Languages Supported Appendix

Bean Language

The purpose of the Bean Language is to be able to implement an Expression or Predicate using a simple method on a bean. The bean name is resolved using a Registry, such as the Spring ApplicationContext, then a method is invoked to evaluate the Expression or Predicate. If no method name is provided then one is chosen using the rules for Bean Binding; using the type of the message body and using any annotations on the bean methods.

The Bean Binding rules are used to bind the Message Exchange to the method parameters; so you can annotate the bean to extract headers or other expressions such as XPath or XQuery from the message.

Using Bean Expressions in Java

from("activemq:topic:OrdersTopic")
  .filter().method("myBean", "isGoldCustomer")
    .to("activemq:BigSpendersQueue");

Using Bean Expressions in Spring XML

<route>
  <from uri="activemq:topic:OrdersTopic"/>
  <filter>
    <method ref="myBean" method="isGoldCustomer"/>
    <to uri="activemq:BigSpendersQueue"/>
  </filter>
</route>

Writing the Expression Bean

The bean in the above examples is just any old Java Bean with a method called isGoldCustomer() that returns some object that is easily converted to a boolean value in this case, as its used as a predicate.

Example:

public class MyBean {
  public boolean isGoldCustomer(Exchange exchange) {
  	 // ...
  }
}

We can also use the Bean Integration annotations.

Example:

public boolean isGoldCustomer(String body) {...}

or

public boolean isGoldCustomer(@Header(name = "foo") Integer fooHeader) {...}

So you can bind parameters of the method to the Exchange, the Message or individual headers, properties, the body or other expressions.

Non-Registry Beans

The Bean Language also supports invoking beans that isn't registered in the Registry. This is usable for quickly to invoke a bean from Java DSL where you don't need to register the bean in the Registry such as the Spring ApplicationContext. Camel can instantiate the bean and invoke the method if given a class or invoke an already existing instance.

Example:

from("activemq:topic:OrdersTopic")
  .filter().expression(BeanLanguage(MyBean.class, "isGoldCustomer"))
  .to("activemq:BigSpendersQueue");

The 2nd parameter isGoldCustomer is an optional parameter to explicit set the method name to invoke. If not provided Camel will try to invoke the most suitable method. If case of ambiguity Camel will thrown an Exception. In these situations the 2nd parameter can solve this problem. Also the code is more readable if the method name is provided. The 1st parameter can also be an existing instance of a Bean such as:

private MyBean my;

from("activemq:topic:OrdersTopic")
  .filter().expression(BeanLanguage.bean(my, "isGoldCustomer"))
  .to("activemq:BigSpendersQueue");

In Camel 2.2: you can avoid the BeanLanguage and have it just as:

private MyBean my;

from("activemq:topic:OrdersTopic")
  .filter().expression(bean(my, "isGoldCustomer"))
  .to("activemq:BigSpendersQueue");

Which also can be done in a bit shorter and nice way:

private MyBean my;

from("activemq:topic:OrdersTopic")
  .filter().method(my, "isGoldCustomer")
  .to("activemq:BigSpendersQueue");

Other Examples

We have some test cases you can look at if it'll help

• MethodFilterTest is a JUnit test case showing the Java DSL use of the bean expression being used in a filter
• aggregator.xml is a Spring XML test case for the Aggregator which uses a bean method call to test for the completion of the aggregation.

Dependencies

The Bean language is part of camel-core.

Constant Expression Language

The Constant Expression Language is really just a way to specify constant strings as a type of expression.

Example usage

The setHeader element of the Spring DSL can utilize a constant expression like:

<route>
  <from uri="seda:a"/>
  <setHeader headerName="theHeader">
    <constant>the value</constant>        
  </setHeader>
  <to uri="mock:b"/>     
</route>

In this case, the Message coming from the seda:a Endpoint will have theHeader header set to the constant value the value.

And the same example using Java DSL:

from("seda:a")
  .setHeader("theHeader", constant("the value"))
  .to("mock:b");

Dependencies

The Constant language is part of camel-core.

EL

Camel supports the unified JSP and JSF Expression Language via the JUEL to allow an Expression or Predicate to be used in the DSL or Xml Configuration.

For example you could use EL inside a Message Filter in XML

<route>
  <from uri="seda:foo"/>
  <filter>
    <el>${in.headers.foo == 'bar'}</el>
    <to uri="seda:bar"/>
  </filter>
</route>

You could also use slightly different syntax, e.g. if the header name is not a valid identifier:

<route>
  <from uri="seda:foo"/>
  <filter>
    <el>${in.headers['My Header'] == 'bar'}</el>
    <to uri="seda:bar"/>
  </filter>
</route>

You could use EL to create an Predicate in a Message Filter or as an Expression for a Recipient List

Variables

Samples

You can use EL dot notation to invoke operations. If you for instance have a body that contains a POJO that has a getFamiliyName method then you can construct the syntax as follows:

"${in.body.familyName}"

Dependencies

To use EL in your camel routes you need to add the a dependency on camel-juel which implements the EL language.

