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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)
• using Blueprint PropertyPlaceholder with Camel Properties component
• using @PropertyInject to inject a property in a POJO
• Camel 2.14.1 Using default value if a property does not exists
• Camel 2.14.1 Include out of the box functions, to lookup property values from OS environment variables, JVM system properties, or the service idiom.
• Camel 2.14.1 Using custom functions, which can be plugged into the property component.

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.

From Camel 2.14.1 onwards you can specify a default value to use if a property with the key does not exists, eg file.url:/some/path where the default value is the text after the colon (eg /some/path).

PropertyResolver

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 Registry
• file: to load the from file system
• classpath: to load from classpath (this is also the default if no prefix is provided)
• blueprint: Camel 2.7: to use a specific OSGi blueprint placeholder service

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");

Using system and environment variables in locations

Available as of Camel 2.7

The location now supports using placeholders for JVM system properties and OS environments variables.

For example:

location=file:${karaf.home}/etc/foo.properties

In the location above we defined a location using the file scheme using the JVM system property with key karaf.home.

To use an OS environment variable instead you would have to prefix with env:

location=file:${env:APP_HOME}/etc/foo.properties

Where APP_HOME is an OS environment.

You can have multiple placeholders in the same location, such as:

location=file:${env:APP_HOME}/etc/${prop.name}.properties

Using system and environment variables to configure property prefixes and suffixes

Available as of Camel 2.12.5, 2.13.3, 2.14.0

propertyPrefix, propertySuffix configuration properties support using placeholders for JVM system properties and OS environments variables.

For example. if PropertiesComponent is configured with the following properties file:

dev.endpoint = result1
test.endpoint = result2

Then with the following route definition:

PropertiesComponent pc = context.getComponent("properties", PropertiesComponent.class);
pc.setPropertyPrefix("${stage}.");
// ...
context.addRoutes(new RouteBuilder() {
    @Override
    public void configure() throws Exception {
        from("direct:start").to("properties:mock:{{endpoint}}");
    }
});

it is possible to change the target endpoint by changing system property stage either to dev (the message will be routed to mock:result1) or test (the message will be routed to mock:result2).

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:

{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/jmxConfigUsingProperties.xml}

You can also define property placeholders in the various attributes on the <camelContext> tag such as trace as shown here:

{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/SpringTraceUsingPropertyTest-context.xml}

Overriding a property setting using a JVM System Property

Available as of Camel 2.5
It is possible to override a property value at runtime using a JVM System property without the need to restart the application to pick up the change. This may also be accomplished from the command line by creating a JVM System property of the same name as the property it replaces with a new value. An example of this is given below

PropertiesComponent pc = context.getComponent("properties", PropertiesComponent.class);
pc.setCache(false);
        
System.setProperty("cool.end", "mock:override");
System.setProperty("cool.result", "override");

context.addRoutes(new RouteBuilder() {
    @Override
    public void configure() throws Exception {
        from("direct:start").to("properties:cool.end");
        from("direct:foo").to("properties:mock:{{cool.result}}");
    }
});
context.start();

getMockEndpoint("mock:override").expectedMessageCount(2);

template.sendBody("direct:start", "Hello World");
template.sendBody("direct:foo", "Hello Foo");

System.clearProperty("cool.end");
System.clearProperty("cool.result");
        
assertMockEndpointsSatisfied();

Using property placeholders for any kind of attribute in the XML DSL

Available as of Camel 2.7

Previously it was only the xs:string type attributes in the XML DSL that support placeholders. For example often a timeout attribute would be a xs:int type and thus you cannot set a string value as the placeholder key. This is now possible from Camel 2.7 onwards using a special placeholder namespace.

In the example below we use the prop prefix for the namespace http://camel.apache.org/schema/placeholder by which we can use the prop prefix in the attributes in the XML DSLs. Notice how we use that in the Multicast to indicate that the option stopOnException should be the value of the placeholder with the key "stop".

