= Spring Data REST - Headers example
This example shows how Spring Data REST auto-populates response headers for item resources and considers these values when conditional `GET` requests are used
== Auto-populated headers
If entities use optimistic locking (usually by demarcating a particular property as version property using a store-specific annotation), Spring Data REST will use the value stored in that property to populate the `ETag` header for `GET` and `HEAD` requests to the item resource.
If http://docs.spring.io/spring-data/jpa/docs/current/reference/html/#auditing[Spring Data's auditing capabilities] are activated (using `@EnableJpaAuditing` in this case), the `Last-Modified` header is populated with the value of the last-modified property. See the `Customer` domain class for how to mark those.
== Conditional GET requests
The response headers can be used to issue conditional GET requests to save bandwidth in case the resource hasn't changed on the server:
.Conditional GET using If-Modified-Since
====
[source,bash]
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$ curl http://localhost:8080/customers/1 -i -H "If-Modified-Since: Wed, 08 Apr 2015 17:24:20 GMT"
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[source,http]
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HTTP/1.1 304 Not Modified
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====
.Conditional GET using If-None-Match
====
[source,bash]
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$ curl http://localhost:8080/customers/1 -i -H "If-None-Match: 0"
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[source,http]
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HTTP/1.1 304 Not Modified
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====
== Cross-Origin Resource Sharing
Client-side JavaScript that issue cross-origin requests require the server to evaluate cross-origin requests and respond appropriately.
.Cross-Origin Request
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[source,bash]
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$ curl 'http://localhost:8080/customers/' -i -H 'Origin: http://localhost'
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[source,http]
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HTTP/1.1 200 OK
Access-Control-Allow-Origin: http://localhost
Vary: Origin
Access-Control-Allow-Credentials: true
----
====
== Spring RESTDocs
The sample uses https://github.com/wilkinsona/spring-restdocs[Spring RESTDocs] to document the HTTP interaction implemented using the test cases. See `WebIntegrationTests.setUp()` for general setup and the individual test methods with their usage of `….andDo(document(…))`.
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