1 package org.apache.tomcat.util.json;
2
3 import java.io.IOException;
4 import java.io.Writer;
5
6 /*
7 Copyright (c) 2006 JSON.org
8
9 Permission is hereby granted, free of charge, to any person obtaining a copy
10 of this software and associated documentation files (the "Software"), to deal
11 in the Software without restriction, including without limitation the rights
12 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
13 copies of the Software, and to permit persons to whom the Software is
14 furnished to do so, subject to the following conditions:
15
16 The above copyright notice and this permission notice shall be included in all
17 copies or substantial portions of the Software.
18
19 The Software shall be used for Good, not Evil.
20
21 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
22 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
23 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
24 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
25 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
26 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
27 SOFTWARE.
28 */
29
30 /**
31 * JSONWriter provides a quick and convenient way of producing JSON text.
32 * The texts produced strictly conform to JSON syntax rules. No whitespace is
33 * added, so the results are ready for transmission or storage. Each instance of
34 * JSONWriter can produce one JSON text.
35 * <p>
36 * A JSONWriter instance provides a <code>value</code> method for appending
37 * values to the
38 * text, and a <code>key</code>
39 * method for adding keys before values in objects. There are <code>array</code>
40 * and <code>endArray</code> methods that make and bound array values, and
41 * <code>object</code> and <code>endObject</code> methods which make and bound
42 * object values. All of these methods return the JSONWriter instance,
43 * permitting a cascade style. For example, <pre>
44 * new JSONWriter(myWriter)
45 * .object()
46 * .key("JSON")
47 * .value("Hello, World!")
48 * .endObject();</pre> which writes <pre>
49 * {"JSON":"Hello, World!"}</pre>
50 * <p>
51 * The first method called must be <code>array</code> or <code>object</code>.
52 * There are no methods for adding commas or colons. JSONWriter adds them for
53 * you. Objects and arrays can be nested up to 20 levels deep.
54 * <p>
55 * This can sometimes be easier than using a JSONObject to build a string.
56 * @author JSON.org
57 * @version 2008-09-18
58 */
59 public class JSONWriter {
60 private static final int maxdepth = 20;
61
62 /**
63 * The comma flag determines if a comma should be output before the next
64 * value.
65 */
66 private boolean comma;
67
68 /**
69 * The current mode. Values:
70 * 'a' (array),
71 * 'd' (done),
72 * 'i' (initial),
73 * 'k' (key),
74 * 'o' (object).
75 */
76 protected char mode;
77
78 /**
79 * The object/array stack.
80 */
81 private JSONObject stack[];
82
83 /**
84 * The stack top index. A value of 0 indicates that the stack is empty.
85 */
86 private int top;
87
88 /**
89 * The writer that will receive the output.
90 */
91 protected Writer writer;
92
93 /**
94 * Make a fresh JSONWriter. It can be used to build one JSON text.
95 */
96 public JSONWriter(Writer w) {
97 this.comma = false;
98 this.mode = 'i';
99 this.stack = new JSONObject[maxdepth];
100 this.top = 0;
101 this.writer = w;
102 }
103
104 /**
105 * Append a value.
106 * @param s A string value.
107 * @return this
108 * @throws JSONException If the value is out of sequence.
109 */
110 private JSONWriter append(String s) throws JSONException {
111 if (s == null) {
112 throw new JSONException("Null pointer");
113 }
114 if (this.mode == 'o' || this.mode == 'a') {
115 try {
116 if (this.comma && this.mode == 'a') {
117 this.writer.write(',');
118 }
119 this.writer.write(s);
120 } catch (IOException e) {
121 throw new JSONException(e);
122 }
123 if (this.mode == 'o') {
124 this.mode = 'k';
125 }
126 this.comma = true;
127 return this;
128 }
129 throw new JSONException("Value out of sequence.");
130 }
131
132 /**
133 * Begin appending a new array. All values until the balancing
134 * <code>endArray</code> will be appended to this array. The
135 * <code>endArray</code> method must be called to mark the array's end.
136 * @return this
137 * @throws JSONException If the nesting is too deep, or if the object is
138 * started in the wrong place (for example as a key or after the end of the
139 * outermost array or object).
140 */
141 public JSONWriter array() throws JSONException {
142 if (this.mode == 'i' || this.mode == 'o' || this.mode == 'a') {
143 this.push(null);
144 this.append("[");
145 this.comma = false;
146 return this;
147 }
148 throw new JSONException("Misplaced array.");
149 }
150
151 /**
152 * End something.
153 * @param m Mode
154 * @param c Closing character
155 * @return this
156 * @throws JSONException If unbalanced.
