DeltaSpike Configuration Mechanism

Introduction

The goal of the DeltaSpike configuration mechanism is to make it obsolete to touch released binaries for changing the configuration of your project. All values which are needed in your code (but should not be hardcoded as static final constants) can be maintained via DeltaSpike’s own configuration mechanism in a very flexible and powerful way.

Benefits for Production

Once a binary like a WAR file or an EAR got created and tested, it must not get changed anymore. The exact same binary which got created by the release manager will get moved to the Test system, then further propagated to the Staging environment and finally (if all people are happy with it) will get moved to the Production system. And all this without any changes on the binary itself!

The Apache DeltaSpike configuration system makes this possible by providing a default configuration inside the binary and allowing to amend this configuration (e.g. database credentials, some URLs from remote REST or SOAP endpoints, etc) from outside like environment settings, JNDI or the current ProjectStage.

Drop-In Configuration

This mechanism also allows for dynamic configuration in case of a JAR drop-in. By adding some JAR to the classpath, all its contained configuration will get picked up and considered in the property value evaluation. You could also use this mechanism to switch implementations of some SPI (Service Provider Interface) in your own code.

CDI-Extension Configuration

In some cases low-level configs are needed, for example during the bootstrapping process of the CDI container.

The good news: our DeltaSpike configuration mechanism does not rely on any other EE mechanism to be booted. Which means it can perfectly get used to even configure those parts itself. Since the mechanism does not rely on CDI it can for example be used to configure CDI-Extensions.

Currently this is, for example, used to configure the value of the current ProjectStage, configured values which can be used in the expressions for @Exclude, 'Deactivatable', etc. DeltaSpike needs such a low-level approach for several features internally, but users can utilize it for their own needs as well. This is done by using the ConfigResolver which resolves and caches `ConfigSource`s per application.

Accessing configured values using ConfigResolver

The ConfigResolver is the central point to access configuration in DeltaSpike. There are several different APIs and ways to access the individual configured values, each suitable for a different purpose:

  • ConfigResolver methods for easy programmatic access to values

  • TypedResolver API for typed configuration values and precise control over resolution

  • @ConfigProperty for injection of configured values into beans

All three mechanisms are described in the following sections.

ConfigResolver methods

ConfigResolver offers several methods for easy access to String values of configured properties.

getPropertyValue()

The method ConfigResolver#getPropertyValue(String key) returns the value configured for a given key as String, or null if no value has been found.

ConfigResolver#getAllPropertyValues(String key) has a similar contract but it returns a list which might be empty if there are no configured values for the given key.

This is a code excerpt about how to do a simple lookup in the deltaspike configuration:

String dbUserName = ConfigResolver.getPropertyValue("databaseconfig.username");

getProjectStageAwarePropertyValue()

The method ConfigResolver#getProjectStageAwarePropertyValue(String key) utilizes the DeltaSpike ProjectStage mechanism to allow configured values to depend on the current ProjectStage of the running system.

This is done by first looking up the ProjectStage (this internally happens with the DeltaSpike ConfigResolver as well) and then go down the following lookup chain until we found a configured value.

  • key + '.' + projectStage , e.g. "databaseconfig.username.Production"

  • key alone , e.g. "databaseconfig.username"

getPropertyAwarePropertyValue()

The method ConfigResolver#getPropertyAwarePropertyValue(String key, String property) first looks up the configured value of the given property and uses this value to determine the final lookup path. All those lookups take the DeltaSpike ProjectStage mechanism into account.

String dbUserName = ConfigResolver.getPropertyAwarePropertyValue("databaseconfig.username", "dbvendor");
Property value resolution sequence

The following lookup sequence will be performed until a value is found: First, the value of the parameter property is resolved:

  • propertyValue = property + '.' + projectStage, e.g. "dbvendor.Production"

  • if nothing found: propertyValue = property, e.g. "dbvendor"

Let’s assume we found the value 'mysql' for our dbvendor. In this case the following lookup chain is used until a value got found:

  • key + '.' + propertyValue + '.' + projectstage, e.g. "databaseconfig.username.mysql.Production"

  • key + '.' + propertyValue, e.g. "databaseconfig.username.mysql"

  • key + '.' + projectStage, e.g. "databaseconfig.username.Production"

  • key, e.g. "databaseconfig.username"

Handling of Default Values

There is a 2nd variant of all those methods where it is possible to provide a default value which gets returned instead of null or if the final result is an empty String.

Performance Hint
The only ConfigResolver operation which is cached is the determination of the ConfigSources. The various getPropertyValue operations are not cached in the ConfigResolver but might be cached in the ConfigSources. This makes the overall calculation a bit slower, but allows for values to change dynamically if someone likes to for example implement a JmxConfigSource (not yet part of DeltaSpike, but easily implementable).

Variable Replacement in Configured Values

Since version 1.6.1, DeltaSpike also supports using 'variables' inside configured values. You can e.g. define a single configuration key for your server and use it in other configuration values

document.server.url=http://localhost:8081
myapp.document.lists=${document.server.url}/docapp/list
myapp.document.admin=${document.server.url}/docadmin/app

A variable name starts with ${ and ends with }.

