org.springframework.http.converter.json

Class GsonHttpMessageConverter

java.lang.Object

org.springframework.http.converter.AbstractHttpMessageConverter<Object>

org.springframework.http.converter.json.GsonHttpMessageConverter

All Implemented Interfaces:

GenericHttpMessageConverter<Object>, HttpMessageConverter<Object>

public class GsonHttpMessageConverter
extends AbstractHttpMessageConverter<Object>
implements GenericHttpMessageConverter<Object>

Implementation of HttpMessageConverter that can read and write JSON using the Google Gson library's Gson class.

This converter can be used to bind to typed beans or untyped HashMaps. By default, it supports application/json and application/*+json.

Tested against Gson 2.3; compatible with Gson 2.0 and higher.

Since:

4.1

Author:

Roy Clarkson

See Also:

setGson(com.google.gson.Gson), AbstractHttpMessageConverter.setSupportedMediaTypes(java.util.List<org.springframework.http.MediaType>)

Field Summary

Fields

Modifier and Type	Field and Description
static Charset	DEFAULT_CHARSET

Fields inherited from class org.springframework.http.converter.AbstractHttpMessageConverter

logger

Constructor Summary

Constructors

Constructor and Description
GsonHttpMessageConverter() Construct a new GsonHttpMessageConverter.

Method Summary

Modifier and Type	Method and Description
boolean	canRead(Class<?> clazz, MediaType mediaType) This implementation checks if the given class is supported, and if the supported media types include the given media type.
boolean	canRead(Type type, Class<?> contextClass, MediaType mediaType) Indicates whether the given type can be read by this converter.
boolean	canWrite(Class<?> clazz, MediaType mediaType) This implementation checks if the given class is supported, and if the supported media types include the given media type.
com.google.gson.Gson	getGson() Return the configured Gson instance for this converter.
protected com.google.gson.reflect.TypeToken<?>	getTypeToken(Type type) Return the Gson TypeToken for the specified type.
Object	read(Type type, Class<?> contextClass, HttpInputMessage inputMessage) Read an object of the given type form the given input message, and returns it.
protected Object	readInternal(Class<?> clazz, HttpInputMessage inputMessage) Abstract template method that reads the actual object.
void	setGson(com.google.gson.Gson gson) Set the Gson instance to use.
void	setJsonPrefix(String jsonPrefix) Specify a custom prefix to use for JSON output.
void	setPrefixJson(boolean prefixJson) Indicate whether the JSON output by this view should be prefixed with "{} &&".
protected boolean	supports(Class<?> clazz) Indicates whether the given class is supported by this converter.
protected void	writeInternal(Object o, HttpOutputMessage outputMessage) Abstract template method that writes the actual body.

Methods inherited from class org.springframework.http.converter.AbstractHttpMessageConverter

canRead, canWrite, getContentLength, getDefaultContentType, getSupportedMediaTypes, read, setSupportedMediaTypes, write

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.springframework.http.converter.HttpMessageConverter

getSupportedMediaTypes, read, write

Field Detail

DEFAULT_CHARSET

public static final Charset DEFAULT_CHARSET

Constructor Detail

GsonHttpMessageConverter

public GsonHttpMessageConverter()

Construct a new GsonHttpMessageConverter.

Method Detail

setGson

public void setGson(com.google.gson.Gson gson)

Set the Gson instance to use. If not set, a default Gson instance is used.

Setting a custom-configured Gson is one way to take further control of the JSON serialization process.

getGson

public com.google.gson.Gson getGson()

Return the configured Gson instance for this converter.

setJsonPrefix

public void setJsonPrefix(String jsonPrefix)

Specify a custom prefix to use for JSON output. Default is none.

See Also:

setPrefixJson(boolean)

setPrefixJson

public void setPrefixJson(boolean prefixJson)

Indicate whether the JSON output by this view should be prefixed with "{} &&". Default is false.

Prefixing the JSON string in this manner is used to help prevent JSON Hijacking. The prefix renders the string syntactically invalid as a script so that it cannot be hijacked. This prefix does not affect the evaluation of JSON, but if JSON validation is performed on the string, the prefix would need to be ignored.

See Also:

setJsonPrefix(java.lang.String)

canRead

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

Description copied from class: AbstractHttpMessageConverter

This implementation checks if the given class is supported, and if the supported media types include the given media type.

Specified by:

canRead in interface HttpMessageConverter<Object>

Overrides:

canRead in class AbstractHttpMessageConverter<Object>

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

canRead

public boolean canRead(Type type,
                       Class<?> contextClass,
                       MediaType mediaType)

Description copied from interface: GenericHttpMessageConverter

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

Specified by:

canRead in interface GenericHttpMessageConverter<Object>

Parameters:

type - the type to test for readability

contextClass - a context class for the target type, for example a class in which the target type appears in a method signature, can be null

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,
                        MediaType mediaType)

Description copied from class: AbstractHttpMessageConverter

This implementation checks if the given class is supported, and if the supported media types include the given media type.

Specified by:

canWrite in interface HttpMessageConverter<Object>

Overrides:

canWrite in class AbstractHttpMessageConverter<Object>

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

supports

protected boolean supports(Class<?> clazz)

Description copied from class: AbstractHttpMessageConverter

Indicates whether the given class is supported by this converter.

Specified by:

supports in class AbstractHttpMessageConverter<Object>

Parameters:

clazz - the class to test for support

Returns:

true if supported; false otherwise

readInternal

protected Object readInternal(Class<?> clazz,
                              HttpInputMessage inputMessage)
                       throws IOException,
                              HttpMessageNotReadableException

Description copied from class: AbstractHttpMessageConverter

Abstract template method that reads the actual object. Invoked from AbstractHttpMessageConverter.read(java.lang.Class<? extends T>, org.springframework.http.HttpInputMessage).

Specified by:

readInternal in class AbstractHttpMessageConverter<Object>

Parameters:

clazz - the type of object to return

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

read

public Object read(Type type,
                   Class<?> contextClass,
                   HttpInputMessage inputMessage)
            throws IOException,
                   HttpMessageNotReadableException

Description copied from interface: GenericHttpMessageConverter

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

Specified by:

read in interface GenericHttpMessageConverter<Object>

Parameters:

type - 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.

contextClass - a context class for the target type, for example a class in which the target type appears in a method signature, can be null

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

getTypeToken

protected com.google.gson.reflect.TypeToken<?> getTypeToken(Type type)

Return the Gson TypeToken for the specified type.

The default implementation returns TypeToken.get(type), but this can be overridden in subclasses to allow for custom generic collection handling. For instance:

 protected TypeToken getTypeToken(Type type) {
   if (type instanceof Class && List.class.isAssignableFrom((Class) type)) {
     return new TypeToken>() {};
   }
   else {
     return super.getTypeToken(type);
   }
 }
 

Parameters:

type - the type for which to return the TypeToken

Returns:

the type token

writeInternal

protected void writeInternal(Object o,
                             HttpOutputMessage outputMessage)
                      throws IOException,
                             HttpMessageNotWritableException

Description copied from class: AbstractHttpMessageConverter

Abstract template method that writes the actual body. Invoked from AbstractHttpMessageConverter.write(T, org.springframework.http.MediaType, org.springframework.http.HttpOutputMessage).

Specified by:

writeInternal in class AbstractHttpMessageConverter<Object>

Parameters:

o - the object to write to the output message

outputMessage - the HTTP output message to write to

Throws:

IOException - in case of I/O errors

HttpMessageNotWritableException - in case of conversion errors