Simple
Since Camel 1.1
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 very small and simple language for evaluating Expression or Predicate without requiring any new dependencies or knowledge of other scripting languages such as Groovy.
The simple language is designed with intent to cover almost all the common use cases when little need for scripting in your Camel routes.
However, for much more complex use cases, then a more powerful language is recommended such as:
| The simple language requires |
The simple language uses ${body} placeholders for complex expressions or functions.
| See also the CSimple language which is compiled. |
| Alternative syntax You can also use the alternative syntax which uses |
Variables
| Variable | Type | Description |
|---|---|---|
camelId | String | the CamelContext name |
camelContext.OGNL | Object | the CamelContext invoked using a Camel OGNL expression. |
exchange | Exchange | the Exchange |
exchange.OGNL | Object | the Exchange invoked using a Camel OGNL expression. |
exchangeId | String | the exchange id |
id | String | the message id |
messageTimestamp | String | the message timestamp (millis since epoc) that this message originates from. Some systems like JMS, Kafka, AWS have a timestamp on the event/message that Camel received. This method returns the timestamp if a timestamp exists. The message timestamp and exchange created are different. An exchange always has a created timestamp which is the local timestamp when Camel created the exchange. The message timestamp is only available in some Camel components when the consumer is able to extract the timestamp from the source event. If the message has no timestamp, then 0 is returned. |
body | Object | the body |
body.OGNL | Object | the body invoked using a Camel OGNL expression. |
bodyAs(type) | Type | Converts the body to the given type determined by its classname. The converted body can be null. |
bodyAs(type).OGNL | Object | Converts the body to the given type determined by its classname and then invoke methods using a Camel OGNL expression. The converted body can be null. |
bodyOneLine | String | Converts the body to a String and removes all line-breaks, so the string is in one line. |
prettyBody | String | Converts the body to a String, and attempts to pretty print if JSon or XML; otherwise the body is returned as the String value. |
originalBody | Object | The original incoming body (only available if allowUseOriginalMessage=true). |
mandatoryBodyAs(type) | Type | Converts the body to the given type determined by its classname, and expects the body to be not null. |
mandatoryBodyAs(type).OGNL | Object | Converts the body to the given type determined by its classname and then invoke methods using a Camel OGNL expression. |
header.foo | Object | refer to the foo header |
header[foo] | Object | refer to the foo header |
headers.foo | Object | refer to the foo header |
headers:foo | Object | refer to the foo header |
headers[foo] | Object | refer to the foo header |
header.foo[bar] | Object | regard foo header as a map and perform lookup on the map with bar as the key |
header.foo.OGNL | Object | refer to the foo header and invoke its value using a Camel OGNL expression. |
headerAs(key,type) | Type | converts the header to the given type determined by its classname |
headers | Map | refer to the headers |
variable.foo | Object | refer to the foo variable |
variable[foo] | Object | refer to the foo variable |
variable.foo.OGNL | Object | refer to the foo variable and invoke its value using a Camel OGNL expression. |
variableAs(key,type) | Type | converts the variable to the given type determined by its classname |
variables | Map | refer to the variables |
exchangeProperty.foo | Object | refer to the foo property on the exchange |
exchangeProperty[foo] | Object | refer to the foo property on the exchange |
exchangeProperty.foo.OGNL | Object | refer to the foo property on the exchange and invoke its value using a Camel OGNL expression. |
messageAs(type) | Type | Converts the message to the given type determined by its classname. The converted message can be null. |
messageAs(type).OGNL | Object | Converts the message to the given type determined by its classname and then invoke methods using a Camel OGNL expression. The converted message can be null. |
sys.foo | String | refer to the JVM system property |
sysenv.foo | String | refer to the system environment variable |
env.foo | String | refer to the system environment variable |
exception | Object | refer to the exception object on the exchange, is null if no exception set on exchange. Will fall back and grab caught exceptions ( |
exception.OGNL | Object | refer to the exchange exception invoked using a Camel OGNL expression object |
exception.message | String | refer to the |
exception.stacktrace | String | refer to the exception.stracktrace on the exchange, is null if no exception set on exchange. Will fall back and grab caught exceptions ( |
date:_command_ | Date | evaluates to a Date object. Supported commands are: |
date:_command:pattern_ | String | Date formatting using |
date-with-timezone:_command:timezone:pattern_ | String | Date formatting using |
bean:_bean expression_ | Object | Invoking a bean expression using the Bean language. Specifying a method name, you must use dot as the separator. We also support the ?method=methodname syntax that is used by the Bean component. Camel will by default lookup a bean by the given name. However, if you need to refer to a bean class (such as calling a static method), then you can prefix with the type, such as |
properties:key:default | String | Lookup a property with the given key. If the key does not exist nor has a value, then an optional default value can be specified. |
