+ * 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));
+ }
+}