org.apache.tamaya.resolver.spi

## Interface ExpressionResolver

- All Known Implementing Classes:
    ConfigResolver, EnvironmentPropertyResolver, FileResolver, ResourceResolver, SystemPropertyResolver, URLResolver

      public interface ExpressionResolver

  This interfaces provides a model for expression evaluation. This enables transparently plugin expression languages as needed. In a Java EE context full fledged EL may be used, whereas in ME only simple replacement mechanisms are better suited to the runtime requirements.

- - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `String` | `evaluate(String expression)` Evaluates the given expression.
    `String` | `getResolverPrefix()` Get the unique resolver prefix.

- - ### Method Detail

    - #### getResolverPrefix

          String getResolverPrefix()

      Get the unique resolver prefix. This allows to address a resolver explicitly, in case of conflicts. By default all registered resolvers are called in order as defined by the `Priority` annotation.
      Returns:
        the prefix that identifies this resolver instance, e.g. 'config:'. The ':' hereby is not required as a separator, but it is recommended to use it, because it fits well, with the other existing resolvers and is easy to read.

    - #### evaluate

          String evaluate(String expression)

      Evaluates the given expression.
      Parameters:
        `expression` - the expression to be evaluated, not null. If a resolver was addressed explicitly, the prefix is removed prior to calling this method.
      Returns:
        the evaluated expression, or null, if the evaluator is not able to resolve the expression.

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