{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/component/properties/SpringOptionalPropertiesDslTest.xml}

In our properties file we have the value defined as

stop=true

Using property placeholder in the Java DSL

Available as of Camel 2.7

Likewise we have added support for defining placeholders in the Java DSL using the new placeholder DSL as shown in the following equivalent example:

{snippet:id=e1|lang=java|url=camel/trunk/camel-core/src/test/java/org/apache/camel/component/properties/OptionalPropertiesDslTest.java}

Using Blueprint property placeholder with Camel routes

Available as of Camel 2.7

Camel supports Blueprint which also offers a property placeholder service. Camel supports convention over configuration, so all you have to do is to define the OSGi Blueprint property placeholder in the XML file as shown below:

{snippet:id=e1|lang=xml|title=Using OSGi blueprint property placeholders in Camel routes|url=camel/trunk/tests/camel-itest-osgi/src/test/resources/org/apache/camel/itest/osgi/blueprint/blueprint-17.xml}

By default Camel detects and uses OSGi blueprint property placeholder service. You can disable this by setting the attribute useBlueprintPropertyResolver to false on the <camelContext> definition.

You can also explicit refer to a specific OSGi blueprint property placeholder by its id. For that you need to use the Camel's <propertyPlaceholder> as shown in the example below:

{snippet:id=e1|lang=xml|title=Explicit referring to a OSGi blueprint placeholder in Camel|url=camel/trunk/tests/camel-itest-osgi/src/test/resources/org/apache/camel/itest/osgi/blueprint/blueprint-16.xml}

Notice how we use the blueprint scheme to refer to the OSGi blueprint placeholder by its id. This allows you to mix and match, for example you can also have additional schemes in the location. For example to load a file from the classpath you can do:

location="blueprint:myblueprint.placeholder,classpath:myproperties.properties"

Each location is separated by comma.

Overriding Blueprint property placeholders outside CamelContext

Available as of Camel 2.10.4

When using Blueprint property placeholder in the Blueprint XML file, you can declare the properties directly in the XML file as shown below:

{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-test-blueprint/src/test/resources/org/apache/camel/test/blueprint/configadmin-outside.xml}

Notice that we have a <bean> which refers to one of the properties. And in the Camel route we refer to the other using the {{ }} notation.

Now if you want to override these Blueprint properties from an unit test, you can do this as shown below:

{snippet:id=e1|lang=java|url=camel/trunk/components/camel-test-blueprint/src/test/java/org/apache/camel/test/blueprint/ConfigAdminOverridePropertiesOutsideCamelContextTest.java}

To do this we override and implement the useOverridePropertiesWithConfigAdmin method. We can then put the properties we want to override on the given props parameter. And the return value must be the persistence-id of the <cm:property-placeholder> tag, which you define in the blueprint XML file.

Using .cfg or .properties file for Blueprint property placeholders

Available as of Camel 2.10.4

When using Blueprint property placeholder in the Blueprint XML file, you can declare the properties in a .properties or .cfg file. If you use Apache ServieMix / Karaf then this container has a convention that it loads the properties from a file in the etc directory with the naming etc/pid.cfg, where pid is the persistence-id.

For example in the blueprint XML file we have the persistence-id="stuff", which mean it will load the configuration file as etc/stuff.cfg.

{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-test-blueprint/src/test/resources/org/apache/camel/test/blueprint/configadmin-loadfile.xml}

Now if you want to unit test this blueprint XML file, then you can override the loadConfigAdminConfigurationFile and tell Camel which file to load as shown below:

{snippet:id=e1|lang=java|url=camel/trunk/components/camel-test-blueprint/src/test/java/org/apache/camel/test/blueprint/ConfigAdminLoadConfigurationFileTest.java}

Notice that this method requires to return a String[] with 2 values. The 1st value is the path for the configuration file to load.
The 2nd value is the persistence-id of the <cm:property-placeholder> tag.

