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## org.springframework.web.servlet.view
Class ContentNegotiatingViewResolver

    java.lang.Object
      org.springframework.context.support.ApplicationObjectSupport
          org.springframework.web.context.support.WebApplicationObjectSupport
              org.springframework.web.servlet.view.ContentNegotiatingViewResolver

All Implemented Interfaces:
  Aware, ApplicationContextAware, Ordered, ServletContextAware, ViewResolver

    public class ContentNegotiatingViewResolver

extends WebApplicationObjectSupport
implements ViewResolver, Ordered

Implementation of `ViewResolver` that resolves a view based on the request file name or `Accept` header.

The `ContentNegotiatingViewResolver` does not resolve views itself, but delegates to other `ViewResolver`s. By default, these other view resolvers are picked up automatically from the application context, though they can also be set explicitly by using the `viewResolvers` property. Note that in order for this view resolver to work properly, the `order` property needs to be set to a higher precedence than the others (the default is `Ordered.HIGHEST_PRECEDENCE`.)

This view resolver uses the requested media type to select a suitable `View` for a request. This media type is determined by using the following criteria:

1. If the requested path has a file extension and if the `setFavorPathExtension(boolean)` property is `true`, the `mediaTypes` property is inspected for a matching media type.
2. If the request contains a parameter defining the extension and if the `setFavorParameter(boolean)` property is `true`, the `mediaTypes` property is inspected for a matching media type. The default name of the parameter is `format` and it can be configured using the `parameterName` property.
3. If there is no match in the `mediaTypes` property and if the Java Activation Framework (JAF) is both enabled and present on the classpath, `FileTypeMap.getContentType(String)` is used instead.
4. If the previous steps did not result in a media type, and `ignoreAcceptHeader` is `false`, the request `Accept` header is used.

Once the requested media type has been determined, this resolver queries each delegate view resolver for a `View` and determines if the requested media type is compatible with the view's content type). The most compatible view is returned.

Additionally, this view resolver exposes the `defaultViews` property, allowing you to override the views provided by the view resolvers. Note that these default views are offered as candicates, and still need have the content type requested (via file extension, parameter, or `Accept` header, described above). You can also set the default content type directly, which will be returned when the other mechanisms (`Accept` header, file extension or parameter) do not result in a match.

For example, if the request path is `/view.html`, this view resolver will look for a view that has the `text/html` content type (based on the `html` file extension). A request for `/view` with a `text/html` request `Accept` header has the same result.

Since:
  3.0
Author:
  Arjen Poutsma, Juergen Hoeller, Rossen Stoyanchev
See Also:
  `ViewResolver`, `InternalResourceViewResolver`, `BeanNameViewResolver`

Field Summary

Fields inherited from interface org.springframework.core.Ordered
`HIGHEST_PRECEDENCE, LOWEST_PRECEDENCE`

Constructor Summary
`ContentNegotiatingViewResolver()`

Method Summary
`protected MediaType` | `getMediaTypeFromFilename(String filename)` Determines the `MediaType` for the given filename.
`protected MediaType` | `getMediaTypeFromParameter(String parameterValue)` Determines the `MediaType` for the given parameter value.
`protected List<MediaType>` | `getMediaTypes(HttpServletRequest request)` Determines the list of `MediaType` for the given `HttpServletRequest`.
`int` | `getOrder()` Return the order value of this object, with a higher value meaning greater in terms of sorting.
`protected void` | `initServletContext(ServletContext servletContext)` Subclasses may override this for custom initialization based on the ServletContext that this application object runs in.
`View` | `resolveViewName(String viewName, Locale locale)` Resolve the given view by name.
`void` | `setDefaultContentType(MediaType defaultContentType)` Set the default content type.
`void` | `setDefaultViews(List<View> defaultViews)` Set the default views to use when a more specific view can not be obtained from the `ViewResolver` chain.
`void` | `setFavorParameter(boolean favorParameter)` Indicate whether a request parameter should be used to determine the requested media type, in favor of looking at the `Accept` header.
`void` | `setFavorPathExtension(boolean favorPathExtension)` Indicate whether the extension of the request path should be used to determine the requested media type, in favor of looking at the `Accept` header.
`void` | `setIgnoreAcceptHeader(boolean ignoreAcceptHeader)` Indicate whether the HTTP `Accept` header should be ignored.
`void` | `setMediaTypes(Map<String,String> mediaTypes)` Set the mapping from file extensions to media types.
`void` | `setOrder(int order)`
`void` | `setParameterName(String parameterName)` Set the parameter name that can be used to determine the requested media type if the `setFavorParameter(boolean)` property is `true`.
`void` | `setUseJaf(boolean useJaf)` Indicate whether to use the Java Activation Framework to map from file extensions to media types.
`void` | `setUseNotAcceptableStatusCode(boolean useNotAcceptableStatusCode)` Indicate whether a `406 Not Acceptable` status code should be returned if no suitable view can be found.
`void` | `setViewResolvers(List<ViewResolver> viewResolvers)` Sets the view resolvers to be wrapped by this view resolver.

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

### ContentNegotiatingViewResolver

    public ContentNegotiatingViewResolver()

Method Detail

### setOrder

    public void setOrder(int order)

### getOrder

    public int getOrder()

  Description copied from interface: `Ordered`
  Return the order value of this object, with a higher value meaning greater in terms of sorting.

  Normally starting with 0, with `Integer.MAX_VALUE` indicating the greatest value. Same order values will result in arbitrary positions for the affected objects.

  Higher values can be interpreted as lower priority. As a consequence, the object with the lowest value has highest priority (somewhat analogous to Servlet "load-on-startup" values).