If you use maven you could just add the following to your pom.xml, substituting the version number for the latest & greatest release (see the download page for the latest versions).

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-juel</artifactId>
  <version>x.x.x</version>
</dependency>

Otherwise you'll also need to include JUEL.

Header Expression Language

The Header Expression Language allows you to extract values of named headers.

Example usage

The recipientList element of the Spring DSL can utilize a header expression like:

In this case, the list of recipients are contained in the header 'myHeader'.

And the same example in Java DSL:

And with a slightly different syntax where you use the builder to the fullest (i.e. avoid using parameters but using stacked operations, notice that header is not a parameter but a stacked method call)

Dependencies

The Header language is part of camel-core.

JXPath

Camel supports JXPath to allow XPath expressions to be used on beans in an Expression or Predicate to be used in the DSL or Xml Configuration. For example you could use JXPath to create an Predicate in a Message Filter or as an Expression for a Recipient List.

You can use XPath expressions directly using smart completion in your IDE as follows

Variables

Options

Using XML configuration

If you prefer to configure your routes in your Spring XML file then you can use JXPath expressions as follows

Examples

Here is a simple example using a JXPath expression as a predicate in a Message Filter

JXPath injection

You can use Bean Integration to invoke a method on a bean and use various languages such as JXPath to extract a value from the message and bind it to a method parameter.

For example

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:

Dependencies

To use JXpath in your camel routes you need to add the a dependency on camel-jxpath which implements the JXpath language.

If you use maven you could just add the following to your pom.xml, substituting the version number for the latest & greatest release (see the download page for the latest versions).

Otherwise, you'll also need Commons JXPath.

Mvel

Camel allows Mvel to be used as an Expression or Predicate the DSL or Xml Configuration.

You could use Mvel to create an Predicate in a Message Filter or as an Expression for a Recipient List

You can use Mvel dot notation to invoke operations. If you for instance have a body that contains a POJO that has a getFamiliyName method then you can construct the syntax as follows:

"request.body.familyName"
   // or 
"getRequest().getBody().getFamilyName()"

Variables

Samples

For example you could use Mvel inside a Message Filter in XML

<route>
  <from uri="seda:foo"/>
  <filter>
    <mvel>request.headers.foo == 'bar'</mvel>
    <to uri="seda:bar"/>
  </filter>
</route>

And the sample using Java DSL:

   from("seda:foo").filter().mvel("request.headers.foo == 'bar'").to("seda:bar");

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:

.setHeader("myHeader").mvel("resource:classpath:script.mvel")

Dependencies

To use Mvel in your camel routes you need to add the a dependency on camel-mvel which implements the Mvel language.

If you use maven you could just add the following to your pom.xml, substituting the version number for the latest & greatest release (see the download page for the latest versions).

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-mvel</artifactId>
  <version>x.x.x</version>
</dependency>

OGNL

Camel allows OGNL to be used as an Expression or Predicate the DSL or Xml Configuration.

You could use OGNL to create an Predicate in a Message Filter or as an Expression for a Recipient List

You can use OGNL dot notation to invoke operations. If you for instance have a body that contains a POJO that has a getFamilyName method then you can construct the syntax as follows:

"request.body.familyName"
   // or 
"getRequest().getBody().getFamilyName()"

Variables

Samples

For example you could use OGNL inside a Message Filter in XML

<route>
  <from uri="seda:foo"/>
  <filter>
    <ognl>request.headers.foo == 'bar'</ognl>
    <to uri="seda:bar"/>
  </filter>
</route>

And the sample using Java DSL:

   from("seda:foo").filter().ognl("request.headers.foo == 'bar'").to("seda:bar");

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:

.setHeader("myHeader").ognl("resource:classpath:myognl.txt")

Dependencies

To use OGNL in your camel routes you need to add the a dependency on camel-ognl which implements the OGNL language.

If you use maven you could just add the following to your pom.xml, substituting the version number for the latest & greatest release (see the download page for the latest versions).

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-ognl</artifactId>
  <version>x.x.x</version>
</dependency>

Otherwise, you'll also need OGNL

Property Expression Language

The Property Expression Language allows you to extract values of named exchange properties.

Example usage

The recipientList element of the Spring DSL can utilize a property expression like:

In this case, the list of recipients are contained in the property 'myProperty'.

And the same example in Java DSL:

And with a slightly different syntax where you use the builder to the fullest (i.e. avoid using parameters but using stacked operations, notice that property is not a parameter but a stacked method call)

Dependencies

The Property language is part of camel-core.

Scripting Languages

Camel supports a number of scripting languages which can be used to create an Expression or Predicate via the standard JSR 223 which is a standard part of Java 6.

