Using PropertyPlaceholder
Since 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 has a
limitation that prevents third-party frameworks from fully leveraging
Spring property placeholders.
For more details see: How do I use Spring Property Placeholder with Camel XML.
Bridging Spring and Camel Property Placeholders
From Camel 2.10: Spring’s property placeholder can be bridged with Camel’s. See below for more details.
The property placeholder is typically used when trying to do any of the following:
-
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
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:
{{file.uri}}
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
.
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.
Camel provides a default implementation
org.apache.camel.component.properties.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 |
---|---|
|
Lookup in the Registry. |
|
Load from the 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.
pc.setLocation("com/mycompany/myprop.properties,com/mycompany/other.properties");
pc.setLocation(new String[] {"com/mycompany/myprop.properties", "com/mycompany/other.properties"});
From Camel 2.19.0: you can set which location can be discarded if
missing by setting optional=true
, (false
by default).
Example:
pc.setLocations("com/mycompany/override.properties;optional=true,com/mycompany/defaults.properties");
Using System and Environment Variables in Locations
Since Camel 2.7
The location now supports using placeholders for JVM system properties and OS environments variables.
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 variable.
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>
Using a Properties from the Registry
Since 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("{{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}?");
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}. ${properties:com/mycompany/bar.properties:bar.quote}.");
Additional Property Placeholder Support in Spring XML
The property placeholders is also supported in many of the Camel Spring
XML tags such as
<package>
, <packageScan>
, <contextScan>
, <jmxAgent>
, <endpoint>
, <routeBuilder>
, <proxy>
and the others.
Example using property placeholders in the <jmxAgent>
tag:
<camelContext xmlns="http://camel.apache.org/schema/spring">
<propertyPlaceholder id="properties" location="org/apache/camel/spring/jmx.properties"/>
<!-- we can use propery placeholders when we define the JMX agent -->
<jmxAgent id="agent" registryPort="{{myjmx.port}}" disabled="{{myjmx.disabled}}"
usePlatformMBeanServer="{{myjmx.usePlatform}}" createConnector="true"
statisticsLevel="RoutesOnly" useHostIPAddress="true"/>
<route id="foo" autoStartup="false">
<from uri="seda:start"/>
<to uri="mock:result"/>
</route>
</camelContext>
Example using property placeholders in the attributes of <camelContext>
:
<camelContext trace="{{foo.trace}}" xmlns="http://camel.apache.org/schema/spring">
<propertyPlaceholder id="properties" location="org/apache/camel/spring/processor/myprop.properties"/>
<template id="camelTemplate" defaultEndpoint="{{foo.cool}}"/>
<route>
<from uri="direct:start"/>
<setHeader name="{{foo.header}}">
<simple>${in.body} World!</simple>
</setHeader>
<to uri="mock:result"/>
</route>
</camelContext>
Using Property Placeholders for Any Kind of Attribute in the XML DSL
Since Camel 2.7
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
.
