	refer to the input foo header
out.header.foo	Object	refer to the out header foo
out.headers.foo	Object	refer to the out header foo
property.foo	Object	refer to the foo property on the exchange
sys.foo	String	refer to the system property
exception.message	String	Camel 2.0. Refer to the exception.message on the exchange, is null if no exception set on exchange. Will fallback and grab caught exceptions (`Exchange.EXCEPTION_CAUGHT`) if the Exchange has any.
date:command:pattern	String	Camel 1.5. Date formatting using the `java.text.SimpleDataFormat` patterns. Supported commands are: now for current timestamp, in.header.xxx or header.xxx to use the Date object in the IN header with the key xxx. out.header.xxx to use the Date object in the OUT header with the key xxx.
bean:bean _expression_	Object	Camel 1.5. Invoking a bean _expression_ using the Bean language. Specifying a method name you must use dot as separator. In Camel 2.0 we also support the ?method=methodname syntax that is used by the Bean component.
properties:locations:key	String	Camel 2.3: Lookup a property with the given key. The `locations` option is optional. See more at Using PropertyPlaceholder.

Operator support

Available as of Camel 2.0
We added a basic set of operators supported in the simple language in Camel 2.0. The parser is limited to only support a single operator.

To enable it the left value must be enclosed in ${ }. The syntax is:

${leftValue} OP rightValue

Where the rightValue can be a String literal enclosed in ' ', null, a constant value or another _expression_ enclosed in ${ }.
Camel will automatically type convert the rightValue type to the leftValue type, so its able to eg. convert a string into a numeric so you can use > comparison for numeric values.


The following operators is supported:


 Operator 
 Description 


 == 
 equals 


 > 
 greater than 


 >= 
 greater than or equals 


 < 
 less than 


 <= 
 less than or equals 


 != 
 not equals 


 contains 
 For testing if contains in a string based value 


 not contains 
 For testing if not contains in a string based value 


 regex 
 For matching against a given regular _expression_ pattern defined as a String value 


 not regex 
 For not matching against a given regular _expression_ pattern defined as a String value 


 in 
 For matching if in a set of values, each element must be separated by comma. 


 not in 
 For matching if not in a set of values, each element must be separated by comma. 


 is 
 For matching if the left hand side type is an instanceof the value. 


 not is 
 For matching if the left hand side type is not an instanceof the value. 


 range 
 For matching if the left hand side is within a range of values defined as numbers: from..to 


 not range 
 For matching if the left hand side is not within a range of values defined as numbers: from..to 



And the following operators can be used to group expressions:


 Operator 
 Description 


 and 
 and is used to group two expressions 


 or 
 or is used to group two expressions 



Notice: Currently and or or can only be used once in a simple language _expression_. This might change in the future.

The syntax for AND is:

${leftValue} OP rightValue and ${leftValue} OP rightValue 



And the syntax for OR is:

${leftValue} OP rightValue or ${leftValue} OP rightValue 



Some examples:

simple("${in.header.foo} == 'foo'")

// ' ' can be omitted
simple("${in.header.foo} == foo")

// here Camel will type convert '100' into the type of in.header.bar and if its an Integer '100' will also be converter to an Integer
simple("${in.header.bar} == '100'")

simple("${in.header.bar} == 100")

// 100 will be converter to the type of in.header.bar so we can do > comparison
simple("${in.header.bar} > 100")

// testing for null
simple("${in.header.baz} == null")

// testing for not null
simple("${in.header.baz} != null")



And a bit more advanced example where the right value is another _expression_

simple("${in.header.date} == ${date:now:yyyyMMdd}")

simple("${in.header.type} == ${bean:orderService?method=getOrderType}")



And an example with contains, testing if the title contains the word Camel

simple("${in.header.title} contains 'Camel'")



And an example with regex, testing if the number header is a 4 digit value:

simple("${in.header.number} regex '\d{4}'")



And finally an example if the header equals any of the values in the list. Each element must be separated by comma, and no space around.

This also works for numbers etc, as Camel will convert each element into the type of the left hand side.

simple("${in.header.type} in 'gold,silver'")



And for all the last 3 we also support the negate test using not:

simple("${in.header.type} not in 'gold,silver'")



And you can test for if the type is a certain instance, eg for instance a String

simple("${in.header.type} is 'java.lang.String'")


We have added a shorthand for all java.lang types so you can write it as:

simple("${in.header.type} is String")



Ranges is also supported. The range interval requires numbers and both from and end is inclusive. For instance to test whether a value is between 100 and 199:

simple("${in.header.number} range 100..199")


Notice we use .. in the range without spaces. Its based on the same syntax as Groovy.

Can be used in Spring XML
As the Spring XML does not have all the power as the Java DSL with all its various builder methods, you had to resort to use some other languages

for testing with simple operators. Now you can do this with the simple language. In the sample below we want to test if the header is a widget order: 

    <from uri="seda:orders">
       <filter>
           <simple>${in.header.type} == 'widget'</simple>
           <to uri="bean:orderService?method=handleWidget"/>
       </filter>
    </from>

 

Using and / or
If you have two expressions you can combine them with the and or or operator.

For instance:

simple("${in.header.title} contains 'Camel' and ${in.header.type' == 'gold'")



And of course the or is also supported. The sample example would be:

simple("${in.header.title} contains 'Camel' or ${in.header.type' == 'gold'")



Notice: Currently and or or can only be used once in a simple language _expression_. This might change in the future.

So you cannot do:

simple("${in.header.title} contains 'Camel' and ${in.header.type' == 'gold' and ${in.header.number} range 100..200")



Samples
In the Spring XML sample below we filter based on a header value:

    <from uri="seda:orders">
       <filter>
           <simple>in.header.foo</simple>
           <to uri="mock:fooOrders"/>
       </filter>
    </from>



The Simple language can be used for the predicate test above in the Message Filter pattern, where we test if the in message has a foo header (a header with the key foo exists). If the _expression_ evaluates to true then the message is routed to the mock:foo endpoint, otherwise its lost in the deep blue sea .

The same example in Java DSL:

    from("seda:orders")
        .filter().simple("in.header.foo").to("seda:fooOrders");



You can also use the simple language for simple text concatenations such as:

   from("direct:hello").transform().simple("Hello ${in.header.user} how are you?").to("mock:reply");


Notice that we must use ${ } placeholders in the _expression_ now to let Camel be able to parse it correctly. 

And this sample uses the date command to output current date.

   from("direct:hello").transform().simple("The today is ${date:now:yyyyMMdd} and its a great day.").to("mock:reply");



And in the sample below we invoke the bean language to invoke a method on a bean to be included in the returned string:

   from("direct:order").transform().simple("OrderId: ${bean:orderIdGenerator}").to("mock:reply");


Where orderIdGenerator is the id of the bean registered in the Registry. If using Spring then its the Spring bean id.

If we want to declare which method to invoke on the order id generator bean we must prepend .method name such as below where we invoke the generateId method.

   from("direct:order").transform().simple("OrderId: ${bean:orderIdGenerator.generateId}").to("mock:reply");



And in Camel 2.0 we can use the ?method=methodname option that we are familiar with the Bean component itself:

   from("direct:order").transform().simple("OrderId: ${bean:orderIdGenerator?method=generateId}").to("mock:reply");



Dependencies
The Bean language is part of camel-core.

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[CONF] Apache Camel > Simple

Simple

Page edited by Claus Ibsen

Simple _expression_ Language

Variables

Operator support

Using and / or

Samples

Dependencies

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