Chapter 138. Velocity Since Camel 1.2 Only producer is supported The Velocity component allows you to process a message using an Apache Velocity template. This can be ideal when using a template to generate responses for requests. 138.1. Dependencies When using velocity with Red Hat build of Camel 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-velocity-starter</artifactId> </dependency> 138.2. URI format Where templateName is the classpath-local URI of the template to invoke; or the complete URL of the remote template (for example, file://folder/myfile.vm ). 138.3. Configuring Options Camel components are configured on two separate levels: component level endpoint level 138.3.1. Configuring Component Options The component level is the highest level which holds general and common configurations that are inherited by the endpoints. For example a component may have security settings, credentials for authentication, urls for network connection and so forth. Some components only have a few options, and others may have many. Because components typically have pre configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all. Configuring components can be done with the Component DSL , in a configuration file (application.properties|yaml), or directly with Java code. 138.3.2. Configuring Endpoint Options Where you find yourself configuring the most is on endpoints, as endpoints often have many options, which allows you to configure what you need the endpoint to do. The options are also categorized into whether the endpoint is used as consumer (from) or as a producer (to), or used for both. Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL as a type safe way of configuring endpoints. A good practice when configuring options is to use Property Placeholders , which allows to not hardcode urls, port numbers, sensitive information, and other settings. In other words placeholders allows to externalize the configuration from your code, and gives more flexibility and reuse. The following two sections lists all the options, firstly for the component followed by the endpoint. 138.4. Component Options The Velocity component supports 5 options, which are listed below. Name Description Default Type allowContextMapAll (producer) Sets whether the context map should allow access to all details. By default only the message body and headers can be accessed. This option can be enabled for full access to the current Exchange and CamelContext. Doing so impose a potential security risk as this opens access to the full power of CamelContext API. false boolean allowTemplateFromHeader (producer) Whether to allow to use resource template from header or not (default false). Enabling this allows to specify dynamic templates via message header. However this can be seen as a potential security vulnerability if the header is coming from a malicious user, so use this with care. false boolean lazyStartProducer (producer) Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel's routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. false boolean autowiredEnabled (advanced) Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. true boolean velocityEngine (advanced) To use the VelocityEngine otherwise a new engine is created. VelocityEngine 138.5. Endpoint Options The Velocity endpoint is configured using URI syntax: with the following path and query parameters: 138.5.1. Path Parameters (1 parameters) Name Description Default Type resourceUri (producer) Required Path to the resource. You can prefix with: classpath, file, http, ref, or bean. classpath, file and http loads the resource using these protocols (classpath is default). ref will lookup the resource in the registry. bean will call a method on a bean to be used as the resource. For bean you can specify the method name after dot, eg bean:myBean.myMethod. String 138.5.2. Query Parameters (7 parameters) Name Description Default Type allowContextMapAll (producer) Sets whether the context map should allow access to all details. By default only the message body and headers can be accessed. This option can be enabled for full access to the current Exchange and CamelContext. Doing so impose a potential security risk as this opens access to the full power of CamelContext API. false boolean allowTemplateFromHeader (producer) Whether to allow to use resource template from header or not (default false). Enabling this allows to specify dynamic templates via message header. However this can be seen as a potential security vulnerability if the header is coming from a malicious user, so use this with care. false boolean contentCache (producer) Sets whether to use resource content cache or not. false boolean encoding (producer) Character encoding of the resource content. String loaderCache (producer) Enables / disables the velocity resource loader cache which is enabled by default. true boolean propertiesFile (producer) The URI of the properties file which is used for VelocityEngine initialization. String lazyStartProducer (producer (advanced)) Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel's routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. false boolean 138.6. Message Headers The Velocity component supports 4 message header(s), which is/are listed below: Name Description Default Type CamelVelocityResourceUri (producer) Constant: VELOCITY_RESOURCE_URI The name of the velocity template. String CamelVelocityTemplate (producer) Constant: VELOCITY_TEMPLATE The content of the velocity template. String CamelVelocityContext (producer) Constant: VELOCITY_CONTEXT The velocity context to use. Context CamelVelocitySupplementalContext (producer) Constant: VELOCITY_SUPPLEMENTAL_CONTEXT To add additional information to the used VelocityContext. The value of this header should be a Map with key/values that will added (override any existing key with the same name). This can be used to pre setup some common key/values you want to reuse in your velocity endpoints. Map Headers set during the Velocity evaluation are returned to the message and added as headers. Then it is possible to return values from Velocity to the Message. For example, to set the header value of fruit in the Velocity template .tm : The fruit header is now accessible from the message.out.headers . 138.7. Velocity Context Camel will provide exchange information in the Velocity context (just a Map ). The Exchange is transfered as: key value exchange The Exchange itself. exchange.properties The Exchange properties. headers The headers of the In message. camelContext The Camel Context instance. request The In message. in The In message. body The In message body. out The Out message (only for InOut message exchange pattern). response The Out message (only for InOut message exchange pattern). You can setup a custom Velocity Context yourself by setting property allowTemplateFromHeader=true and setting the message header CamelVelocityContext just like this VelocityContext velocityContext = new VelocityContext(variableMap); exchange.getIn().setHeader("CamelVelocityContext", velocityContext); 138.8. Hot reloading The Velocity template resource is, by default, hot reloadable for both file and classpath resources (expanded jar). If you set contentCache=true , Camel will only load the resource once, and thus hot reloading is not possible. This scenario can be used in production, when the resource never changes. 