Chapter 13. Introduction Abstract This chapter provides an overview of all the expression languages supported by Apache Camel. 13.1. Overview of the Languages Table of expression and predicate languages Table 13.1, "Expression and Predicate Languages" gives an overview of the different syntaxes for invoking expression and predicate languages. Table 13.1. Expression and Predicate Languages Language Static Method Fluent DSL Method XML Element Annotation Artifact See Bean Integration in the Apache Camel Development Guide on the customer portal. bean() EIP ().method() method @Bean Camel core Chapter 14, Constant constant() EIP ().constant() constant @Constant Camel core Chapter 15, EL el() EIP ().el() el @EL camel-juel Chapter 17, Groovy groovy() EIP ().groovy() groovy @Groovy camel-groovy Chapter 18, Header header() EIP ().header() header @Header Camel core Chapter 19, JavaScript javaScript() EIP ().javaScript() javaScript @JavaScript camel-script Chapter 20, JoSQL sql() EIP ().sql() sql @SQL camel-josql Chapter 21, JsonPath None EIP ().jsonpath() jsonpath @JsonPath camel-jsonpath Chapter 22, JXPath None EIP ().jxpath() jxpath @JXPath camel-jxpath Chapter 23, MVEL mvel() EIP ().mvel() mvel @MVEL camel-mvel Chapter 24, The Object-Graph Navigation Language(OGNL) ognl() EIP ().ognl() ognl @OGNL camel-ognl Chapter 25, PHP (DEPRECATED) php() EIP ().php() php @PHP camel-script Chapter 26, Exchange Property property() EIP ().property() property @Property Camel core Chapter 27, Python (DEPRECATED) python() EIP ().python() python @Python camel-script Chapter 28, Ref ref() EIP ().ref() ref N/A Camel core Chapter 29, Ruby (DEPRECATED) ruby() EIP ().ruby() ruby @Ruby camel-script Chapter 30, The Simple Language / Chapter 16, The File Language simple() EIP ().simple() simple @Simple Camel core Chapter 31, SpEL spel() EIP ().spel() spel @SpEL camel-spring Chapter 32, The XPath Language xpath() EIP ().xpath() xpath @XPath Camel core Chapter 33, XQuery xquery() EIP ().xquery() xquery @XQuery camel-saxon 13.2. How to Invoke an Expression Language Prerequisites Before you can use a particular expression language, you must ensure that the required JAR files are available on the classpath. If the language you want to use is not included in the Apache Camel core, you must add the relevant JARs to your classpath. If you are using the Maven build system, you can modify the build-time classpath simply by adding the relevant dependency to your POM file. For example, if you want to use the Ruby language, add the following dependency to your POM file: If you are going to deploy your application in a Red Hat Fuse OSGi container, you also need to ensure that the relevant language features are installed (features are named after the corresponding Maven artifact). For example, to use the Groovy language in the OSGi container, you must first install the camel-groovy feature by entering the following OSGi console command: Note If you are using an expression or predicate in the routes, refer the value as an external resource by using resource:classpath:path or resource:file:path . For example, resource:classpath:com/foo/myscript.groovy . Camel on EAP deployment The camel-groovy component is supported by the Camel on EAP (Wildfly Camel) framework, which offers a simplified deployment model on the Red Hat JBoss Enterprise Application Platform (JBoss EAP) container. Approaches to invoking As shown in Table 13.1, "Expression and Predicate Languages" , there are several different syntaxes for invoking an expression language, depending on the context in which it is used. You can invoke an expression language: As a static method As a fluent DSL method As an XML element As an annotation As a static method Most of the languages define a static method that can be used in any context where an org.apache.camel.Expression type or an org.apache.camel.Predicate type is expected. The static method takes a string expression (or predicate) as its argument and returns an Expression object (which is usually also a Predicate object). For example, to implement a content-based router that processes messages in XML format, you could route messages based on the value of the /order/address/countryCode element, as follows: As a fluent DSL method The Java fluent DSL supports another style of invoking expression languages. Instead of providing the expression as an argument to an Enterprise Integration Pattern (EIP), you can provide the