org.springframework.http.converter

Class FormHttpMessageConverter

java.lang.Object

org.springframework.http.converter.FormHttpMessageConverter

All Implemented Interfaces:

HttpMessageConverter<MultiValueMap<String,?>>

Direct Known Subclasses:

AllEncompassingFormHttpMessageConverter

public class FormHttpMessageConverter
extends Object
implements HttpMessageConverter<MultiValueMap<String,?>>

Implementation of HttpMessageConverter to read and write 'normal' HTML forms and also to write (but not read) multipart data (e.g. file uploads).

In other words, this converter can read and write the "application/x-www-form-urlencoded" media type as MultiValueMap<String, String>, and it can also write (but not read) the "multipart/form-data" and "multipart/mixed" media types as MultiValueMap<String, Object>.

Multipart Data

By default, "multipart/form-data" is used as the content type when writing multipart data. As of Spring Framework 5.2 it is also possible to write multipart data using other multipart subtypes such as "multipart/mixed" and "multipart/related", as long as the multipart subtype is registered as a supported media type and the desired multipart subtype is specified as the content type when writing the multipart data. Note that "multipart/mixed" is registered as a supported media type by default.

When writing multipart data, this converter uses other HttpMessageConverters to write the respective MIME parts. By default, basic converters are registered for byte array, String, and Resource. These can be overridden via setPartConverters(java.util.List<org.springframework.http.converter.HttpMessageConverter<?>>) or augmented via addPartConverter(org.springframework.http.converter.HttpMessageConverter<?>).

Examples

The following snippet shows how to submit an HTML form using the "multipart/form-data" content type.

 RestTemplate restTemplate = new RestTemplate();
 // AllEncompassingFormHttpMessageConverter is configured by default

 MultiValueMap<String, Object> form = new LinkedMultiValueMap<>();
 form.add("field 1", "value 1");
 form.add("field 2", "value 2");
 form.add("field 2", "value 3");
 form.add("field 3", 4);  // non-String form values supported as of 5.1.4

 restTemplate.postForLocation("https://example.com/myForm", form);

The following snippet shows how to do a file upload using the "multipart/form-data" content type.

 MultiValueMap<String, Object> parts = new LinkedMultiValueMap<>();
 parts.add("field 1", "value 1");
 parts.add("file", new ClassPathResource("myFile.jpg"));

 restTemplate.postForLocation("https://example.com/myFileUpload", parts);

The following snippet shows how to do a file upload using the "multipart/mixed" content type.

 MultiValueMap<String, Object> parts = new LinkedMultiValueMap<>();
 parts.add("field 1", "value 1");
 parts.add("file", new ClassPathResource("myFile.jpg"));

 HttpHeaders requestHeaders = new HttpHeaders();
 requestHeaders.setContentType(MediaType.MULTIPART_MIXED);

 restTemplate.postForLocation("https://example.com/myFileUpload",
     new HttpEntity<>(parts, requestHeaders));

The following snippet shows how to do a file upload using the "multipart/related" content type.

 MediaType multipartRelated = new MediaType("multipart", "related");

 restTemplate.getMessageConverters().stream()
     .filter(FormHttpMessageConverter.class::isInstance)
     .map(FormHttpMessageConverter.class::cast)
     .findFirst()
     .orElseThrow(() -> new IllegalStateException("Failed to find FormHttpMessageConverter"))
     .addSupportedMediaTypes(multipartRelated);

 MultiValueMap<String, Object> parts = new LinkedMultiValueMap<>();
 parts.add("field 1", "value 1");
 parts.add("file", new ClassPathResource("myFile.jpg"));

 HttpHeaders requestHeaders = new HttpHeaders();
 requestHeaders.setContentType(multipartRelated);

 restTemplate.postForLocation("https://example.com/myFileUpload",
     new HttpEntity<>(parts, requestHeaders));

Miscellaneous

Some methods in this class were inspired by org.apache.commons.httpclient.methods.multipart.MultipartRequestEntity.

