JsonReader Class
Definition
Important
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Reads a JSON (RFC 4627) encoded value as a stream of tokens.
[Android.Runtime.Register("android/util/JsonReader", DoNotGenerateAcw=true)]
public sealed class JsonReader : Java.Lang.Object, IDisposable, Java.Interop.IJavaPeerable, Java.IO.ICloseable[<Android.Runtime.Register("android/util/JsonReader", DoNotGenerateAcw=true)>]
type JsonReader = class
inherit Object
interface ICloseable
interface IJavaObject
interface IDisposable
interface IJavaPeerable- Inheritance
- Attributes
- Implements
Remarks
Reads a JSON (RFC 4627) encoded value as a stream of tokens. This stream includes both literal values (strings, numbers, booleans, and nulls) as well as the begin and end delimiters of objects and arrays. The tokens are traversed in depth-first order, the same order that they appear in the JSON document. Within JSON objects, name/value pairs are represented by a single token.
<h3>Parsing JSON</h3> To create a recursive descent parser for your own JSON streams, first create an entry point method that creates a JsonReader.
Next, create handler methods for each structure in your JSON text. You'll need a method for each object type and for each array type. <ul> <li>Within <strong>array handling</strong> methods, first call #beginArray to consume the array's opening bracket. Then create a while loop that accumulates values, terminating when #hasNext is false. Finally, read the array's closing bracket by calling #endArray. <li>Within <strong>object handling</strong> methods, first call #beginObject to consume the object's opening brace. Then create a while loop that assigns values to local variables based on their name. This loop should terminate when #hasNext is false. Finally, read the object's closing brace by calling #endObject. </ul>
When a nested object or array is encountered, delegate to the corresponding handler method.
When an unknown name is encountered, strict parsers should fail with an exception. Lenient parsers should call #skipValue() to recursively skip the value's nested tokens, which may otherwise conflict.
If a value may be null, you should first check using #peek(). Null literals can be consumed using either #nextNull() or #skipValue().
<h3>Example</h3> Suppose we'd like to parse a stream of messages such as the following:
{@code
[
{
"id": 912345678901,
"text": "How do I read JSON on Android?",
"geo": null,
"user": {
"name": "android_newb",
"followers_count": 41
}
},
{
"id": 912345678902,
"text": "@android_newb just use android.util.JsonReader!",
"geo": [50.454722, -104.606667],
"user": {
"name": "jesse",
"followers_count": 2
}
}
]}
This code implements the parser for the above structure:
{@code
public List<Message> readJsonStream(InputStream in) throws IOException {
JsonReader reader = new JsonReader(new InputStreamReader(in, "UTF-8"));
try {
return readMessagesArray(reader);
} finally {
reader.close();
}
}
public List<Message> readMessagesArray(JsonReader reader) throws IOException {
List<Message> messages = new ArrayList<Message>();
reader.beginArray();
while (reader.hasNext()) {
messages.add(readMessage(reader));
}
reader.endArray();
return messages;
}
public Message readMessage(JsonReader reader) throws IOException {
long id = -1;
String text = null;
User user = null;
List<Double> geo = null;
reader.beginObject();
while (reader.hasNext()) {
String name = reader.nextName();
if (name.equals("id")) {
id = reader.nextLong();
} else if (name.equals("text")) {
text = reader.nextString();
} else if (name.equals("geo") && reader.peek() != JsonToken.NULL) {
geo = readDoublesArray(reader);
} else if (name.equals("user")) {
user = readUser(reader);
} else {
reader.skipValue();
}
}
reader.endObject();
return new Message(id, text, user, geo);
}
public List<Double> readDoublesArray(JsonReader reader) throws IOException {
List<Double> doubles = new ArrayList<Double>();
reader.beginArray();
while (reader.hasNext()) {
doubles.add(reader.nextDouble());
}
reader.endArray();
return doubles;
}
public User readUser(JsonReader reader) throws IOException {
String username = null;
int followersCount = -1;
reader.beginObject();
while (reader.hasNext()) {
String name = reader.nextName();
if (name.equals("name")) {
username = reader.nextString();
} else if (name.equals("followers_count")) {
followersCount = reader.nextInt();
} else {
reader.skipValue();
}
}
reader.endObject();
return new User(username, followersCount);
}}
<h3>Number Handling</h3> This reader permits numeric values to be read as strings and string values to be read as numbers. For example, both elements of the JSON array [1, "1"] may be read using either #nextInt or #nextString. This behavior is intended to prevent lossy numeric conversions: double is JavaScript's only numeric type and very large values like 9007199254740993 cannot be represented exactly on that platform. To minimize precision loss, extremely large values should be written and read as strings in JSON.
