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## org.springframework.web.servlet.resource
Class ResourceHttpRequestHandler

    java.lang.Object
      org.springframework.context.support.ApplicationObjectSupport
          org.springframework.web.context.support.WebApplicationObjectSupport
              org.springframework.web.servlet.support.WebContentGenerator
                  org.springframework.web.servlet.resource.ResourceHttpRequestHandler

All Implemented Interfaces:
  ApplicationContextAware, ServletContextAware, HttpRequestHandler

    public class ResourceHttpRequestHandler

extends WebContentGenerator
implements HttpRequestHandler

`HttpRequestHandler` that serves static resources optimized for superior browser performance (according to the guidelines of Page Speed, YSlow, etc.) by allowing for flexible cache settings (`"cacheSeconds" property`, last-modified support).

The #setLocations "locations" property takes a list of Spring {@link Resource} locations from which static resources are allowed to be served by this handler. For a given request, the list of locations will be consulted in order for the presence of the requested resource, and the first found match will be written to the response, with {@code Expires} and {@code Cache-Control} headers set as configured. The handler also properly evaluates the {@code Last-Modified} header (if present) so that a {@code 304} status code will be returned as appropriate, avoiding unnecessary overhead for resources that are already cached by the client. The use of {@code Resource} locations allows resource requests to easily be mapped to locations other than the web application root. For example, resources could be served from a classpath location such as "classpath:/META-INF/public-web-resources/", allowing convenient packaging and serving of resources such as a JavaScript library from within jar files.

To ensure that users with a primed browser cache get the latest changes to application-specific resources upon deployment of new versions of the application, it is recommended that a version string is used in the URL mapping pattern that selects this handler. Such patterns can be easily parameterized using Spring EL. See the reference manual for further examples of this approach.

Rather than being directly configured as a bean, this handler will typically be configured through use of the `<mvc:resources/>` XML configuration element.

Since:
  3.0.4
Author:
  Keith Donald, Jeremy Grelle, Juergen Hoeller

Field Summary

Fields inherited from class org.springframework.web.servlet.support.WebContentGenerator
`METHOD_GET, METHOD_HEAD, METHOD_POST`

Fields inherited from class org.springframework.context.support.ApplicationObjectSupport
`logger`

Constructor Summary
`ResourceHttpRequestHandler()`

Method Summary
`protected MediaType` | `getMediaType(Resource resource)` Determine an appropriate media type for the given resource.
`protected Resource` | `getResource(HttpServletRequest request)`
`void` | `handleRequest(HttpServletRequest request, HttpServletResponse response)` Processes a resource request.
`protected void` | `setHeaders(HttpServletResponse response, Resource resource, MediaType mediaType)` Set headers on the given servlet response.
`void` | `setLocations(List<Resource> locations)` Set a `List` of `Resource` paths to use as sources for serving static resources.
`protected void` | `writeContent(HttpServletResponse response, Resource resource)` Write the actual content out to the given servlet response, streaming the resource's content.

Methods inherited from class org.springframework.web.servlet.support.WebContentGenerator
`applyCacheSeconds, applyCacheSeconds, cacheForSeconds, cacheForSeconds, checkAndPrepare, checkAndPrepare, getCacheSeconds, getSupportedMethods, isRequireSession, isUseCacheControlHeader, isUseCacheControlNoStore, isUseExpiresHeader, preventCaching, setCacheSeconds, setRequireSession, setSupportedMethods, setUseCacheControlHeader, setUseCacheControlNoStore, setUseExpiresHeader`

Methods inherited from class org.springframework.web.context.support.WebApplicationObjectSupport
`getServletContext, getTempDir, getWebApplicationContext, initApplicationContext, initServletContext, isContextRequired, setServletContext`

Methods inherited from class org.springframework.context.support.ApplicationObjectSupport
`getApplicationContext, getMessageSourceAccessor, initApplicationContext, requiredContextClass, setApplicationContext`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### ResourceHttpRequestHandler

    public ResourceHttpRequestHandler()

Method Detail

### setLocations

    public void setLocations(List<Resource> locations)

  Set a `List` of `Resource` paths to use as sources for serving static resources.

### handleRequest

    public void handleRequest(HttpServletRequest request,
                              HttpServletResponse response)
                       throws ServletException,
                              IOException

  Processes a resource request.

  Checks for the existence of the requested resource in the configured list of locations. If the resource does not exist, a `404` response will be returned to the client. If the resource exists, the request will be checked for the presence of the `Last-Modified` header, and its value will be compared against the last-modified timestamp of the given resource, returning a `304` status code if the `Last-Modified` value is greater. If the resource is newer than the `Last-Modified` value, or the header is not present, the content resource of the resource will be written to the response with caching headers set to expire one year in the future.

  Specified by:
    `handleRequest` in interface `HttpRequestHandler`
  Parameters:
    `request` - current HTTP request
    `response` - current HTTP response
  Throws:
    `ServletException` - in case of general errors
    `IOException` - in case of I/O errors

### getResource

    protected Resource getResource(HttpServletRequest request)

### getMediaType

    protected MediaType getMediaType(Resource resource)

  Determine an appropriate media type for the given resource.

  Parameters:
    `resource` - the resource to check
  Returns:
    the corresponding media type, or `null` if none found

### setHeaders

    protected void setHeaders(HttpServletResponse response,
                              Resource resource,
                              MediaType mediaType)
                       throws IOException

  Set headers on the given servlet response. Called for GET requests as well as HEAD requests.

  Parameters:
    `response` - current servlet response
    `resource` - the identified resource (never `null`)
    `mediaType` - the resource's media type (never `null`)
  Throws:
    `IOException` - in case of errors while setting the headers

### writeContent

    protected void writeContent(HttpServletResponse response,
                                Resource resource)
                         throws IOException

  Write the actual content out to the given servlet response, streaming the resource's content.

  Parameters:
    `response` - current servlet response
    `resource` - the identified resource (never `null`)
  Throws:
    `IOException` - in case of errors while writing the content

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