[[simple-language]]
== Simple Language

*Available as of Camel version 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 really small and simple language for evaluating
Expressions and Predicates
without requiring any new dependencies or knowledge of
<<xpath-language,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:

* <<groovy-language,Groovy>>
* <<spel-language,SpEL>>
* <<mvel-component,MVEL>>
* <<ognl-language,OGNL>>

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.

TIP: *Alternative syntax* 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.


=== Simple Language options

// language options: START
The Simple language supports 2 options, which are listed below.



[width="100%",cols="2,1m,1m,6",options="header"]
|===
| Name | Default | Java Type | Description
| resultType |  | String | Sets the class name of the result type (type from output)
| trim | true | Boolean | Whether to trim the value to remove leading and trailing whitespaces and line breaks
|===
// language options: END

=== Variables

[width="100%",cols="10%,10%,80%",options="header",]
|=======================================================================
|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 input message id

|body |Object |the input body

|in.body |Object |*deprecated* the input body

|body.*OGNL* |Object |the input body invoked using a Camel OGNL expression.

|in.body.*OGNL* |Object |*deprecated* the input 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.

|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.

|out.body |Object |*deprecated* the output body

|header.foo |Object |refer to the input foo header

|header:foo |Object |refer to the input foo header

|header[foo] |Object |refer to the input foo header

|headers.foo |Object |refer to the input foo header

|headers:foo |Object |refer to the input foo header

|headers[foo] |Object |refer to the input foo header

|in.header.foo |Object |*deprecated* refer to the input foo header

|in.header:foo |Object |*deprecated* refer to the input foo header

|in.header[foo] |Object |*deprecated* refer to the input foo header

|in.headers.foo |Object |*deprecated* refer to the input foo header

|in.headers:foo |Object |*deprecated* refer to the input foo header

|in.headers[foo] |Object |*deprecated* refer to the input foo header

|header.foo[bar] |Object |regard input foo header as a map and perform lookup on the
map with bar as key

|in.header.foo[bar] |Object |*deprecated* regard input foo header as a map and perform lookup on the
map with bar as key

|in.headers.foo[bar] |Object |*deprecated* regard input foo header as a map and perform lookup on the
map with bar as key

|header.foo.*OGNL* |Object |refer to the input foo header and invoke its value using a
Camel OGNL expression.

|in.header.foo.*OGNL* |Object |*deprecated* refer to the input foo header and invoke its value using a
Camel OGNL expression.

|in.headers.foo.*OGNL* |Object |*deprecated* refer to the input foo header and invoke its value using a
Camel OGNL expression.

|out.header.foo |Object |*deprecated* refer to the out header foo

|out.header:foo |Object |*deprecated* refer to the out header foo

|out.header[foo] |Object |*deprecated* refer to the out header foo

|out.headers.foo |Object |*deprecated* refer to the out header foo

|out.headers:foo |Object |*deprecated* refer to the out header foo

|out.headers[foo] |Object |*deprecated* refer to the out header foo

|headerAs(_key_,_type_) |Type |converts the header to the given type determined by its
classname

|headers |Map |refer to the input headers

|in.headers |Map |*deprecated* refer to the input headers

|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.

|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 fallback and grab caught exceptions
(`Exchange.EXCEPTION_CAUGHT`) if the Exchange has any.

|exception.*OGNL* |Object |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 |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_ |Date |evaluates to a Date object.
Supported commands are: *now* for current timestamp, *in.header.xxx* or
*header.xxx* to use the Date object header with the key xxx.
*exchangeProperty.xxx* to use the Date object in the exchange property with the key xxx.
*file* for the last modified timestamp of the file (available with a File consumer).
Command accepts offsets such as: *now-24h* or *in.header.xxx+1h* or even *now+1h30m-100*.

|date:_command:pattern_ |String |Date formatting using `java.text.SimpleDataFormat` patterns.

|date-with-timezone:_command:timezone:pattern_ |String |Date formatting using `java.text.SimpleDataFormat` timezones and patterns.

|bean:_bean expression_ |Object |Invoking a bean expression using the <<bean-component,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,Bean>>
component.

|properties-location:_http://locationskey[locations:key]_ |String |Lookup a property with the given key. The `locations`
option is optional. See more at
Using PropertyPlaceholder.

|`properties:key:default` |String |Lookup a property with the given key. If the key does
not exists or has no value, then an optional default value can be
specified.

|routeId |String |Returns the id of the current route the
Exchange is being routed.

|stepId |String |Returns the id of the current step the
Exchange is being routed.

|threadName |String |Returns the name of the current thread. Can be used for
logging purpose.

|ref:xxx |Object |To lookup 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: `org.apache.camel.Exchange.FILE_NAME`

|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)

|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 splitted 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.

|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 strack-trace). This can be used if you do not want to
log sensitive data from the message itself.
|=======================================================================

=== OGNL expression support

INFO: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-language,Simple>> and <<simple-language,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:

[source,java]
--------------------------------
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:

[source,java]
--------------------------------------
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

[source,java]
----------------------------------
simple("${body?.address?.street}")
----------------------------------

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

[source,java]
---------------------------
simple("${body[foo].name}")
---------------------------

To assume the body is `Map` based and lookup 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':

[source,java]
---------------------------------
simple("${body['foo bar'].name}")
---------------------------------

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

[source,java]
------------------------------
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:

[source,java]
----------------------------
simple("${body[foo]?.name}")
----------------------------

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

[source,java]
----------------------------------
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.

