JSR382
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tomas-langer and struberg Config source change support.
Gives Config more info about config source`s support for changes and
 scannability.

Resolves #95

Signed-off-by: Tomas Langer <tomas.langer@oracle.com>
Latest commit 4f4a7b5 Oct 19, 2018

README.adoc

ConfigJSR

ConfigJSR

JSR-382 - Configuration API for Java, v1.0

Specification Leads: Emily Jiang, Mark Struberg

This is the official Source Repository of this very JSR.

Status

Configuration API for Java JSR Draft - Work In Progress!

How to Contribute?

Source Repository

The source code is available under the Apache License, v2.0 and hosted at https://github.com/eclipse/ConfigJSR

Mailing Lists

The Expert Group list is only used for announcements and voting.

configjsr-experts@eclipse.org

All the normal interaction is going on on the general discussion list

configjsr-discuss@eclipse.org

To subscribe to a list just send a mail to configjsr-discuss-join (at) eclipse.org

Rationale

The majority of applications need to be configured based on a running environment. It must be possible to modify configuration data from outside an application so that the application itself does not need to be repackaged.

The configuration data can come from different locations and in different formats (e.g. system properties, system environment variables, .properties, .xml, datasource). We call these config locations ConfigSources. If the same property is defined in multiple ConfigSources, we apply a policy to specify which one of the values will effectively be used.

Under some circumstances, some data sources may change dynamically. The changed values should be fed into the client without the need for restarting the application. This requirement is particularly important for microservices running in a cloud environment. The JavaConfig approach allows to pick up configured values immediately after they got changed.

Influences and History

There are a number of Config projects which directly influenced this proposal and acted as basis for this API, such as:

The approach of those got merged together into MicroProfile Config (https://github.com/eclipse/microprofile-config). This now serves as a starting point for this very JSR.

Implementations

JavaConfig does not contain an implementation itself but only provides the specified API and, a TCK and documentation.

Design

The current configuration of an application can be accessed via ConfigProvider#getConfig().

A Config consists of the information collected from the registered javax.config.spi.ConfigSource s. These ConfigSource s get sorted according to their ordinal. That way it is possible to overwrite configuration with lower importance from outside.

By default there are 3 default ConfigSources:

  • System.getProperties() (ordinal=400)

  • System.getenv() (ordinal=300)

  • all META-INF/javaconfig.properties files on the ClassPath. (default ordinal=100, separately configurable via a config_ordinal property inside each file)

Therefore, the default values can be specified in the above files packaged with the application and the value can be overwritten later for each deployment. A higher ordinal number takes precedence over a lower number.

Custom ConfigSources

It is possible to write and register a custom ConfigSources. An example would be a ConfigSource which gets the configured values from a shared database table in a cluster.

Building

The whole JavaConfig project can be built via Apache Maven

$> mvn clean install