org.apache.tamaya.resolver.spi

Interface ExpressionEvaluator

All Known Implementing Classes:

DefaultExpressionEvaluator

public interface ExpressionEvaluator

Interface that provides an SPI that can be accessed from the current ServiceContext, which allows to pass expression that contain placeholders and variable expressions. Expressions passed hereby use UNIX styled variable syntax as follows:

     ${expression}
     My name is ${expression}.
     Also multiple expressions are support, e.g. ${expression1}, ${expression2}.
 

By default all registered instances of ExpressionResolver are called to evaluate an expression, depending on the annotatated Priority on the resolver classes. Nevertheless with ExpressionResolver.getResolverPrefix() each resolver instance defines a unique id, by which a resolver can be explicitly addressed as follows:

     ${env:MACHINE_NAME}
     My name is ${sys:instance.name}.
     Also multiple expressions are supported, e.g. ${resource:META-INF/version.conf}, ${file:C:/temp/version.txt},
     ${url:http://configserver/name}.
 

Basically this service is consumed by an instance of PropertyFilter, which takes the configuration values found and passes them to this evaluator, when expressions are detected. This also done iteratively, so also multi-stepped references (references, which themselves must be evaluated as well) are supported.

Method Summary

Methods

Modifier and Type	Method and Description
String	evaluateExpression(String key, String value) Evaluates the current expression.

Method Detail

evaluateExpression

String evaluateExpression(String key,
                        String value)

Evaluates the current expression.

Parameters:

key - the key, not null.

value - the value to be filtered/evaluated.

Returns:

the filtered/evaluated value, including null.