+ * 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 20 levels deep.
+ *
+ * This can sometimes be easier than using a JSONObject to build a string.
+ * @author JSON.org
+ * @version 2015-12-09
+ */
+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 Writer writer;
+
+ /**
+ * Make a fresh JSONWriter. It can be used to build one JSON text.
+ */
+ public JSONWriter(Writer 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.write(',');
+ }
+ this.writer.write(string);
+ } catch (IOException e) {
+ 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 mode Mode
+ * @param c Closing character
+ * @return this
+ * @throws JSONException If unbalanced.
+ */
+ private JSONWriter end(char mode, char c) throws JSONException {
+ if (this.mode != mode) {
+ throw new JSONException(mode == 'a'
+ ? "Misplaced endArray."
+ : "Misplaced endObject.");
+ }
+ this.pop(mode);
+ try {
+ this.writer.write(c);
+ } catch (IOException e) {
+ 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 {
+ this.stack[this.top - 1].putOnce(string, Boolean.TRUE);
+ if (this.comma) {
+ this.writer.write(',');
+ }
+ this.writer.write(JSONObject.quote(string));
+ this.writer.write(':');
+ this.comma = false;
+ this.mode = 'o';
+ return this;
+ } catch (IOException e) {
+ 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;
+ }
+
+
+ /**
+ * 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(new Double(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(JSONObject.valueToString(object));
+ }
+}