Properties Component

Since Camel 2.3

The properties component is used for property placeholders in your Camel application, such as endpoint URIs. It is not a regular Camel component with producer and consumer for routing messages. However for historical reasons it was named PropertiesComponent and this name is commonly known and therfore we keep using it.

Spring Boot Auto-Configuration

The component supports 10 options, which are listed below.

Name Description Default Type

camel.component.properties.auto-discover-properties-sources

Whether to automatically discovery instances of PropertiesSource from registry and service factory.

true

Boolean

camel.component.properties.default-fallback-enabled

If false, the component does not attempt to find a default for the key by looking after the colon separator.

true

Boolean

camel.component.properties.encoding

Encoding to use when loading properties file from the file system or classpath. If no encoding has been set, then the properties files is loaded using ISO-8859-1 encoding (latin-1) as documented by java.util.Properties#load(java.io.InputStream)

String

camel.component.properties.environment-variable-mode

Sets the OS environment variables mode (0 = never, 1 = fallback, 2 = override). The default mode (override) is to use OS environment variables if present, and override any existing properties. OS environment variable mode is checked before JVM system property mode

2

Integer

camel.component.properties.ignore-missing-location

Whether to silently ignore if a location cannot be located, such as a properties file not found.

false

Boolean

camel.component.properties.initial-properties

Sets initial properties which will be used before any locations are resolved. The option is a java.util.Properties type.

String

camel.component.properties.location

A list of locations to load properties. You can use comma to separate multiple locations. This option will override any default locations and only use the locations from this option.

String

camel.component.properties.override-properties

Sets a special list of override properties that take precedence and will use first, if a property exist. The option is a java.util.Properties type.

String

camel.component.properties.properties-parser

To use a custom PropertiesParser. The option is a org.apache.camel.component.properties.PropertiesParser type.

String

camel.component.properties.system-properties-mode

Sets the JVM system property mode (0 = never, 1 = fallback, 2 = override). The default mode (override) is to use system properties if present, and override any existing properties. OS environment variable mode is checked before JVM system property mode

2

Integer

Resolving property from Java code
You can use the method resolvePropertyPlaceholders on the CamelContext to resolve a property from any Java code.

Using PropertyPlaceholder

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.

Bridging Spring and Camel property placeholders
You can bridge the Spring property placeholder with Camel, see further below for more details.

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

  • Using default value if a property does not exists

  • Include out of the box functions, to lookup property values from OS environment variables, JVM system properties, or the service idiom.

  • 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.

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).

Do not use colon in the property key. The colon is used as a separator token when you are providing a default value.

Defining location

The properties component 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");

You can set which location can be discarded if missing by by setting the optional attribute, which is false by default, i.e:

pc.setLocations(
    "com/mycompany/override.properties;optional=true"
    "com/mycompany/defaults.properties");

Using system and environment variables in locations

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.

Some OS’es (such as Linux) do not support dashes in environment variable names, so here we are using APP_HOME. But if you specify APP-HOME then Camel 3 will automatic lookup the value as APP_HOME (with underscore) as fallback.

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

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

Configuring in Java DSL

You have to create and register the PropertiesComponent under the name properties such as:

PropertiesComponent pc = camelContext.getPropertiesComponent();
pc.setLocation("classpath:com/mycompany/myprop.properties");

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>

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:

<camelContext ...>
  <propertyPlaceholder id="myPropertyPlaceholder">
    <propertiesLocation
      resolver = "classpath"
      path     = "com/my/company/something/my-properties-1.properties"
      optional = "false"/>
    <propertiesLocation
      resolver = "classpath"
      path     = "com/my/company/something/my-properties-2.properties"
      optional = "false"/>
    <propertiesLocation
      resolver = "file"
      path     = "${karaf.home}/etc/my-override.properties"
      optional = "true"/>
   </propertyPlaceholder>
</camelContext>
Specifying the cache option inside XML
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

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("{{cool.end}}");

You can also use placeholders as a part of the endpoint uri:

// properties
cool.foo=result

// route
from("direct:start").to("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("mock:{{cool.concat}}");

Notice how cool.concat refer to another property.

And you can use placeholders several times:

// 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}?");

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:

Using JVM system properties or Environment variables as override or fallback values

The properties components supports using JVM system properties and also OS environment variables as values which can either be used as override or fallback values.

The default mode is that both of them are in override mode, and they are check in the following order:

  1. OS environment variable (override mode)

  2. JVM system property (override mode)

  3. Property files and other locations

  4. OS environment variable (fallback mode)

  5. JVM system property (fallback mode)

The check stops at first found property value for the key.

