com.google.gson

Class GsonBuilder

java.lang.Object

com.google.gson.GsonBuilder

public final class GsonBuilder
extends Object

Use this builder to construct a Gson instance when you need to set configuration options other than the default. For Gson with default configuration, it is simpler to use new Gson(). GsonBuilder is best used by creating it, and then invoking its various configuration methods, and finally calling create.

The following is an example shows how to use the GsonBuilder to construct a Gson instance:

 Gson gson = new GsonBuilder()
     .registerTypeAdapter(Id.class, new IdTypeAdapter())
     .enableComplexMapKeySerialization()
     .serializeNulls()
     .setDateFormat(DateFormat.LONG)
     .setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE)
     .setPrettyPrinting()
     .setVersion(1.0)
     .create();
 

NOTES:

• the order of invocation of configuration methods does not matter.
• The default serialization of Date and its subclasses in Gson does not contain time-zone information. So, if you are using date/time instances, use GsonBuilder and its setDateFormat methods.

Author:

Inderjeet Singh, Joel Leitch, Jesse Wilson

Constructor Summary

Constructors

Constructor and Description
GsonBuilder() Creates a GsonBuilder instance that can be used to build Gson with various configuration settings.

Method Summary

Methods

Modifier and Type	Method and Description
GsonBuilder	addDeserializationExclusionStrategy(ExclusionStrategy strategy) Configures Gson to apply the passed in exclusion strategy during deserialization.
GsonBuilder	addSerializationExclusionStrategy(ExclusionStrategy strategy) Configures Gson to apply the passed in exclusion strategy during serialization.
Gson	create() Creates a Gson instance based on the current configuration.
GsonBuilder	disableHtmlEscaping() By default, Gson escapes HTML characters such as < > etc.
GsonBuilder	disableInnerClassSerialization() Configures Gson to exclude inner classes during serialization.
GsonBuilder	enableComplexMapKeySerialization() Enabling this feature will only change the serialized form if the map key is a complex type (i.e.
GsonBuilder	excludeFieldsWithModifiers(int... modifiers) Configures Gson to excludes all class fields that have the specified modifiers.
GsonBuilder	excludeFieldsWithoutExposeAnnotation() Configures Gson to exclude all fields from consideration for serialization or deserialization that do not have the Expose annotation.
GsonBuilder	generateNonExecutableJson() Makes the output JSON non-executable in Javascript by prefixing the generated JSON with some special text.
GsonBuilder	registerTypeAdapter(Type type, Object typeAdapter) Configures Gson for custom serialization or deserialization.
GsonBuilder	registerTypeAdapterFactory(TypeAdapterFactory factory) Register a factory for type adapters.
GsonBuilder	registerTypeHierarchyAdapter(Class<?> baseType, Object typeAdapter) Configures Gson for custom serialization or deserialization for an inheritance type hierarchy.
GsonBuilder	serializeNulls() Configure Gson to serialize null fields.
GsonBuilder	serializeSpecialFloatingPointValues() Section 2.4 of JSON specification disallows special double values (NaN, Infinity, -Infinity).
GsonBuilder	setDateFormat(int style) Configures Gson to to serialize Date objects according to the style value provided.
GsonBuilder	setDateFormat(int dateStyle, int timeStyle) Configures Gson to to serialize Date objects according to the style value provided.
GsonBuilder	setDateFormat(String pattern) Configures Gson to serialize Date objects according to the pattern provided.
GsonBuilder	setExclusionStrategies(ExclusionStrategy... strategies) Configures Gson to apply a set of exclusion strategies during both serialization and deserialization.
GsonBuilder	setFieldNamingPolicy(FieldNamingPolicy namingConvention) Configures Gson to apply a specific naming policy to an object's field during serialization and deserialization.
GsonBuilder	setFieldNamingStrategy(FieldNamingStrategy fieldNamingStrategy) Configures Gson to apply a specific naming policy strategy to an object's field during serialization and deserialization.
GsonBuilder	setLenient() By default, Gson is strict and only accepts JSON as specified by RFC 4627.
GsonBuilder	setLongSerializationPolicy(LongSerializationPolicy serializationPolicy) Configures Gson to apply a specific serialization policy for Long and long objects.
GsonBuilder	setPrettyPrinting() Configures Gson to output Json that fits in a page for pretty printing.
GsonBuilder	setVersion(double ignoreVersionsAfter) Configures Gson to enable versioning support.

