Simple Expression Language

The Simple Expression Language was a really simple language you can use, but has since grown more powerful. Its primarily intended for being a really small and simple language for evaluating Expression and Predicate without requiring any new dependencies or knowledge of XPath; so its ideal for testing in camel-core. Its ideal 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:

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.

Alternative syntax

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From Camel 2.5 onwards you can also use the alternative syntax which uses $simple{ } as placeholders.
This can be used in situations to avoid clashes when using for example Spring property placeholder together with Camel.

Configuring result type

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From Camel 2.8 onwards you can configure the result type of the Simple expression. For example to set the type as a java.lang.Boolean or a java.lang.Integer etc.

File language is now merged with Simple language

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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.

Simple Language Changes in Camel 2.9 onwards

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The Simple language have been improved from Camel 2.9 onwards to use a better syntax parser, which can do index precise error messages, so you know exactly what is wrong and where the problem is. For example if you have made a typo in one of the operators, then previously the parser would not be able to detect this, and cause the evaluation to be true. There is a few changes in the syntax which are no longer backwards compatible. When using Simple language as a Predicate then the literal text must be enclosed in either single or double quotes. For example: "${body} == 'Camel'". Notice how we have single quotes around the literal. The old style of using "body" and "header.foo" to refer to the message body and header is @deprecated, and its encouraged to always use ${ } tokens for the built-in functions.
The range operator now requires the range to be in single quote as well as shown: "${header.zip} between '30000..39999'".

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

Variable

Type

Description

camelId

String

Camel 2.10: the CamelContext name

camelContext.OGNL

Object

Camel 2.11: the CamelContext invoked using a Camel OGNL expression.

exchangeId

String

Camel 2.3: the exchange id

id

String

the input message id

body

Object

the input body

in.body

Object

the input body

body.OGNL

Object

Camel 2.3: the input body invoked using a Camel OGNL expression.

in.body.OGNL

Object

Camel 2.3: the input body invoked using a Camel OGNL expression.

bodyAs(type)

Type

Camel 2.3: Converts the body to the given type determined by its classname. The converted body can be null.

mandatoryBodyAs(type)

Type

Camel 2.5: Converts the body to the given type determined by its classname, and expects the body to be not null.

out.body

Object

the output body

header.foo

Object

refer to the input foo header

header[foo]

Object

Camel 2.9.2: refer to the input foo header

headers.foo

Object

refer to the input foo header

headers[foo]

Object

Camel 2.9.2: refer to the input foo header

in.header.foo

Object

refer to the input foo header

in.header[foo]

Object

Camel 2.9.2: refer to the input foo header

in.headers.foo

Object

refer to the input foo header

in.headers[foo]

Object

Camel 2.9.2: refer to the input foo header

header.foo[bar]

Object

Camel 2.3: regard input foo header as a map and perform lookup on the map with bar as key

in.header.foo[bar]

Object

Camel 2.3: regard input foo header as a map and perform lookup on the map with bar as key

in.headers.foo[bar]

Object

Camel 2.3: regard input foo header as a map and perform lookup on the map with bar as key

header.foo.OGNL

Object

Camel 2.3: refer to the input foo header and invoke its value using a Camel OGNL expression.

in.header.foo.OGNL

Object

Camel 2.3: refer to the input foo header and invoke its value using a Camel OGNL expression.

in.headers.foo.OGNL

Object

Camel 2.3: refer to the input foo header and invoke its value using a Camel OGNL expression.

out.header.foo

Object

refer to the out header foo

out.header[foo]

Object

Camel 2.9.2: refer to the out header foo

out.headers.foo

Object

refer to the out header foo

out.headers[foo]

Object

Camel 2.9.2: refer to the out header foo

headerAs(key,type)

Type

Camel 2.5: Converts the header to the given type determined by its classname

headers

Map

Camel 2.9: refer to the input headers

in.headers

Map

Camel 2.9: refer to the input headers

property.foo

Object

refer to the foo property on the exchange

property[foo]

