java.lang.Object | |
↳ | android.util.JsonReader |
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.
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.
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()
.
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()
.
[
{
"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: public List
finally { reader.close(); } } public ListreadJsonStream(InputStream in) throws IOException { JsonReader reader = new JsonReader(new InputStreamReader(in, "UTF-8")); try { return readMessagesArray(reader); readMessagesArray(JsonReader reader) throws IOException { List messages = new ArrayList (); 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 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 readDoublesArray(JsonReader reader) throws IOException { List doubles = new ArrayList (); 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); }}
[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.
Public Constructors | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Creates a new instance that reads a JSON-encoded stream from
in . |
Public Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Consumes the next token from the JSON stream and asserts that it is the
beginning of a new array.
| |||||||||||
Consumes the next token from the JSON stream and asserts that it is the
beginning of a new object.
| |||||||||||
Closes this JSON reader and the underlying
Reader . | |||||||||||
Consumes the next token from the JSON stream and asserts that it is the
end of the current array.
| |||||||||||
Consumes the next token from the JSON stream and asserts that it is the
end of the current array.
| |||||||||||
Returns true if the current array or object has another element.
| |||||||||||
Returns true if this parser is liberal in what it accepts.
| |||||||||||
Returns the
boolean value of the next token,
consuming it. | |||||||||||
Returns the
double value of the next token,
consuming it. | |||||||||||
Returns the
int value of the next token,
consuming it. | |||||||||||
Returns the
long value of the next token,
consuming it. | |||||||||||
Returns the next token, a
property name , and
consumes it. | |||||||||||
Consumes the next token from the JSON stream and asserts that it is a
literal null.
| |||||||||||
Returns the
string value of the next token,
consuming it. | |||||||||||
Returns the type of the next token without consuming it.
| |||||||||||
Configure this parser to be be liberal in what it accepts.
| |||||||||||
Skips the next value recursively.
| |||||||||||
Returns a string containing a concise, human-readable description of this
object.
|
[Expand]
Inherited Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.lang.Object
| |||||||||||
From interface
java.io.Closeable
| |||||||||||
From interface
java.lang.AutoCloseable
|
Creates a new instance that reads a JSON-encoded stream from in
.
Consumes the next token from the JSON stream and asserts that it is the beginning of a new array.
IOException |
---|
Consumes the next token from the JSON stream and asserts that it is the beginning of a new object.
IOException |
---|
Closes this JSON reader and the underlying Reader
.
IOException |
---|
Consumes the next token from the JSON stream and asserts that it is the end of the current array.
IOException |
---|
Consumes the next token from the JSON stream and asserts that it is the end of the current array.
IOException |
---|
Returns true if the current array or object has another element.
IOException |
---|
Returns true if this parser is liberal in what it accepts.
Returns the boolean
value of the next token,
consuming it.
IllegalStateException | if the next token is not a boolean or if this reader is closed. |
---|---|
IOException |
Returns the double
value of the next token,
consuming it. If the next token is a string, this method will attempt to
parse it as a double using parseDouble(String)
.
IllegalStateException | if the next token is not a literal value. |
---|---|
IOException |
Returns the int
value of the next token,
consuming it. If the next token is a string, this method will attempt to
parse it as an int. If the next token's numeric value cannot be exactly
represented by a Java int
, this method throws.
IllegalStateException | if the next token is not a literal value. |
---|---|
NumberFormatException | if the next literal value cannot be parsed as a number, or exactly represented as an int. |
IOException |
Returns the long
value of the next token,
consuming it. If the next token is a string, this method will attempt to
parse it as a long. If the next token's numeric value cannot be exactly
represented by a Java long
, this method throws.
IllegalStateException | if the next token is not a literal value. |
---|---|
NumberFormatException | if the next literal value cannot be parsed as a number, or exactly represented as a long. |
IOException |
Returns the next token, a property name
, and
consumes it.
IOException | if the next token in the stream is not a property name. |
---|
Consumes the next token from the JSON stream and asserts that it is a literal null.
IllegalStateException | if the next token is not null or if this reader is closed. |
---|---|
IOException |
Returns the string
value of the next token,
consuming it. If the next token is a number, this method will return its
string form.
IllegalStateException | if the next token is not a string or if this reader is closed. |
---|---|
IOException |
Returns the type of the next token without consuming it.
IOException |
---|
Configure this parser to be be liberal in what it accepts. By default, this parser is strict and only accepts JSON as specified by RFC 4627. Setting the parser to lenient causes it to ignore the following syntax errors:
//
or #
and
ending with a newline character.
/*
and ending with
*
/
. Such comments may not be nested.
'single quoted'
.
'single quoted'
.
;
instead of ,
.
=
or =>
instead of
:
.
;
instead of ,
.
Skips the next value recursively. If it is an object or array, all nested elements are skipped. This method is intended for use when the JSON token stream contains unrecognized or unhandled values.
IOException |
---|
Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression:
getClass().getName() + '@' + Integer.toHexString(hashCode())
See Writing a useful
toString
method
if you intend implementing your own toString
method.