org.springframework.web.bind

Class WebDataBinder

java.lang.Object

org.springframework.validation.DataBinder

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, Brian Clozel

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

Fields

Modifier and Type	Field and Description
static String	DEFAULT_FIELD_DEFAULT_PREFIX Default prefix that field default parameters start with, followed by the field name: e.g.
static 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

Constructors

Constructor and Description
WebDataBinder(Object target) Create a new WebDataBinder instance, with default object name.
WebDataBinder(Object target, String objectName) Create a new WebDataBinder instance.

Method Summary

Modifier and Type	Method and Description
protected void	bindMultipart(Map<String,List<MultipartFile>> multipartFiles, MutablePropertyValues mpvs) Bind all multipart files contained in the given request, if any (in case of a multipart request).
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 Object	getEmptyValue(String field, Class<?> fieldType) Determine an empty value for the specified field.
String	getFieldDefaultPrefix() Return the prefix for parameters that mark default fields.
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(String fieldDefaultPrefix) Specify a prefix that can be used for parameters that indicate default value fields, having "prefix + field" as name.
void	setFieldMarkerPrefix(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

addCustomFormatter, addCustomFormatter, addCustomFormatter, addValidators, applyPropertyValues, bind, checkAllowedFields, checkRequiredFields, close, convertIfNecessary, convertIfNecessary, convertIfNecessary, createBeanPropertyBindingResult, createDirectFieldBindingResult, findCustomEditor, getAllowedFields, getAutoGrowCollectionLimit, getBindingErrorProcessor, getBindingResult, getConversionService, getDisallowedFields, getInternalBindingResult, getObjectName, getPropertyAccessor, getPropertyEditorRegistry, getRequiredFields, getSimpleTypeConverter, getTarget, getTypeConverter, getValidator, getValidators, initBeanPropertyAccess, initDirectFieldAccess, isAllowed, isAutoGrowNestedPaths, isIgnoreInvalidFields, isIgnoreUnknownFields, registerCustomEditor, registerCustomEditor, replaceValidators, 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 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 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(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(Object target,
                     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(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

getFieldMarkerPrefix

public String getFieldMarkerPrefix()

Return the prefix for parameters that mark potentially empty fields.

setFieldDefaultPrefix

public void setFieldDefaultPrefix(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

getFieldDefaultPrefix

public 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 Object getEmptyValue(String field,
                               Class<?> fieldType)

Determine an empty value for the specified field.

Default implementation returns:

• Boolean.FALSE for boolean fields
• an empty array for array types
• Collection implementations for Collection types
• Map implementations for Map 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)

bindMultipart

protected void bindMultipart(Map<String,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)