JsonEncoder final

final class JsonEncoder extends Converter<Object?, String>

This class converts JSON objects to strings.

Example:

const JsonEncoder encoder = JsonEncoder();
const data = {'text': 'foo', 'value': '2'};

final String jsonString = encoder.convert(data);
print(jsonString); // {"text":"foo","value":"2"}

Example of pretty-printed output:

const JsonEncoder encoder = JsonEncoder.withIndent('  ');

const data = {'text': 'foo', 'value': '2'};
final String jsonString = encoder.convert(data);
print(jsonString);
// {
//   "text": "foo",
//   "value": "2"
// }

Inheritance

Object → Converter<S, T> → JsonEncoder

Constructors

JsonEncoder() const

const JsonEncoder([(Object? Function(dynamic object))? toEncodable])

Creates a JSON encoder.

The JSON encoder handles numbers, strings, booleans, null, lists and maps with string keys directly.

Any other object is attempted converted by toEncodable to an object that is of one of the convertible types.

If toEncodable is omitted, it defaults to calling .toJson() on the object.

Implementation

const JsonEncoder([Object? toEncodable(dynamic object)?])
  : indent = null,
    _toEncodable = toEncodable;

JsonEncoder.withIndent() const

const JsonEncoder.withIndent(
  String? indent, [
  (Object? Function(dynamic object))? toEncodable,
])

Creates a JSON encoder that creates multi-line JSON.

The encoding of elements of lists and maps are indented and put on separate lines. The indent string is prepended to these elements, once for each level of indentation.

If indent is null, the output is encoded as a single line.

The JSON encoder handles numbers, strings, booleans, null, lists and maps with string keys directly.

Any other object is attempted converted by toEncodable to an object that is of one of the convertible types.

If toEncodable is omitted, it defaults to calling .toJson() on the object.

Implementation

const JsonEncoder.withIndent(
  this.indent, [
  Object? toEncodable(dynamic object)?,
]) : _toEncodable = toEncodable;

Properties

hashCode no setter inherited

int get hashCode

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Inherited from Object.

Implementation

external int get hashCode;

indent final

final String? indent

The string used for indention.

When generating multi-line output, this string is inserted once at the beginning of each indented line for each level of indentation.

If null, the output is encoded as a single line.

Implementation

final String? indent;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

Methods

bind() override

Stream<String> bind(Stream<Object?> stream)

Transforms the provided stream.

Returns a new stream with events that are computed from events of the provided stream.

The StreamTransformer interface is completely generic, so it cannot say what subclasses do. Each StreamTransformer should document clearly how it transforms the stream (on the class or variable used to access the transformer), as well as any differences from the following typical behavior:

• When the returned stream is listened to, it starts listening to the input stream.
• Subscriptions of the returned stream forward (in a reasonable time) a StreamSubscription.pause call to the subscription of the input stream.
• Similarly, canceling a subscription of the returned stream eventually (in reasonable time) cancels the subscription of the input stream.

"Reasonable time" depends on the transformer and stream. Some transformers, like a "timeout" transformer, might make these operations depend on a duration. Others might not delay them at all, or just by a microtask.

Transformers are free to handle errors in any way. A transformer implementation may choose to propagate errors, or convert them to other events, or ignore them completely, but if errors are ignored, it should be documented explicitly.

Implementation

Stream<String> bind(Stream<Object?> stream) => super.bind(stream);

cast() inherited

Converter<RS, RT> cast<RS, RT>()

Provides a Converter<RS, RT> view of this stream transformer.

The resulting transformer will check at run-time that all conversion inputs are actually instances of S, and it will check that all conversion output produced by this converter are actually instances of RT.

Inherited from Converter.

Implementation

Converter<RS, RT> cast<RS, RT>() => Converter.castFrom<S, T, RS, RT>(this);

convert() override

String convert(Object? object)

Converts object to a JSON String.

Directly serializable values are num, String, bool, and Null, as well as some List and Map values. For List, the elements must all be serializable. For Map, the keys must be String and the values must be serializable.

If a value of any other type is attempted to be serialized, the toEncodable function provided in the constructor is called with the value as argument. The result, which must be a directly serializable value, is serialized instead of the original value.

If the conversion throws, or returns a value that is not directly serializable, a JsonUnsupportedObjectError exception is thrown. If the call throws, the error is caught and stored in the JsonUnsupportedObjectError's cause field.

If a List or Map contains a reference to itself, directly or through other lists or maps, it cannot be serialized and a JsonCyclicError is thrown.

object should not change during serialization.

If an object is serialized more than once, convert may cache the text for it. In other words, if the content of an object changes after it is first serialized, the new values may not be reflected in the result.

Implementation

String convert(Object? object) =>
    _JsonStringStringifier.stringify(object, _toEncodable, indent);

fuse() override

Converter<Object?, T> fuse<T>(Converter<String, T> other)

Fuses this with other.

Encoding with the resulting converter is equivalent to converting with this before converting with other.

Implementation

Converter<Object?, T> fuse<T>(Converter<String, T> other) {
  if (other is Utf8Encoder) {
    &#47;&#47; The instance check guarantees that `T` is (a subtype of) List<int>,
    &#47;&#47; but the static type system doesn't know that, and so we cast.
    return JsonUtf8Encoder(indent, _toEncodable) as Converter<Object?, T>;
  }
  return super.fuse<T>(other);
}

noSuchMethod() inherited

dynamic noSuchMethod(Invocation invocation)

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

Implementation

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

startChunkedConversion() override

ChunkedConversionSink<Object?> startChunkedConversion(Sink<String> sink)

Starts a chunked conversion.

The converter works more efficiently if the given sink is a StringConversionSink.

Returns a chunked-conversion sink that accepts at most one object. It is an error to invoke add more than once on the returned sink.

Implementation

ChunkedConversionSink<Object?> startChunkedConversion(Sink<String> sink) {
  if (sink is _Utf8EncoderSink) {
    return _JsonUtf8EncoderSink(
      sink._sink,
      _toEncodable,
      JsonUtf8Encoder._utf8Encode(indent),
      JsonUtf8Encoder._defaultBufferSize,
    );
  }
  return _JsonEncoderSink(
    sink is StringConversionSink ? sink : StringConversionSink.from(sink),
    _toEncodable,
    indent,
  );
}

toString() inherited

String toString()

A string representation of this object.

Some classes have a default textual representation, often paired with a static parse function (like int.parse). These classes will provide the textual representation as their string representation.

Other classes have no meaningful textual representation that a program will care about. Such classes will typically override toString to provide useful information when inspecting the object, mainly for debugging or logging.

Inherited from Object.

Implementation

external String toString();

Operators

operator ==() inherited

bool operator ==(Object other)

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Inherited from Object.

Implementation

external bool operator ==(Object other);