Dispatch: Scala library for accessing HTTP services

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[color=rgb(51, 51, 51) !important]Scala library for accessing HTTP services http://dispatch.databinder.net/

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dispatch-master.zip (121.89 KB)

2017-1-20 00:53:06 上传

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关键词：Accessing dispatch services Library service services library

1. Diving in
   
2. 
   
3. If you have sbt installed, Dispatch is two steps away. Open a shell and change to an empty or unimportant directory, then paste:
   
4. 
   
5. echo 'libraryDependencies +=
   
6.   "net.databinder.dispatch" %% "dispatch-core" % "0.11.2"' > build.sbt
   
7. sbt console
   
8. After “the internet” has downloaded, you’re good to go.

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1. Defining requests
   
2. 
   
3. We’ll start with a very simple request.
   
4. 
   
5. import dispatch._, Defaults._
   
6. val svc = url("http://api.hostip.info/country.php")
   
7. val country = Http(svc OK as.String)
   
8. The above defines and initiates a request to the given host where 2xx responses are handled as a string. Since Dispatch is fully asynchronous, country represents a future of the string rather than the string itself.

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1. Deferring action
   
2. 
   
3. You can act on the response once it’s available with a for-expression.
   
4. 
   
5. for (c <- country)
   
6.   println(c)
   
7. This for-expression applies to any successful response that is eventually produced. If no successful response is produced, nothing is printed. This is how for-expressions work in general. Consider a more familiar example:
   
8. 
   
9. val opt: Option[String] = None
   
10. for (o <- opt)
    
11.   println(o)
    
12. An option may or may not contain a value, just like a future may or may not produce a successful response. But while any given option already knows what it is, a future may not. So the future behaves asynchronously in for-expressions, to avoid holding up operations subsequent that do not depend on its value.

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1. Demanding answers
   
2. 
   
3. As with options, you can require that a future value be available at any time:
   
4. 
   
5. val c = country()
   
6. But the wise use of futures defers this operation as long as is practical, or doesn’t perform it at all. To see how, keep reading.

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1. Transformations
   
2. 
   
3. A future is like an option that doesn’t know what it is yet; that doesn’t stop it from transforming into something else. We could transform an option of a string into an option of its length. Same goes for futures.
   
4. 
   
5. import dispatch._, Defaults._
   
6. val svc = url("http://api.hostip.info/country.php")
   
7. val country = Http(svc OK as.String)
   
8. val length = for (c <- country) yield c.length
   
9. The length value is a future of integer.

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Thanks!!!!!!!!