/*
* Copyright (C) 2010 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.json;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
// Note: this class was written without inspecting the non-free org.json sourcecode.
/**
* Implements {@link JSONObject#toString} and {@link JSONArray#toString}. Most
* application developers should use those methods directly and disregard this
* API. For example:<pre>
* JSONObject object = ...
* String json = object.toString();</pre>
*
* <p>Stringers only encode well-formed JSON strings. In particular:
* <ul>
* <li>The stringer must have exactly one top-level array or object.
* <li>Lexical scopes must be balanced: every call to {@link #array} must
* have a matching call to {@link #endArray} and every call to {@link
* #object} must have a matching call to {@link #endObject}.
* <li>Arrays may not contain keys (property names).
* <li>Objects must alternate keys (property names) and values.
* <li>Values are inserted with either literal {@link #value(Object) value}
* calls, or by nesting arrays or objects.
* </ul>
* Calls that would result in a malformed JSON string will fail with a
* {@link JSONException}.
*
* <p>This class provides no facility for pretty-printing (ie. indenting)
* output. To encode indented output, use {@link JSONObject#toString(int)} or
* {@link JSONArray#toString(int)}.
*
* <p>Some implementations of the API support at most 20 levels of nesting.
* Attempts to create more than 20 levels of nesting may fail with a {@link
* JSONException}.
*
* <p>Each stringer may be used to encode a single top level value. Instances of
* this class are not thread safe. Although this class is nonfinal, it was not
* designed for inheritance and should not be subclassed. In particular,
* self-use by overrideable methods is not specified. See <i>Effective Java</i>
* Item 17, "Design and Document or inheritance or else prohibit it" for further
* information.
*/
public class JSONStringer {
/** The output data, containing at most one top-level array or object. */
final StringBuilder out = new StringBuilder();
/**
* Lexical scoping elements within this stringer, necessary to insert the
* appropriate separator characters (ie. commas and colons) and to detect
* nesting errors.
*/
enum Scope {
/**
* An array with no elements requires no separators or newlines before
* it is closed.
*/
EMPTY_ARRAY,
/**
* A array with at least one value requires a comma and newline before
* the next element.
*/
NONEMPTY_ARRAY,
/**
* An object with no keys or values requires no separators or newlines
* before it is closed.
*/
EMPTY_OBJECT,
/**
* An object whose most recent element is a key. The next element must
* be a value.
*/
DANGLING_KEY,
/**
* An object with at least one name/value pair requires a comma and
* newline before the next element.
*/
NONEMPTY_OBJECT,
/**
* A special bracketless array needed by JSONStringer.join() and
* JSONObject.quote() only. Not used for JSON encoding.
*/
NULL,
}
/**
* Unlike the original implementation, this stack isn't limited to 20
* levels of nesting.
*/
private final List<Scope> stack = new ArrayList<Scope>();
/**
* A string containing a full set of spaces for a single level of
* indentation, or null for no pretty printing.
*/
private final String indent;
public JSONStringer() {
indent = null;
}
JSONStringer(int indentSpaces) {
char[] indentChars = new char[indentSpaces];
Arrays.fill(indentChars, ' ');
indent = new String(indentChars);
}
/**
* Begins encoding a new array. Each call to this method must be paired with
* a call to {@link #endArray}.
*
* @return this stringer.
*/
public JSONStringer array() throws JSONException {
return open(Scope.EMPTY_ARRAY, "[");
}
/**
* Ends encoding the current array.
*
* @return this stringer.
*/
public JSONStringer endArray() throws JSONException {
return close(Scope.EMPTY_ARRAY, Scope.NONEMPTY_ARRAY, "]");
}
/**
* Begins encoding a new object. Each call to this method must be paired
* with a call to {@link #endObject}.
*
* @return this stringer.
*/
public JSONStringer object() throws JSONException {
return open(Scope.EMPTY_OBJECT, "{");
}
/**
* Ends encoding the current object.
*
* @return this stringer.
*/
public JSONStringer endObject() throws JSONException {
return close(Scope.EMPTY_OBJECT, Scope.NONEMPTY_OBJECT, "}");
}
/**
* Enters a new scope by appending any necessary whitespace and the given
* bracket.
*/
JSONStringer open(Scope empty, String openBracket) throws JSONException {
if (stack.isEmpty() && out.length() > 0) {
throw new JSONException("Nesting problem: multiple top-level roots");
}
beforeValue();
stack.add(empty);
out.append(openBracket);
return this;
}
/**
* Closes the current scope by appending any necessary whitespace and the
* given bracket.
*/
JSONStringer close(Scope empty, Scope nonempty, String closeBracket) throws JSONException {
Scope context = peek();
if (context != nonempty && context != empty) {
throw new JSONException("Nesting problem");
}
stack.remove(stack.size() - 1);
if (context == nonempty) {
newline();
}
out.append(closeBracket);
return this;
}
/**
* Returns the value on the top of the stack.
