Module com.google.gson
Package com.google.gson

Class 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 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, 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.
    • By default no explicit Strictness is set; some of the Gson methods behave as if Strictness.LEGACY_STRICT was used whereas others behave as if Strictness.LENIENT was used. Prefer explicitly setting a strictness with setStrictness(Strictness) to avoid this legacy behavior.

    Author:
    Inderjeet Singh, Joel Leitch, Jesse Wilson

    • 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

        @CanIgnoreReturnValue
public GsonBuilder setVersion​(double version)
        Configures Gson to enable versioning support. Versioning support works based on the annotation types Since and Until. It allows including or excluding fields and classes based on the specified version. See the documentation of these annotation types for more information.

        By default versioning support is disabled and usage of @Since and @Until has no effect.

        Parameters:
        version - the version number to use.
        Returns:
        a reference to this GsonBuilder object to fulfill the "Builder" pattern
        Throws:
        IllegalArgumentException - if the version number is NaN or negative
        See Also:
        Since, Until

      • excludeFieldsWithModifiers

        @CanIgnoreReturnValue
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.

        This is a convenience method which behaves as if an ExclusionStrategy which excludes these fields was registered with this builder.

        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

        @CanIgnoreReturnValue
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

        @CanIgnoreReturnValue
public GsonBuilder excludeFieldsWithoutExposeAnnotation()
        Configures Gson to exclude all fields from consideration for serialization and deserialization that do not have the Expose annotation.

        This is a convenience method which behaves as if an ExclusionStrategy which excludes these fields was registered with this builder.

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

      • serializeNulls

        @CanIgnoreReturnValue
public GsonBuilder serializeNulls()
        Configures 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

        @CanIgnoreReturnValue
public GsonBuilder enableComplexMapKeySerialization()
        Configures Gson to serialize Map objects with complex keys as JSON arrays. 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<>();
 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":3}.

        Given the assumption above, a Map<Point, String> will be serialized 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<>();
 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

        @CanIgnoreReturnValue
public GsonBuilder disableInnerClassSerialization()
        Configures Gson to exclude inner classes (= non-static nested classes) during serialization and deserialization. This is a convenience method which behaves as if an ExclusionStrategy which excludes inner classes was registered with this builder. This means inner classes will be serialized as JSON null, and will be deserialized as Java null with their JSON data being ignored. And fields with an inner class as type will be ignored during serialization and deserialization.

        By default Gson serializes and deserializes inner classes, but ignores references to the enclosing instance. Deserialization might not be possible at all when disableJdkUnsafe() is used (and no custom InstanceCreator is registered), or it can lead to unexpected NullPointerExceptions when the deserialized instance is used afterwards.

        In general using inner classes with Gson should be avoided; they should be converted to static nested classes if possible.

        Returns:
        a reference to this GsonBuilder object to fulfill the "Builder" pattern
        Since:
        1.3

      • setLongSerializationPolicy

        @CanIgnoreReturnValue
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

      • setFieldNamingStrategy

        @CanIgnoreReturnValue
public GsonBuilder setFieldNamingStrategy​(FieldNamingStrategy fieldNamingStrategy)
        Configures Gson to apply a specific naming strategy to an object's fields during serialization and deserialization.

        The created Gson instance might only use the field naming strategy once for a field and cache the result. It is not guaranteed that the strategy will be used again every time the value of a field is serialized or deserialized.

        Parameters:
        fieldNamingStrategy - the naming strategy to apply to the fields
        Returns:
        a reference to this GsonBuilder object to fulfill the "Builder" pattern
        Since:
        1.3

      • setExclusionStrategies

        @CanIgnoreReturnValue
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 serialization/deserialization. The strategies are added to the existing strategies (if any); the existing strategies are not replaced.

        Fields are excluded for serialization and deserialization when shouldSkipField returns true, or when shouldSkipClass returns true for the field type. Gson behaves as if the field did not exist; its value is not serialized and on deserialization if a JSON member with this name exists it is skipped by default.
        When objects of an excluded type (as determined by shouldSkipClass) are serialized a JSON null is written to output, and when deserialized the JSON value is skipped and null is returned.

        The created Gson instance might only use an exclusion strategy once for a field or class and cache the result. It is not guaranteed that the strategy will be used again every time the value of a field or a class is serialized or deserialized.

        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

        @CanIgnoreReturnValue
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.

        See the documentation of setExclusionStrategies(ExclusionStrategy...) for a detailed description of the effect of exclusion strategies.

        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

        @CanIgnoreReturnValue
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.

        See the documentation of setExclusionStrategies(ExclusionStrategy...) for a detailed description of the effect of exclusion strategies.

