Class WebDataBinder

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

WARNING: Data binding can lead to security issues by exposing parts of the object graph that are not meant to be accessed or modified by external clients. Therefore, the design and use of data binding should be considered carefully with regard to security. For more details, please refer to the dedicated sections on data binding for Spring Web MVC and Spring WebFlux in the reference manual.

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 than empty.

Since:
1.2
Author:
Juergen Hoeller, Scott Andrews, Brian Clozel
See Also:

  • Field Details

    • 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: for example, "_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:

    • 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: for example, "!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:

  • Constructor Details

    • WebDataBinder

      public WebDataBinder(@Nullable 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:

    • WebDataBinder

      public WebDataBinder(@Nullable 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 Details

    • setFieldMarkerPrefix

      public void setFieldMarkerPrefix(@Nullable 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 (for example, "_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:

    • getFieldMarkerPrefix

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

    • setFieldDefaultPrefix

      public void setFieldDefaultPrefix(@Nullable 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 (for example, "!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:

    • getFieldDefaultPrefix

      public @Nullable 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.

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    • isBindEmptyMultipartFiles

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

    • resolvePrefixValue

      protected @Nullable Object resolvePrefixValue(String name, Class<?> type, BiFunction<String,Class<?>,Object> resolver)
      Check if a value can be resolved if getFieldDefaultPrefix() or getFieldMarkerPrefix() is prepended.
      Parameters:
      name - the name of the value to resolve
      type - the type of value expected
      resolver - delegate resolver to use for the checks
      Returns:
      the resolved value, or null
      Since:
      6.1

    • 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
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    • 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)
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    • 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)
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    • adaptEmptyArrayIndices

      protected void adaptEmptyArrayIndices(MutablePropertyValues mpvs)
      Check for property values with names that end on "[]". This is used by some clients for array syntax without an explicit index value. If such values are found, drop the brackets to adapt to the expected way of expressing the same for data binding purposes.
      Parameters:
      mpvs - the property values to be bound (can be modified)
      Since:
      5.3

    • getEmptyValue

      protected @Nullable Object getEmptyValue(String field, @Nullable Class<?> fieldType)
      Determine an empty value for the specified field.

      The default implementation delegates to getEmptyValue(Class) if the field type is known, otherwise falls back to null.

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

    • getEmptyValue

      public @Nullable Object getEmptyValue(Class<?> fieldType)
      Determine an empty value for the specified field.

      The 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:
      fieldType - the type of the field
      Returns:
      the empty value (for most fields: null)
      Since:
      5.0

    • 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). To be called by subclasses.

      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 - a Map of field name String to MultipartFile object
      mpvs - the property values to be bound (can be modified)
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