The following scripting languages are integrated into the DSL:

However any JSR 223 scripting language can be used using the generic DSL methods.

public void testArgumentsExample() throws Exception {
    getMockEndpoint("mock:result").expectedMessageCount(0);
    getMockEndpoint("mock:unmatched").expectedMessageCount(1);

    // additional arguments to ScriptEngine
    Map<String, Object> arguments = new HashMap<>();
    arguments.put("foo", "bar");
    arguments.put("baz", 7);

    // those additional arguments is provided as a header on the Camel Message
    template.sendBodyAndHeader("direct:start", "hello", ScriptBuilder.ARGUMENTS, arguments);

    assertMockEndpointsSatisfied();


 

.setHeader("myHeader").groovy("context.resolvePropertyPlaceholders('{{' + request.headers.get('foo') + '}}')")

.setHeader("myHeader").groovy("properties.resolve(request.headers.get('foo'))")

.setHeader("myHeader").groovy("resource:classpath:mygroovy.groovy")

<dependency>
 <groupId>org.apache.camel</groupId>
 <artifactId>camel-script</artifactId>
 <version>x.x.x</version>
</dependency>

See Also

• Languages
• DSL
• Xml Configuration

BeanShell

Camel supports BeanShell among other Scripting Languages to allow an Expression or Predicate to be used in the DSL or Xml Configuration.

To use a BeanShell expression use the following Java code:

...choice()
    .when(script("beanshell", "request.getHeaders().get(\"foo\").equals(\"bar\")"))
       .to("...")

Or the something like this in your Spring XML:

<filter>
  <language language="beanshell">request.getHeaders().get("Foo") == null</language>
  ...

You could follow the examples above to create an Predicate in a Message Filter or as an Expression for a Recipient List

public void testArgumentsExample() throws Exception {
    getMockEndpoint("mock:result").expectedMessageCount(0);
    getMockEndpoint("mock:unmatched").expectedMessageCount(1);

    // additional arguments to ScriptEngine
    Map<String, Object> arguments = new HashMap<>();
    arguments.put("foo", "bar");
    arguments.put("baz", 7);

    // those additional arguments is provided as a header on the Camel Message
    template.sendBodyAndHeader("direct:start", "hello", ScriptBuilder.ARGUMENTS, arguments);

    assertMockEndpointsSatisfied();


 

.setHeader("myHeader").groovy("context.resolvePropertyPlaceholders('{{' + request.headers.get('foo') + '}}')")

.setHeader("myHeader").groovy("properties.resolve(request.headers.get('foo'))")

.setHeader("myHeader").groovy("resource:classpath:mygroovy.groovy")

<dependency>
 <groupId>org.apache.camel</groupId>
 <artifactId>camel-script</artifactId>
 <version>x.x.x</version>
</dependency>

JavaScript

Camel supports JavaScript/ECMAScript among other Scripting Languages to allow an Expression or Predicate to be used in the DSL or Xml Configuration.

To use a JavaScript expression use the following Java code

... javaScript("someJavaScriptExpression") ... 

For example you could use the javaScript function to create an Predicate in a Message Filter or as an Expression for a Recipient List

Example

In the sample below we use JavaScript to create a Predicate use in the route path, to route exchanges from admin users to a special queue.

    from("direct:start")
        .choice()
            .when().javaScript("request.headers.get('user') == 'admin'").to("seda:adminQueue")
        .otherwise()
            .to("seda:regularQueue");

And a Spring DSL sample as well:

    <route>
        <from uri="direct:start"/>
        <choice>
            <when>
                <javaScript>request.headers.get('user') == 'admin'</javaScript>
                <to uri="seda:adminQueue"/>
            </when>
            <otherwise>
                <to uri="seda:regularQueue"/>
            </otherwise>
        </choice>
    </route>

public void testArgumentsExample() throws Exception {
    getMockEndpoint("mock:result").expectedMessageCount(0);
    getMockEndpoint("mock:unmatched").expectedMessageCount(1);

    // additional arguments to ScriptEngine
    Map<String, Object> arguments = new HashMap<>();
    arguments.put("foo", "bar");
    arguments.put("baz", 7);

    // those additional arguments is provided as a header on the Camel Message
    template.sendBodyAndHeader("direct:start", "hello", ScriptBuilder.ARGUMENTS, arguments);

    assertMockEndpointsSatisfied();


 

.setHeader("myHeader").groovy("context.resolvePropertyPlaceholders('{{' + request.headers.get('foo') + '}}')")

.setHeader("myHeader").groovy("properties.resolve(request.headers.get('foo'))")

.setHeader("myHeader").groovy("resource:classpath:mygroovy.groovy")

<dependency>
 <groupId>org.apache.camel</groupId>
 <artifactId>camel-script</artifactId>
 <version>x.x.x</version>
</dependency>

Groovy

Camel supports Groovy among other Scripting Languages to allow an Expression or Predicate to be used in the DSL or Xml Configuration.

To use a Groovy expression use the following Java code

... groovy("someGroovyExpression") ... 