*/
private Scope peek() throws JSONException {
if (stack.isEmpty()) {
throw new JSONException("Nesting problem");
}
return stack.get(stack.size() - 1);
}
/**
* Replace the value on the top of the stack with the given value.
*/
private void replaceTop(Scope topOfStack) {
stack.set(stack.size() - 1, topOfStack);
}
/**
* Encodes {@code value}.
*
* @param value a {@link JSONObject}, {@link JSONArray}, String, Boolean,
* Integer, Long, Double or null. May not be {@link Double#isNaN() NaNs}
* or {@link Double#isInfinite() infinities}.
* @return this stringer.
*/
public JSONStringer value(Object value) throws JSONException {
if (stack.isEmpty()) {
throw new JSONException("Nesting problem");
}
if (value instanceof JSONArray) {
((JSONArray) value).writeTo(this);
return this;
} else if (value instanceof JSONObject) {
((JSONObject) value).writeTo(this);
return this;
}
beforeValue();
if (value == null
|| value instanceof Boolean
|| value == JSONObject.NULL) {
out.append(value);
} else if (value instanceof Number) {
out.append(JSONObject.numberToString((Number) value));
} else {
string(value.toString());
}
return this;
}
/**
* Encodes {@code value} to this stringer.
*
* @return this stringer.
*/
public JSONStringer value(boolean value) throws JSONException {
if (stack.isEmpty()) {
throw new JSONException("Nesting problem");
}
beforeValue();
out.append(value);
return this;
}
/**
* Encodes {@code value} to this stringer.
*
* @param value a finite value. May not be {@link Double#isNaN() NaNs} or
* {@link Double#isInfinite() infinities}.
* @return this stringer.
*/
public JSONStringer value(double value) throws JSONException {
if (stack.isEmpty()) {
throw new JSONException("Nesting problem");
}
beforeValue();
out.append(JSONObject.numberToString(value));
return this;
}
/**
* Encodes {@code value} to this stringer.
*
* @return this stringer.
*/
public JSONStringer value(long value) throws JSONException {
if (stack.isEmpty()) {
throw new JSONException("Nesting problem");
}
beforeValue();
out.append(value);
return this;
}
private void string(String value) {
out.append("\"");
for (int i = 0, length = value.length(); i < length; i++) {
char c = value.charAt(i);
/*
* From RFC 4627, "All Unicode characters may be placed within the
* quotation marks except for the characters that must be escaped:
* quotation mark, reverse solidus, and the control characters
* (U+0000 through U+001F)."
*/
switch (c) {
case '"':
case '\\':
case '/':
out.append('\\').append(c);
break;
case '\t':
out.append("\\t");
break;
case '\b':
out.append("\\b");
break;
case '\n':
out.append("\\n");
break;
case '\r':
out.append("\\r");
break;
case '\f':
out.append("\\f");
break;
default:
if (c <= 0x1F) {
out.append(String.format("\\u%04x", (int) c));
} else {
out.append(c);
}
break;
}
}
out.append("\"");
}
private void newline() {
if (indent == null) {
return;
}
out.append("\n");
for (int i = 0; i < stack.size(); i++) {
out.append(indent);
}
}
/**
* Encodes the key (property name) to this stringer.
*
* @param name the name of the forthcoming value. May not be null.
* @return this stringer.
*/
public JSONStringer key(String name) throws JSONException {
if (name == null) {
throw new JSONException("Names must be non-null");
}
beforeKey();
string(name);
return this;
}
/**
* Inserts any necessary separators and whitespace before a name. Also
* adjusts the stack to expect the key's value.
*/
private void beforeKey() throws JSONException {
Scope context = peek();
if (context == Scope.NONEMPTY_OBJECT) { // first in object
out.append(',');
} else if (context != Scope.EMPTY_OBJECT) { // not in an object!
throw new JSONException("Nesting problem");
}
newline();
replaceTop(Scope.DANGLING_KEY);
}
/**
* Inserts any necessary separators and whitespace before a literal value,
* inline array, or inline object. Also adjusts the stack to expect either a
* closing bracket or another element.
*/
private void beforeValue() throws JSONException {
if (stack.isEmpty()) {
return;
}
Scope context = peek();
if (context == Scope.EMPTY_ARRAY) { // first in array
replaceTop(Scope.NONEMPTY_ARRAY);
newline();
} else if (context == Scope.NONEMPTY_ARRAY) { // another in array
out.append(',');
newline();
} else if (context == Scope.DANGLING_KEY) { // value for key
out.append(indent == null ? ":" : ": ");
replaceTop(Scope.NONEMPTY_OBJECT);
} else if (context != Scope.NULL) {
throw new JSONException("Nesting problem");
}
}
/**
* Returns the encoded JSON string.
*
* <p>If invoked with unterminated arrays or unclosed objects, this method's
* return value is undefined.
*
* <p><strong>Warning:</strong> although it contradicts the general contract
* of {@link Object#toString}, this method returns null if the stringer
* contains no data.
*/
@Override public String toString() {
return out.length() == 0 ? null : out.toString();
}
}