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 or classpath. You can prefix the locations with either file: or classpath: where classpath: is 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>
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.
cool.end=mock:result
from("direct:start").to("properties:#{cool.end}");
You can also use placeholders as a part of the endpoint uri:
cool.foo=result
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:
cool.foo=result
cool.concat=mock:#{cool.foo}
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:.
cool.foo=result
from("direct:start").to("mock:#{cool.foo}");
And you can use them in multiple wherever you want them:
cool.start=direct:start
cool.showid=true
cool.result=result
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:
cheese.quote=Camel rocks
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.quote=Beer tastes good
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>, <jmxAgent>, <endpoint>, <routeBuilder>, <proxy> and the others.
The example below has property placeholder in the <jmxAgent> tag:
Error formatting macro: snippet: java.lang.IndexOutOfBoundsException: Index: 20, Size: 20
You can also define property placeholders in the various attributes on the <camelContext> tag such as trace as shown here:
Error formatting macro: snippet: java.lang.IndexOutOfBoundsException: Index: 20, Size: 20
Unit tests
See the unit tests in camel-core and camel-spring
- PropertiesComponentTest.java
- PropertiesComponentEndpointTest.java
- PropertiesComponentSimpleLanguageTest.java
- SpringPropertiesComponentTest.xml
- SpringPropertiesComponent2Test.xml
- SpringPropertiesComponent3Test.xml