The stuff.cfg file is just a plain properties file with the property placeholders such as:

## this is a comment
greeting=Bye

Using .cfg file and overriding properties for Blueprint property placeholders

You can do both as well. Here is a complete example. First we have the Blueprint XML file:

{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-test-blueprint/src/test/resources/org/apache/camel/test/blueprint/configadmin-loadfileoverride.xml}

And in the unit test class we do as follows:

{snippet:id=e1|lang=java|url=camel/trunk/components/camel-test-blueprint/src/test/java/org/apache/camel/test/blueprint/ConfigAdminLoadConfigurationFileAndOverrideTest.java}

And the etc/stuff.cfg configuration file contains

greeting=Bye
echo=Yay
destination=mock:result

Bridging Spring and Camel property placeholders

Available as of Camel 2.10

The Spring Framework does not allow 3rd party frameworks such as Apache Camel to seamless hook into the Spring property placeholder mechanism. However you can easily bridge Spring and Camel by declaring a Spring bean with the type org.apache.camel.spring.spi.BridgePropertyPlaceholderConfigurer, which is a Spring org.springframework.beans.factory.config.PropertyPlaceholderConfigurer type.

To bridge Spring and Camel you must define a single bean as shown below:

{snippet:id=e1|lang=xml|title=Bridging Spring and Camel property placeholders|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/component/properties/CamelSpringPropertyPlaceholderConfigurerTest.xml}

You must not use the spring <context:property-placeholder> namespace at the same time; this is not possible.

After declaring this bean, you can define property placeholders using both the Spring style, and the Camel style within the <camelContext> tag as shown below:

{snippet:id=e2|lang=xml|title=Using bridge property placeholders|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/component/properties/CamelSpringPropertyPlaceholderConfigurerTest.xml}

Notice how the hello bean is using pure Spring property placeholders using the ${ } notation. And in the Camel routes we use the Camel placeholder notation with {{ }}.

Clashing Spring property placeholders with Camels Simple language

Take notice when using Spring bridging placeholder then the spring ${ } syntax clashes with the Simple in Camel, and therefore take care. For example:

<setHeader headerName="Exchange.FILE_NAME">
  <simple>{{file.rootdir}}/${in.header.CamelFileName}</simple>
</setHeader>

clashes with Spring property placeholders, and you should use $simple{ } to indicate using the Simple language in Camel.

<setHeader headerName="Exchange.FILE_NAME">
  <simple>{{file.rootdir}}/$simple{in.header.CamelFileName}</simple>
</setHeader>

An alternative is to configure the PropertyPlaceholderConfigurer with ignoreUnresolvablePlaceholders option to true.

Overriding properties from Camel test kit

Available as of Camel 2.10

When Testing with Camel and using the Properties component, you may want to be able to provide the properties to be used from directly within the unit test source code.
This is now possible from Camel 2.10 onwards, as the Camel test kits, eg CamelTestSupport class offers the following methods

• useOverridePropertiesWithPropertiesComponent
• ignoreMissingLocationWithPropertiesComponent

So for example in your unit test classes, you can override the useOverridePropertiesWithPropertiesComponent method and return a java.util.Properties that contains the properties which should be preferred to be used.

{snippet:id=e1|lang=java|title=Providing properties from within unit test source|url=camel/trunk/components/camel-test-blueprint/src/test/java/org/apache/camel/test/blueprint/ConfigAdminOverridePropertiesTest.java}

This can be done from any of the Camel Test kits, such as camel-test, camel-test-spring, and camel-test-blueprint.

The ignoreMissingLocationWithPropertiesComponent can be used to instruct Camel to ignore any locations which was not discoverable, for example if you run the unit test, in an environment that does not have access to the location of the properties.

Using @PropertyInject

Available as of Camel 2.12

Camel allows to inject property placeholders in POJOs using the @PropertyInject annotation which can be set on fields and setter methods.
For example you can use that with RouteBuilder classes, such as shown below:

public class MyRouteBuilder extends RouteBuilder {

    @PropertyInject("hello")
    private String greeting;

    @Override
    public void configure() throws Exception {
        from("direct:start")
            .transform().constant(greeting)
            .to("{{result}}");
    }

}

Notice we have annotated the greeting field with @PropertyInject and define it to use the key "hello". Camel will then lookup the property with this key and inject its value, converted to a String type.

You can also use multiple placeholders and text in the key, for example we can do:

    @PropertyInject("Hello {{name}} how are you?")
    private String greeting;

This will lookup the placeholder with they key "name".