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:prop="http://camel.apache.org/schema/placeholder"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring.xsd">
<!-- Notice in the declaration above, we have defined the prop prefix as the Camel placeholder namespace -->
<bean id="damn" class="java.lang.IllegalArgumentException">
<constructor-arg index="0" value="Damn"/>
</bean>
<camelContext xmlns="http://camel.apache.org/schema/spring">
<propertyPlaceholder id="properties" location="classpath:org/apache/camel/component/properties/myprop.properties"
xmlns="http://camel.apache.org/schema/spring"/>
<route>
<from uri="direct:start"/>
<!-- use prop namespace, to define a property placeholder, which maps to option stopOnException={{stop}} -->
<multicast prop:stopOnException="stop">
<to uri="mock:a"/>
<throwException ref="damn"/>
<to uri="mock:b"/>
</multicast>
</route>
</camelContext>
</beans>
In our properties file we have the value defined as:
stop=true
Using Property Placeholder in the Java DSL
Since 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:
from("direct:start")
// use a property placeholder for the option stopOnException on the Multicast EIP
// which should have the value of {{stop}} key being looked up in the properties file
.multicast()
.placeholder("stopOnException", "stop")
.to("mock:a")
.throwException(new IllegalAccessException("Damn"))
.to("mock:b");
Using Blueprint Property Placeholder with Camel Routes
Since 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:
<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>
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 {{ }}
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:
<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"
prefixToken="[[" suffixToken="]]" propertyPrefix="prefix."/>
<!-- in the route we can use {{ }} placeholders which will lookup in blueprint -->
<route>
<from uri="direct:start"/>
<to uri="mock:foo"/>
<to uri="[[result]]"/>
</route>
</camelContext>
</blueprint>
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
Since 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:
<!-- blueprint property placeholders -->
<cm:property-placeholder persistent-id="my-placeholders" update-strategy="reload">
<cm:default-properties>
<cm:property name="greeting" value="Hello"/>
<cm:property name="destination" value="mock:result"/>
</cm:default-properties>
</cm:property-placeholder>
<!-- a bean that uses a blueprint property placeholder -->
<bean id="myCoolBean" class="org.apache.camel.test.blueprint.MyCoolBean">
<property name="say" value="${greeting}"/>
</bean>
<camelContext xmlns="http://camel.apache.org/schema/blueprint">
<route>
<from uri="direct:start"/>
<bean ref="myCoolBean" method="saySomething"/>
<to uri="{{destination}}"/>
</route>
</camelContext>
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:
protected String useOverridePropertiesWithConfigAdmin(Dictionary props) {
// add the properties we want to override
props.put("greeting", "Bye");
// return the PID of the config-admin we are using in the blueprint xml file
return "my-placeholders";
}
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 a .cfg
or .properties
File For Blueprint Property Placeholders
Since 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
.
<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/v1.1.0"
xsi:schemaLocation="
http://aries.apache.org/blueprint/xmlns/blueprint-cm/v1.1.0 http://aries.apache.org/schemas/blueprint-cm/blueprint-cm-1.1.0.xsd
http://www.osgi.org/xmlns/blueprint/v1.0.0 https://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd">
<!-- blueprint property placeholders, that will use etc/stuff.cfg as the properties file -->
<cm:property-placeholder persistent-id="stuff" update-strategy="reload"/>
<!-- a bean that uses a blueprint property placeholder -->
<bean id="myCoolBean" class="org.apache.camel.test.blueprint.MyCoolBean">
<property name="say" value="${greeting}"/>
</bean>
<camelContext xmlns="http://camel.apache.org/schema/blueprint">
<route>
<from uri="direct:start"/>
<bean ref="myCoolBean" method="saySomething"/>
<to uri="mock:result"/>
</route>
</camelContext>
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:
@Override
protected String[] loadConfigAdminConfigurationFile() {
// String[0] = tell Camel the path of the .cfg file to use for OSGi ConfigAdmin in the blueprint XML file
// String[1] = tell Camel the persistence-id of the cm:property-placeholder in the blueprint XML file
return new String[]{"src/test/resources/etc/stuff.cfg", "stuff"};
}
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 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:
== this is a comment
greeting=Bye
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:
<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/v1.1.0"
xsi:schemaLocation="
http://aries.apache.org/blueprint/xmlns/blueprint-cm/v1.1.0 http://aries.apache.org/schemas/blueprint-cm/blueprint-cm-1.1.0.xsd
http://www.osgi.org/xmlns/blueprint/v1.0.0 https://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd">
<!-- blueprint property placeholders, that will use etc/stuff.cfg as the properties file -->
<cm:property-placeholder persistent-id="stuff" update-strategy="reload">
<cm:default-properties>
<cm:property name="greeting" value="Hello" />
<cm:property name="echo" value="Hey" />
<cm:property name="destination" value="mock:original" />
</cm:default-properties>
</cm:property-placeholder>
<!-- a bean that uses a blueprint property placeholder -->
<bean id="myCoolBean" class="org.apache.camel.test.blueprint.MyCoolBean">
<property name="say" value="${greeting}"/>
<property name="echo" value="${echo}"/>
</bean>
<camelContext xmlns="http://camel.apache.org/schema/blueprint">
<route>
<from uri="direct:start"/>
<bean ref="myCoolBean" method="saySomething"/>
<to uri="{{destination}}"/>
<bean ref="myCoolBean" method="echoSomething"/>
<to uri="{{destination}}"/>
</route>
</camelContext>
</blueprint>
And in the unit test class we do as follows:
/**
* This example will load a Blueprint .cfg file (which will initialize configadmin), and also override its property
* placeholders from this unit test source code directly (the change will reload blueprint container).
