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## org.springframework.web.method.annotation
Class ModelAttributeMethodProcessor

    java.lang.Object
      org.springframework.web.method.annotation.ModelAttributeMethodProcessor

All Implemented Interfaces:
  HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler

Direct Known Subclasses:
  ServletModelAttributeMethodProcessor

    public class ModelAttributeMethodProcessor

extends Object
implements HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler

Resolves method arguments annotated with `@ModelAttribute` and handles return values from methods annotated with `@ModelAttribute`.

Model attributes are obtained from the model or if not found possibly created with a default constructor if it is available. Once created, the attributed is populated with request data via data binding and also validation may be applied if the argument is annotated with `@javax.validation.Valid`.

When this handler is created with `annotationNotRequired=true`, any non-simple type argument and return value is regarded as a model attribute with or without the presence of an `@ModelAttribute`.

Since:
  3.1
Author:
  Rossen Stoyanchev

Field Summary
`protected Log` | `logger`

Constructor Summary
`ModelAttributeMethodProcessor(boolean annotationNotRequired)`

Method Summary
`protected void` | `bindRequestParameters(WebDataBinder binder, NativeWebRequest request)` Extension point to bind the request to the target object.
`protected Object` | `createAttribute(String attributeName, MethodParameter parameter, WebDataBinderFactory binderFactory, NativeWebRequest request)` Extension point to create the model attribute if not found in the model.
`void` | `handleReturnValue(Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest)` Add non-null return values to the `ModelAndViewContainer`.
`protected boolean` | `isBindExceptionRequired(WebDataBinder binder, MethodParameter parameter)` Whether to raise a `BindException` on bind or validation errors.
`Object` | `resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest request, WebDataBinderFactory binderFactory)` Resolve the argument from the model or if not found instantiate it with its default if it is available.
`boolean` | `supportsParameter(MethodParameter parameter)` Whether the given method parameter is supported by this resolver.
`boolean` | `supportsReturnType(MethodParameter returnType)` Return `true` if there is a method-level `@ModelAttribute` or if it is a non-simple type when `annotationNotRequired=true`.
`protected void` | `validateIfApplicable(WebDataBinder binder, MethodParameter parameter)` Validate the model attribute if applicable.

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

Field Detail

### logger

    protected Log logger

Constructor Detail

### ModelAttributeMethodProcessor

    public ModelAttributeMethodProcessor(boolean annotationNotRequired)

Parameters:
  `annotationNotRequired` - if "true", non-simple method arguments and return values are considered model attributes with or without a `@ModelAttribute` annotation.

Method Detail

### supportsParameter

    public boolean supportsParameter(MethodParameter parameter)

  Description copied from interface: `HandlerMethodArgumentResolver`
  Whether the given method parameter is supported by this resolver.

  Specified by:
    `supportsParameter` in interface `HandlerMethodArgumentResolver`
  Parameters:
    `parameter` - the method parameter to check
  Returns:
    true if the parameter is annotated with `ModelAttribute` or in default resolution mode also if it is not a simple type.

### resolveArgument

    public final Object resolveArgument(MethodParameter parameter,
                                        ModelAndViewContainer mavContainer,
                                        NativeWebRequest request,
                                        WebDataBinderFactory binderFactory)
                                 throws Exception

  Resolve the argument from the model or if not found instantiate it with its default if it is available. The model attribute is then populated with request values via data binding and optionally validated if `@java.validation.Valid` is present on the argument.

  Specified by:
    `resolveArgument` in interface `HandlerMethodArgumentResolver`
  Parameters:
    `parameter` - the method parameter to resolve. This parameter must have previously been passed to `HandlerMethodArgumentResolver.supportsParameter(org.springframework.core.MethodParameter)` and it must have returned `true`
    `mavContainer` - the ModelAndViewContainer for the current request
    `request` - the current request
    `binderFactory` - a factory for creating `WebDataBinder` instances
  Returns:
    the resolved argument value, or `null`.
  Throws:
    `BindException` - if data binding and validation result in an error and the next method parameter is not of type `Errors`.
    `Exception` - if WebDataBinder initialization fails.

### createAttribute

    protected Object createAttribute(String attributeName,
                                     MethodParameter parameter,
                                     WebDataBinderFactory binderFactory,
                                     NativeWebRequest request)
                              throws Exception

  Extension point to create the model attribute if not found in the model. The default implementation uses the default constructor.

  Parameters:
    `attributeName` - the name of the attribute, never `null`
    `parameter` - the method parameter
    `binderFactory` - for creating WebDataBinder instance
    `request` - the current request
  Returns:
    the created model attribute, never `null`
  Throws:
    `Exception`

### bindRequestParameters

    protected void bindRequestParameters(WebDataBinder binder,
                                         NativeWebRequest request)

  Extension point to bind the request to the target object.

  Parameters:
    `binder` - the data binder instance to use for the binding
    `request` - the current request

### validateIfApplicable

    protected void validateIfApplicable(WebDataBinder binder,
                                        MethodParameter parameter)

  Validate the model attribute if applicable.

  The default implementation checks for `@javax.validation.Valid`.

  Parameters:
    `binder` - the DataBinder to be used
    `parameter` - the method parameter

### isBindExceptionRequired

    protected boolean isBindExceptionRequired(WebDataBinder binder,
                                              MethodParameter parameter)

  Whether to raise a `BindException` on bind or validation errors. The default implementation returns `true` if the next method argument is not of type `Errors`.

  Parameters:
    `binder` - the data binder used to perform data binding
    `parameter` - the method argument

### supportsReturnType

    public boolean supportsReturnType(MethodParameter returnType)

  Return `true` if there is a method-level `@ModelAttribute` or if it is a non-simple type when `annotationNotRequired=true`.

  Specified by:
    `supportsReturnType` in interface `HandlerMethodReturnValueHandler`
  Parameters:
    `returnType` - the method return type to check
  Returns:
    `true` if this handler supports the supplied return type; `false` otherwise

### handleReturnValue

    public void handleReturnValue(Object returnValue,
                                  MethodParameter returnType,
                                  ModelAndViewContainer mavContainer,
                                  NativeWebRequest webRequest)
                           throws Exception

  Add non-null return values to the `ModelAndViewContainer`.

  Specified by:
    `handleReturnValue` in interface `HandlerMethodReturnValueHandler`
  Parameters:
    `returnValue` - the value returned from the handler method
    `returnType` - the type of the return value. This type must have previously been passed to `HandlerMethodReturnValueHandler.supportsReturnType(org.springframework.core.MethodParameter)` and it must have returned `true`
    `mavContainer` - the ModelAndViewContainer for the current request
    `webRequest` - the current request
  Throws:
    `Exception` - if the return value handling results in an error

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