For example you could use the groovy function to create an Predicate in a Message Filter or as an Expression for a Recipient List

Dependency

You should add the camel-groovy dependeny when using Groovy language with Camel. The generic camel-script is not optimized for best Groovy experience, and hence you should add camel-groovy as dependency.

Customizing Groovy Shell

Sometimes you may need to use custom GroovyShell instance in your Groovy expressions. To provide custom GroovyShell, add implementation of the org.apache.camel.language.groovy.GroovyShellFactory SPI interface to your Camel registry. For example after adding the following bean to your Spring context...

public class CustomGroovyShellFactory implements GroovyShellFactory {
 
  public GroovyShell createGroovyShell(Exchange exchange) {
    ImportCustomizer importCustomizer = new ImportCustomizer();
    importCustomizer.addStaticStars("com.example.Utils");
    CompilerConfiguration configuration = new CompilerConfiguration();
    configuration.addCompilationCustomizers(importCustomizer);
    return new GroovyShell(configuration);
  }

}

...Camel will use your custom GroovyShell instance (containing your custom static imports), instead of the default one.

Example

// lets route if a line item is over $100
from("queue:foo").filter(groovy("request.lineItems.any { i -> i.value > 100 }")).to("queue:bar")

And the Spring DSL:

        <route>
            <from uri="queue:foo"/>
            <filter>
                <groovy>request.lineItems.any { i -> i.value > 100 }</groovy>
                <to uri="queue:bar"/>
            </filter>
        </route>

public void testArgumentsExample() throws Exception {
    getMockEndpoint("mock:result").expectedMessageCount(0);
    getMockEndpoint("mock:unmatched").expectedMessageCount(1);

    // additional arguments to ScriptEngine
    Map<String, Object> arguments = new HashMap<>();
    arguments.put("foo", "bar");
    arguments.put("baz", 7);

    // those additional arguments is provided as a header on the Camel Message
    template.sendBodyAndHeader("direct:start", "hello", ScriptBuilder.ARGUMENTS, arguments);

    assertMockEndpointsSatisfied();


 

.setHeader("myHeader").groovy("context.resolvePropertyPlaceholders('{{' + request.headers.get('foo') + '}}')")

.setHeader("myHeader").groovy("properties.resolve(request.headers.get('foo'))")

.setHeader("myHeader").groovy("resource:classpath:mygroovy.groovy")

<dependency>
 <groupId>org.apache.camel</groupId>
 <artifactId>camel-script</artifactId>
 <version>x.x.x</version>
</dependency>

Python

Camel supports Python among other Scripting Languages to allow an Expression or Predicate to be used in the DSL or Xml Configuration.

To use a Python expression use the following Java code

... python("somePythonExpression") ... 

For example you could use the python function to create an Predicate in a Message Filter or as an Expression for a Recipient List

Example

In the sample below we use Python to create a Predicate use in the route path, to route exchanges from admin users to a special queue.

    from("direct:start")
        .choice()
            .when().python("request.headers['user'] == 'admin'").to("seda:adminQueue")
        .otherwise()
            .to("seda:regularQueue");

And a Spring DSL sample as well:

    <route>
        <from uri="direct:start"/>
        <choice>
            <when>
                <python>request.headers['user'] == 'admin'</python>
                <to uri="seda:adminQueue"/>
            </when>
            <otherwise>
                <to uri="seda:regularQueue"/>
            </otherwise>
        </choice>
    </route>

public void testArgumentsExample() throws Exception {
    getMockEndpoint("mock:result").expectedMessageCount(0);
    getMockEndpoint("mock:unmatched").expectedMessageCount(1);

    // additional arguments to ScriptEngine
    Map<String, Object> arguments = new HashMap<>();
    arguments.put("foo", "bar");
    arguments.put("baz", 7);

    // those additional arguments is provided as a header on the Camel Message
    template.sendBodyAndHeader("direct:start", "hello", ScriptBuilder.ARGUMENTS, arguments);

    assertMockEndpointsSatisfied();


 

.setHeader("myHeader").groovy("context.resolvePropertyPlaceholders('{{' + request.headers.get('foo') + '}}')")

.setHeader("myHeader").groovy("properties.resolve(request.headers.get('foo'))")

.setHeader("myHeader").groovy("resource:classpath:mygroovy.groovy")

<dependency>
 <groupId>org.apache.camel</groupId>
 <artifactId>camel-script</artifactId>
 <version>x.x.x</version>
</dependency>

PHP

Camel supports PHP among other Scripting Languages to allow an Expression or Predicate to be used in the DSL or Xml Configuration.

To use a PHP expression use the following Java code

... php("somePHPExpression") ... 

