/*
* Copyright (c) 2002 JSON.org
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* The Software shall be used for Good, not Evil.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
package com.amazonaws.util.json;
import java.io.IOException;
import java.io.Writer;
/**
* JSONWriter provides a quick and convenient way of producing JSON text.
* The texts produced strictly conform to JSON syntax rules. No whitespace is
* added, so the results are ready for transmission or storage. Each instance of
* JSONWriter can produce one JSON text.
* <p>
* A JSONWriter instance provides a <code>value</code> method for appending
* values to the
* text, and a <code>key</code>
* method for adding keys before values in objects. There are <code>array</code>
* and <code>endArray</code> methods that make and bound array values, and
* <code>object</code> and <code>endObject</code> methods which make and bound
* object values. All of these methods return the JSONWriter instance,
* permitting a cascade style. For example, <pre>
* new JSONWriter(myWriter)
* .object()
* .key("JSON")
* .value("Hello, World!")
* .endObject();</pre> which writes <pre>
* {"JSON":"Hello, World!"}</pre>
* <p>
* The first method called must be <code>array</code> or <code>object</code>.
* 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.
* <p>
* This can sometimes be easier than using a JSONObject to build a string.
*
* @version 2010-03-11
*/
public class JSONWriter {
private static final int maxdepth = 20;
/**
* 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 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 s A string value.
* @return this
* @throws JSONException If the value is out of sequence.
*/
private JSONWriter append(String s) throws JSONException {
if (s == 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(s);
} 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
* <code>endArray</code> will be appended to this array. The
* <code>endArray</code> 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.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
* <code>array</code>.
* @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
* <code>object</code>.
* @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 s 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 s) throws JSONException {
if (s == null) {
throw new JSONException("Null key.");
}
if (this.mode == 'k') {
try {
stack[top - 1].putOnce(s, Boolean.TRUE);
if (this.comma) {
this.writer.write(',');
}
this.writer.write(JSONObject.quote(s));
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
* <code>endObject</code> will be appended to this object. The
* <code>endObject</code> 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 c 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 <code>true</code> or the value
* <code>false</code>.
* @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 o The object to append. It can be null, or a Boolean, Number,
* String, JSONObject, or JSONArray, or an object with a toJSONString()
* method.
* @return this
* @throws JSONException If the value is out of sequence.
*/
public JSONWriter value(Object o) throws JSONException {
return this.append(JSONObject.valueToString(o));
}
}