Using Using PropertyPlaceholder
Available as of Camel 2.3
Camel now provides a new PropertiesComponent
in 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 has a limitation which that prevents 3rd third-party frameworks to leverage from fully leveraging Spring property placeholders to the fullest. See more at
For more details see: How do I use Spring Property Placeholder with Camel XML.
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From Camel 2.10
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: Spring's property placeholder can be bridged with Camel
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's. See below for more details.
The property placeholder is generally in use when doing:typically used when trying to do any of the following:
- Lookup lookup or creating endpoints.
- lookup Lookup of beans in the Registry.
- additional Additional supported in Spring XML (see below in examples).
- using Blueprint Using Blueprint
PropertyPlaceholder
with Camel Properties component. - using 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.
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Format
The syntax to use Camel's property placeholder is to use value of a Camel property can be obtained by specifying its key name within a property placeholder, using the following format: {{key
}} for .
For example:
...
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
Property placeholders can be used to specify parts, or all, of an endpoint's URI by embedding one or more placeholders in the URI's string definition.
From Camel 2.14.1 onwards : you can specify a default value to use if a property with the key does not exists, eg e.g., file.url:/some/path
where the default value is the text after the colon (eg /, e.g., /some/path
).
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From Camel 2.14.1: do not use a colon in the property key. The colon character is used as a token separator
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when
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providing a default value
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.
Using PropertyResolver
Camel provides a pluggable mechanism which allows 3rd part to provide that allows third-parties to specify their own resolver to use for the lookup of 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:
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To indicate which source to use the location must contain the appropriate prefix.
The list of prefixes is:
Prefix | Description |
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| Lookup in the Registry. |
| Load |
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the from file system. |
|
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Load from the classpath (this is also the default if no prefix is provided). | |
|
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Use a specific OSGi blueprint placeholder service. |
Defining
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Location
The PropertiesResolver
need to know a must be configured with the location(s) where to resolve the use when resolving 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:
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One or more locations can be given. Specifying multiple locations can be done a couple of ways: using either a single comma separated string, or an array of strings.
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From Camel 2.19.0: you can set which location can be discarded if missing by setting optional=true
, (false
by default).
Example:
java
Using System and Environment Variables in Locations
Available as of Camel 2.7
The location now supports
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:
Code Block |
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location=file:${karaf.home}/etc/foo.properties
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In the location above we defined a location using the file scheme using the JVM system property with key karaf.home
.
To use an OS environment variable instead you would have to prefix with env:
Code Block |
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location=file:${env:APP_HOME}/etc/foo.properties
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Where APP_HOME
is an OS environment.
You can have multiple placeholders in the same location, such as:
Code Block |
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location=file:${env:APP_HOME}/etc/${prop.name}.properties
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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:
No Format |
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dev.endpoint = result1
test.endpoint = result2 |
Then with the following route definition:
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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}}");
}
});
Example:
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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
:
...
Where APP_HOME
is an OS environment variable.
You can have multiple placeholders in the same location, such as:
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Using System or Environment Variables to Configure Property Prefixes and Suffixes
From Camel 2.12.5, 2.13.3, 2.14.0: propertyPrefix
, propertySuffix
configuration properties support the use of placeholders for de-referencing JVM system properties and OS environments variables.
Example:
Assume the PropertiesComponent
is configured with the following properties file:
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The same properties file is then referenced from a route definition:
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By using the configuration options propertyPrefix
it's possible to change the target endpoint simply by changing the value of the 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:
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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.
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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:
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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.
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Using the <propertyPlaceholder>
tag makes the configuration a bit more fresh such as:
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Tip | ||
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| ||
Camel 2.10 onwards supports specifying a value for the cache option both inside the Spring as well as the Blueprint XML. |
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:
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<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.
Code Block |
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// properties
cool.end=mock:result
// route
from("direct:start").to("properties:{{cool.end}}");
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You can also use placeholders as a part of the endpoint uri:
Code Block |
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// 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:
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Setting the properties location through the location tag works just fine but sometime you have a number of resources to take into account and starting from Camel 2.19.0 you can set the properties location with a dedicated propertiesLocation
:
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From Camel 2.10: Camel supports specifying a value for the cache
option both inside the Spring as well as the Blueprint XML.
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:
...
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.
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You can also use placeholders as a part of the endpoint URI:
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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:
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In the example above the to endpoint will be resolved to mock:result
.
You can also use property placeholders directly in the endpoint uris without having to use properties:
.
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have properties with refer to each other such as:
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And you can use them in multiple wherever you want them:
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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:
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Examples
You can also use property placeholders directly in the endpoint URIs without having to use properties:
.