Methods inherited from class java.lang.Object

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

Constructor Detail

GsonBuilder

public GsonBuilder()

Creates a GsonBuilder instance that can be used to build Gson with various configuration settings. GsonBuilder follows the builder pattern, and it is typically used by first invoking various configuration methods to set desired options, and finally calling create().

Method Detail

setVersion

public GsonBuilder setVersion(double ignoreVersionsAfter)

Configures Gson to enable versioning support.

Parameters:

ignoreVersionsAfter - any field or type marked with a version higher than this value are ignored during serialization or deserialization.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

excludeFieldsWithModifiers

public GsonBuilder excludeFieldsWithModifiers(int... modifiers)

Configures Gson to excludes all class fields that have the specified modifiers. By default, Gson will exclude all fields marked transient or static. This method will override that behavior.

Parameters:

modifiers - the field modifiers. You must use the modifiers specified in the Modifier class. For example, Modifier.TRANSIENT, Modifier.STATIC.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

generateNonExecutableJson

public GsonBuilder generateNonExecutableJson()

Makes the output JSON non-executable in Javascript by prefixing the generated JSON with some special text. This prevents attacks from third-party sites through script sourcing. See Gson Issue 42 for details.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.3

excludeFieldsWithoutExposeAnnotation

public GsonBuilder excludeFieldsWithoutExposeAnnotation()

Configures Gson to exclude all fields from consideration for serialization or deserialization that do not have the Expose annotation.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

serializeNulls

public GsonBuilder serializeNulls()

Configure Gson to serialize null fields. By default, Gson omits all fields that are null during serialization.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.2

enableComplexMapKeySerialization

public GsonBuilder enableComplexMapKeySerialization()

Enabling this feature will only change the serialized form if the map key is a complex type (i.e. non-primitive) in its serialized JSON form. The default implementation of map serialization uses toString() on the key; however, when this is called then one of the following cases apply:

Maps as JSON objects

For this case, assume that a type adapter is registered to serialize and deserialize some Point class, which contains an x and y coordinate, to/from the JSON Primitive string value "(x,y)". The Java map would then be serialized as a JsonObject.

Below is an example:

  Gson gson = new GsonBuilder()
       .register(Point.class, new MyPointTypeAdapter())
       .enableComplexMapKeySerialization()
       .create();

   Map<Point, String> original = new LinkedHashMap<Point, String>();
   original.put(new Point(5, 6), "a");
   original.put(new Point(8, 8), "b");
   System.out.println(gson.toJson(original, type));
 

The above code prints this JSON object:

  {
     "(5,6)": "a",
     "(8,8)": "b"
   }
 

Maps as JSON arrays

For this case, assume that a type adapter was NOT registered for some Point class, but rather the default Gson serialization is applied. In this case, some new Point(2,3) would serialize as {"x":2,"y":5}.

Given the assumption above, a Map<Point, String> will be serialize as an array of arrays (can be viewed as an entry set of pairs).

