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The ShadowBuilder service (see the PropertyShadowBuilder API)

Shadow Services

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The PropertyShadowBuilder service is used to build a special, delegating kind of service implementation .Effectively, it is used to allow that, essentially, allows a property of another service to be exposed as its own service.

For example, the tapestry-core module provides a Request property as a shadow of the RequestGlobals service's request property:

public Request build()
{
  return shadowBuilder.build(requestGlobals, "request", Request.class);
}

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This can be thought of as similar to:

public Request build()
{
  return requestGlobals.getRequest();
}

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A typical method is implemented as (approximately):

private final RequestGlobals source;

public String getParameter(String name)
{
  return source.getRequest().getParameter(name);
}

That is, the shadow implementation holds onto the target object (in the above example, the RequestGlobals service) and invokes a method on it directly, not using reflection, no differently than you would if you wrote the code yourself.

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