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And you can use them in multiple wherever you want them:
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You can also your property placeholders when using ProducerTemplate for example:
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Example with Simple language
The Simple language now also support using property placeholders, for example in the route below:
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You can also specify the location in the Simple language for example:
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Additional
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Property Placeholder Support 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
Example:
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language | xml |
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You can also define Example:
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language | xml |
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Overriding a
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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
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Example:
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Using
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Property Placeholders for Any Kind of Attribute in the XML DSL
Available as of Camel 2.7
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If you use OSGi Blueprint then this only works from 2.11.1 or 2.10.5
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on.
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 on 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
".
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...
In our properties file we have the value defined as
...
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Using
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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:
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language | xml |
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Using Blueprint
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Property Placeholder with Camel
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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:unmigrated-inline-wiki-markup
{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}
useBlueprintPropertyResolver
to false on the <camelContext>
definition.Info | ||
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Notice how we can use the Camel syntax for placeholders {{ }} in the Camel route, which will lookup the value from OSGi blueprint. |
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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.
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Notice how we can use the Camel syntax for placeholders {{ }}
in the Camel route, which will lookup the value from OSGi blueprint.
The blueprint syntax for placeholders is ${}
. So outside the <camelContext>
you must use the ${}
syntax. Where as inside <camelContext>
you must use {{ }}
syntax. OSGi blueprint allows you to configure the syntax, so you can actually align those if you want.
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:
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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 Wiki Markup 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:
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...
Each location is separated by comma.
Overriding Blueprint
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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: Wiki Markup <bean>
which refers to one of the properties. And in the Camel route we refer to the other using the the {{ }}
notation.
Now if you want to override these Blueprint properties from an unit test, you can do this as shown below: Wiki Markup 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 the <cm:property-placeholder>
tag, which you define in the blueprint XML file.
Using a .cfg
...
or .properties
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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 or .cfg
file. If you use Apache ServieMix ServiceMix/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 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
. Wiki Markup loadConfigAdminConfigurationFile
and tell Camel which file to load as shown below: Wiki Markup String[]
with 2 values. The 1st value is the path for the configuration file to load.
The 2nd second value is the persistence-id of the the <cm:property-placeholder>
tag.
The The stuff.cfg
file is just a plain properties file with the property placeholders such as:
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Using a .cfg
file and
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Overriding Properties for Blueprint
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Property Placeholders
You can do both as well. Here is a complete example. First we have the Blueprint XML file: Wiki Markup Wiki Markup etc/stuff.cfg
configuration file contains
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:
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Bridging Spring and Camel
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Property Placeholders
Available as of Camel 2.10
The Spring Framework does not allow 3rd third-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: : Wiki Markup <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 the <camelContext>
tag as shown below: Wiki Markup ${}
notation. And in the Camel routes we use the Camel placeholder notation with {{ }}
.
Clashing Spring
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Property Placeholders with Camels Simple
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Language
Take notice when using Spring bridging placeholder then the spring spring ${}
syntax clashes with the Simple in Camel, and therefore take care. For example
Example:
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clashes with Spring property placeholders, and you should use use $simple{}
to indicate using the Simple language in Camel.
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An alternative is to configure the PropertyPlaceholderConfigurer
with ignoreUnresolvablePlaceholders
option to true
.
Overriding
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Properties from Camel
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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 e.g., 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. Wiki Markup 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 . For example if you run the unit test, in an environment that does not have access to the location of the properties.
Using Using @PropertyInject
Available as of Camel 2.12
Camel allows to inject property placeholders in POJOs using the 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:
...
...
Notice we have annotated the greeting field with 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:
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This will lookup the placeholder with they key "name
".
You can also add a default value if the key does not exists, such as:
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Using
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Out of the
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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.service.host
- Camel 2.16.1: A function to lookup the property from OS environment variables using the service naming idiom returning the hostname part only.service.
portport
- Camel 2.16.1: A function to lookup the property from OS environment variables using the service naming idiom returning the port part only.
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:
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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 a log:foo
and and log:bar
value.
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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 using hostname : port
NAME
_SERVICE_HOST
NAME
_SERVICE_PORT
in other words the service uses uses _SERVICE_HOST
and and _SERVICE_PORT
as prefix. So if the service is named FOO
, then the OS environment variables should be set as
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For example if the the FOO
service a remote HTTP service, then we can refer to the service in the Camel endpoint uriURI, and use the HTTP component to make the HTTP call:
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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:
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Using
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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
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Here we have a Camel XML route where we have defined the the <propertyPlaceholder>
to use a custom function, which we refer to be the bean id - eg id - e.g., the beerFunction
. As the beer function uses "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:
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The function must implement the org.apache.camel.component.properties.PropertiesFunction
interface. The method getName
is the name of the function, e.g., 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:
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See Also
- Properties component