Routes as Rack Endpoints in Java

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229 Routes as Rack Endpoints
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You ll see usage of the :to option in routes throughout this chapter What s most interesting about :to is that its value is what s referred to as a Rack endpoint To illustrate, consider the following simple example:
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match "/hello", :to => proc {|env| [200, {}, ["Hello world"]] }
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2: Routing
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The router is very loosely coupled to controllers! The shorthand syntax (like "items#show") relies on the action method of controller classes to return a Rack endpoint that executes the action requested
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>> ItemsControlleraction(:show) => #<Proc:0x01e96cd0@>
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This behavior means that adding a route that dispatches to a Sinatra3 application is super-easy Just point :to => YourSinatraApp The Sinatra application class itself is a Rack endpoint
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class HelloApp < Sinatra::Base get "/" do "Hello World!" end end Example::Applicationroutesdraw do match "/hello", :to => HelloApp end
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2210 Accept Header
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You can also trigger a branching on respond_to by setting the Accept header in the request When you do this, there s no need to add the :format part of the URL (However, note that out in the real world, it s difficult to get this technique to work reliably because of HTTP client/browser inconsistencies) Here s a wget example that does not specify an xml format, but does set the Accept header to application/xml:
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wget http://localhost:3000/items/show/3 -O - --header="Accept: text/xml" Resolving localhost 127001, ::1 Connecting to localhost|127001|:3000 connected HTTP request sent, awaiting response 200 OK Length: 295 [application/xml] <item> <created-at type="datetime">2007-02-16T04:33:00-05:00</created-at> <description>Violin treatise</description> <id type="integer">3</id> <maker>Leopold Mozart</maker> <medium>paper</medium> <modified-at type="datetime"></modified-at>
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22 The routesrb File
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<year type="integer">1744</year> </item>
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The result is exactly the same as in the previous example
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Routes
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2211 Segment Key Constraints
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Sometimes you want not only to recognize a route, but to recognize it at a finer-grained level than just what components or fields it has You can do this through the use of the :constraint option (and possibly regular expressions) For example, you could route all show requests so that they went to an error action if their id fields were non-numerical You d do this by creating two routes, one that handled numerical ids, and a fall-through route that handled the rest:
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match ':controller/show/:id' => :show, :constraints => {:id => /\d+/} match ':controller/show/:id' => :show_error
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The example constraint we ve been using
:constraints => {:id => /\d+/}
seems like it would match "foo32bar" It doesn t because Rails implicitly anchors it at both ends In fact, as of this writing, adding explicit anchors ^ and $ causes exceptions to be raised
Apparently, it s so common to set constraints on the :id param, that Rails 3 lets you shorten our previous example to simply
match ':controller/show/:id' => :show, :id => /\d+/ match ':controller/show/:id' => :show_error
Regular expressions in routes can be useful, especially when you have routes that differ from each other only with respect to the patterns of their components But they re not a full-blown substitute for data-integrity checking A URL that matches a route with regular expressions could be like the vetting of Sarah Palin, not thorough enough4 You probably still want to make sure that the values you re dealing with are usable and appropriate for your application s domain From the example, you might conclude that :constraints checking applies to elements of the params hash However, you can also check a grab-bag of other request
4 In 2008, American presidential candidate John McCain was widely mocked and later defeated, partly because of his ill-advised choice of running mate, the little-known Governor of Alaska, Sarah Palin
2: Routing
attributes that return a string, such as :subdomain and :referrer Matching methods of request that return numeric or boolean values are unsupported and will raise a somewhat cryptic exception during route matching
# only allow users admin subdomain to do old-school routing match ':controller/:action/:id' => :show, :constraints => {:subdomain => 'admin'}
If for some reason you need more powerful constraints checking, you have full access to the request object, by passing a block or any other object that responds to call as the value of :constraints like:
# protect records with id under 100 match 'records/:id' => "records#protected", :constraints => proc {|req| reqparams[:id]to_i < 100 }