You can control these modes using the systemPropertiesMode and environmentVariableMode options on the properties component.

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

In the example below we use the prop prefix for the namespace 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".

In our properties file we have the value defined as

stop=true

Using Blueprint property placeholder with Camel routes

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:

<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xmlns:cm="http://aries.apache.org/blueprint/xmlns/blueprint-cm/v1.0.0"
           xsi:schemaLocation="
           http://www.osgi.org/xmlns/blueprint/v1.0.0 https://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd">

    <!-- OSGI blueprint property placeholder -->
    <cm:property-placeholder id="myblueprint.placeholder" persistent-id="camel.blueprint">
        <!-- list some properties as needed -->
        <cm:default-properties>
            <cm:property name="result" value="mock:result"/>
        </cm:default-properties>
    </cm:property-placeholder>

    <camelContext xmlns="http://camel.apache.org/schema/blueprint">
        <!-- in the route we can use {{ }} placeholders which will lookup in blueprint
             as Camel will auto detect the OSGi blueprint property placeholder and use it -->
        <route>
            <from uri="direct:start"/>
            <to uri="mock:foo"/>
            <to uri="{{result}}"/>
        </route>
    </camelContext>
</blueprint>

Using OSGi blueprint property placeholders in Camel routes

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.

About placeholder syntax

Notice how we can use the Camel syntax for placeholders {{ and }} 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 {{ and }} 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:

<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xmlns:cm="http://aries.apache.org/blueprint/xmlns/blueprint-cm/v1.0.0"
           xsi:schemaLocation="
           http://www.osgi.org/xmlns/blueprint/v1.0.0 https://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd">

    <!-- OSGI blueprint property placeholder -->
    <cm:property-placeholder id="myblueprint.placeholder" persistent-id="camel.blueprint">
        <!-- list some properties as needed -->
        <cm:default-properties>
            <cm:property name="prefix.result" value="mock:result"/>
        </cm:default-properties>
    </cm:property-placeholder>

    <camelContext xmlns="http://camel.apache.org/schema/blueprint">
        <!-- using Camel properties component and refer to the blueprint property placeholder by its id -->
        <propertyPlaceholder id="properties" location="blueprint:myblueprint.placeholder"/>

        <!-- in the route we can use {{ }} placeholders which will lookup in blueprint -->
        <route>
            <from uri="direct:start"/>
            <to uri="mock:foo"/>
            <to uri="{{prefix.result}}"/>
        </route>
    </camelContext>
</blueprint>

Explicit referring to a OSGi blueprint placeholder in Camel

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

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

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 {{ and }} notation.

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

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

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.

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:

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:

And in the unit test class we do as follows:

And the etc/stuff.cfg configuration file contains

greeting=Bye
echo=Yay
destination=mock:result

Bridging Spring and Camel property placeholders

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:

Bridging Spring and Camel property placeholders

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:

Using bridge property placeholders

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 {{ and }}.

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 name="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 name="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

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.
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.

Providing properties from within unit test source

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

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

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.name - A function to lookup the property from OS environment variables using the service naming idiom returning the hostname part only

  • service.port - 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:

  <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 (advanced)

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">
    <propertiesFunction ref="beerFunction"/>
  </propertyPlaceholder>

  <route>
    <from uri="direct:start"/>
    <to uri="{`{beer:FOO}`}"/>
    <to uri="{`{beer:BAR}`}"/>
  </route>
</camelContext>
The location attribute (on propertyPlaceholder tag) is not mandatory

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 = (org.apache.camel.componennt.properties.PropertiesComponent) context.getPropertiesComponent();
pc.addFunction(new MyBeerFunction());

Using 3rd-party properties sources

The properties component allows to plugin 3rd party sources to load and lookup properties via the PropertySource API from camel-api. For example the camel-microprofile-config component is implemented using this. The 3rd-party PropertySource can automatic be discoverd from classpath when Camel is starting up. This is done by include the file META-INF/services/org/apache/camel/property-source-factory file which refers to the fully qualified class name of the PropertySource implementation. See the camel-microprofile-config for an example.

You can also register 3rd-part property sources via Java API

PropertiesComponent pc = ...
pc.addPropertySource(myPropertySource);

LoadablePropertySource

A PropertySource can define that it supports loading all its properties from the source at once, for example from file system. This allows Camel properties component to load these properties at once during startup.

PropertySource

The regular PropertySource will lookup the property on-demand, for example to lookup values from a backend source such as a database or HashiCorp Vault etc.