propertiesExist:key | String | Checks whether a property placeholder with the given key exists or not. The result can be negated by prefixing the key with |
fromRouteId | String | Returns the original route id where this exchange was created. |
routeId | String | Returns the route id of the current route the Exchange is being routed. |
routeGroup | String | Returns the route group of the current route the Exchange is being routed. Not all routes have a group assigned, so this may be null. |
stepId | String | Returns the id of the current step the Exchange is being routed. |
threadId | String | Returns the id of the current thread. Can be used for logging. |
threadName | String | Returns the name of the current thread. Can be used for logging. |
hostname | String | Returns the local hostname (may be empty if not possible to resolve). |
ref:xxx | Object | To look up a bean from the Registry with the given id. |
type:name.field | Object | 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: |
empty(type) | depends on parameter | Creates a new empty object of the type given as parameter. The type-parameter-Strings are case-insensitive.
|
null | null | represents a null |
random(value) | Integer | returns a random Integer between 0 (included) and value (excluded) |
random(min,max) | Integer | returns a random Integer between min (included) and max (excluded) |
replace(from,to) | String | replace all the string values in the message body. To make it easier to replace single and double quotes, then you can use XML escaped values |
replace(from,to,exp) | String | replace all the string values in the given expression. To make it easier to replace single and double quotes, then you can use XML escaped values |
substring(num1) | String | returns a substring of the message body. If the number is positive, then the returned string is clipped from the beginning. If the number is negative, then the returned string is clipped from the ending. |
substring(num1,num2) | String | returns a substring of the message body. If the number is positive, then the returned string is clipped from the beginning. If the number is negative, then the returned string is clipped from the ending. |
substring(num1,num2,exp) | String | replace all the string values in the given expression. If the number is positive, then the returned string is clipped from the beginning. If the number is negative, then the returned string is clipped from the ending. |
collate(group) | List | The collate function iterates the message body and groups the data into sub lists of specified size. This can be used with the Splitter EIP to split a message body and group/batch the split sub message into a group of N sub lists. This method works similar to the collate method in Groovy. |
skip(number) | Iterator | The skip function iterates the message body and skips the first number of items. This can be used with the Splitter EIP to split a message body and skip the first N number of items. |
join(separator,prefix,exp) | String | The join function iterates the message body (by default) and joins the data into a string. The separator is by default a comma. The prefix is optional. The join uses the message body as source by default. It is possible to refer to another source (simple language) such as a header via the exp parameter. For example |
messageHistory | String | The message history of the current exchange - how it has been routed. This is similar to the route stack-trace message history the error handler logs in case of an unhandled exception. |
messageHistory(false) | String | As messageHistory but without the exchange details (only includes the route stack-trace). This can be used if you do not want to log sensitive data from the message itself. |
uuid(type) | String | Returns a UUID using the Camel |
hash(exp,algorithm) | String | Returns a hashed value (string in hex decimal) using JDK MessageDigest. The algorithm can be SHA-256 (default) or SHA3-256. |
jsonpath(exp) | Object | When working with JSon data, then this allows using the JsonPath language, for example, to extract data from the message body (in JSon format). This requires having camel-jsonpath JAR on the classpath. |
jsonpath(input,exp) | Object | When working with JSon data, then this allows using the JsonPath language, for example, to extract data from the message body (in JSon format). This requires having camel-jsonpath JAR on the classpath. For input, you can choose |
jq(exp) | Object | When working with JSon data, then this allows using the JQ language, for example, to extract data from the message body (in JSon format). This requires having camel-jq JAR on the classpath. |
jq(input,exp) | Object | When working with JSon data, then this allows using the JQ language, for example, to extract data from the message body (in JSon format). This requires having camel-jq JAR on the classpath. For input, you can choose |
xpath(exp) | Object | When working with XML data, then this allows using the XPath language, for example, to extract data from the message body (in XML format). This requires having camel-xpath JAR on the classpath. |
xpath(input,exp) | Object | When working with XML data, then this allows using the XPath language, for example, to extract data from the message body (in XML format). This requires having camel-xpath JAR on the classpath. For input you can choose |
pretty(exp) | String | Converts the inlined expression to a String, and attempts to pretty print if JSon or XML, otherwise the expression is returned as the String value. |
OGNL expression support
When using OGNL then camel-bean JAR is required to be on the classpath.
