Spring Framework

org.springframework.web.bind
Class WebDataBinder

java.lang.Object
  extended by org.springframework.validation.DataBinder
      extended by org.springframework.web.bind.WebDataBinder
All Implemented Interfaces:
PropertyEditorRegistry, TypeConverter
Direct Known Subclasses:
PortletRequestDataBinder, ServletRequestDataBinder, WebRequestDataBinder

public class WebDataBinder
extends DataBinder

Special DataBinder for data binding from web request parameters to JavaBean objects. Designed for web environments, but not dependent on the Servlet API; serves as base class for more specific DataBinder variants, such as ServletRequestDataBinder.

Includes support for field markers which address a common problem with HTML checkboxes and select options: detecting that a field was part of the form, but did not generate a request parameter because it was empty. A field marker allows to detect that state and reset the corresponding bean property accordingly. Default values, for parameters that are otherwise not present, can specify a value for the field other then empty.

Since:
1.2
Author:
Juergen Hoeller, Scott Andrews
See Also:
DataBinder.registerCustomEditor(java.lang.Class, java.beans.PropertyEditor), DataBinder.setAllowedFields(java.lang.String...), DataBinder.setRequiredFields(java.lang.String...), setFieldMarkerPrefix(java.lang.String), setFieldDefaultPrefix(java.lang.String), ServletRequestDataBinder

Field Summary
static java.lang.String DEFAULT_FIELD_DEFAULT_PREFIX
          Default prefix that field default parameters start with, followed by the field name: e.g.
static java.lang.String DEFAULT_FIELD_MARKER_PREFIX
          Default prefix that field marker parameters start with, followed by the field name: e.g.
 
Fields inherited from class org.springframework.validation.DataBinder
DEFAULT_AUTO_GROW_COLLECTION_LIMIT, DEFAULT_OBJECT_NAME, logger
 
Constructor Summary
WebDataBinder(java.lang.Object target)
          Create a new WebDataBinder instance, with default object name.
WebDataBinder(java.lang.Object target, java.lang.String objectName)
          Create a new WebDataBinder instance.
 
Method Summary
protected  void bindMultipart(java.util.Map<java.lang.String,java.util.List<MultipartFile>> multipartFiles, MutablePropertyValues mpvs)
          Bind all multipart files contained in the given request, if any (in case of a multipart request).
protected  void bindMultipartFiles(java.util.Map<java.lang.String,MultipartFile> multipartFiles, MutablePropertyValues mpvs)
          Deprecated. as of Spring 3.0, in favor of bindMultipart(java.util.Map>, org.springframework.beans.MutablePropertyValues) which binds all multipart files, even if more than one sent for the same name
protected  void checkFieldDefaults(MutablePropertyValues mpvs)
          Check the given property values for field defaults, i.e.
protected  void checkFieldMarkers(MutablePropertyValues mpvs)
          Check the given property values for field markers, i.e.
protected  void doBind(MutablePropertyValues mpvs)
          This implementation performs a field default and marker check before delegating to the superclass binding process.
protected  java.lang.Object getEmptyValue(java.lang.String field, java.lang.Class fieldType)
          Determine an empty value for the specified field.
 java.lang.String getFieldDefaultPrefix()
          Return the prefix for parameters that mark default fields.
 java.lang.String getFieldMarkerPrefix()
          Return the prefix for parameters that mark potentially empty fields.
 boolean isBindEmptyMultipartFiles()
          Return whether to bind empty MultipartFile parameters.
 void setBindEmptyMultipartFiles(boolean bindEmptyMultipartFiles)
          Set whether to bind empty MultipartFile parameters.
 void setFieldDefaultPrefix(java.lang.String fieldDefaultPrefix)
          Specify a prefix that can be used for parameters that indicate default value fields, having "prefix + field" as name.
 void setFieldMarkerPrefix(java.lang.String fieldMarkerPrefix)
          Specify a prefix that can be used for parameters that mark potentially empty fields, having "prefix + field" as name.
 