        Parameters:
        strategy - an exclusion strategy to apply during deserialization.
        Returns:
        a reference to this GsonBuilder object to fulfill the "Builder" pattern
        Since:
        1.7

      • setFormattingStyle

        @CanIgnoreReturnValue
public GsonBuilder setFormattingStyle​(FormattingStyle formattingStyle)
        Configures Gson to output JSON that uses a certain kind of formatting style (for example newline and indent). This option only affects JSON serialization. By default Gson produces compact JSON output without any formatting.
        Parameters:
        formattingStyle - the formatting style to use.
        Returns:
        a reference to this GsonBuilder object to fulfill the "Builder" pattern
        Since:
        2.11.0

      • disableHtmlEscaping

        @CanIgnoreReturnValue
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

        @CanIgnoreReturnValue
public GsonBuilder setDateFormat​(String pattern)
        Configures Gson to serialize Date objects according to the pattern provided. You can call this method or setDateFormat(int, 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 and in case the java.sql module is present, also 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; can be null to reset the pattern
        Returns:
        a reference to this GsonBuilder object to fulfill the "Builder" pattern
        Throws:
        IllegalArgumentException - if the pattern is invalid
        Since:
        1.2

      • setDateFormat

        @Deprecated
@CanIgnoreReturnValue
public GsonBuilder setDateFormat​(int dateStyle)
        Deprecated.
        Counterintuitively, despite this method taking only a 'date style' Gson will use a format which includes both date and time, with the 'time style' being the last value set by setDateFormat(int, int). Therefore prefer using setDateFormat(int, int) and explicitly provide the desired 'time style'.
        Configures Gson to serialize Date objects according to the date 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. This methods leaves the current 'time style' unchanged.

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

        Parameters:
        dateStyle - 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
        Throws:
        IllegalArgumentException - if the style is invalid
        Since:
        1.2

      • setDateFormat

        @CanIgnoreReturnValue
public GsonBuilder setDateFormat​(int dateStyle,
                                 int timeStyle)
        Configures Gson 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, such as DateFormat.MEDIUM. See the documentation of the DateFormat class 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
        Throws:
        IllegalArgumentException - if the style values are invalid
        Since:
        1.2

      • registerTypeAdapter

        @CanIgnoreReturnValue
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. And when registering an adapter for a class which has subclasses, you might also want to register the adapter for subclasses, or use registerTypeHierarchyAdapter(Class, Object) instead.

        JsonSerializer and JsonDeserializer are made "null-safe". This means when trying to serialize null, Gson will write a JSON null and the serializer is not called. Similarly when deserializing a JSON null, Gson will emit null without calling the deserializer. If it is desired to handle null values, a TypeAdapter should be used instead.

        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
        Throws:
        IllegalArgumentException - if the type adapter being registered is for Object class or JsonElement or any of its subclasses
        See Also:
        registerTypeHierarchyAdapter(Class, Object)

      • registerTypeAdapterFactory

        @CanIgnoreReturnValue
public GsonBuilder registerTypeAdapterFactory​(TypeAdapterFactory factory)
        Registers 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.

        The created Gson instance might only use the factory once to create an adapter for a specific type and cache the result. It is not guaranteed that the factory will be used again every time the type is serialized or deserialized.

        Since:
        2.1

      • registerTypeHierarchyAdapter

        @CanIgnoreReturnValue
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
        Throws:
        IllegalArgumentException - if the type adapter being registered is for JsonElement or any of its subclasses
        Since:
        1.7

      • serializeSpecialFloatingPointValues

        @CanIgnoreReturnValue
public GsonBuilder serializeSpecialFloatingPointValues()
        Section 6 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

      • disableJdkUnsafe

        @CanIgnoreReturnValue
public GsonBuilder disableJdkUnsafe()
        Disables usage of JDK's sun.misc.Unsafe.

        By default Gson uses Unsafe to create instances of classes which don't have a no-args constructor. However, Unsafe might not be available for all Java runtimes. For example Android does not provide Unsafe, or only with limited functionality. Additionally Unsafe creates instances without executing any constructor or initializer block, or performing initialization of field values. This can lead to surprising and difficult to debug errors. Therefore, to get reliable behavior regardless of which runtime is used, and to detect classes which cannot be deserialized in an early stage of development, this method allows disabling usage of Unsafe.

        Returns:
        a reference to this GsonBuilder object to fulfill the "Builder" pattern
        Since:
        2.9.0

      • addReflectionAccessFilter

        @CanIgnoreReturnValue
public GsonBuilder addReflectionAccessFilter​(ReflectionAccessFilter filter)
        Adds a reflection access filter. A reflection access filter prevents Gson from using reflection for the serialization and deserialization of certain classes. The logic in the filter specifies which classes those are.

        Filters will be invoked in reverse registration order, that is, the most recently added filter will be invoked first.

        By default Gson has no filters configured and will try to use reflection for all classes for which no TypeAdapter has been registered, and for which no built-in Gson TypeAdapter exists.

        The created Gson instance might only use an access filter once for a class or its members and cache the result. It is not guaranteed that the filter will be used again every time a class or its members are accessed during serialization or deserialization.

        Parameters:
        filter - filter to add
        Returns:
        a reference to this GsonBuilder object to fulfill the "Builder" pattern
        Since:
        2.9.1

      • 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