Camel’s OGNL support is for invoking methods only. You cannot access fields. Camel support accessing the length field of Java arrays.
The Simple and Bean languages now support 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:
simple("${body.address}")
simple("${body.address.street}")
simple("${body.address.zip}")Camel understands the shorthand names for getters, but you can invoke any method or use the real name such as:
simple("${body.address}")
simple("${body.getAddress.getStreet}")
simple("${body.address.getZip}")
simple("${body.doSomething}")You can also use the null safe operator (?.) to avoid NPE if, for example, the body does NOT have an address
simple("${body?.address?.street}")It is also possible to index in Map or List types, so you can do:
simple("${body[foo].name}")To assume the body is Map based and look up the value with foo as key, and invoke the getName method on that value.
If the key has space, then you must enclose the key with quotes, for example, 'foo bar':
simple("${body['foo bar'].name}")You can access the Map or List objects directly using their key name (with or without dots) :
simple("${body[foo]}")
simple("${body[this.is.foo]}")Suppose there was no value with the key foo then you can use the null safe operator to avoid the NPE as shown:
simple("${body[foo]?.name}")You can also access List types, for example, to get lines from the address you can do:
simple("${body.address.lines[0]}")
simple("${body.address.lines[1]}")
simple("${body.address.lines[2]}")There is a special last keyword which can be used to get the last value from a list.
simple("${body.address.lines[last]}")And to get the 2nd last you can subtract a number, so we can use last-1 to indicate this:
simple("${body.address.lines[last-1]}")And the third last is, of course:
simple("${body.address.lines[last-2]}")And you can call the size method on the list with
simple("${body.address.lines.size}")Camel supports the length field for Java arrays as well, e.g.:
String[] lines = new String[]{"foo", "bar", "cat"};
exchange.getIn().setBody(lines);
simple("There are ${body.length} lines")And yes, you can combine this with the operator support as shown below:
simple("${body.address.zip} > 1000")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:
${leftValue} OP rightValue Where the rightValue can be a String literal enclosed in ' ', null, a constant value or another expression enclosed in ${ }.
| There must be spaces around the operator. |
Camel will automatically type convert the rightValue type to the leftValue type, so it is able to e.g., convert a string into a numeric, so you can use > comparison for numeric values.