*/
public class ConfigAdminLoadConfigurationFileAndOverrideTest extends CamelBlueprintTestSupport {
@Override
protected String getBlueprintDescriptor() {
// which blueprint XML file to use for this test
return "org/apache/camel/test/blueprint/configadmin-loadfileoverride.xml";
}
@Override
protected String[] loadConfigAdminConfigurationFile() {
// which .cfg file to use, and the name of the persistence-id
return new String[]{"src/test/resources/etc/stuff.cfg", "stuff"};
}
@Override
protected String useOverridePropertiesWithConfigAdmin(Dictionary props) throws Exception {
// override / add extra properties
props.put("destination", "mock:extra");
// return the persistence-id to use
return "stuff";
}
@Test
public void testConfigAdmin() throws Exception {
// mock:original comes from <cm:default-properties>/<cm:property name="destination" value="mock:original" />
getMockEndpoint("mock:original").setExpectedMessageCount(0);
// mock:result comes from loadConfigAdminConfigurationFile()
getMockEndpoint("mock:result").setExpectedMessageCount(0);
// mock:extra comes from useOverridePropertiesWithConfigAdmin()
getMockEndpoint("mock:extra").expectedBodiesReceived("Bye World", "Yay Bye WorldYay Bye World");
template.sendBody("direct:start", "World");
assertMockEndpointsSatisfied();
}
}
And the etc/stuff.cfg
configuration file contains:
greeting=Bye
echo=Yay
destination=mock:result
Bridging Spring and Camel Property Placeholders
Since 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:
<!-- bridge spring property placeholder with Camel -->
<!-- you must NOT use the <context:property-placeholder at the same time, only this bridge bean -->
<bean id="bridgePropertyPlaceholder" class="org.apache.camel.spring.spi.BridgePropertyPlaceholderConfigurer">
<property name="location" value="classpath:org/apache/camel/component/properties/cheese.properties"/>
</bean>
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:
<!-- a bean that uses Spring property placeholder -->
<!-- the ${hi} is a spring property placeholder -->
<bean id="hello" class="org.apache.camel.component.properties.HelloBean">
<property name="greeting" value="${hi}"/>
</bean>
<camelContext xmlns="http://camel.apache.org/schema/spring">
<!-- in this route we use Camels property placeholder {{ }} style -->
<route>
<from uri="direct:{{cool.bar}}"/>
<bean ref="hello"/>
<to uri="{{cool.end}}"/>
</route>
</camelContext>
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 ${}
syntax clashes with the Simple in
Camel, and therefore take care.
Example:
<setHeader name="Exchange.FILE_NAME">
<simple>{{file.rootdir}}/${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
Since 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
-
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.
@Override
protected Properties useOverridePropertiesWithPropertiesComponent() {
Properties extra = new Properties();
extra.put("destination", "mock:extra");
extra.put("greeting", "Bye");
return extra;
}
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
Since 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
Since 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:
<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)
Since 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 - 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:
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.spi.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:
PropertiesComponent pc = context.getPropertiesComponent();
pc.addFunction(new MyBeerFunction());