Object

Camel 2.9.2: refer to the foo property on the exchange

property.foo.OGNL

Object

Camel 2.8: refer to the foo property on the exchange and invoke its value using a Camel OGNL expression.

sys.foo

String

refer to the system property

sysenv.foo

String

Camel 2.3: refer to the system environment

exception

Object

Camel 2.4: Refer to the exception object 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.

exception.OGNL

Object

Camel 2.4: Refer to the exchange exception invoked using a Camel OGNL expression object

exception.message

String

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.

exception.stacktrace

String

Camel 2.6. Refer to the exception.stracktrace 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

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

Invoking a bean expression using the Bean language. Specifying a method name you must use dot as separator. 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.

routeId

String

Camel 2.11: Returns the id of the current route the Exchange is being routed.

threadName

String

Camel 2.3: Returns the name of the current thread. Can be used for logging purpose.

ref:xxx

Object

Camel 2.6: To lookup a bean from the Registry with the given id.

type:name.field

Object

Camel 2.11: To refer to a type or field by its FQN name. To refer to a field you can append .FIELD_NAME. For example you can refer to the constant field from Exchange as: org.apache.camel.Exchange.FILE_NAME

.

null

 

Camel 2.12.3: represents a null

OGNL expression support

Available as of Camel 2.3

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Camel's OGNL support is for invoking methods only. You cannot access fields.
From Camel 2.11.1 onwards we added special support for accessing the length field of Java arrays.

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

Its 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.

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If the key has space, then you must enclose the key with quotes, for example 'foo bar':

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 ${ }.

Important

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There must be spaces around the operator.

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 are 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. From Camel 2.9 onwards the range values must be enclosed in single quotes.

not range

For matching if the left hand side is not within a range of values defined as numbers: from..to. From Camel 2.9 onwards the range values must be enclosed in single quotes.

And the following unary operators can be used:

Operator

Description

++

Camel 2.9: To increment a number by one. The left hand side must be a function, otherwise parsed as literal.

--

Camel 2.9: To decrement a number by one. The left hand side must be a function, otherwise parsed as literal.

\

Camel 2.9.3 to 2.10.x To escape a value, eg \$, to indicate a $ sign. Special: Use \n for new line, \t for tab, and \r for carriage return. Notice: Escaping is not supported using the File Language. Notice: From Camel 2.11 onwards the escape character is no longer support, but replaced with the following three special escaping.

\n

Camel 2.11: To use newline character.

\t

Camel 2.11: To use tab character.

\r

Camel 2.11: To use carriage return character.

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

Operator

Description

and

deprecated use && instead. The logical and operator is used to group two expressions.

or

deprecated use || instead. The logical or operator is used to group two expressions.

&&

Camel 2.9: The logical and operator is used to group two expressions.

||

Camel 2.9: The logical or operator is used to group two expressions.

Using and,or operators

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In Camel 2.4 or older the and or or can only be used once in a simple language expression. From Camel 2.5 onwards you can use these operators multiple times.

The syntax for AND is:

And the syntax for OR is:

Some examples:

Comparing with different types

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When you compare with different types such as String and int, then you have to take a bit care. Camel will use the type from the left hand side as 1st priority. And fallback to the right hand side type if both values couldn't be compared based on that type.
This means you can flip the values to enforce a specific type. Suppose the bar value above is a String. Then you can flip the equation:

which then ensures the int type is used as 1st priority.

This may change in the future if the Camel team improves the binary comparison operations to prefer numeric types over String based. It's most often the String type which causes problem when comparing with numbers.

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. Its based on the same syntax as Groovy.

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

Can be used in Spring XML

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As the Spring XML does not have all the power as the Java DSL with all its various builder methods, you have 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:

Using and / or

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

Camel 2.9 onwards

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Use && or || from Camel 2.9 onwards.

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 its lost in the deep blue sea (wink).

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 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.

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 its 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.

Its 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

And in a Content Based Router we can use the Simple language to refer to this enum, to check the message which enum it matches.

Using new lines or tabs in XML DSLs

Available as of Camel 2.9.3

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

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.

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