* A JSONWriter instance provides a value method for appending
* values to the
* text, and a key
* method for adding keys before values in objects. There are array
* and endArray methods that make and bound array values, and
* object and endObject methods which make and bound
* object values. All of these methods return the JSONWriter instance,
* permitting a cascade style. For example,
* new JSONWriter(myWriter)
* .object()
* .key("JSON")
* .value("Hello, World!")
* .endObject(); which writes
* {"JSON":"Hello, World!"}
*
* The first method called must be array or object.
* There are no methods for adding commas or colons. JSONWriter adds them for
* you. Objects and arrays can be nested up to 200 levels deep.
*
* This can sometimes be easier than using a JSONObject to build a string.
* @author JSON.org
* @version 2016-08-08
*/
public class JSONWriter {
private static final int maxdepth = 200;
/**
* The comma flag determines if a comma should be output before the next
* value.
*/
private boolean comma;
/**
* The current mode. Values:
* 'a' (array),
* 'd' (done),
* 'i' (initial),
* 'k' (key),
* 'o' (object).
*/
protected char mode;
/**
* The object/array stack.
*/
private final JSONObject stack[];
/**
* The stack top index. A value of 0 indicates that the stack is empty.
*/
private int top;
/**
* The writer that will receive the output.
*/
protected Appendable writer;
/**
* Make a fresh JSONWriter. It can be used to build one JSON text.
*/
public JSONWriter(Appendable w) {
this.comma = false;
this.mode = 'i';
this.stack = new JSONObject[maxdepth];
this.top = 0;
this.writer = w;
}
/**
* Append a value.
* @param string A string value.
* @return this
* @throws JSONException If the value is out of sequence.
*/
private JSONWriter append(String string) throws JSONException {
if (string == null) {
throw new JSONException("Null pointer");
}
if (this.mode == 'o' || this.mode == 'a') {
try {
if (this.comma && this.mode == 'a') {
this.writer.append(',');
}
this.writer.append(string);
} catch (IOException e) {
// Android as of API 25 does not support this exception constructor
// however we won't worry about it. If an exception is happening here
// it will just throw a "Method not found" exception instead.
throw new JSONException(e);
}
if (this.mode == 'o') {
this.mode = 'k';
}
this.comma = true;
return this;
}
throw new JSONException("Value out of sequence.");
}
/**
* Begin appending a new array. All values until the balancing
* endArray will be appended to this array. The
* endArray method must be called to mark the array's end.
* @return this
* @throws JSONException If the nesting is too deep, or if the object is
* started in the wrong place (for example as a key or after the end of the
* outermost array or object).
*/
public JSONWriter array() throws JSONException {
if (this.mode == 'i' || this.mode == 'o' || this.mode == 'a') {
this.push(null);
this.append("[");
this.comma = false;
return this;
}
throw new JSONException("Misplaced array.");
}
/**
* End something.
* @param m Mode
* @param c Closing character
* @return this
* @throws JSONException If unbalanced.
*/
private JSONWriter end(char m, char c) throws JSONException {
if (this.mode != m) {
throw new JSONException(m == 'a'
? "Misplaced endArray."
: "Misplaced endObject.");
}
this.pop(m);
try {
this.writer.append(c);
} catch (IOException e) {
// Android as of API 25 does not support this exception constructor
// however we won't worry about it. If an exception is happening here
// it will just throw a "Method not found" exception instead.
throw new JSONException(e);
}
this.comma = true;
return this;
}
/**
* End an array. This method most be called to balance calls to
* array.
* @return this
* @throws JSONException If incorrectly nested.
*/
public JSONWriter endArray() throws JSONException {
return this.end('a', ']');
}
/**
* End an object. This method most be called to balance calls to
* object.
* @return this
* @throws JSONException If incorrectly nested.
*/
public JSONWriter endObject() throws JSONException {
return this.end('k', '}');
}
/**
* Append a key. The key will be associated with the next value. In an
* object, every value must be preceded by a key.
* @param string A key string.
* @return this
* @throws JSONException If the key is out of place. For example, keys
* do not belong in arrays or if the key is null.
*/
public JSONWriter key(String string) throws JSONException {
if (string == null) {
throw new JSONException("Null key.");
}
if (this.mode == 'k') {
try {
JSONObject topObject = this.stack[this.top - 1];
// don't use the built in putOnce method to maintain Android support
if(topObject.has(string)) {
throw new JSONException("Duplicate key \"" + string + "\"");
}
topObject.put(string, true);
if (this.comma) {
this.writer.append(',');
}
this.writer.append(JSONObject.quote(string));
this.writer.append(':');
this.comma = false;
this.mode = 'o';
return this;
} catch (IOException e) {
// Android as of API 25 does not support this exception constructor
// however we won't worry about it. If an exception is happening here
// it will just throw a "Method not found" exception instead.
throw new JSONException(e);
}
}
throw new JSONException("Misplaced key.");
}
/**
* Begin appending a new object. All keys and values until the balancing
* endObject will be appended to this object. The
* endObject method must be called to mark the object's end.