Methods inherited from class org.springframework.validation.DataBinder
applyPropertyValues, bind, checkAllowedFields, checkRequiredFields, close, convertIfNecessary, convertIfNecessary, findCustomEditor, getAllowedFields, getAutoGrowCollectionLimit, getBindingErrorProcessor, getBindingResult, getConversionService, getDisallowedFields, getErrors, getInternalBindingResult, getObjectName, getPropertyAccessor, getPropertyEditorRegistry, getRequiredFields, getSimpleTypeConverter, getTarget, getTypeConverter, getValidator, initBeanPropertyAccess, initDirectFieldAccess, isAllowed, isAutoGrowNestedPaths, isIgnoreInvalidFields, isIgnoreUnknownFields, registerCustomEditor, registerCustomEditor, setAllowedFields, setAutoGrowCollectionLimit, setAutoGrowNestedPaths, setBindingErrorProcessor, setConversionService, setDisallowedFields, setExtractOldValueForEditor, setIgnoreInvalidFields, setIgnoreUnknownFields, setMessageCodesResolver, setRequiredFields, setValidator, validate, validate
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

DEFAULT_FIELD_MARKER_PREFIX

public static final java.lang.String DEFAULT_FIELD_MARKER_PREFIX
Default prefix that field marker parameters start with, followed by the field name: e.g. "_subscribeToNewsletter" for a field "subscribeToNewsletter".

Such a marker parameter indicates that the field was visible, that is, existed in the form that caused the submission. If no corresponding field value parameter was found, the field will be reset. The value of the field marker parameter does not matter in this case; an arbitrary value can be used. This is particularly useful for HTML checkboxes and select options.

See Also:
setFieldMarkerPrefix(java.lang.String), Constant Field Values

DEFAULT_FIELD_DEFAULT_PREFIX

public static final java.lang.String DEFAULT_FIELD_DEFAULT_PREFIX
Default prefix that field default parameters start with, followed by the field name: e.g. "!subscribeToNewsletter" for a field "subscribeToNewsletter".

Default parameters differ from field markers in that they provide a default value instead of an empty value.

See Also:
setFieldDefaultPrefix(java.lang.String), Constant Field Values
Constructor Detail

WebDataBinder

public WebDataBinder(java.lang.Object target)
Create a new WebDataBinder instance, with default object name.

Parameters:
target - the target object to bind onto (or null if the binder is just used to convert a plain parameter value)
See Also:
DataBinder.DEFAULT_OBJECT_NAME

WebDataBinder

public WebDataBinder(java.lang.Object target,
                     java.lang.String objectName)
Create a new WebDataBinder instance.

Parameters:
target - the target object to bind onto (or null if the binder is just used to convert a plain parameter value)
objectName - the name of the target object
Method Detail

setFieldMarkerPrefix

public void setFieldMarkerPrefix(java.lang.String fieldMarkerPrefix)
Specify a prefix that can be used for parameters that mark potentially empty fields, having "prefix + field" as name. Such a marker parameter is checked by existence: You can send any value for it, for example "visible". This is particularly useful for HTML checkboxes and select options.

Default is "_", for "_FIELD" parameters (e.g. "_subscribeToNewsletter"). Set this to null if you want to turn off the empty field check completely.

HTML checkboxes only send a value when they're checked, so it is not possible to detect that a formerly checked box has just been unchecked, at least not with standard HTML means.

One way to address this is to look for a checkbox parameter value if you know that the checkbox has been visible in the form, resetting the checkbox if no value found. In Spring web MVC, this typically happens in a custom onBind implementation.

This auto-reset mechanism addresses this deficiency, provided that a marker parameter is sent for each checkbox field, like "_subscribeToNewsletter" for a "subscribeToNewsletter" field. As the marker parameter is sent in any case, the data binder can detect an empty field and automatically reset its value.

See Also:
DEFAULT_FIELD_MARKER_PREFIX, BaseCommandController.onBind(javax.servlet.http.HttpServletRequest, java.lang.Object, org.springframework.validation.BindException)

getFieldMarkerPrefix

public java.lang.String getFieldMarkerPrefix()
Return the prefix for parameters that mark potentially empty fields.


setFieldDefaultPrefix

public void setFieldDefaultPrefix(java.lang.String fieldDefaultPrefix)
Specify a prefix that can be used for parameters that indicate default value fields, having "prefix + field" as name. The value of the default field is used when the field is not provided.