Since:

3.0

Author:

Arjen Poutsma, Rossen Stoyanchev, Juergen Hoeller, Sam Brannen

See Also:

AllEncompassingFormHttpMessageConverter, MultiValueMap

Field Summary

Fields

Modifier and Type	Field and Description
static Charset	DEFAULT_CHARSET The default charset used by the converter.

Constructor Summary

Constructors

Constructor and Description
FormHttpMessageConverter()

Method Summary

Modifier and Type	Method and Description
void	addPartConverter(HttpMessageConverter<?> partConverter) Add a message body converter.
void	addSupportedMediaTypes(MediaType... supportedMediaTypes) Add MediaType objects to be supported by this converter.
boolean	canRead(Class<?> clazz, MediaType mediaType) Indicates whether the given class can be read by this converter.
boolean	canWrite(Class<?> clazz, MediaType mediaType) Indicates whether the given class can be written by this converter.
protected byte[]	generateMultipartBoundary() Generate a multipart boundary.
protected String	getFilename(Object part) Return the filename of the given multipart part.
protected MediaType	getFormContentType(MediaType contentType) Return the content type used to write forms, given the preferred content type.
protected HttpEntity<?>	getHttpEntity(Object part) Return an HttpEntity for the given part Object.
List<MediaType>	getSupportedMediaTypes() Return the list of MediaType objects supported by this converter.
MultiValueMap<String,String>	read(Class<? extends MultiValueMap<String,?>> clazz, HttpInputMessage inputMessage) Read an object of the given type from the given input message, and returns it.
protected String	serializeForm(MultiValueMap<String,Object> formData, Charset charset)
void	setCharset(Charset charset) Set the default character set to use for reading and writing form data when the request or response Content-Type header does not explicitly specify it.
void	setMultipartCharset(Charset charset) Set the character set to use when writing multipart data to encode file names.
void	setPartConverters(List<HttpMessageConverter<?>> partConverters) Set the message body converters to use.
void	setSupportedMediaTypes(List<MediaType> supportedMediaTypes) Set the list of MediaType objects supported by this converter.
void	write(MultiValueMap<String,?> map, MediaType contentType, HttpOutputMessage outputMessage) Write an given object to the given output message.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_CHARSET

public static final Charset DEFAULT_CHARSET

The default charset used by the converter.

Constructor Detail

FormHttpMessageConverter

public FormHttpMessageConverter()

Method Detail

setSupportedMediaTypes

public void setSupportedMediaTypes(List<MediaType> supportedMediaTypes)

Set the list of MediaType objects supported by this converter.

See Also:

addSupportedMediaTypes(MediaType...), getSupportedMediaTypes()

addSupportedMediaTypes

public void addSupportedMediaTypes(MediaType... supportedMediaTypes)

Add MediaType objects to be supported by this converter.

The supplied MediaType objects will be appended to the list of supported MediaType objects.

Parameters:

supportedMediaTypes - a var-args list of MediaType objects to add

Since:

5.2

See Also:

setSupportedMediaTypes(List)

getSupportedMediaTypes

public List<MediaType> getSupportedMediaTypes()

Return the list of MediaType objects supported by this converter.

Specified by:

getSupportedMediaTypes in interface HttpMessageConverter<MultiValueMap<String,?>>

Returns:

the list of supported media types, potentially an immutable copy

See Also:

setSupportedMediaTypes(List), addSupportedMediaTypes(MediaType...)

setPartConverters

public void setPartConverters(List<HttpMessageConverter<?>> partConverters)

Set the message body converters to use. These converters are used to convert objects to MIME parts.

addPartConverter

public void addPartConverter(HttpMessageConverter<?> partConverter)

Add a message body converter. Such a converter is used to convert objects to MIME parts.

setCharset

public void setCharset(@Nullable
                       Charset charset)

Set the default character set to use for reading and writing form data when the request or response Content-Type header does not explicitly specify it.

As of 4.3, this is also used as the default charset for the conversion of text bodies in a multipart request.

As of 5.0, this is also used for part headers including Content-Disposition (and its filename parameter) unless (the mutually exclusive) multipartCharset is also set, in which case part headers are encoded as ASCII and filename is encoded with the encoded-word syntax from RFC 2047.