* @return this
* @throws JSONException If the nesting is too deep, or if the object is
* started in the wrong place (for example as a key or after the end of the
* outermost array or object).
*/
public JSONWriter object() throws JSONException {
if (this.mode == 'i') {
this.mode = 'o';
}
if (this.mode == 'o' || this.mode == 'a') {
this.append("{");
this.push(new JSONObject());
this.comma = false;
return this;
}
throw new JSONException("Misplaced object.");
}
/**
* Pop an array or object scope.
* @param c The scope to close.
* @throws JSONException If nesting is wrong.
*/
private void pop(char c) throws JSONException {
if (this.top <= 0) {
throw new JSONException("Nesting error.");
}
char m = this.stack[this.top - 1] == null ? 'a' : 'k';
if (m != c) {
throw new JSONException("Nesting error.");
}
this.top -= 1;
this.mode = this.top == 0
? 'd'
: this.stack[this.top - 1] == null
? 'a'
: 'k';
}
/**
* Push an array or object scope.
* @param jo The scope to open.
* @throws JSONException If nesting is too deep.
*/
private void push(JSONObject jo) throws JSONException {
if (this.top >= maxdepth) {
throw new JSONException("Nesting too deep.");
}
this.stack[this.top] = jo;
this.mode = jo == null ? 'a' : 'k';
this.top += 1;
}
/**
* Make a JSON text of an Object value. If the object has an
* value.toJSONString() method, then that method will be used to produce the
* JSON text. The method is required to produce a strictly conforming text.
* If the object does not contain a toJSONString method (which is the most
* common case), then a text will be produced by other means. If the value
* is an array or Collection, then a JSONArray will be made from it and its
* toJSONString method will be called. If the value is a MAP, then a
* JSONObject will be made from it and its toJSONString method will be
* called. Otherwise, the value's toString method will be called, and the
* result will be quoted.
*
*
* Warning: This method assumes that the data structure is acyclical.
*
* @param value
* The value to be serialized.
* @return a printable, displayable, transmittable representation of the
* object, beginning with { (left
* brace) and ending with } (right
* brace).
* @throws JSONException
* If the value is or contains an invalid number.
*/
public static String valueToString(Object value) throws JSONException {
if (value == null || value.equals(null)) {
return "null";
}
if (value instanceof JSONString) {
Object object;
try {
object = ((JSONString) value).toJSONString();
} catch (Exception e) {
throw new JSONException(e);
}
if (object instanceof String) {
return (String) object;
}
throw new JSONException("Bad value from toJSONString: " + object);
}
if (value instanceof Number) {
// not all Numbers may match actual JSON Numbers. i.e. Fractions or Complex
final String numberAsString = JSONObject.numberToString((Number) value);
try {
// Use the BigDecimal constructor for it's parser to validate the format.
@SuppressWarnings("unused")
BigDecimal unused = new BigDecimal(numberAsString);
// Close enough to a JSON number that we will return it unquoted
return numberAsString;
} catch (NumberFormatException ex){
// The Number value is not a valid JSON number.
// Instead we will quote it as a string
return JSONObject.quote(numberAsString);
}
}
if (value instanceof Boolean || value instanceof JSONObject
|| value instanceof JSONArray) {
return value.toString();
}
if (value instanceof Map) {
Map map = (Map) value;
return new JSONObject(map).toString();
}
if (value instanceof Collection) {
Collection coll = (Collection) value;
return new JSONArray(coll).toString();
}
if (value.getClass().isArray()) {
return new JSONArray(value).toString();
}
if(value instanceof Enum){
return JSONObject.quote(((Enum)value).name());
}
return JSONObject.quote(value.toString());
}
/**
* Append either the value true or the value
* false.
* @param b A boolean.
* @return this
* @throws JSONException
*/
public JSONWriter value(boolean b) throws JSONException {
return this.append(b ? "true" : "false");
}
/**
* Append a double value.
* @param d A double.
* @return this
* @throws JSONException If the number is not finite.
*/
public JSONWriter value(double d) throws JSONException {
return this.value(Double.valueOf(d));
}
/**
* Append a long value.
* @param l A long.
* @return this
* @throws JSONException
*/
public JSONWriter value(long l) throws JSONException {
return this.append(Long.toString(l));
}
/**
* Append an object value.
* @param object The object to append. It can be null, or a Boolean, Number,
* String, JSONObject, or JSONArray, or an object that implements JSONString.
* @return this
* @throws JSONException If the value is out of sequence.
*/
public JSONWriter value(Object object) throws JSONException {
return this.append(valueToString(object));
}
}