The following operators are supported:
| Operator | Description |
|---|---|
== | equals |
=~ | equals ignore case (will ignore case when comparing String values) |
> | greater than |
>= | greater than or equals |
< | less than |
<= | less than or equals |
!= | not equals |
!=~ | not equals ignore case (will ignore case when comparing String values) |
contains | For testing if contains in a string-based value |
!contains | For testing if it does not contain in a string-based value |
~~ | For testing if contains by ignoring case sensitivity in a string-based value |
!~~ | For testing if it does not contain by ignoring case sensitivity in a string-based value |
regex | For matching against a given regular expression pattern defined as a String value |
!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. If you want to include an empty value, then it must be defined using double comma, e.g. |
!in | For matching if not in a set of values, each element must be separated by comma. If you want to include an empty value, then it must be defined using double comma, e.g. |
is | For matching if the left-hand side type is an instance of the value. |
!is | For matching if the left-hand side type is not an instance of the value. |
range | For matching if the left-hand side is within a range of values defined as numbers: |
!range | For matching if the left-hand side is not within a range of values defined as numbers: |
startsWith | For testing if the left-hand side string starts with the right-hand string. |
starts with | Same as the startsWith operator. |
endsWith | For testing if the left-hand side string ends with the right-hand string. |
ends with | Same as the endsWith operator. |
And the following unary operators can be used:
| Operator | Description |
|---|---|
++ | To increment a number by one. The left-hand side must be a function, otherwise parsed as literal. |
— | To decrement a number by one. The left-hand side must be a function, otherwise parsed as literal. |
\n | To use newline character. |
\t | To use tab character. |
\r | To use carriage return character. |
\} | To use the |
And the following logical operators can be used to group expressions:
| Operator | Description |
|---|---|
&& | The logical and operator is used to group two expressions. |
|| | The logical or operator is used to group two expressions. |
The syntax for AND is:
${leftValue} OP rightValue && ${leftValue} OP rightValueAnd the syntax for OR is:
${leftValue} OP rightValue || ${leftValue} OP rightValueSome examples:
// exact equals match
simple("${header.foo} == 'foo'")
// ignore case when comparing, so if the header has value FOO, this will match
simple("${header.foo} =~ 'foo'")
// here Camel will type convert '100' into the type of header.bar and if it is an Integer '100' will also be converter to an Integer
simple("${header.bar} == '100'")
simple("${header.bar} == 100")
// 100 will be converter to the type of header.bar, so we can do > comparison
simple("${header.bar} > 100")
// if the value of header.bar was 100, value returned will be 101. header.bar itself will not be changed.
simple("${header.bar}++")Comparing with different types
When you compare with different types such as String and int, then you have to take a bit of care. Camel will use the type from the left-hand side as first 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:
simple("100 < ${header.bar}")which then ensures the int type is used as first priority.
This may change in the future if the Camel team improves the binary comparison operations to prefer numeric types to String-based. It’s most often the String type which causes problems when comparing with numbers.
// testing for null
simple("${header.baz} == null")
// testing for not null
simple("${header.baz} != null")And a bit more advanced example where the right value is another expression
simple("${header.date} == ${date:now:yyyyMMdd}")
simple("${header.type} == ${bean:orderService?method=getOrderType}")And an example with contains, testing if the title contains the word Camel
simple("${header.title} contains 'Camel'")And an example with regex, testing if the number header is a 4-digit value:
simple("${header.number} regex '\\d{4}'")And finally an example if the header equals any of the values in the list. Each element must be separated by comma, and no space around.
This also works for numbers etc., as Camel will convert each element into the type of the left-hand side.
simple("${header.type} in 'gold,silver'")And for all the last 3, we also support the negate test using not:
simple("${header.type} !in 'gold,silver'")And you can test if the type is a certain instance, e.g., for instance a String
simple("${header.type} is 'java.lang.String'")We have added a shorthand for all java.lang types, so you can write it as:
simple("${header.type} is 'String'")Ranges are also supported. The range interval requires numbers and both from and end are inclusive. For instance, to test whether a value is between 100 and 199:
simple("${header.number} range 100..199")Notice we use .. in the range without spaces. It is based on the same syntax as Groovy.
simple("${header.number} range '100..199'")As the XML DSL does not have all the power as the Java DSL with all its various builder methods, you have to resort to using some other languages for testing with simple operators. Now you can do this with the simple language. In the sample below, we want to test it if the header is a widget order:
<from uri="seda:orders">
<filter>
<simple>${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 && or || operator.
