## Apache Tamaya Quickstart

The fastest way to start with Tamaya is just using the Core implementation, implementing the API in small, minimalistic way. For that add the following Maven dependency to your project:

    <dependency>
        <groupId>org.apache.tamaya</groupId>
        <artifactId>tamaya-core</artifactId>
        <version>0.2-incubating</version>
    </dependency>

Given that you can add your configuration properties to the following locations in your classpath:

    META-INF/javaconfiguration.properties

Additionally also system properties are taken into account, hereby overriding the default properties. Overall Tamaya by default defines the following configuration model per default (most significant first):

1. System Properties

2. `META-INF/javaconfiguration.properties`

There many modules that extend the capabilities of Tamaya. These modules doe not depend on core, so alternative implementations of the Tamaya API should work similarly.

### Multiple configuration files

By default you can provide multiple `javaconfig.properties` files, e.g. as part of multiple jars loaded into your system. The system internally creates one `PropertySource` for each file found on the classpath. All `PropertySource` instances created are ordered by their ordinal value (an int).

Tamaya Core defines the following default ordinals (used, if no custom ordinal is defined):

Source | Ordinal
System Properties | 400
Environment Variables | 300
Java Configuration Properties | 100

That means that the value of a configuration variable `x` overhanded via `-Dx=yes` has a higher precedence then the entry for configuration variable `x` specified in a `javaconfig.properties` as `x=no`.

These ordinal values can be either hardcoded, or be dynamically configurable as key within each configuration resource. The ladder can be done by defining a special Tamaya ordinal value as follows:

    # override default Tamaya ordinal for property files
    tamaya.ordinal=123

This assigns an ordinal of 123 to each entry in that configuration resource.

### Using additional features of Tamaya

There many modules that extend the capabilities of Tamaya. These modules doe not depend on core, so alternative implementations of the Tamaya API should work similarly. Following a small extract of most important modules available (or available soon):

#### Dynamic Resolution and Value Placeholders

    <dependency>
      <artifactId>org.apache.tamaya.ext</id>
      <artifactId>tamaya-resolver</artifactId>
      <version>0.2-incubating</version>
    </dependency>

With that it is possible to define values with Unix styled placeholders that are resolved on configuration access, e.g. `mykey=my${dynamicValue}´. For further details refer to the module documentation. This module also provides a `Resolver` singleton:

    String myExpression = ...;
    String resolved = Resolver.evaluateExpression(myExpression);

#### Ant-styled Path Resolution of Resources

    <dependency>
      <artifactId>org.apache.tamaya.ext</id>
      <artifactId>tamaya-resolution</artifactId>
      <version>0.2-incubating</version>
    </dependency>

This module provides a `Resolver` singleton that allows to resolve configuration resources using a ant-styled resource description, e.g.

    Collection<URL> urls = ResourceResolver.getResources("META-INF/cfg/**/*.properties");

For further details refer to the module documentation.

#### Configuration Injection

    <dependency>
      <artifactId>org.apache.tamaya.ext</id>
      <artifactId>tamaya-inject</artifactId>
      <version>0.2-incubating</version>
    </dependency>

With this extension you can let Tamaya inject configuration into instances of annotated classes or let Tamaya implement a configuration template.

Corresponding configuration:

    public class MyType {
       @ConfiguredProperty("name")
       private String typeName;

       public String getName() {
          return name;
       }
    }

    MyType type = new MyType();
    ConfigurationInjector.configure(type);

Or the same as template:

    public interface MyTypeTemplate {
       @ConfiguredProperty("name")
       public String getName();
    }

    MyTypeTemplate type = ConfigurationInjector.createTemplate(MyTypeTemplate.class);

Currently the following resolvers are available:

Conf | Cross-reference to another configuration entry
URL | Referencing a resource addressable by an URL.
File | Reference to a file, replacing the expression with the file’s text value.
Resource | Reference to classpath resource, replacing the expression with the resource’s text value.