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HTTP is a request-and-response protocol. Technically, there is no way to have the server to actively push data to the client. However, there are a few approaches to emulate push -- it is also called Ajax Push. These approaches could be summarized in two categories, client polling and comet[1], that are both supported in ZK.

Different approaches have different pros and cons, and we will discuss them in the Configuration section.

No matter which implementation you choose, the use is the same. The Event Queue is the high-level API, and this is a suggested approach for its simplicity. However, if you prefer to access the low-level API directly, you could refer to the Asynchronous Tasks and Synchronous Tasks sections, depending on whether you task can be executed asynchronously.

  1. More precisely, it is so-called long polling.

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