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Version: 4.14.8

Using Simple expressions

The Simple Expression Language is primarily intended for evaluating expressions or predicates. It also supports the File Expression Language. It only returns plain text, no xml.

Simple expressions are supported by the Set Header, Set Headers, Filter, Content Router and Split components.

tip

Simple expressions are also used to set or calculate with date and time. Please refer to our extensive reference Using time in Dovetail for more details.

Frequently used headers

These expressions are often used with the Set Header or Set Headers components.

OccurrenceHeader nameExpression (example)
Sets full message body to a header of your choice[Any]${bodyAs(String)}
Adds an attachment to emailContent-Dispositionattachment;filename=text.csv
Specifies the content type of an xml messageContent-Typetext/xml
Specifies the content type of a json messageContent-Typetext/json or application/json
Specifies the content type of a well formed e-mail in HTML formatContent-Typetext/html
Specifies the content type of an e-mail in plain text formatContent-Typetext/plain
Specifies the filename with a timestamp of the message exportCamelFileNameproducts_${date:now:yyyyMMdd_HHmmssSS}.xml
Specifies the filename without the original extension of the message exportCamelFileNamejohn_${file:onlyname.noext}.jpg
Replaces a character range in a value of a header with another range[Any]${header.HeaderName.replaceAll('A','B')}
Adds a random number to the value of an existing header[Any]${header.CamelFileName}_${random(100)}
Determines the length of the message body[Any]${bodyAs(String).length}
Trims the value to remove leading and trailing whitespaces and line breaks[Any]${header.HeaderName.trim()}
Gets the error message of the exchange[Any]${exchangeProperty.CamelExceptionCaught.getMessage()}
Add one to a header value if it's a number (i.e. 2 becomes 3)[Any]${header.CamelSplitIndex}++
Substract one from a header value if it's a number (i.e. 2 becomes 1)[Any]${header.CamelSplitIndex}--

Frequently used content filters

These expressions are often used in combination with the Filter and Content Router components.

OccurrenceExpression (example)
Allow messages to pass through if the header contains a specific character range${header.HeaderName} contains 'A'
Allow messages to pass through if the header contains the same specific character range as a flow property'${header.Authorization}' == '#{InboundAuthorizationCode}'
Allow messages to pass through if the length of the consumed file is larger than 0 kB${header.CamelFileLength} > 0
Allow messages to pass through if one header doesn't contain a specific character range and simultaneously another header doesn't contain a specific character range too${header.abc} not contains 'this' && ${header.def} not contains 'that'
Allow messages to pass through if the body contains a specific character range or another specific character range${bodyAs(String)} contains 'this' || ${bodyAs(String)} contains 'that'
Allow messages to pass through if a message header doesn't exist.${header.abc} == null
Allow messages to pass through if a message header has a specific value.${header.abc} == 'this'
Allow messages to pass through if a message header is empty.${header.abc} == ''
Allow messages to pass through if a message header is not empty.${header.abc} != ''
Allow messages to pass through if the body length is larger than 2 characters${bodyAs(String).length} > 2

Operator support

Things to keep in mind

  • To refer a header in the simple expression language use the notation as follows: ${header.headername}
  • Enclose a literal string in ' '
  • There must be spaces around the operator
  • Syntax: ${header} [operator] 'value'
  • Dovetail will automatically type convert the value type to the header type, so it is possible to for example, convert a string into a numeric so you can use > comparison for numeric values
  • Keep in mind that simple headers are not case sensitive. When a header variable named errormessage is set at an earlier stage, a header variable set to ERRORMESSAGE will update the previously set header variable errormessage and will not create a new header variable.

Frequently used operators

OperatorDescription
==Equals
>Greater than
>=Greater than or equals
<Less than
<=Less than or equals
!=Not equals
containsFor testing if contains in a string based value
not containsFor testing if not contains in a string based value
regexFor matching against a given regular expression pattern defined as a String value
not regexFor not matching against a given regular expression pattern defined as a String value
starts withFor testing if the left hand side string starts with the right hand string
ends withFor testing if the left hand side string ends with the right hand string
&&The logical AND operator is used to group two expressions
||The logical OR operator is used to group two expressions

Refer to Simple - Operator support for a full list of supported operators.

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Useful and original tips and tricks are always welcome. Let us know and we'll add them to this reference!