Simple Expression Language

The Simple Expression Language was a really simple language when it was created, but has since grown more powerful. It is primarily intended for being a really small and simple language for evaluating Expressions and Predicates without requiring any new dependencies or knowledge of XPath; so it is ideal for testing in camel-core. The idea was to cover 95% of the common use cases when you need a little bit of expression based script in your Camel routes.

However for much more complex use cases you are generally recommended to choose a more expressive and powerful language such as:

• SpEL
• Mvel
• Groovy
• JavaScript
• 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 functions in the same expression: "Hello ${in.header.name} this is ${in.header.me} speaking".
However you can not nest functions in Camel 2.8.x or older (i.e. having another ${ } placeholder in an existing, is not allowed).
From Camel 2.9 onwards you can nest functions.

Variables

OGNL expression support

Available as of Camel 2.3

The Simple and Bean language now supports a Camel OGNL notation for invoking beans in a chain like fashion.
Suppose the Message IN body contains a POJO which has a getAddress() method.

Then you can use Camel OGNL notation to access the address object:

Camel understands the shorthand names for getters, but you can invoke any method or use the real name such as:

You can also use the null safe operator (?.) to avoid NPE if for example the body does NOT have an address

It is also possible to index in Map or List types, so you can do:

To assume the body is Map based and lookup the value with foo as key, and invoke the getName method on that value.

You can access the Map or List objects directly using their key name (with or without dots) :

Suppose there was no value with the key foo then you can use the null safe operator to avoid the NPE as shown:

You can also access List types, for example to get lines from the address you can do:

There is a special last keyword which can be used to get the last value from a list.

And to get the 2nd last you can subtract a number, so we can use last-1 to indicate this:

And the 3rd last is of course:

And you can call the size method on the list with

From Camel 2.11.1 onwards we added support for the length field for Java arrays as well, eg:

And yes you can combine this with the operator support as shown below:

Operator support

The parser is limited to only support a single operator.

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

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 it is able to eg. convert a string into a numeric so you can use > comparison for numeric values.

The following operators are supported:

And the following unary operators can be used:

And the following logical operators can be used to group expressions:

The syntax for AND is:

And the syntax for OR is:

Some examples:

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

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

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

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.

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

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

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

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

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

From Camel 2.9 onwards the range value must be in single quotes

Using and / or

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

For instance:

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

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:

Samples

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

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:fooOrders endpoint, otherwise it is lost in the deep blue sea .

The same example in Java DSL:

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

Notice that we must use ${ } placeholders in the expression now to allow Camel to parse it correctly.

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

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

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

We can use the ?method=methodname option that we are familiar with the Bean component itself:

And from Camel 2.3 onwards you can also convert the body to a given type, for example to ensure that it is a String you can do:

There are a few types which have a shorthand notation, so we can use String instead of java.lang.String. These are: byte[], String, Integer, Long. All other types must use their FQN name, e.g. org.w3c.dom.Document.

It is also possible to lookup a value from a header Map in Camel 2.3 onwards:

In the code above we lookup the header with name type and regard it as a java.util.Map and we then lookup with the key gold and return the value.
If the header is not convertible to Map an exception is thrown. If the header with name type does not exist null is returned.

From Camel 2.9 onwards you can nest functions, such as shown below:

Referring to constants or enums

Available as of Camel 2.11

Suppose you have an enum for customers

Using new lines or tabs in XML DSLs

Available as of Camel 2.9.3

From Camel 2.9.3 onwards it is easier to specify new lines or tabs in XML DSLs as you can escape the value now

Leading and trailing whitespace handling

Available as of Camel 2.10.0

From Camel 2.10.0 onwards, the trim attribute of the expression can be used to control whether the leading and trailing whitespace characters are removed or preserved. The default value is true, which removes the whitespace characters.

Setting result type

Available as of Camel 2.8

You can now provide a result type to the Simple expression, which means the result of the evaluation will be converted to the desired type. This is most useable to define types such as booleans, integers, etc.

For example to set a header as a boolean type you can do:

And in XML DSL

Changing function start and end tokens

Available as of Camel 2.9.1

You can configure the function start and end tokens - ${ } using the setters changeFunctionStartToken and changeFunctionEndToken on SimpleLanguage, using Java code. From Spring XML you can define a <bean> tag with the new changed tokens in the properties as shown below:

In the example above we use [ ] as the changed tokens.

Notice by changing the start/end token you change those in all the Camel applications which share the same camel-core on their classpath.
For example in an OSGi server this may affect many applications, where as a Web Application as a WAR file it only affects the Web Application.

Loading script from external resource

Available as of Camel 2.11

You can externalize the script and have Camel load it from a resource such as "classpath:", "file:", or "http:".
This is done using the following syntax: "resource:scheme:location", eg to refer to a file on the classpath you can do:

Setting Spring beans to Exchange properties

Available as of Camel 2.6

You can set a spring bean into an exchange property as shown below:

Dependencies

The Simple language is part of camel-core.