You can also add a default value if the key does not exists, such as:

    @PropertyInject(value = "myTimeout", defaultValue = "5000")
    private int timeout;

Using out of the box functions

Available as of Camel 2.14.1

The Properties component includes the following functions out of the box

• env - A function to lookup the property from OS environment variables
• sys - A function to lookup the property from Java JVM system properties
• service - A function to lookup the property from OS environment variables using the service naming idiom

As you can see these functions is intended to make it easy to lookup values from the environment. As they are provided out of the box, they can easily be used as shown below:

  <camelContext xmlns="http://camel.apache.org/schema/blueprint">
 
    <route>
      <from uri="direct:start"/>
      <to uri="{{env:SOMENAME}}"/>
      <to uri="{{sys:MyJvmPropertyName}}"/>
    </route>
  </camelContext>

You can use default values as well, so if the property does not exists, you can define a default value as shown below, where the default value is a log:foo and log:bar value.

  <camelContext xmlns="http://camel.apache.org/schema/blueprint">
 
    <route>
      <from uri="direct:start"/>
      <to uri="{{env:SOMENAME:log:foo}}"/>
      <to uri="{{sys:MyJvmPropertyName:log:bar}}"/>
    </route>
  </camelContext>

The service function is for looking up a service which is defined using OS environment variables using the service naming idiom, to refer to a service location using hostname : port

• NAME_SERVICE_HOST
• NAME_SERVICE_PORT

in other words the service uses _SERVICE_HOST and _SERVICE_PORT as prefix. So if the service is named FOO, then the OS environment variables should be set as

export $FOO_SERVICE_HOST=myserver
export $FOO_SERVICE_PORT=8888

For example if the FOO service a remote HTTP service, then we can refer to the service in the Camel endpoint uri, and use the HTTP component to make the HTTP call:

  <camelContext xmlns="http://camel.apache.org/schema/blueprint">
 
    <route>
      <from uri="direct:start"/>
      <to uri="http://{{service:FOO}}/myapp"/>
    </route>
  </camelContext>

And we can use default values if the service has not been defined, for example to call a service on localhost, maybe for unit testing etc

  <camelContext xmlns="http://camel.apache.org/schema/blueprint">
 
    <route>
      <from uri="direct:start"/>
      <to uri="http://{{service:FOO:localhost:8080}}/myapp"/>
    </route>
  </camelContext>

Using custom functions

Available as of Camel 2.14.1

The Properties component allow to plugin 3rd party functions which can be used during parsing of the property placeholders. These functions are then able to do custom logic to resolve the placeholders, such as looking up in databases, do custom computations, or whatnot. The name of the function becomes the prefix used in the placeholder. This is best illustrated in the example code below

  <bean id="beerFunction" class="MyBeerFunction"/>

  <camelContext xmlns="http://camel.apache.org/schema/blueprint">
    <propertyPlaceholder id="properties" location="none" ignoreMissingLocation="true">
      <propertiesFunction ref="beerFunction"/>
    </propertyPlaceholder>

    <route>
      <from uri="direct:start"/>
      <to uri="{{beer:FOO}}"/>
      <to uri="{{beer:BAR}}"/>
    </route>
  </camelContext>

Here we have a Camel XML route where we have defined the <propertyPlaceholder> to use a custom function, which we refer to be the bean id - eg the beerFunction. As the beer function uses "beer" as its name, then the placeholder syntax can trigger the beer function by starting with beer:value.

The implementation of the function is only two methods as shown below:

    public static final class MyBeerFunction implements PropertiesFunction {

        @Override
        public String getName() {
            return "beer";
        }

        @Override
        public String apply(String remainder) {
            return "mock:" + remainder.toLowerCase();
        }
    }

The function must implement the org.apache.camel.component.properties.PropertiesFunction interface. The method getName is  the name of the function, eg beer. And the apply method is where we implement the custom logic to do. As the sample code is from an unit test, it just returns a value to refer to a mock endpoint.

To register a custom function from Java code is as shown below:

        PropertiesComponent pc = context.getComponent("properties", PropertiesComponent.class);
        pc.addFunction(new MyBeerFunction());

See Also

• Properties component