JsonReader

public final class JsonReader
extends Object implements Closeable

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.

Parsing JSON

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.

• Within array handling 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().
• Within object handling 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().

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().

Example

 [
   {
     "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
     }
   }
 ]

   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);
   }

Number Handling

Each JsonReader may be used to read a single JSON stream. Instances of this class are not thread safe.

Summary

Inherited methods
From class java.lang.Object Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait(long millis, int nanos) Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed. final void wait(long millis) Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object, or a specified amount of time has elapsed. final void wait() Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object.
From interface java.io.Closeable abstract void close() Closes this stream and releases any system resources associated with it.
From interface java.lang.AutoCloseable abstract void close() Closes this resource, relinquishing any underlying resources.

Public constructors

JsonReader (Reader in)

Public methods

void beginArray ()

void beginObject ()

void close ()

void endArray ()

void endObject ()

boolean hasNext ()

boolean isLenient ()

boolean nextBoolean ()

double nextDouble ()

int nextInt ()

long nextLong ()

String nextName ()

void nextNull ()

String nextString ()

JsonToken peek ()

void setLenient (boolean lenient)

void skipValue ()

String toString ()