For example you could use the php function to create an Predicate in a Message Filter or as an Expression for a Recipient List

public void testArgumentsExample() throws Exception {
    getMockEndpoint("mock:result").expectedMessageCount(0);
    getMockEndpoint("mock:unmatched").expectedMessageCount(1);

    // additional arguments to ScriptEngine
    Map<String, Object> arguments = new HashMap<>();
    arguments.put("foo", "bar");
    arguments.put("baz", 7);

    // those additional arguments is provided as a header on the Camel Message
    template.sendBodyAndHeader("direct:start", "hello", ScriptBuilder.ARGUMENTS, arguments);

    assertMockEndpointsSatisfied();


 

.setHeader("myHeader").groovy("context.resolvePropertyPlaceholders('{{' + request.headers.get('foo') + '}}')")

.setHeader("myHeader").groovy("properties.resolve(request.headers.get('foo'))")

.setHeader("myHeader").groovy("resource:classpath:mygroovy.groovy")

<dependency>
 <groupId>org.apache.camel</groupId>
 <artifactId>camel-script</artifactId>
 <version>x.x.x</version>
</dependency>

Ruby

Camel supports Ruby among other Scripting Languages to allow an Expression or Predicate to be used in the DSL or Xml Configuration.

To use a Ruby expression use the following Java code

... ruby("someRubyExpression") ... 

For example you could use the ruby function to create an Predicate in a Message Filter or as an Expression for a Recipient List

Example

In the sample below we use Ruby to create a Predicate use in the route path, to route exchanges from admin users to a special queue.

    from("direct:start")
        .choice()
            .when().ruby("$request.headers['user'] == 'admin'").to("seda:adminQueue")
        .otherwise()
            .to("seda:regularQueue");

And a Spring DSL sample as well:

    <route>
        <from uri="direct:start"/>
        <choice>
            <when>
                <ruby>$request.headers['user'] == 'admin'</ruby>
                <to uri="seda:adminQueue"/>
            </when>
            <otherwise>
                <to uri="seda:regularQueue"/>
            </otherwise>
        </choice>
    </route>

public void testArgumentsExample() throws Exception {
    getMockEndpoint("mock:result").expectedMessageCount(0);
    getMockEndpoint("mock:unmatched").expectedMessageCount(1);

    // additional arguments to ScriptEngine
    Map<String, Object> arguments = new HashMap<>();
    arguments.put("foo", "bar");
    arguments.put("baz", 7);

    // those additional arguments is provided as a header on the Camel Message
    template.sendBodyAndHeader("direct:start", "hello", ScriptBuilder.ARGUMENTS, arguments);

    assertMockEndpointsSatisfied();


 

.setHeader("myHeader").groovy("context.resolvePropertyPlaceholders('{{' + request.headers.get('foo') + '}}')")

.setHeader("myHeader").groovy("properties.resolve(request.headers.get('foo'))")

.setHeader("myHeader").groovy("resource:classpath:mygroovy.groovy")

<dependency>
 <groupId>org.apache.camel</groupId>
 <artifactId>camel-script</artifactId>
 <version>x.x.x</version>
</dependency>

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.

Deprecated: The ${} placeholders can be omitted if the expression starts with the token, or if the token is only 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 e.g., having another ${} placeholder in an existing, is not allowed. From Camel 2.9 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 accessors, but you can invoke any method or use the real name such as:

You can also use the null safe operator (?.) to avoid a 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 a 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 penultimate line use subtraction. In this case use last-1 for this:

And the third last is of course:

And you can call the size method on the list with

From Camel 2.11.1 we added support for the length field for Java arrays as well. Example:

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 possible to for example, 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 four 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 three we also support the negate test using not:

And you can test if the type is a certain instance, e.g., 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: 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:

Note: 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:

From Camel 2.3: 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:

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: you can nest functions, such as shown below:

Referring to Constants or Enums

Available from Camel 2.11

Suppose you have an enum for customers:{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/Customer.java}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.{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/CBRSimpleTypeTest.java}

Using New Lines or Tabs in XML DSLs

Available from Camel 2.9.3

From Camel 2.9.3: 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 from Camel 2.10.0

From Camel 2.10.0: the trim attribute of the expression can be used to control whether the leading and trailing whitespace characters are removed or preserved. The default of trim=true removes all whitespace characters.

Setting the Result Type

Available from 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 usable to define types such as boolean's, integer's, 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 from 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 from 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, e.g., to refer to a file on the classpath you can do:

Setting Spring beans to Exchange properties

Available from 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.

File Expression Language

The File Expression Language is an extension to the Simple language, adding file related capabilities. These capabilities are related to common use cases working with file path and names. The goal is to allow expressions to be used with the File and FTP components for setting dynamic file patterns for both consumer and producer.

Syntax

This language is an extension to the Simple language so the Simple syntax applies also. So the table below only lists the additional. By contrast to the Simple language, the File Language also supports the use of Constant expressions to enter a fixed filename, for example.

All the file tokens use the same expression name as the method on the java.io.File object. For example: file:absolute refers to the java.io.File.getAbsolute() method.

File Token Example

Relative Paths

We have a java.io.File handle for the file hello.txt in the following relative directory: .\filelanguage\test. And we configure our endpoint to use this starting directory .\filelanguage.