157 */
158 private JSONWriter end(char m, char c) throws JSONException {
159 if (this.mode != m) {
160 throw new JSONException(m == 'o' ? "Misplaced endObject." :
161 "Misplaced endArray.");
162 }
163 this.pop(m);
164 try {
165 this.writer.write(c);
166 } catch (IOException e) {
167 throw new JSONException(e);
168 }
169 this.comma = true;
170 return this;
171 }
172
173 /**
174 * End an array. This method most be called to balance calls to
175 * <code>array</code>.
176 * @return this
177 * @throws JSONException If incorrectly nested.
178 */
179 public JSONWriter endArray() throws JSONException {
180 return this.end('a', ']');
181 }
182
183 /**
184 * End an object. This method most be called to balance calls to
185 * <code>object</code>.
186 * @return this
187 * @throws JSONException If incorrectly nested.
188 */
189 public JSONWriter endObject() throws JSONException {
190 return this.end('k', '}');
191 }
192
193 /**
194 * Append a key. The key will be associated with the next value. In an
195 * object, every value must be preceded by a key.
196 * @param s A key string.
197 * @return this
198 * @throws JSONException If the key is out of place. For example, keys
199 * do not belong in arrays or if the key is null.
200 */
201 public JSONWriter key(String s) throws JSONException {
202 if (s == null) {
203 throw new JSONException("Null key.");
204 }
205 if (this.mode == 'k') {
206 try {
207 if (this.comma) {
208 this.writer.write(',');
209 }
210 stack[top - 1].putOnce(s, Boolean.TRUE);
211 this.writer.write(JSONObject.quote(s));
212 this.writer.write(':');
213 this.comma = false;
214 this.mode = 'o';
215 return this;
216 } catch (IOException e) {
217 throw new JSONException(e);
218 }
219 }
220 throw new JSONException("Misplaced key.");
221 }
222
223
224 /**
225 * Begin appending a new object. All keys and values until the balancing
226 * <code>endObject</code> will be appended to this object. The
227 * <code>endObject</code> method must be called to mark the object's end.
228 * @return this
229 * @throws JSONException If the nesting is too deep, or if the object is
230 * started in the wrong place (for example as a key or after the end of the
231 * outermost array or object).
232 */
233 public JSONWriter object() throws JSONException {
234 if (this.mode == 'i') {
235 this.mode = 'o';
236 }
237 if (this.mode == 'o' || this.mode == 'a') {
238 this.append("{");
239 this.push(new JSONObject());
240 this.comma = false;
241 return this;
242 }
243 throw new JSONException("Misplaced object.");
244
245 }
246
247
248 /**
249 * Pop an array or object scope.
250 * @param c The scope to close.
251 * @throws JSONException If nesting is wrong.
252 */
253 private void pop(char c) throws JSONException {
254 if (this.top <= 0) {
255 throw new JSONException("Nesting error.");
256 }
257 char m = this.stack[this.top - 1] == null ? 'a' : 'k';
258 if (m != c) {
259 throw new JSONException("Nesting error.");
260 }
261 this.top -= 1;
262 this.mode = this.top == 0 ? 'd' : this.stack[this.top - 1] == null ? 'a' : 'k';
263 }
264
265 /**
266 * Push an array or object scope.
267 * @param c The scope to open.
268 * @throws JSONException If nesting is too deep.
269 */
270 private void push(JSONObject jo) throws JSONException {
271 if (this.top >= maxdepth) {
272 throw new JSONException("Nesting too deep.");
273 }
274 this.stack[this.top] = jo;
275 this.mode = jo == null ? 'a' : 'k';
276 this.top += 1;
277 }
278
279
280 /**
281 * Append either the value <code>true</code> or the value
282 * <code>false</code>.
283 * @param b A boolean.
284 * @return this
285 * @throws JSONException
286 */
287 public JSONWriter value(boolean b) throws JSONException {
288 return this.append(b ? "true" : "false");
289 }
290
291 /**
292 * Append a double value.
293 * @param d A double.
294 * @return this
295 * @throws JSONException If the number is not finite.
296 */
297 public JSONWriter value(double d) throws JSONException {
298 return this.value(new Double(d));
299 }
300
301 /**
302 * Append a long value.
303 * @param l A long.
304 * @return this
305 * @throws JSONException
306 */
307 public JSONWriter value(long l) throws JSONException {
308 return this.append(Long.toString(l));
309 }
310
311
312 /**
313 * Append an object value.
314 * @param o The object to append. It can be null, or a Boolean, Number,
315 * String, JSONObject, or JSONArray, or an object with a toJSONString()
316 * method.
317 * @return this
318 * @throws JSONException If the value is out of sequence.
319 */
320 public JSONWriter value(Object o) throws JSONException {
321 return this.append(JSONObject.valueToString(o));
322 }
323 }