Each JsonReader may be used to read a single JSON stream. Instances of this class are not thread safe.
Java documentation for android.util.JsonReader.
Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.
Constructors
| JsonReader(Reader) |
Creates a new instance that reads a JSON-encoded stream from |
Properties
| Class |
Returns the runtime class of this |
| Handle |
The handle to the underlying Android instance. (Inherited from Object) |
| HasNext |
Returns true if the current array or object has another element. |
| JniIdentityHashCode | (Inherited from Object) |
| JniPeerMembers | |
| Lenient |
Returns true if this parser is liberal in what it accepts. -or- Configure this parser to be be liberal in what it accepts. |
| PeerReference | (Inherited from Object) |
| ThresholdClass |
This API supports the Mono for Android infrastructure and is not intended to be used directly from your code. (Inherited from Object) |
| ThresholdType |
This API supports the Mono for Android infrastructure and is not intended to be used directly from your code. (Inherited from Object) |
Methods
| BeginArray() |
Consumes the next token from the JSON stream and asserts that it is the beginning of a new array. |
| BeginArrayAsync() | |
| BeginObject() |
Consumes the next token from the JSON stream and asserts that it is the beginning of a new object. |
| BeginObjectAsync() | |
| Clone() |
Creates and returns a copy of this object. (Inherited from Object) |
| Close() |
Closes this JSON reader and the underlying |
| Dispose() | (Inherited from Object) |
| Dispose(Boolean) | (Inherited from Object) |
| EndArray() |
Consumes the next token from the JSON stream and asserts that it is the end of the current array. |
| EndArrayAsync() | |
| EndObject() |
Consumes the next token from the JSON stream and asserts that it is the end of the current object. |
| EndObjectAsync() | |
| Equals(Object) |
Indicates whether some other object is "equal to" this one. (Inherited from Object) |
| GetHashCode() |
Returns a hash code value for the object. (Inherited from Object) |
| JavaFinalize() |
Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. (Inherited from Object) |
| NextBoolean() |
Returns the |
| NextBooleanAsync() | |
| NextDouble() |
Returns the |
| NextDoubleAsync() | |
| NextInt() |
Returns the |
| NextIntAsync() | |
| NextLong() |
Returns the |
| NextLongAsync() | |
| NextName() |
Returns the next token, a |
| NextNameAsync() | |
| NextNull() |
Consumes the next token from the JSON stream and asserts that it is a literal null. |
| NextNullAsync() | |
| NextString() |
Returns the |
| NextStringAsync() | |
| Notify() |
Wakes up a single thread that is waiting on this object's monitor. (Inherited from Object) |
| NotifyAll() |
Wakes up all threads that are waiting on this object's monitor. (Inherited from Object) |
| Peek() |
Returns the type of the next token without consuming it. |
| PeekAsync() | |
| SetHandle(IntPtr, JniHandleOwnership) |
Sets the Handle property. (Inherited from Object) |
| SkipValue() |
Skips the next value recursively. |
| SkipValueAsync() | |
| ToArray<T>() | (Inherited from Object) |
| ToString() |
Returns a string representation of the object. (Inherited from Object) |
| UnregisterFromRuntime() | (Inherited from Object) |
| Wait() |
Causes the current thread to wait until it is awakened, typically by being <em>notified</em> or <em>interrupted</em>. (Inherited from Object) |
| Wait(Int64, Int32) |
Causes the current thread to wait until it is awakened, typically by being <em>notified</em> or <em>interrupted</em>, or until a certain amount of real time has elapsed. (Inherited from Object) |
| Wait(Int64) |
Causes the current thread to wait until it is awakened, typically by being <em>notified</em> or <em>interrupted</em>, or until a certain amount of real time has elapsed. (Inherited from Object) |
Explicit Interface Implementations
| IJavaPeerable.Disposed() | (Inherited from Object) |
| IJavaPeerable.DisposeUnlessReferenced() | (Inherited from Object) |
| IJavaPeerable.Finalized() | (Inherited from Object) |
| IJavaPeerable.JniManagedPeerState | (Inherited from Object) |
| IJavaPeerable.SetJniIdentityHashCode(Int32) | (Inherited from Object) |
| IJavaPeerable.SetJniManagedPeerState(JniManagedPeerStates) | (Inherited from Object) |
| IJavaPeerable.SetPeerReference(JniObjectReference) | (Inherited from Object) |
Extension Methods
| JavaCast<TResult>(IJavaObject) |
Performs an Android runtime-checked type conversion. |
| JavaCast<TResult>(IJavaObject) | |
| GetJniTypeName(IJavaPeerable) | |