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Symbols are named configuration settings for Tapestry IOC-based services. Tapestry provides mechanisms for easy access to symbols from within such services.

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The value on the inside is the symbol name. By convention, the symbol name is segmented with periods (for example, "tapestry.production-mode").

Built-in Symbols

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The Configuration page lists most of the symbol names used by Tapestry's built-in services.

Using Symbols in your Services

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Note: When injecting a symbol as a string into a service, you must use the @Inject annotation as well as @Value or @Symbol; otherwise Tapestry will inject the service's service id.

Symbols in Component Classes and Templates

It's easy to use a symbol in a component class:

  @Inject
  @Symbol(SymbolConstants.PRODUCTION_MODE)
  private boolean productionMode;
  . . .
  void setupRender() {
    if (productionMode) {
        . . .
    }
  }

You can even use them directly in a component template, using the "symbol" binding prefix:

<t:if test="!symbol:tapestry.production-mode">
  <p>WARNING: We're running in development mode (slower, and less secure)</p>
</t:if>

Symbol Resolution

Symbols are resolved by the SymbolSource service. The SymbolSource service checks against an ordered list of SymbolProvider objects.

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From the previous example:

  public void contributeApplicationDefaults(MappedConfiguration<String, String> configuration)
  {
    configuration.add("some-service-id", "WackyCollaborator");
  }

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It is possible and valid to define one symbol in terms of one or more other symbols.

  public void contributeFactoryDefaults(MappedConfiguration<String, String> configuration)
  {
      configuration.add("report.url", "http://${report.host}:${report.port}/${report.path}");
      configuration.add("report.host", "www.myreportsite.com");
      configuration.add("report.port", "80");
      configuration.add("report.path", "/report.cgi");
  }

The ordinary default for report.url will be: http://www.myreportsite.com:80/report.cgi.

However, this can be changed by making an overriding contribution to the ApplicationDefaults service configuration.

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