org.springframework.boot.configurationprocessor.json.JSONStringer Maven / Gradle / Ivy
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/*
* 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.springframework.boot.configurationprocessor.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 source code.
/**
* Implements {@link JSONObject#toString} and {@link JSONArray#toString}. Most application
* developers should use those methods directly and disregard this API. For example:
* JSONObject object = ...
* String json = object.toString();
*
* Stringers only encode well-formed JSON strings. In particular:
*
* - The stringer must have exactly one top-level array or object.
*
- 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}.
*
- Arrays may not contain keys (property names).
*
- Objects must alternate keys (property names) and values.
*
- Values are inserted with either literal {@link #value(Object) value} calls, or by
* nesting arrays or objects.
*
* Calls that would result in a malformed JSON string will fail with a
* {@link JSONException}.
*
* 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)}.
*
* 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}.
*
* 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 Effective Java 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,
/**
* An 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 stack = new ArrayList<>();
/**
* 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() {
this.indent = null;
}
JSONStringer(int indentSpaces) {
char[] indentChars = new char[indentSpaces];
Arrays.fill(indentChars, ' ');
this.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.
* @throws JSONException if processing of json failed
*/
public JSONStringer array() throws JSONException {
return open(Scope.EMPTY_ARRAY, "[");
}
/**
* Ends encoding the current array.
* @return this stringer.
* @throws JSONException if processing of json failed
*/
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.
* @throws JSONException if processing of json failed
*/
public JSONStringer object() throws JSONException {
return open(Scope.EMPTY_OBJECT, "{");
}
/**
* Ends encoding the current object.
* @return this stringer.
* @throws JSONException if processing of json failed
*/
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.
* @param empty any necessary whitespace
* @param openBracket the open bracket
* @return this object
* @throws JSONException if processing of json failed
*/
JSONStringer open(Scope empty, String openBracket) throws JSONException {
if (this.stack.isEmpty() && this.out.length() > 0) {
throw new JSONException("Nesting problem: multiple top-level roots");
}
beforeValue();
this.stack.add(empty);
this.out.append(openBracket);
return this;
}
/**
* Closes the current scope by appending any necessary whitespace and the given
* bracket.
* @param empty any necessary whitespace
* @param nonempty the current scope
* @param closeBracket the close bracket
* @return the JSON stringer
* @throws JSONException if processing of json failed
*/
JSONStringer close(Scope empty, Scope nonempty, String closeBracket)
throws JSONException {
Scope context = peek();
if (context != nonempty && context != empty) {
throw new JSONException("Nesting problem");
}
this.stack.remove(this.stack.size() - 1);
if (context == nonempty) {
newline();
}
this.out.append(closeBracket);
return this;
}
/**
* Returns the value on the top of the stack.
* @return the scope
* @throws JSONException if processing of json failed
*/
private Scope peek() throws JSONException {
if (this.stack.isEmpty()) {
throw new JSONException("Nesting problem");
}
return this.stack.get(this.stack.size() - 1);
}
/**
* Replace the value on the top of the stack with the given value.
* @param topOfStack the scope at the top of the stack
*/
private void replaceTop(Scope topOfStack) {
this.stack.set(this.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.
* @throws JSONException if processing of json failed
*/
public JSONStringer value(Object value) throws JSONException {
if (this.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) {
this.out.append(value);
}
else if (value instanceof Number) {
this.out.append(JSONObject.numberToString((Number) value));
}
else {
string(value.toString());
}
return this;
}
/**
* Encodes {@code value} to this stringer.
* @param value the value to encode
* @return this stringer.
* @throws JSONException if processing of json failed
*/
public JSONStringer value(boolean value) throws JSONException {
if (this.stack.isEmpty()) {
throw new JSONException("Nesting problem");
}
beforeValue();
this.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.
* @throws JSONException if processing of json failed
*/
public JSONStringer value(double value) throws JSONException {
if (this.stack.isEmpty()) {
throw new JSONException("Nesting problem");
}
beforeValue();
this.out.append(JSONObject.numberToString(value));
return this;
}
/**
* Encodes {@code value} to this stringer.
* @param value the value to encode
* @return this stringer.
* @throws JSONException if processing of json failed
*/
public JSONStringer value(long value) throws JSONException {
if (this.stack.isEmpty()) {
throw new JSONException("Nesting problem");
}
beforeValue();
this.out.append(value);
return this;
}
private void string(String value) {
this.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 '/':
this.out.append('\\').append(c);
break;
case '\t':
this.out.append("\\t");
break;
case '\b':
this.out.append("\\b");
break;
case '\n':
this.out.append("\\n");
break;
case '\r':
this.out.append("\\r");
break;
case '\f':
this.out.append("\\f");
break;
default:
if (c <= 0x1F) {
this.out.append(String.format("\\u%04x", (int) c));
}
else {
this.out.append(c);
}
break;
}
}
this.out.append("\"");
}
private void newline() {
if (this.indent == null) {
return;
}
this.out.append("\n");
for (int i = 0; i < this.stack.size(); i++) {
this.out.append(this.indent);
}
}
/**
* Encodes the key (property name) to this stringer.
* @param name the name of the forthcoming value. May not be null.
* @return this stringer.
* @throws JSONException if processing of json failed
*/
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.
* @throws JSONException if processing of json failed
*/
private void beforeKey() throws JSONException {
Scope context = peek();
if (context == Scope.NONEMPTY_OBJECT) { // first in object
this.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.
* @throws JSONException if processing of json failed
*/
private void beforeValue() throws JSONException {
if (this.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
this.out.append(',');
newline();
}
else if (context == Scope.DANGLING_KEY) { // value for key
this.out.append(this.indent == null ? ":" : ": ");
replaceTop(Scope.NONEMPTY_OBJECT);
}
else if (context != Scope.NULL) {
throw new JSONException("Nesting problem");
}
}
/**
* Returns the encoded JSON string.
*
* If invoked with unterminated arrays or unclosed objects, this method's return value
* is undefined.
*
* Warning: although it contradicts the general contract of
* {@link Object#toString}, this method returns null if the stringer contains no data.
* @return the encoded JSON string.
*/
@Override
public String toString() {
return this.out.length() == 0 ? null : this.out.toString();
}
}