The file tokens returned are:

Absolute Paths

We have a java.io.File handle for the file hello.txt in the following absolute directory: \workspace\camel\camel-core\target\filelanguage\test. And we configure out endpoint to use the absolute starting directory: \workspace\camel\camel-core\target\filelanguage.

The file tokens return are:

Examples

You can enter a fixed Constant expression such as myfile.txt:

fileName="myfile.txt"

Lets assume we use the file consumer to read files and want to move the read files to backup folder with the current date as a sub folder. This can be achieved using an expression like:

fileName="backup/${date:now:yyyyMMdd}/${file:name.noext}.bak"

relative folder names are also supported so suppose the backup folder should be a sibling folder then you can append .. as:

fileName="../backup/${date:now:yyyyMMdd}/${file:name.noext}.bak"

As this is an extension to the Simple language we have access to all the goodies from this language also, so in this use case we want to use the in.header.type as a parameter in the dynamic expression:

fileName="../backup/${date:now:yyyyMMdd}/type-${in.header.type}/backup-of-${file:name.noext}.bak"

If you have a custom Date you want to use in the expression then Camel supports retrieving dates from the message header.

fileName="orders/order-${in.header.customerId}-${date:in.header.orderDate:yyyyMMdd}.xml"

And finally we can also use a bean expression to invoke a POJO class that generates some String output (or convertible to String) to be used:

fileName="uniquefile-${bean:myguidgenerator.generateid}.txt"

And of course all this can be combined in one expression where you can use the File Language, Simple and the Bean language in one combined expression. This is pretty powerful for those common file path patterns.

Using Spring's PropertyPlaceholderConfigurer with the File Component

In Camel you can use the File Language directly from the Simple language which makes a Content Based Router easier to do in Spring XML, where we can route based on file extensions as shown below:

<from uri="file://input/orders"/>
  <choice>
    <when>
      <simple>${file:ext} == 'txt'</simple>
      <to uri="bean:orderService?method=handleTextFiles"/>
    </when>
    <when>
      <simple>${file:ext} == 'xml'</simple>
      <to uri="bean:orderService?method=handleXmlFiles"/>
    </when>
    <otherwise>
      <to uri="bean:orderService?method=handleOtherFiles"/>
    </otherwise>
  </choice>

If you use the fileName option on the File endpoint to set a dynamic filename using the File Language then make sure you use the alternative syntax (available from Camel 2.5) to avoid clashing with Spring's PropertyPlaceholderConfigurer.

<bean id="propertyPlaceholder" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
  <property name="location" value="classpath:bundle-context.cfg"/>
</bean>

<bean id="sampleRoute" class="SampleRoute">
  <property name="fromEndpoint" value="${fromEndpoint}"/>
  <property name="toEndpoint" value="${toEndpoint}"/>
</bean>

fromEndpoint=activemq:queue:test
toEndpoint=file://fileRoute/out?fileName=test-$simple{date:now:yyyyMMdd}.txt

Notice how we use the $simple{} syntax in the toEndpoint above. If you don't do this, they will clash and Spring will throw an exception:

org.springframework.beans.factory.BeanDefinitionStoreException:
Invalid bean definition with name 'sampleRoute' defined in class path resource [bundle-context.xml]:
Could not resolve placeholder 'date:now:yyyyMMdd'

Dependencies

The File language is part of camel-core.

SQL Language

The SQL support is added by JoSQL and is primarily used for performing SQL queries on in-memory objects. If you prefer to perform actual database queries then check out the JPA component.

To use SQL in your camel routes you need to add the a dependency on camel-josql which implements the SQL language.

If you use maven you could just add the following to your pom.xml, substituting the version number for the latest & greatest release (see the download page for the latest versions).

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-josql</artifactId>
  <version>x.x.x</version>
  <!-- use the same version as your Camel core version -->
</dependency>

Camel supports SQL to allow an Expression or Predicate to be used in the DSL or Xml Configuration. For example you could use SQL to create an Predicate in a Message Filter or as an Expression for a Recipient List.

from("queue:foo").setBody().sql("select * from MyType").to("queue:bar")

And the spring DSL:

   <from uri="queue:foo"/>
   <setBody>
       <sql>select * from MyType</sql>
   </setBody>
   <to uri="queue:bar"/>

Variables

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:

.setHeader("myHeader").sql("resource:classpath:mysql.sql")

XPath

Camel supports XPath to allow an Expression or Predicate to be used in the DSL or Xml Configuration. For example you could use XPath to create an Predicate in a Message Filter or as an Expression for a Recipient List.

Namespaces

You can easily use namespaces with XPath expressions using the Namespaces helper class.{snippet:id=example|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/XPathWithNamespacesFilterTest.java}

Variables

Variables in XPath is defined in different namespaces. The default namespace is http://camel.apache.org/schema/spring.