Below is an example of serializing complex types as JSON arrays:

 Gson gson = new GsonBuilder()
       .enableComplexMapKeySerialization()
       .create();

   Map<Point, String> original = new LinkedHashMap<Point, String>();
   original.put(new Point(5, 6), "a");
   original.put(new Point(8, 8), "b");
   System.out.println(gson.toJson(original, type));
 

 The JSON output would look as follows:
 
   [
     [
       {
         "x": 5,
         "y": 6
       },
       "a"
     ],
     [
       {
         "x": 8,
         "y": 8
       },
       "b"
     ]
   ]
 

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.7

disableInnerClassSerialization

public GsonBuilder disableInnerClassSerialization()

Configures Gson to exclude inner classes during serialization.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.3

setLongSerializationPolicy

public GsonBuilder setLongSerializationPolicy(LongSerializationPolicy serializationPolicy)

Configures Gson to apply a specific serialization policy for Long and long objects.

Parameters:

serializationPolicy - the particular policy to use for serializing longs.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.3

setFieldNamingPolicy

public GsonBuilder setFieldNamingPolicy(FieldNamingPolicy namingConvention)

Configures Gson to apply a specific naming policy to an object's field during serialization and deserialization.

Parameters:

namingConvention - the JSON field naming convention to use for serialization and deserialization.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

setFieldNamingStrategy

public GsonBuilder setFieldNamingStrategy(FieldNamingStrategy fieldNamingStrategy)

Configures Gson to apply a specific naming policy strategy to an object's field during serialization and deserialization.

Parameters:

fieldNamingStrategy - the actual naming strategy to apply to the fields

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.3

setExclusionStrategies

public GsonBuilder setExclusionStrategies(ExclusionStrategy... strategies)

Configures Gson to apply a set of exclusion strategies during both serialization and deserialization. Each of the strategies will be applied as a disjunction rule. This means that if one of the strategies suggests that a field (or class) should be skipped then that field (or object) is skipped during serializaiton/deserialization.

Parameters:

strategies - the set of strategy object to apply during object (de)serialization.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.4

addSerializationExclusionStrategy

public GsonBuilder addSerializationExclusionStrategy(ExclusionStrategy strategy)

Configures Gson to apply the passed in exclusion strategy during serialization. If this method is invoked numerous times with different exclusion strategy objects then the exclusion strategies that were added will be applied as a disjunction rule. This means that if one of the added exclusion strategies suggests that a field (or class) should be skipped then that field (or object) is skipped during its serialization.

Parameters:

strategy - an exclusion strategy to apply during serialization.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.7

addDeserializationExclusionStrategy

public GsonBuilder addDeserializationExclusionStrategy(ExclusionStrategy strategy)

Configures Gson to apply the passed in exclusion strategy during deserialization. If this method is invoked numerous times with different exclusion strategy objects then the exclusion strategies that were added will be applied as a disjunction rule. This means that if one of the added exclusion strategies suggests that a field (or class) should be skipped then that field (or object) is skipped during its deserialization.

Parameters:

strategy - an exclusion strategy to apply during deserialization.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.7

setPrettyPrinting

public GsonBuilder setPrettyPrinting()

Configures Gson to output Json that fits in a page for pretty printing. This option only affects Json serialization.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

setLenient

public GsonBuilder setLenient()

By default, Gson is strict and only accepts JSON as specified by RFC 4627. This option makes the parser liberal in what it accepts.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

See Also:

JsonReader.setLenient(boolean)

disableHtmlEscaping

public GsonBuilder disableHtmlEscaping()

By default, Gson escapes HTML characters such as < > etc. Use this option to configure Gson to pass-through HTML characters as is.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.3

setDateFormat

public GsonBuilder setDateFormat(String pattern)

Configures Gson to serialize Date objects according to the pattern provided. You can call this method or setDateFormat(int) multiple times, but only the last invocation will be used to decide the serialization format.

The date format will be used to serialize and deserialize Date, Timestamp and Date.

Note that this pattern must abide by the convention provided by SimpleDateFormat class. See the documentation in SimpleDateFormat for more information on valid date and time patterns.

Parameters:

pattern - the pattern that dates will be serialized/deserialized to/from

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.2

setDateFormat

public GsonBuilder setDateFormat(int style)

Configures Gson to to serialize Date objects according to the style value provided. You can call this method or setDateFormat(String) multiple times, but only the last invocation will be used to decide the serialization format.