Variable support is enabled by default. If you like to use the ConfigResolver without variable support you need to use the methods with the evaluateVariables parameter set to false.

TypedResolver API

Very often the configured values represent more than just strings — number types and booleans are commonly used as configuration types. ConfigResolver provides a builder-style API to access configuration values as specific types.

The API is accessed by a call to ConfigResolver.resolve(propertyKey).

The simplest usage of the API is resolution of a String property, equivalent to a call to ConfigResolver.getPropertyValue(propertyKey).

Simple example of TypedResolver
String userName = ConfigResolver.resolve("user.name").getValue();

The call to ConfigResolver.resolve(..) returns a builder which has methods to refine the resolution, including the following:

  • as(Class<N> clazz) — defines the return type of the property

  • parameterizedBy(String propertyName) — sets a parameter for the resolution, similarly as in ConfigResolver.getPropertyAwarePropertyValue

  • withCurrentProjectStage(boolean with) — indicates whether the current ProjectStage should be taken into account for the resolution

  • strictly(boolean strictly) — indicates, whether the property value resolution sequence should be taken into account. When set to true, the sequence is not followed.

  • withDefault(T value) — sets the default value, used in case the resolution returns null

  • getValue() — terminates the builder and returns the resolved value with the appropriate type

A more complete example of TypedResolver
Integer dbPort = ConfigResolver
    .resolve("db.port")
    .as(Integer.class)
    .withProjectStage(true)
    .parameterizedBy("db.vendor")
    .withDefault(3306)
    .getValue();

Supported types

The types supported out of the box include: String, Integer, Long, Float, Double, Boolean, Class. Custom types can be supported by providing an implementation of the ConfigResolver.Converter interface.

Date deadline = ConfigResolver.resolve("deadline").as(Date.class, new CustomDateConverter()).getValue());
public class CustomDateConverter implements ConfigResolver.Converter<Date> {

    @Override
    public Date convert(String value)
    {
        String[] parts = value.split("-");
        return new GregorianCalendar(Integer.valueOf(parts[0]), Integer.valueOf(parts[1]),
                Integer.valueOf(parts[2])).getTime();
    }
}

Injection of configured values into beans using @ConfigProperty

DeltaSpike provides a way to inject configured values into your code via the qualifier @ConfigProperty. The supported types are the same as the supported types of the TypedResolver.

@ApplicationScoped
public class SomeRandomService
{
    @Inject
    @ConfigProperty(name = "endpoint.poll.interval")
    private Integer pollInterval;

    @Inject
    @ConfigProperty(name = "endpoint.poll.servername")
    private String pollUrl;

    ...
 }

Custom ConfigProperty types

Custom types can be injected using @ConfigProperty by providing a custom producer. DeltaSpike provides a base implementation for custom producers in the class BaseConfigPropertyProducer which offers the following methods: * getStringPropertyValue — looks for the property name in @ConfigProperty annotation on the injection point. If not found, it looks for it in other annotations on the injection point. * getPropertyValue — a shortcut to ConfigResolver#getProjectStageAwarePropertyValue * getAnnotation — extracts any annotation type from the injection point, useful when a custom annotation is used instead of @ConfigProperty

The following example uses getStringPropertyValue and a custom @Location annotation annotated @ConfigProperty. In such case, the @Location annotation is bound to a single fixed property name and acts as a type-safe replacement for @ConfigProperty(name = "locationId").

@ApplicationScoped
public class CustomConfigPropertyProducer extends BaseConfigPropertyProducer {

    @Produces
    @Dependent
    @Location
    public LocationId produceLocationId(InjectionPoint injectionPoint)
    {
        String configuredValue = getStringPropertyValue(injectionPoint);

        return LocationId.valueOf(configuredValue.trim().toUpperCase());
    }
}
@Target({ FIELD, METHOD })
@Retention(RUNTIME)
@ConfigProperty(name = "locationId", defaultValue = "LOCATION_X")
@Qualifier
public @interface Location {}

The @ConfigProperty annotation doesn’t need to be used at all. Instead, a custom annotation can be provided and obtained in the producer using getAnnotation and getPropertyValue:

@ApplicationScoped
public class NumberConfigPropertyProducer extends BaseConfigPropertyProducer
{
    @Produces
    @Dependent
    @NumberConfig(name = "unused")
    public Float produceNumberProperty(InjectionPoint injectionPoint) throws ParseException
    {
        // resolve the annotation
        NumberConfig metaData = getAnnotation(injectionPoint, NumberConfig.class);

        // get the configured value from the underlying configuration system
        String configuredValue = getPropertyValue(metaData.name(), metaData.defaultValue());

        // format according to the given pattern
        DecimalFormat df = new DecimalFormat(metaData.pattern(), new DecimalFormatSymbols(Locale.US));
        return df.parse(configuredValue).floatValue();
    }
}
@Qualifier
public @interface NumberConfig
{
    @Nonbinding
    String name();

    @Nonbinding
    String defaultValue() default ConfigProperty.NULL;

    @Nonbinding
    String pattern() default "#0.00";
}

Providing configuration using ConfigSources

A ConfigSource is exactly what its name says: a source for configured values. The ConfigResolver uses all configured implementations of ConfigSource to lookup the property in question.