Camel will resolve variables according to either:

• namespace given
• no namespace given

Namespace Given

If the namespace is given then Camel is instructed exactly what to return. However when resolving either IN or OUT Camel will try to resolve a header with the given local part first, and return it. If the local part has the value body then the body is returned instead.

No Namespace Given

If there is no namespace given then Camel resolves only based on the local part. Camel will try to resolve a variable in the following steps:

• From variables that has been set using the variable(name, value) fluent builder.
• From message.in.header if there is a header with the given key.
• From exchange.properties if there is a property with the given key.

Functions

Camel adds the following XPath functions that can be used to access the exchange:

Here's an example showing some of these functions in use.{snippet:id=ex|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/language/XPathFunctionTest.java}And the new functions introduced in Camel 2.5:{snippet:id=ex|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/builder/xml/XPathFunctionsTest.java}

Using XML Configuration

If you prefer to configure your routes in your Spring XML file then you can use XPath expressions as follows

Notice how we can reuse the namespace prefixes, foo in this case, in the XPath expression for easier namespace based XPath expressions! See also this discussion on the mailinglist about using your own namespaces with XPath.

Setting the Result Type

The XPath expression will return a result type using native XML objects such as org.w3c.dom.NodeList. But many times you want a result type to be a String. To do this you have to instruct the XPath which result type to use.

In Java DSL:

In Spring DSL you use the resultType attribute to provide a fully qualified classname:

In @XPath:
Available as of Camel 2.1

Where we use the XPath function concat to prefix the order name with foo-. In this case we have to specify that we want a String as result type so the concat function works.

Using XPath on Headers

Available as of Camel 2.11

Some users may have XML stored in a header. To apply an XPath statement to a header's value you can do this by defining the headerName attribute.

In XML DSL:{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-test-blueprint/src/test/resources/org/apache/camel/test/blueprint/xpath/XPathHeaderNameTest.xml}And in Java DSL you specify the headerName as the 2nd parameter as shown:

Examples

Here is a simple example using an XPath expression as a predicate in a Message Filter{snippet:id=example|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/XPathFilterTest.java}If you have a standard set of namespaces you wish to work with and wish to share them across many different XPath expressions you can use the NamespaceBuilder as shown in this example{snippet:id=example|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/XPathWithNamespaceBuilderFilterTest.java}In this sample we have a choice construct. The first choice evaulates if the message has a header key type that has the value Camel. The 2nd choice evaluates if the message body has a name tag <name> which values is Kong.
If neither is true the message is routed in the otherwise block:{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/builder/xml/XPathHeaderTest.java}And the spring XML equivalent of the route:{snippet:id=example|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/SpringXPathHeaderTest-context.xml}

XPath Injection

You can use Bean Integration to invoke a method on a bean and use various languages such as XPath to extract a value from the message and bind it to a method parameter.

The default XPath annotation has SOAP and XML namespaces available. If you want to use your own namespace URIs in an XPath expression you can use your own copy of the XPath annotation to create whatever namespace prefixes you want to use.{snippet:id=example|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/component/xslt/MyXPath.java}e.g., cut and paste upper code to your own project in a different package and/or annotation name then add whatever namespace prefix/URIs you want in scope when you use your annotation on a method parameter. Then when you use your annotation on a method parameter all the namespaces you want will be available for use in your XPath expression.

Example:

Using XPathBuilder Without an Exchange

Available as of Camel 2.3

You can now use the org.apache.camel.builder.XPathBuilder without the need for an Exchange. This comes handy if you want to use it as a helper to do custom XPath evaluations. It requires that you pass in a CamelContext since a lot of the moving parts inside the XPathBuilder requires access to the Camel Type Converter and hence why CamelContext is needed.

For example you can do something like this:

This will match the given predicate.

You can also evaluate for example as shown in the following three examples:

Evaluating with a String result is a common requirement and thus you can do it a bit simpler:

Using Saxon with XPathBuilder

Available as of Camel 2.3

You need to add camel-saxon as dependency to your project. It's now easier to use Saxon with the XPathBuilder which can be done in several ways as shown below. Where as the latter ones are the easiest ones.

Using a factory{snippet:id=e1|lang=java|url=camel/trunk/components/camel-saxon/src/test/java/org/apache/camel/builder/saxon/XPathTest.java}Using the object model
{snippet:id=e2|lang=java|url=camel/trunk/components/camel-saxon/src/test/java/org/apache/camel/builder/saxon/XPathTest.java}The easy one{snippet:id=e3|lang=java|url=camel/trunk/components/camel-saxon/src/test/java/org/apache/camel/builder/saxon/XPathTest.java}

Setting a Custom XPathFactory Using System Property

Available as of Camel 2.3

Camel now supports reading the JVM system property javax.xml.xpath.XPathFactory that can be used to set a custom XPathFactory to use.

