# Guide to OpenIG
Chapter 12. Customizing OpenIG

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## 12.3. Implementing a Handler

The `Handler` interface exposes a handle method, which takes an Exchange object. It processes the request in exchange.request and produces a response in exchange.response. A handler can elect to dispatch the exchange to another handler or chain.

| Note
If an existing response exists in the exchange object and the filter intends to replace it with its own, it must first check to see if the existing response has an entity, and if it does, must call its close method in order to signal that the processing of the response from a remote server is complete.