Note that this style value should be one of the predefined constants in the DateFormat class. See the documentation in DateFormat for more information on the valid style constants.

Parameters:

style - the predefined date style that date objects will be serialized/deserialized to/from

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.2

setDateFormat

public GsonBuilder setDateFormat(int dateStyle,
                        int timeStyle)

Configures Gson to to serialize Date objects according to the style value provided. You can call this method or setDateFormat(String) multiple times, but only the last invocation will be used to decide the serialization format.

Note that this style value should be one of the predefined constants in the DateFormat class. See the documentation in DateFormat for more information on the valid style constants.

Parameters:

dateStyle - the predefined date style that date objects will be serialized/deserialized to/from

timeStyle - the predefined style for the time portion of the date objects

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.2

registerTypeAdapter

public GsonBuilder registerTypeAdapter(Type type,
                              Object typeAdapter)

Configures Gson for custom serialization or deserialization. This method combines the registration of an TypeAdapter, InstanceCreator, JsonSerializer, and a JsonDeserializer. It is best used when a single object typeAdapter implements all the required interfaces for custom serialization with Gson. If a type adapter was previously registered for the specified type, it is overwritten.

This registers the type specified and no other types: you must manually register related types! For example, applications registering boolean.class should also register Boolean.class.

Parameters:

type - the type definition for the type adapter being registered

typeAdapter - This object must implement at least one of the TypeAdapter, InstanceCreator, JsonSerializer, and a JsonDeserializer interfaces.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

registerTypeAdapterFactory

public GsonBuilder registerTypeAdapterFactory(TypeAdapterFactory factory)

Register a factory for type adapters. Registering a factory is useful when the type adapter needs to be configured based on the type of the field being processed. Gson is designed to handle a large number of factories, so you should consider registering them to be at par with registering an individual type adapter.

Since:

2.1

registerTypeHierarchyAdapter

public GsonBuilder registerTypeHierarchyAdapter(Class<?> baseType,
                                       Object typeAdapter)

Configures Gson for custom serialization or deserialization for an inheritance type hierarchy. This method combines the registration of a TypeAdapter, JsonSerializer and a JsonDeserializer. If a type adapter was previously registered for the specified type hierarchy, it is overridden. If a type adapter is registered for a specific type in the type hierarchy, it will be invoked instead of the one registered for the type hierarchy.

Parameters:

baseType - the class definition for the type adapter being registered for the base class or interface

typeAdapter - This object must implement at least one of TypeAdapter, JsonSerializer or JsonDeserializer interfaces.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.7

serializeSpecialFloatingPointValues

public GsonBuilder serializeSpecialFloatingPointValues()

Section 2.4 of JSON specification disallows special double values (NaN, Infinity, -Infinity). However, Javascript specification (see section 4.3.20, 4.3.22, 4.3.23) allows these values as valid Javascript values. Moreover, most JavaScript engines will accept these special values in JSON without problem. So, at a practical level, it makes sense to accept these values as valid JSON even though JSON specification disallows them.

Gson always accepts these special values during deserialization. However, it outputs strictly compliant JSON. Hence, if it encounters a float value Float.NaN, Float.POSITIVE_INFINITY, Float.NEGATIVE_INFINITY, or a double value Double.NaN, Double.POSITIVE_INFINITY, Double.NEGATIVE_INFINITY, it will throw an IllegalArgumentException. This method provides a way to override the default behavior when you know that the JSON receiver will be able to handle these special values.

Returns:

a reference to this GsonBuilder object to fulfill the "Builder" pattern

Since:

1.3

create

public Gson create()

Creates a Gson instance based on the current configuration. This method is free of side-effects to this GsonBuilder instance and hence can be called multiple times.

Returns:

an instance of Gson configured with the options currently set in this builder