Each 'ConfigSource' has a specified 'ordinal' which can be configured using the key deltaspike_ordinal. This ordinal get’s used to determine the importance of the values taken from the very ConfigSource. A higher ordinal means that the values taken from this ConfigSource will override values from less important ConfigSources. This is the trick which allows to amend configuration from outside a binary - given those outside ConfigSources have a higher deltaspike_ordinal than the ones who pickup the values from within the release binaries.

ConfigSources Provided by Default

By default there are implementations for the following configuration sources (listed in the lookup order):

  • System properties (deltaspike_ordinal = 400)

  • Environment properties (deltaspike_ordinal = 300)

  • JNDI values (deltaspike_ordinal = 200, the base name is "java:comp/env/deltaspike/")

  • Properties file values (apache-deltaspike.properties) (deltaspike_ordinal = 100, default filename is "META-INF/apache-deltaspike.properties")

It is possible to change this order and to add custom configuration sources.

Important Tips Especially for Custom Implementations
- The config-source with the highest ordinal gets used first. - If a custom implementation should be invoked before the default implementations, use an ordinal-value > 400. - If a custom implementation should be invoked after the default implementations, use an ordinal-value < 100. - The ConfigResolver performs no caching. If your custom ConfigSource operation is expensive, then you might think about introducing some caching.

Reordering of the Default Order of ConfigSources

To change the lookup order, you have to configure the ordinal in the corresponding configuration source (e.g. to change the configuration ordinal of the configuration source for system properties, you have to set the system property with the ordinal key 'deltaspike_ordinal' and the new value).

Example with /META-INF/apache-deltaspike.properties: If the properties file/s should be used before the other implementations, you have to configure an ordinal > 400. That means, you have to add for example deltaspike_ordinal=401.

Each single property file is treated as own ConfigSource and thus can have different deltaspike_ordinal values!

In case of property files which are supported by default (/META-INF/apache-deltaspike.properties) every file is handled as independent config-source, but all of them have ordinal 400 by default (and can be reordered in a fine-grained manner).

Custom ConfigSources

ConfigSources are picked up using the `java.util.ServiceLoader' mechanism.

To add a custom config-source, you have to implement the interface ConfigSource and register your implementation in a file /META-INF/services/org.apache.deltaspike.core.spi.config.ConfigSource by writing the fully qualified class name of the custom implementation/s into it.

If you need dynamic ConfigSources you can also register a ConfigSourceProvider in a similar way. This is useful if you like to dynamically pick up multiple ConfigSources of the same kind. For example, if you like to pick up all myproject.properties files from all the JARs in your classpath.

Please note that a single ConfigSource should be either registered directly or via a ConfigSourceProvider, but never both ways.

Have a look at the abstract base-implementation of ConfigSource DeltaSpike is using internally, if a custom implementation should load the ordinal value from the config-source like the default implementations provided by DeltaSpike do.

PropertyFileConfig

For registering all your own property files of a certain name in your classpath to get picked up as ConfigSources you can also provide a class which implements the PropertyFileConfig interface.

The method isOptional indicates whether your custom property file is mandatory. If a mandatory property file is not found during deployment, DeltaSpike throws an IllegalStateException and stops the deployment.

public class MyCustomPropertyFileConfig implements PropertyFileConfig
{
    @Override
    public String getPropertyFileName()
    {
        return "myconfig.properties";
    }

    @Override
    public boolean isOptional()
    {
        return false;
    }
}

Note: If you are using WildFly with EAR packaging and with ear-subdeployments-isolated=true, then your EAR should have a deployment dependency to the module that contains the property file.

<jboss-deployment-structure>
    <ear-subdeployments-isolated>true</ear-subdeployments-isolated>
      <deployment>
            <dependencies>
            <!-- This module contains the custom PropertyFileConfig and the property file -->
                  <module name="deployment.yourproject.ear.yoursubmodule.jar"  meta-inf="import" />
            </dependencies>
     </deployment>
</jboss-deployment-structure>

Filtering configured values

It is possible to perform filtering on all configured values on their way between the ConfigSource and user code. This might be useful for example for decryption of values from an encrypted ConfigSource or to hide passwords from a log.

DeltaSpike doesn’t provide any filters by default but custom filters can be provided by implementing the ConfigFilter interface. This is then enabled either using the ServiceLoader mechanism or by calling ConfigResolver.addConfigFilter(ConfigFilter). Provided ConfigFilters are then enabled for the whole application.

Once some filters are provided, all operations of ConfigResolver return filtered values.

A custom ConfigFilter
public class DecryptingConfigFilter implements ConfigFilter
{
    @Override
    public String filterValue(String key, String value)
    {
        if (key.contains("encrypted"))
        {
            return decrypt(value);
        }
        return value;
    }

    @Override
    public String filterValueForLog(String key, String value)
    {
        return "<value encrypted>";
    }
}