This unit test shows how this can be done to use Saxon instead:{snippet:id=e4|lang=java|url=camel/trunk/components/camel-saxon/src/test/java/org/apache/camel/builder/saxon/XPathTest.java}Camel will log at INFO level if it uses a non default XPathFactory such as:

To use Apache Xerces you can configure the system property:

Enabling Saxon from Spring DSL

Available as of Camel 2.10

Similarly to Java DSL, to enable Saxon from Spring DSL you have three options:

Specifying the factory

Specifying the object model

Shortcut

Namespace Auditing to Aid Debugging

Available as of Camel 2.10

A large number of XPath-related issues that users frequently face are linked to the usage of namespaces. You may have some misalignment between the namespaces present in your message and those that your XPath expression is aware of or referencing. XPath predicates or expressions that are unable to locate the XML elements and attributes due to namespaces issues may simply look like "they are not working", when in reality all there is to it is a lack of namespace definition.

Namespaces in XML are completely necessary, and while we would love to simplify their usage by implementing some magic or voodoo to wire namespaces automatically, truth is that any action down this path would disagree with the standards and would greatly hinder interoperability.

Therefore, the utmost we can do is assist you in debugging such issues by adding two new features to the XPath Expression Language and are thus accessible from both predicates and expressions.

Logging the Namespace Context of Your XPath Expression/Predicate

Every time a new XPath expression is created in the internal pool, Camel will log the namespace context of the expression under the org.apache.camel.builder.xml.XPathBuilder logger. Since Camel represents Namespace Contexts in a hierarchical fashion (parent-child relationships), the entire tree is output in a recursive manner with the following format:

Any of these options can be used to activate this logging:

1. Enable TRACE logging on the org.apache.camel.builder.xml.XPathBuilder logger, or some parent logger such as org.apache.camel or the root logger.
2. Enable the logNamespaces option as indicated in Auditing Namespaces, in which case the logging will occur on the INFO level.

AuditingNamespaces

Auditing namespaces

Camel is able to discover and dump all namespaces present on every incoming message before evaluating an XPath expression, providing all the richness of information you need to help you analyse and pinpoint possible namespace issues. To achieve this, it in turn internally uses another specially tailored XPath expression to extract all namespace mappings that appear in the message, displaying the prefix and the full namespace URI(s) for each individual mapping.

Some points to take into account:

• The implicit XML namespace (xmlns:xml="http://www.w3.org/XML/1998/namespace") is suppressed from the output because it adds no value.
• Default namespaces are listed under the DEFAULT keyword in the output.
• Keep in mind that namespaces can be remapped under different scopes. Think of a top-level 'a' prefix which in inner elements can be assigned a different namespace, or the default namespace changing in inner scopes. For each discovered prefix, all associated URIs are listed.

You can enable this option in Java DSL and Spring DSL.

Java DSL:

Spring DSL:

The result of the auditing will be appear at the INFO level under the org.apache.camel.builder.xml.XPathBuilder logger and will look like the following:

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, e.g., to refer to a file on the classpath you can do:

Dependencies

The XPath language is part of camel-core.

XQuery

Camel supports XQuery to allow an Expression or Predicate to be used in the DSL or Xml Configuration. For example you could use XQuery to create an Predicate in a Message Filter or as an Expression for a Recipient List.

Options

Examples

You can also use functions inside your query, in which case you need an explicit type conversion (or you will get a org.w3c.dom.DOMException: HIERARCHY_REQUEST_ERR) by passing the Class as a second argument to the xquery() method.

Variables

The IN message body will be set as the contextItem. Besides this these Variables is also added as parameters:

Using XML configuration

If you prefer to configure your routes in your Spring XML file then you can use XPath expressions as follows

Notice how we can reuse the namespace prefixes, foo in this case, in the XPath expression for easier namespace based XQuery expressions!

When you use functions in your XQuery expression you need an explicit type conversion which is done in the xml configuration via the @type attribute:

Using XQuery as transformation

We can do a message translation using transform or setBody in the route, as shown below:

Notice that xquery will use DOMResult by default, so if we want to grab the value of the person node, using text() we need to tell xquery to use String as result type, as shown:

Using XQuery as an endpoint

Sometimes an XQuery expression can be quite large; it can essentally be used for Templating. So you may want to use an XQuery Endpoint so you can route using XQuery templates.

The following example shows how to take a message of an ActiveMQ queue (MyQueue) and transform it using XQuery and send it to MQSeries.

Examples

Here is a simple example using an XQuery expression as a predicate in a Message Filter

This example uses XQuery with namespaces as a predicate in a Message Filter

Learning XQuery

XQuery is a very powerful language for querying, searching, sorting and returning XML. For help learning XQuery try these tutorials

• Mike Kay's XQuery Primer
• the W3Schools XQuery Tutorial

You might also find the XQuery function reference useful

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:

Dependencies

To use XQuery in your camel routes you need to add the a dependency on camel-saxon which implements the XQuery language.

If you use maven you could just add the following to your pom.xml, substituting the version number for the latest & greatest release (see the download page for the latest versions).