Using PropertyPlaceholder
Available as of Camel 2.3
Camel now provides a new PropertiesComponent
in camel-core which allows you to use property placeholders when defining Camel Endpoint URIs.
This works much like you would do if using Spring's <property-placeholder>
tag. However Spring have a limitation which prevents 3rd party frameworks to leverage Spring property placeholders to the fullest. See more at How do I use Spring Property Placeholder with Camel XML.
The property placeholder is generally in use when doing:
- lookup or creating endpoints
- lookup of beans in the Registry
- additional supported in Spring XML (see below in examples)
Syntax
The syntax to use Camel's property placeholder is to use {{key
}} for example {{file.uri
}} where file.uri
is the property key.
You can use property placeholders in parts of the endpoint URI's which for example you can use placeholders for parameters in the URIs.
PropertyResolver
As usually Camel provides a pluggable mechanism which allows 3rd part to provide their own resolver to lookup properties. Camel provides a default implementation org.apache.camel.component.properties.DefaultPropertiesResolver
which is capable of loading properties from the file system, classpath or Registry. You can prefix the locations with either:
ref:
Camel 2.4: to lookup in the Registryfile:
to load the from file systemclasspath:
to load from classpath (this is also the default if no prefix is provided)
Defining location
The PropertiesResolver
need to know a location(s) where to resolve the properties. You can define 1 to many locations. If you define the location in a single String property you can separate multiple locations with comma such as:
pc.setLocation("com/mycompany/myprop.properties,com/mycompany/other.properties");
Configuring in Java DSL
You have to create and register the PropertiesComponent
under the name properties
such as:
PropertiesComponent pc = new PropertiesComponent(); pc.setLocation("classpath:com/mycompany/myprop.properties"); context.addComponent("properties", pc);
Configuring in Spring XML
Spring XML offers two variations to configure. You can define a spring bean as a PropertiesComponent
which resembles the way done in Java DSL. Or you can use the <propertyPlaceholder>
tag.
<bean id="properties" class="org.apache.camel.component.properties.PropertiesComponent"> <property name="location" value="classpath:com/mycompany/myprop.properties"/> </bean>
Using the <propertyPlaceholder>
tag makes the configuration a bit more fresh such as:
<camelContext ...> <propertyPlaceholder id="properties" location="com/mycompany/myprop.properties"/> </camelContext>
Using a Properties from the Registry
Available as of Camel 2.4
For example in OSGi you may want to expose a service which returns the properties as a java.util.Properties
object.
Then you could setup the Properties component as follows:
<propertyPlaceholder id="properties" location="ref:myProperties"/>
Where myProperties
is the id to use for lookup in the OSGi registry. Notice we use the ref:
prefix to tell Camel that it should lookup the properties for the Registry.
Examples using properties component
When using property placeholders in the endpoint URIs you can either use the properties:
component or define the placeholders directly in the URI. We will show example of both cases, starting with the former.
// properties cool.end=mock:result // route from("direct:start").to("properties:{{cool.end}}");
You can also use placeholders as a part of the endpoint uri:
// properties cool.foo=result // route from("direct:start").to("properties:mock:{{cool.foo}}");
In the example above the to endpoint will be resolved to mock:result
.
You can also have properties with refer to each other such as:
// properties cool.foo=result cool.concat=mock:#{cool.foo} // route from("direct:start").to("properties:mock:{{cool.concat}}");
Notice how cool.concat
refer to another property.
The properties:
component also offers you to override and provide a location in the given uri using the locations
option:
from("direct:start").to("properties:bar.end?locations=com/mycompany/bar.properties");
Examples
You can also use property placeholders directly in the endpoint uris without having to use properties:
.
// properties cool.foo=result // route from("direct:start").to("mock:{{cool.foo}}");
And you can use them in multiple wherever you want them:
// properties cool.start=direct:start cool.showid=true cool.result=result // route from("{{cool.start}}") .to("log:{{cool.start}}?showBodyType=false&showExchangeId={{cool.showid}}") .to("mock:{{cool.result}}");
You can also your property placeholders when using ProducerTemplate for example:
template.sendBody("{{cool.start}}", "Hello World");
Example with Simple language
The Simple language now also support using property placeholders, for example in the route below:
// properties cheese.quote=Camel rocks // route from("direct:start") .transform().simple("Hi ${body} do you think ${properties:cheese.quote}?");
You can also specify the location in the Simple language for example:
// bar.properties bar.quote=Beer tastes good // route from("direct:start") .transform().simple("Hi ${body}. ${properties:com/mycompany/bar.properties:bar.quote}.");
Additional property placeholder supported in Spring XML
The property placeholders is also supported in many of the Camel Spring XML tags such as <package>, <packageScan>, <contextScan>, <jmxAgent>, <endpoint>, <routeBuilder>, <proxy>
and the others.
The example below has property placeholder in the <jmxAgent> tag:
You can also define property placeholders in the various attributes on the <camelContext> tag such as trace
as shown here:
Unit tests
See the unit tests in camel-core and camel-spring
- PropertiesComponentTest.java
- PropertiesComponentEndpointTest.java
- PropertiesComponentSimpleLanguageTest.java
- SpringPropertiesComponentTest.xml
- SpringPropertiesComponent2Test.xml
- SpringPropertiesComponent3Test.xml