expression as a sub-clause of the DSL command. For example, instead of invoking an XPath expression as filter(xpath(" Expression ")) , you can invoke the expression as, filter().xpath(" Expression ") . For example, the preceding content-based router can be re-implemented in this style of invocation, as follows: As an XML element You can also invoke an expression language in XML, by putting the expression string inside the relevant XML element. For example, the XML element for invoking XPath in XML is xpath (which belongs to the standard Apache Camel namespace). You can use XPath expressions in a XML DSL content-based router, as follows: Alternatively, you can specify a language expression using the language element, where you specify the name of the language in the language attribute. For example, you can define an XPath expression using the language element as follows: As an annotation Language annotations are used in the context of bean integration . The annotations provide a convenient way of extracting information from a message or header and then injecting the extracted data into a bean's method parmeters. For example, consider the bean, myBeanProc , which is invoked as a predicate of the filter() EIP. If the bean's checkCredentials method returns true , the message is allowed to proceed; but if the method returns false , the message is blocked by the filter. The filter pattern is implemented as follows: The implementation of the MyBeanProcessor class exploits the @XPath annotation to extract the username and password from the underlying XML message, as follows: The @XPath annotation is placed just before the parameter into which it gets injected. Notice how the XPath expression explicitly selects the text node, by appending /text() to the path, which ensures that just the content of the element is selected, not the enclosing tags. As a Camel endpoint URI Using the Camel Language component, you can invoke a supported language in an endpoint URI. There are two alternative syntaxes. To invoke a language script stored in a file (or other resource type defined by Scheme ), use the following URI syntax: Where the scheme can be file: , classpath: , or http: . For example, the following route executes the mysimplescript.txt from the classpath: To invoke an embedded language script, use the following URI syntax: For example, to run the Simple language script stored in the script string: For more details about the Language component, see Language in the Apache Camel Component Reference Guide .

Commands:
<dependency> <groupId>org.apache.camel</groupId> <artifactId>camel-groovy</artifactId> <!-- Use the same version as your Camel core version --> <version>USD{camel.version}</version> </dependency>
karaf@root> features:install camel-groovy
from(" SourceURL ") .choice .when( xpath("/order/address/countryCode = 'us'") ) .to("file://countries/us/") .when( xpath("/order/address/countryCode = 'uk'") ) .to("file://countries/uk/") .otherwise() .to("file://countries/other/") .to(" TargetURL ");
from(" SourceURL ") .choice .when(). xpath("/order/address/countryCode = 'us'") .to("file://countries/us/") .when(). xpath("/order/address/countryCode = 'uk'") .to("file://countries/uk/") .otherwise() .to("file://countries/other/") .to(" TargetURL ");
<from uri="file://input/orders"/> <choice> <when> <xpath>/order/address/countryCode = 'us'</xpath> <to uri="file://countries/us/"/> </when> <when> <xpath>/order/address/countryCode = 'uk'</xpath> <to uri="file://countries/uk/"/> </when> <otherwise> <to uri="file://countries/other/"/> </otherwise> </choice>
<language language="xpath">/order/address/countryCode = 'us'</language>
// Java MyBeanProcessor myBeanProc = new MyBeanProcessor(); from(" SourceURL ") .filter().method(myBeanProc, "checkCredentials") .to(" TargetURL ");
// Java import org.apache.camel.language.XPath; public class MyBeanProcessor { boolean void checkCredentials( @XPath("/credentials/username/text()") String user, @XPath("/credentials/password/text()") String pass ) { // Check the user/pass credentials } }
language:// LanguageName :resource: Scheme : Location [? Options ]
from("direct:start") .to("language:simple:classpath:org/apache/camel/component/language/mysimplescript.txt") .to("mock:result");
language:// LanguageName [: Script ][? Options ]
String script = URLEncoder.encode("Hello USD{body}", "UTF-8"); from("direct:start") .to("language:simple:" + script) .to("mock:result");