138.9. Dynamic templates Since Camel 2.1 Camel provides two headers by which you can define a different resource location for a template or the template content itself. If any of these headers is set then Camel uses this over the endpoint configured resource. This allows you to provide a dynamic template at runtime. Header Type Description CamelVelocityResourceUri String A URI for the template resource to use instead of the endpoint configured. CamelVelocityTemplate String The template to use instead of the endpoint configured. 138.10. Samples For example, you can use: from("activemq:My.Queue"). to("velocity:com/acme/MyResponse.vm"); To use a Velocity template to formulate a response to a message for InOut message exchanges (where there is a JMSReplyTo header). If you want to use InOnly and consume the message and send it to another destination, you could use the following route: from("activemq:My.Queue"). to("velocity:com/acme/MyResponse.vm"). to("activemq:Another.Queue"); And to use the content cache, for example, for use in production, where the .vm template never changes: from("activemq:My.Queue"). to("velocity:com/acme/MyResponse.vm?contentCache=true"). to("activemq:Another.Queue"); And a file based resource: from("activemq:My.Queue"). to("velocity:file://myfolder/MyResponse.vm?contentCache=true"). to("activemq:Another.Queue"); It is possible to specify which template the component should use dynamically via a header, for example: from("direct:in"). setHeader("CamelVelocityResourceUri").constant("path/to/my/template.vm"). to("velocity:dummy?allowTemplateFromHeader=true""); It is possible to specify a template directly as a header the component should use dynamically via a header, so for example: from("direct:in"). setHeader("CamelVelocityTemplate").constant("Hi this is a velocity template that can do templating USD{body}"). to("velocity:dummy?allowTemplateFromHeader=true""); 138.11. The Email Sample In this sample, to use the Velocity templating for an order confirmation email. The email template is laid out in Velocity as: letter.vm And the java code (from an unit test): private Exchange createLetter() { Exchange exchange = context.getEndpoint("direct:a").createExchange(); Message msg = exchange.getIn(); msg.setHeader("firstName", "Claus"); msg.setHeader("lastName", "Ibsen"); msg.setHeader("item", "Camel in Action"); msg.setBody("PS: beer is on me, James"); return exchange; } @Test public void testVelocityLetter() throws Exception { MockEndpoint mock = getMockEndpoint("mock:result"); mock.expectedMessageCount(1); mock.message(0).body(String.class).contains("Thanks for the order of Camel in Action"); template.send("direct:a", createLetter()); mock.assertIsSatisfied(); } @Override protected RouteBuilder createRouteBuilder() { return new RouteBuilder() { public void configure() { from("direct:a") .to("velocity:org/apache/camel/component/velocity/letter.vm") .to("mock:result"); } }; } 138.12. Spring Boot Auto-Configuration The component supports 6 options, which are listed below. Name Description Default Type camel.component.velocity.allow-context-map-all Sets whether the context map should allow access to all details. By default only the message body and headers can be accessed. This option can be enabled for full access to the current Exchange and CamelContext. Doing so impose a potential security risk as this opens access to the full power of CamelContext API. false Boolean camel.component.velocity.allow-template-from-header Whether to allow to use resource template from header or not (default false). Enabling this allows to specify dynamic templates via message header. However this can be seen as a potential security vulnerability if the header is coming from a malicious user, so use this with care. false Boolean camel.component.velocity.autowired-enabled Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. true Boolean camel.component.velocity.enabled Whether to enable auto configuration of the velocity component. This is enabled by default. Boolean camel.component.velocity.lazy-start-producer Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel's routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. false Boolean camel.component.velocity.velocity-engine To use the VelocityEngine otherwise a new engine is created. The option is a org.apache.velocity.app.VelocityEngine type. VelocityEngine

Commands:
<dependency> <groupId>org.apache.camel.springboot</groupId> <artifactId>camel-velocity-starter</artifactId> </dependency>
velocity:templateName[?options]
velocity:resourceUri
USDin.setHeader("fruit", "Apple")
VelocityContext velocityContext = new VelocityContext(variableMap); exchange.getIn().setHeader("CamelVelocityContext", velocityContext);
from("activemq:My.Queue"). to("velocity:com/acme/MyResponse.vm");
from("activemq:My.Queue"). to("velocity:com/acme/MyResponse.vm"). to("activemq:Another.Queue");
from("activemq:My.Queue"). to("velocity:com/acme/MyResponse.vm?contentCache=true"). to("activemq:Another.Queue");
from("activemq:My.Queue"). to("velocity:file://myfolder/MyResponse.vm?contentCache=true"). to("activemq:Another.Queue");
from("direct:in"). setHeader("CamelVelocityResourceUri").constant("path/to/my/template.vm"). to("velocity:dummy?allowTemplateFromHeader=true"");
from("direct:in"). setHeader("CamelVelocityTemplate").constant("Hi this is a velocity template that can do templating USD{body}"). to("velocity:dummy?allowTemplateFromHeader=true"");
Dear USD{headers.lastName}, USD{headers.firstName} Thanks for the order of USD{headers.item}. Regards Camel Riders Bookstore USD{body}
private Exchange createLetter() { Exchange exchange = context.getEndpoint("direct:a").createExchange(); Message msg = exchange.getIn(); msg.setHeader("firstName", "Claus"); msg.setHeader("lastName", "Ibsen"); msg.setHeader("item", "Camel in Action"); msg.setBody("PS: Next beer is on me, James"); return exchange; } @Test public void testVelocityLetter() throws Exception { MockEndpoint mock = getMockEndpoint("mock:result"); mock.expectedMessageCount(1); mock.message(0).body(String.class).contains("Thanks for the order of Camel in Action"); template.send("direct:a", createLetter()); mock.assertIsSatisfied(); } @Override protected RouteBuilder createRouteBuilder() { return new RouteBuilder() { public void configure() { from("direct:a") .to("velocity:org/apache/camel/component/velocity/letter.vm") .to("mock:result"); } }; }