public class DefaultJsonReader extends Object implements JsonReader
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 a JSON stream in Java?",
"geo": null,
"user": {
"name": "json_newb",
"followers_count": 41
}
},
{
"id": 912345678902,
"text": "@json_newb just use JsonReader!",
"geo": [50.454722, -104.606667],
"user": {
"name": "jesse",
"followers_count": 2
}
}
]
This code implements the parser for the above structure: public List<Message> readJsonStream(InputStream in) {
JsonReader reader = new JsonReader(new InputStreamReader(in, "UTF-8"));
try {
return readMessagesArray(reader);
} finally {
reader.close();
}
}
public List<Message> readMessagesArray(JsonReader reader) {
List<Message> messages = new ArrayList<Message>();
reader.beginArray();
while (reader.hasNext()) {
messages.add(readMessage(reader));
}
reader.endArray();
return messages;
}
public Message readMessage(JsonReader reader) {
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) {
List<Double> doubles = new ArrayList<Double>();
reader.beginArray();
while (reader.hasNext()) {
doubles.add(reader.nextDouble());
}
reader.endArray();
return doubles;
}
public User readUser(JsonReader reader) {
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.
<script> tag.
Prefixing JSON files with ")]}'\n" makes them non-executable
by <script> tags, disarming the attack. Since the prefix is malformed
JSON, strict parsing fails when it is encountered. This class permits the
non-execute prefix when lenient parsing is
enabled.
Each JsonReader may be used to read a single JSON stream. Instances
of this class are not thread safe.
| Constructor and Description |
|---|
DefaultJsonReader(StringReader in)
Creates a new instance that reads a JSON-encoded stream from
in. |
| Modifier and Type | Method and Description |
|---|---|
void |
beginArray()
Consumes the next token from the JSON stream and asserts that it is the
beginning of a new array.
|
void |
beginObject()
Consumes the next token from the JSON stream and asserts that it is the
beginning of a new object.
|
void |
close()
Closes this JSON reader and the underlying
Reader. |
void |
endArray()
Consumes the next token from the JSON stream and asserts that it is the
end of the current array.
|
void |
endObject()
Consumes the next token from the JSON stream and asserts that it is the
end of the current object.
|
int |
getColumnNumber() |
String |
getInput() |
int |
getLineNumber() |
boolean |
hasNext()
Returns true if the current array or object has another element.
|
boolean |
isLenient()
Returns true if this parser is liberal in what it accepts.
|
boolean |
nextBoolean()
Returns the
boolean value of the next token,
consuming it. |
double |
nextDouble()
Returns the
double value of the next token,
consuming it. |
int |
nextInt()
Returns the
int value of the next token,
consuming it. |
com.google.gwt.core.client.JavaScriptObject |
nextJavaScriptObject(boolean useSafeEval)
Returns the
JavaScriptObject of the next token, consuming it. |
long |
nextLong()
Returns the
long value of the next token,
consuming it. |
String |
nextName()
Returns the next token, a
property name, and
consumes it. |
void |
nextNull()
Consumes the next token from the JSON stream and asserts that it is a
literal null.
|
Number |
nextNumber()
Returns the
Number value of the next token, consuming it. |
String |
nextString()
Returns the
string value of the next token,
consuming it. |
String |
nextValue()
Reads the next value recursively and returns it as a String.
|
JsonToken |
peek()
Returns the type of the next token without consuming it.
|
void |
setLenient(boolean lenient)
Configure this parser to be be liberal in what it accepts.
|
void |
skipValue()
Skips the next value recursively.
|
String |
toString() |
public DefaultJsonReader(StringReader in)
in.public final void setLenient(boolean lenient)
JsonReader")]}'\n".
NaNs or infinities.
// 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 ,.
setLenient in interface JsonReaderpublic final boolean isLenient()
public void beginArray()
JsonReaderbeginArray in interface JsonReaderpublic void endArray()
JsonReaderendArray in interface JsonReaderpublic void beginObject()
JsonReaderbeginObject in interface JsonReaderpublic void endObject()
JsonReaderendObject in interface JsonReaderpublic boolean hasNext()
JsonReaderhasNext in interface JsonReaderpublic JsonToken peek()
JsonReaderpeek in interface JsonReaderpublic String nextName()
JsonReaderproperty name, and
consumes it.nextName in interface JsonReaderpublic String nextString()
JsonReaderstring value of the next token,
consuming it. If the next token is a number, this method will return its
string form.nextString in interface JsonReaderpublic boolean nextBoolean()
JsonReaderboolean value of the next token,
consuming it.nextBoolean in interface JsonReaderpublic void nextNull()
JsonReadernextNull in interface JsonReaderpublic double nextDouble()
JsonReaderdouble 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 Double.parseDouble(String).nextDouble in interface JsonReaderpublic long nextLong()
JsonReaderlong 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.nextLong in interface JsonReaderpublic int nextInt()
JsonReaderint 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.nextInt in interface JsonReaderpublic void close()
JsonReaderReader.close in interface JsonReaderpublic void skipValue()
JsonReaderskipValue in interface JsonReaderpublic int getLineNumber()
getLineNumber in interface JsonReaderpublic int getColumnNumber()
getColumnNumber in interface JsonReaderpublic String getInput()
getInput in interface JsonReaderpublic String nextValue()
JsonReadernextValue in interface JsonReaderpublic Number nextNumber()
JsonReaderNumber value of the next token, consuming it.
This method will attempt to return the best matching number.
For non-decimal number, if it fits into an int, an int is returned,
else a long else a BigInteger.
For decimal number, a double is returned.
If the next token's numeric value cannot be exactly represented by a Java Number, this method throws.nextNumber in interface JsonReaderpublic com.google.gwt.core.client.JavaScriptObject nextJavaScriptObject(boolean useSafeEval)
JsonReaderJavaScriptObject of the next token, consuming it.nextJavaScriptObject in interface JsonReaderuseSafeEval - whether it should use JsonUtils.safeEval(String) or JsonUtils.unsafeEval(String)JavaScriptObjectCopyright © 2016. All Rights Reserved.