Default is "!", for "!FIELD" parameters (e.g. "!subscribeToNewsletter"). Set this to null if you want to turn off the field defaults completely.

HTML checkboxes only send a value when they're checked, so it is not possible to detect that a formerly checked box has just been unchecked, at least not with standard HTML means. A default field is especially useful when a checkbox represents a non-boolean value.

The presence of a default parameter preempts the behavior of a field marker for the given field.

See Also:
DEFAULT_FIELD_DEFAULT_PREFIX, BaseCommandController.onBind(javax.servlet.http.HttpServletRequest, java.lang.Object, org.springframework.validation.BindException)

getFieldDefaultPrefix

public java.lang.String getFieldDefaultPrefix()
Return the prefix for parameters that mark default fields.


setBindEmptyMultipartFiles

public void setBindEmptyMultipartFiles(boolean bindEmptyMultipartFiles)
Set whether to bind empty MultipartFile parameters. Default is "true".

Turn this off if you want to keep an already bound MultipartFile when the user resubmits the form without choosing a different file. Else, the already bound MultipartFile will be replaced by an empty MultipartFile holder.

See Also:
MultipartFile

isBindEmptyMultipartFiles

public boolean isBindEmptyMultipartFiles()
Return whether to bind empty MultipartFile parameters.


doBind

protected void doBind(MutablePropertyValues mpvs)
This implementation performs a field default and marker check before delegating to the superclass binding process.

Overrides:
doBind in class DataBinder
Parameters:
mpvs - the property values to bind, as MutablePropertyValues instance
See Also:
checkFieldDefaults(org.springframework.beans.MutablePropertyValues), checkFieldMarkers(org.springframework.beans.MutablePropertyValues)

checkFieldDefaults

protected void checkFieldDefaults(MutablePropertyValues mpvs)
Check the given property values for field defaults, i.e. for fields that start with the field default prefix.

The existence of a field defaults indicates that the specified value should be used if the field is otherwise not present.

Parameters:
mpvs - the property values to be bound (can be modified)
See Also:
getFieldDefaultPrefix()

checkFieldMarkers

protected void checkFieldMarkers(MutablePropertyValues mpvs)
Check the given property values for field markers, i.e. for fields that start with the field marker prefix.

The existence of a field marker indicates that the specified field existed in the form. If the property values do not contain a corresponding field value, the field will be considered as empty and will be reset appropriately.

Parameters:
mpvs - the property values to be bound (can be modified)
See Also:
getFieldMarkerPrefix(), getEmptyValue(String, Class)

getEmptyValue

protected java.lang.Object getEmptyValue(java.lang.String field,
                                         java.lang.Class fieldType)
Determine an empty value for the specified field.

Default implementation returns Boolean.FALSE for boolean fields and an empty array of array types. Else, null is used as default.

Parameters:
field - the name of the field
fieldType - the type of the field
Returns:
the empty value (for most fields: null)

bindMultipartFiles

@Deprecated
protected void bindMultipartFiles(java.util.Map<java.lang.String,MultipartFile> multipartFiles,
                                             MutablePropertyValues mpvs)
Deprecated. as of Spring 3.0, in favor of bindMultipart(java.util.Map>, org.springframework.beans.MutablePropertyValues) which binds all multipart files, even if more than one sent for the same name

Bind the multipart files contained in the given request, if any (in case of a multipart request).

Multipart files will only be added to the property values if they are not empty or if we're configured to bind empty multipart files too.

Parameters:
multipartFiles - Map of field name String to MultipartFile object
mpvs - the property values to be bound (can be modified)
See Also:
MultipartFile, setBindEmptyMultipartFiles(boolean)

bindMultipart

protected void bindMultipart(java.util.Map<java.lang.String,java.util.List<MultipartFile>> multipartFiles,
                             MutablePropertyValues mpvs)
Bind all multipart files contained in the given request, if any (in case of a multipart request).

Multipart files will only be added to the property values if they are not empty or if we're configured to bind empty multipart files too.

Parameters:
multipartFiles - Map of field name String to MultipartFile object
mpvs - the property values to be bound (can be modified)
See Also:
MultipartFile, setBindEmptyMultipartFiles(boolean)

Spring Framework