[source,java]
-------------------------------------
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:

[source,java]
---------------------------------------
simple("${body.address.lines[last-1]}")
---------------------------------------

And the 3rd last is of course:

[source,java]
---------------------------------------
simple("${body.address.lines[last-2]}")
---------------------------------------

And you can call the size method on the list with

[source,java]
------------------------------------
simple("${body.address.lines.size}")
------------------------------------

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

[source,java]
---------------------------------------------------
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:

[source,java]
------------------------------------
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:

[source]
--------------------------
${leftValue} OP rightValue
--------------------------

Where the `rightValue` can be a String literal enclosed in `' '`,
`null`, a constant value or another expression enclosed in $\{ }.

IMPORTANT: There *must* be spaces around the operator.

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:

[width="100%",cols="50%,50%",options="header",]
|===
|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 not contains in a string based value

|~~ |For testing if contains by ignoring case sensitivity in a string based value

|!~~ |For testing if not contains 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, eg ',,bronze,silver,gold', which
is a set of four values with an empty value and then the three medals.

|!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, eg ',,bronze,silver,gold', which
is a set of four values with an empty value and then the three medals.

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

|!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`..

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

|startsWith |For testing if the left hand side string starts
with the right hand string.

|endsWith |For testing if the left hand side string ends with
the right hand string.
|===

And the following unary operators can be used:

[width="100%",cols="50%,50%",options="header",]
|===
|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.

|\ |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,File Language>>. *Notice:* From Camel 2.11
onwards the escape character is no longer support, but replaced with the
following three special escaping.

|\n |To use newline character.

|\t |To use tab character.

|\r |To use carriage return character.

|\} |To use the } character as text
|===

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

[width="100%",cols="50%,50%",options="header",]
|===
|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:

[source]
----------------------------------------------------------
${leftValue} OP rightValue && ${leftValue} OP rightValue
----------------------------------------------------------

And the syntax for OR is:

[source]
---------------------------------------------------------
${leftValue} OP rightValue || ${leftValue} OP rightValue
---------------------------------------------------------

Some examples:

[source,java]
----
// exact equals match
simple("${in.header.foo} == 'foo'")

// ignore case when comparing, so if the header has value FOO this will match
simple("${in.header.foo} =~ 'foo'")

// here Camel will type convert '100' into the type of in.header.bar and if it is 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")
----

==== Comparing with different types

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:

[source,java]
----
simple("100 < ${in.header.bar}")
----

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.

[source,java]
----
// 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

[source,java]
----
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

[source,java]
----
simple("${in.header.title} contains 'Camel'")
----

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

[source,java]
----
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.

[source,java]
----
simple("${in.header.type} in 'gold,silver'")
----

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

[source,java]
----
simple("${in.header.type} !in 'gold,silver'")
----

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

[source,java]
----
simple("${in.header.type} is 'java.lang.String'")
----

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

[source,java]
----
simple("${in.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:

[source,java]
----
simple("${in.header.number} range 100..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

[source,java]
----
simple("${in.header.number} range '100..199'")
----

==== Using Spring XML

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:

[source,xml]
----
<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 `&&` or `||`
operator.

For instance:

[source,java]
-----
simple("${in.header.title} contains 'Camel' && ${in.header.type'} == 'gold'")
-----

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

[source,java]
-----
simple("${in.header.title} contains 'Camel' || ${in.header.type'} == 'gold'")
-----

*Notice:* Currently `&&` or `||` can only be used *once* in a simple
language expression. This might change in the future. +
 So you *cannot* do:

[source,java]
-----
simple("${in.header.title} contains 'Camel' && ${in.header.type'} == 'gold' && ${in.header.number} range 100..200")
-----


=== Samples

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

[source,xml]
--------------------------------------------
<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:fooOrders` endpoint, otherwise the message is dropped.

The same example in Java DSL:

[source,java]
----
from("seda:orders")
    .filter().simple("${in.header.foo}")
        .to("seda:fooOrders");
----

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

[source,java]
----
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
allow Camel to parse it correctly.

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

[source,java]
----
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:

[source,java]
----
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.

[source,java]
----
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,Bean>> component itself:

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

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:

[source,xml]
----
<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 lookup a value from a header `Map` in *Camel 2.3*
onwards:

[source,xml]
----
<transform>
  <simple>The gold value is ${header.type[gold]}</simple>
</transform>
----

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:

[source,xml]
----
<setHeader headerName="myHeader">
  <simple>${properties:${header.someKey}}</simple>
</setHeader>
----

=== Referring to constants or enums

Suppose you have an enum for customers

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

=== Using new lines or tabs in XML DSLs

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

[source,xml]
----
<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.

[source,xml]
----
<setBody>
  <simple trim="false">You get some trailing whitespace characters.     </simple>
</setBody>
----

=== Setting result type

You can now provide a result type to the <<simple-language,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:

[source,java]
----
.setHeader("cool", simple("true", Boolean.class))
----

And in XML DSL

[source,xml]
----
<setHeader headerName="cool">
  <!-- use resultType to indicate that the type should be a java.lang.Boolean -->
  <simple resultType="java.lang.Boolean">true</simple>
</setHeader>
----

=== 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"`,
eg to refer to a file on the classpath you can do:

[source,java]
----
.setHeader("myHeader").simple("resource:classpath:mysimple.txt")
----

=== Setting Spring beans to Exchange properties

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

[source,xml]
----
<bean id="myBeanId" class="my.package.MyCustomClass" />
...
<route>
  ...
  <setProperty propertyName="monitoring.message">
    <simple>ref:myBeanId</simple>
  </setProperty>
  ...
</route>
----