By default this is set to "UTF-8".

setMultipartCharset

public void setMultipartCharset(Charset charset)

Set the character set to use when writing multipart data to encode file names. Encoding is based on the encoded-word syntax defined in RFC 2047 and relies on MimeUtility from javax.mail.

As of 5.0 by default part headers, including Content-Disposition (and its filename parameter) will be encoded based on the setting of setCharset(Charset) or UTF-8 by default.

Since:

4.1.1

See Also:

Encoded-Word

canRead

public boolean canRead(Class<?> clazz,
                       @Nullable
                       MediaType mediaType)

Description copied from interface: HttpMessageConverter

Indicates whether the given class can be read by this converter.

Specified by:

canRead in interface HttpMessageConverter<MultiValueMap<String,?>>

Parameters:

clazz - the class to test for readability

mediaType - the media type to read (can be null if not specified); typically the value of a Content-Type header.

Returns:

true if readable; false otherwise

canWrite

public boolean canWrite(Class<?> clazz,
                        @Nullable
                        MediaType mediaType)

Description copied from interface: HttpMessageConverter

Indicates whether the given class can be written by this converter.

Specified by:

canWrite in interface HttpMessageConverter<MultiValueMap<String,?>>

Parameters:

clazz - the class to test for writability

mediaType - the media type to write (can be null if not specified); typically the value of an Accept header.

Returns:

true if writable; false otherwise

read

public MultiValueMap<String,String> read(@Nullable
                                         Class<? extends MultiValueMap<String,?>> clazz,
                                         HttpInputMessage inputMessage)
                                  throws IOException,
                                         HttpMessageNotReadableException

Description copied from interface: HttpMessageConverter

Read an object of the given type from the given input message, and returns it.

Specified by:

read in interface HttpMessageConverter<MultiValueMap<String,?>>

Parameters:

clazz - the type of object to return. This type must have previously been passed to the canRead method of this interface, which must have returned true.

inputMessage - the HTTP input message to read from

Returns:

the converted object

Throws:

IOException - in case of I/O errors

HttpMessageNotReadableException - in case of conversion errors

write

public void write(MultiValueMap<String,?> map,
                  @Nullable
                  MediaType contentType,
                  HttpOutputMessage outputMessage)
           throws IOException,
                  HttpMessageNotWritableException

Description copied from interface: HttpMessageConverter

Write an given object to the given output message.

Specified by:

write in interface HttpMessageConverter<MultiValueMap<String,?>>

Parameters:

map - the object to write to the output message. The type of this object must have previously been passed to the canWrite method of this interface, which must have returned true.

contentType - the content type to use when writing. May be null to indicate that the default content type of the converter must be used. If not null, this media type must have previously been passed to the canWrite method of this interface, which must have returned true.

outputMessage - the message to write to

Throws:

IOException - in case of I/O errors

HttpMessageNotWritableException - in case of conversion errors

getFormContentType

protected MediaType getFormContentType(@Nullable
                                       MediaType contentType)

Return the content type used to write forms, given the preferred content type. By default, this method returns the given content type, but adds the charset if it does not have one. If contentType is null, application/x-www-form-urlencoded; charset=UTF-8 is returned.

Subclasses can override this method to change this behavior.

Parameters:

contentType - the preferred content type (can be null)

Returns:

the content type to be used

Since:

5.2.2

serializeForm

protected String serializeForm(MultiValueMap<String,Object> formData,
                               Charset charset)

generateMultipartBoundary

protected byte[] generateMultipartBoundary()

Generate a multipart boundary.

This implementation delegates to MimeTypeUtils.generateMultipartBoundary().

getHttpEntity

protected HttpEntity<?> getHttpEntity(Object part)

Return an HttpEntity for the given part Object.

Parameters:

part - the part to return an HttpEntity for

Returns:

the part Object itself it is an HttpEntity, or a newly built HttpEntity wrapper for that part

getFilename

@Nullable
protected String getFilename(Object part)

Return the filename of the given multipart part. This value will be used for the Content-Disposition header.

The default implementation returns Resource.getFilename() if the part is a Resource, and null in other cases. Can be overridden in subclasses.

Parameters:

part - the part to determine the file name for

Returns:

the filename, or null if not known