For instance:
simple("${header.title} contains 'Camel' && ${header.type'} == 'gold'")And of course the || is also supported. The sample would be:
simple("${header.title} contains 'Camel' || ${header.type'} == 'gold'")Examples
In the XML DSL sample below, we filter based on a header value:
<from uri="seda:orders">
<filter>
<simple>${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:fooOrders endpoint, otherwise the message is dropped.
The same example in Java DSL:
from("seda:orders")
.filter().simple("${header.foo}")
.to("seda:fooOrders");You can also use the simple language for simple text concatenations such as:
from("direct:hello")
.transform().simple("Hello ${header.user} how are you?")
.to("mock:reply");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.
from("direct:hello")
.transform().simple("The today is ${date:now:yyyyMMdd} and it is 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 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.
from("direct:order")
.transform().simple("OrderId: ${bean:orderIdGenerator.generateId}")
.to("mock:reply");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");You can also convert the body to a given type, for example, to ensure that it is a String you can do:
<transform>
<simple>Hello ${bodyAs(String)} how are you?</simple>
</transform>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 look up a value from a header Map:
<transform>
<simple>The gold value is ${header.type[gold]}</simple>
</transform>In the code above we look up the header with name type and regard it as a java.util.Map and we then look up with the key gold and return the value. If the header is not convertible to Map, an exception is thrown. If the header with name type does not exist null is returned.
You can nest functions, such as shown below:
<setHeader name="myHeader">
<simple>${properties:${header.someKey}}</simple>
</setHeader>Substring
You can use the substring function to more easily clip the message body. For example if the message body contains the following 10 letters ABCDEFGHIJ then:
<setBody>
<simple>${substring(3)}</simple>
</setBody>Then the message body after the substring will be DEFGHIJ. If you want to clip from the end instead, then use negative values such as substring(-3).
You can also clip from both ends at the same time such as substring(1,-1) that will clip the first and last character in the String.
If the number is higher than the length of the message body, then an empty string is returned, for example substring(99).
Instead of the message body then a simple expression can be nested as input, for example, using a variable, as shown below:
<setBody>
<simple>${substring(1,-1,${variable.foo})}</simple>
</setBody>Replacing double and single quotes
You can use the replace function to more easily replace all single or double quotes in the message body, using the XML escape syntax. This avoids to fiddle with enclosing a double quote or single quotes with outer quotes, that can get confusing to be correct as you may need to escape the quotes as well. So instead you can use the XML escape syntax where double quote is " and single quote is ' (yeah that is the name).
For example, to replace all double quotes with single quotes:
from("direct:order")
.transform().simple("${replace(" , ')}")
.to("mock:reply");And to replace all single quotes with double quotes:
<setBody>
<simple>${replace(' , ")}</simple>
</setBody>Or to remove all double quotes:
<setBody>
<simple>${replace(" , ∅)}</simple>
</setBody>Setting the result type
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 usable to define types such as booleans, integers, etc.
For example, to set a header as a boolean type, you can do:
.setHeader("cool", simple("true", Boolean.class))And in XML DSL
<setHeader name="cool">
<!-- use resultType to indicate that the type should be a java.lang.Boolean -->
<simple resultType="java.lang.Boolean">true</simple>
</setHeader>Using new lines or tabs in XML DSLs
It is easier to specify new lines or tabs in XML DSLs as you can escape the value now
<transform>
<simple>The following text\nis on a new line</simple>
</transform>Leading and trailing whitespace handling
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.
<setBody>
<simple trim="false">You get some trailing whitespace characters. </simple>
</setBody>Loading script from external resource
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", e.g., to refer to a file on the classpath you can do:
.setHeader("myHeader").simple("resource:classpath:mysimple.txt")Spring Boot Auto-Configuration
When using simple with Spring Boot make sure to use the following Maven dependency to have support for auto configuration:
<dependency>
<groupId>org.apache.camel.springboot</groupId>
<artifactId>camel-core-starter</artifactId>
<version>x.x.x</version>
<!-- use the same version as your Camel core version -->
</dependency>The component supports 112 options, which are listed below.