  Specified by:
    `getOrder` in interface `Ordered`
  Returns:
    the order value

### setFavorPathExtension

    public void setFavorPathExtension(boolean favorPathExtension)

  Indicate whether the extension of the request path should be used to determine the requested media type, in favor of looking at the `Accept` header. The default value is `true`.

  For instance, when this flag is `true` (the default), a request for `/hotels.pdf` will result in an `AbstractPdfView` being resolved, while the `Accept` header can be the browser-defined `text/html,application/xhtml+xml`.

### setFavorParameter

    public void setFavorParameter(boolean favorParameter)

  Indicate whether a request parameter should be used to determine the requested media type, in favor of looking at the `Accept` header. The default value is `false`.

  For instance, when this flag is `true`, a request for `/hotels?format=pdf` will result in an `AbstractPdfView` being resolved, while the `Accept` header can be the browser-defined `text/html,application/xhtml+xml`.

### setParameterName

    public void setParameterName(String parameterName)

  Set the parameter name that can be used to determine the requested media type if the `setFavorParameter(boolean)` property is `true`. The default parameter name is `format`.

### setIgnoreAcceptHeader

    public void setIgnoreAcceptHeader(boolean ignoreAcceptHeader)

  Indicate whether the HTTP `Accept` header should be ignored. Default is `false`.

  If set to `true`, this view resolver will only refer to the file extension and/or parameter, as indicated by the `favorPathExtension` and `favorParameter` properties.

### setUseNotAcceptableStatusCode

    public void setUseNotAcceptableStatusCode(boolean useNotAcceptableStatusCode)

  Indicate whether a `406 Not Acceptable` status code should be returned if no suitable view can be found.

  Default is `false`, meaning that this view resolver returns `null` for `resolveViewName(String, Locale)` when an acceptable view cannot be found. This will allow for view resolvers chaining. When this property is set to `true`, `resolveViewName(String, Locale)` will respond with a view that sets the response status to `406 Not Acceptable` instead.

### setMediaTypes

    public void setMediaTypes(Map<String,String> mediaTypes)

  Set the mapping from file extensions to media types.

  When this mapping is not set or when an extension is not present, this view resolver will fall back to using a `FileTypeMap` when the Java Action Framework is available.

### setDefaultViews

    public void setDefaultViews(List<View> defaultViews)

  Set the default views to use when a more specific view can not be obtained from the `ViewResolver` chain.

### setDefaultContentType

    public void setDefaultContentType(MediaType defaultContentType)

  Set the default content type.

  This content type will be used when file extension, parameter, nor `Accept` header define a content-type, either through being disabled or empty.

### setUseJaf

    public void setUseJaf(boolean useJaf)

  Indicate whether to use the Java Activation Framework to map from file extensions to media types.

  Default is `true`, i.e. the Java Activation Framework is used (if available).

### setViewResolvers

    public void setViewResolvers(List<ViewResolver> viewResolvers)

  Sets the view resolvers to be wrapped by this view resolver.

  If this property is not set, view resolvers will be detected automatically.

### initServletContext

    protected void initServletContext(ServletContext servletContext)

  Description copied from class: `WebApplicationObjectSupport`
  Subclasses may override this for custom initialization based on the ServletContext that this application object runs in.

  The default implementation is empty. Called by `WebApplicationObjectSupport.initApplicationContext(org.springframework.context.ApplicationContext)` as well as `WebApplicationObjectSupport.setServletContext(javax.servlet.ServletContext)`.

  Overrides:
    `initServletContext` in class `WebApplicationObjectSupport`
  Parameters:
    `servletContext` - the ServletContext that this application object runs in (never `null`)

### resolveViewName

    public View resolveViewName(String viewName,
                                Locale locale)
                         throws Exception

  Description copied from interface: `ViewResolver`
  Resolve the given view by name.

  Note: To allow for ViewResolver chaining, a ViewResolver should return `null` if a view with the given name is not defined in it. However, this is not required: Some ViewResolvers will always attempt to build View objects with the given name, unable to return `null` (rather throwing an exception when View creation failed).

  Specified by:
    `resolveViewName` in interface `ViewResolver`
  Parameters:
    `viewName` - name of the view to resolve
    `locale` - Locale in which to resolve the view. ViewResolvers that support internationalization should respect this.
  Returns:
    the View object, or `null` if not found (optional, to allow for ViewResolver chaining)
  Throws:
    `Exception` - if the view cannot be resolved (typically in case of problems creating an actual View object)

### getMediaTypes

    protected List<MediaType> getMediaTypes(HttpServletRequest request)

  Determines the list of `MediaType` for the given `HttpServletRequest`.

  The default implementation invokes `getMediaTypeFromFilename(String)` if favorPathExtension property is `true`. If the property is `false`, or when a media type cannot be determined from the request path, this method will inspect the `Accept` header of the request.

  This method can be overridden to provide a different algorithm.

  Parameters:
    `request` - the current servlet request
  Returns:
    the list of media types requested, if any

### getMediaTypeFromFilename

    protected MediaType getMediaTypeFromFilename(String filename)

  Determines the `MediaType` for the given filename.

  The default implementation will check the media types property first for a defined mapping. If not present, and if the Java Activation Framework can be found on the classpath, it will call `FileTypeMap.getContentType(String)`

  This method can be overridden to provide a different algorithm.

  Parameters:
    `filename` - the current request file name (i.e. `hotels.html`)
  Returns:
    the media type, if any

### getMediaTypeFromParameter

    protected MediaType getMediaTypeFromParameter(String parameterValue)

  Determines the `MediaType` for the given parameter value.

  The default implementation will check the media types property for a defined mapping.

  This method can be overriden to provide a different algorithm.

  Parameters:
    `parameterValue` - the parameter value (i.e. `pdf`).
  Returns:
    the media type, if any

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