Added in API level 11

JsonWriter


class JsonWriter : Closeable
kotlin.Any
   ↳ android.util.JsonWriter

Writes a JSON (RFC 4627) encoded value to a stream, one token at a time. The stream includes both literal values (strings, numbers, booleans and nulls) as well as the begin and end delimiters of objects and arrays.

Encoding JSON

To encode your data as JSON, create a new JsonWriter. Each JSON document must contain one top-level array or object. Call methods on the writer as you walk the structure's contents, nesting arrays and objects as necessary:
  • To write arrays, first call beginArray(). Write each of the array's elements with the appropriate #value methods or by nesting other arrays and objects. Finally close the array using endArray().
  • To write objects, first call beginObject(). Write each of the object's properties by alternating calls to name with the property's value. Write property values with the appropriate #value method or by nesting other objects or arrays. Finally close the object using endObject().

Example

Suppose we'd like to encode a stream of messages such as the following:
<code>[
    {
      "id": 912345678901,
      "text": "How do I write JSON on Android?",
      "geo": null,
      "user": {
        "name": "android_newb",
        "followers_count": 41
       }
    },
    {
      "id": 912345678902,
      "text": "@android_newb just use android.util.JsonWriter!",
      "geo": [50.454722, -104.606667],
      "user": {
        "name": "jesse",
        "followers_count": 2
      }
    }
  ]</code>
This code encodes the above structure:
<code>public void writeJsonStream(OutputStream out, List&lt;Message&gt; messages) throws IOException {
      JsonWriter writer = new JsonWriter(new OutputStreamWriter(out, "UTF-8"));
      writer.setIndent("  ");
      writeMessagesArray(writer, messages);
      writer.close();
    }
 
    public void writeMessagesArray(JsonWriter writer, List&lt;Message&gt; messages) throws IOException {
      writer.beginArray();
      for (Message message : messages) {
        writeMessage(writer, message);
      }
      writer.endArray();
    }
 
    public void writeMessage(JsonWriter writer, Message message) throws IOException {
      writer.beginObject();
      writer.name("id").value(message.getId());
      writer.name("text").value(message.getText());
      if (message.getGeo() != null) {
        writer.name("geo");
        writeDoublesArray(writer, message.getGeo());
      } else {
        writer.name("geo").nullValue();
      }
      writer.name("user");
      writeUser(writer, message.getUser());
      writer.endObject();
    }
 
    public void writeUser(JsonWriter writer, User user) throws IOException {
      writer.beginObject();
      writer.name("name").value(user.getName());
      writer.name("followers_count").value(user.getFollowersCount());
      writer.endObject();
    }
 
    public void writeDoublesArray(JsonWriter writer, List&lt;Double&gt; doubles) throws IOException {
      writer.beginArray();
      for (Double value : doubles) {
        writer.value(value);
      }
      writer.endArray();
    }</code>

Each JsonWriter may be used to write a single JSON stream. Instances of this class are not thread safe. Calls that would result in a malformed JSON string will fail with an IllegalStateException.

Summary

Public constructors

Creates a new instance that writes a JSON-encoded stream to out.

Public methods
JsonWriter!

Begins encoding a new array.

JsonWriter!

Begins encoding a new object.

Unit

Flushes and closes this writer and the underlying Writer.

JsonWriter!

Ends encoding the current array.

JsonWriter!

Ends encoding the current object.

Unit

Ensures all buffered data is written to the underlying Writer and flushes that writer.

Boolean

Returns true if this writer has relaxed syntax rules.

JsonWriter!
name(name: String!)

Encodes the property name.

JsonWriter!

Encodes null.

Unit
setIndent(indent: String!)

Sets the indentation string to be repeated for each level of indentation in the encoded document.

Unit
setLenient(lenient: Boolean)

Configure this writer to relax its syntax rules.

JsonWriter!
value(value: String!)

Encodes value.

JsonWriter!
value(value: Boolean)

Encodes value.

JsonWriter!
value(value: Double)

Encodes value.

JsonWriter!
value(value: Long)

Encodes value.

JsonWriter!
value(value: Number!)

Encodes value.

Public constructors

JsonWriter

Added in API level 11
JsonWriter(out: Writer!)

Creates a new instance that writes a JSON-encoded stream to out. For best performance, ensure Writer is buffered; wrapping in BufferedWriter if necessary.

Public methods

beginArray

Added in API level 11
fun beginArray(): JsonWriter!

Begins encoding a new array. Each call to this method must be paired with a call to endArray.

Return
JsonWriter! this writer.

beginObject

Added in API level 11
fun beginObject(): JsonWriter!

Begins encoding a new object. Each call to this method must be paired with a call to endObject.

Return
JsonWriter! this writer.

close

Added in API level 11
fun close(): Unit

Flushes and closes this writer and the underlying Writer.

Exceptions
java.lang.Exception if this resource cannot be closed
java.io.IOException if the JSON document is incomplete.

endArray

Added in API level 11
fun endArray(): JsonWriter!

Ends encoding the current array.

Return
JsonWriter! this writer.

endObject

Added in API level 11
fun endObject(): JsonWriter!

Ends encoding the current object.

Return
JsonWriter! this writer.

flush

Added in API level 11
fun flush(): Unit

Ensures all buffered data is written to the underlying Writer and flushes that writer.

isLenient

Added in API level 11
fun isLenient(): Boolean

Returns true if this writer has relaxed syntax rules.

name

Added in API level 11
fun name(name: String!): JsonWriter!

Encodes the property name.

Parameters
name String!: the name of the forthcoming value. May not be null.
Return
JsonWriter! this writer.

nullValue

Added in API level 11
fun nullValue(): JsonWriter!

Encodes null.

Return
JsonWriter! this writer.

setIndent

Added in API level 11
fun setIndent(indent: String!): Unit

Sets the indentation string to be repeated for each level of indentation in the encoded document. If indent.isEmpty() the encoded document will be compact. Otherwise the encoded document will be more human-readable.

Parameters
indent String!: a string containing only whitespace.

setLenient

Added in API level 11
fun setLenient(lenient: Boolean): Unit

Configure this writer to relax its syntax rules. By default, this writer only emits well-formed JSON as specified by RFC 4627. Setting the writer to lenient permits the following:

  • Top-level values of any type. With strict writing, the top-level value must be an object or an array.
  • Numbers may be NaNs or infinities.

value

Added in API level 11
fun value(value: String!): JsonWriter!

Encodes value.

Parameters
value String!: the literal string value, or null to encode a null literal.
Return
JsonWriter! this writer.

value

Added in API level 11
fun value(value: Boolean): JsonWriter!

Encodes value.

Return
JsonWriter! this writer.

value

Added in API level 11
fun value(value: Double): JsonWriter!

Encodes value.

Parameters
value Double: a finite value. May not be NaNs or infinities unless this writer is lenient.
Return
JsonWriter! this writer.

value

Added in API level 11
fun value(value: Long): JsonWriter!

Encodes value.

Return
JsonWriter! this writer.

value

Added in API level 11
fun value(value: Number!): JsonWriter!

Encodes value.

Parameters
value Number!: a finite value. May not be NaNs or infinities unless this writer is lenient.
Return
JsonWriter! this writer.