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: Spring's property placeholder can be bridged with Camel's. See below for more details.
The property placeholder is generally in use when doing:
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typically used when trying to do any of the following:
- Lookup or creating endpoints.
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- Lookup of beans in the Registry.
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- Additional supported in Spring XML (see below in examples)
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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:
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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:
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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 Blueprint
PropertyPlaceholderwith Camel Properties component. - Using
@PropertyInjectto 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.
Format
The value of a Camel property can be obtained by specifying its key name within a property placeholder, using the following format: {{key}}.
For example:
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where file.uri is the property key.
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: you can specify a default value to use if a property with the key does not exists, e.g., file.url:/some/path where the default value is the text after the colon, 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 when providing a default value.
Using PropertyResolver
Camel provides a pluggable mechanism that allows third-parties to specify their own resolver to use for the lookup of properties.
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Camel provides a default implementation
org.apache.camel.component.properties.
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DefaultPropertiesResolver which is capable of loading properties from the file system, classpath or Registry. 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 the from file system. |
| Load from the classpath (this is also the default if no prefix is provided). |
| Use a specific OSGi blueprint placeholder service. |
Defining Location
The PropertiesResolver must be configured with the location(s) to use when resolving properties. 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 placeholders for JVM system properties and OS environments variables.
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:
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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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Using the <propertyPlaceholder> tag makes the configuration a bit more fresh 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:
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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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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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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 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.
Example:
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Example:
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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.
Example:
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Using 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 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 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 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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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:
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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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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:
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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:<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: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 a .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 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 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.loadConfigAdminConfigurationFile and tell Camel which file to load as shown below:String[] with 2 values. The 1st value is the path for the configuration file to load. The second 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:
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Using a .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:etc/stuff.cfg configuration file contains:
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Bridging Spring and Camel Property Placeholders
Available as of Camel 2.10
The Spring Framework does not allow 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:<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:${} 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.
Example:
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clashes with Spring property placeholders, and you should 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 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, as the Camel test kits, e.g., CamelTestSupport class offers the following methods
useOverridePropertiesWithPropertiesComponentignoreMissingLocationWithPropertiesComponent
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.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:
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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:
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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 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.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.port- 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 log:foo 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 hostname : port
NAME_SERVICE_HOSTNAME_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
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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:
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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 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 <propertyPlaceholder> to use a custom function, which we refer to be the bean id - e.g., 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:
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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., 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
Using the <propertyPlaceholder> tag makes the configuration a bit more fresh such as:
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<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:
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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}}");
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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:
| Code Block |
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// properties
cool.foo=result
cool.concat=mock:#{cool.foo}
// route
from("direct:start").to("properties:mock:{{cool.concat}}");
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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:
| Code Block |
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from("direct:start").to("properties:bar.end?locations=com/mycompany/bar.properties");
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Examples
You can also use property placeholders directly in the endpoint uris without having to use properties:.
| Code Block |
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// properties
cool.foo=result
// route
from("direct:start").to("mock:{{cool.foo}}");
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And you can use them in multiple wherever you want them:
| Code Block |
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// 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}}");
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You can also your property placeholders when using ProducerTemplate for example:
| Code Block |
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template.sendBody("{{cool.start}}", "Hello World");
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Example with Simple language
The Simple language now also support using property placeholders, for example in the route below:
| Code Block |
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// properties
cheese.quote=Camel rocks
// route
from("direct:start")
.transform().simple("Hi ${body} do you think ${properties:cheese.quote}?");
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You can also specify the location in the Simple language for example:
| Code Block |
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// bar.properties
bar.quote=Beer tastes good
// route
from("direct:start")
.transform().simple("Hi ${body}. ${properties:com/mycompany/bar.properties:bar.quote}.");
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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:
| Wiki Markup |
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{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:
| Wiki Markup |
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{snippet:id=e1|lang=xml|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/SpringTraceUsingPropertyTest-context.xml} |
Unit tests
See the unit tests in camel-core and camel-spring
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