While this class is neither feature-rich nor the most performant one, it's sufficient enough + * for its use-case. + */ + public static class JsonObjectBuilder { + + private StringBuilder builder = new StringBuilder(); + + private boolean hasAtLeastOneField = false; + + public JsonObjectBuilder() { + builder.append("{"); + } + + /** + * Appends a null field to the JSON. + * + * @param key The key of the field. + * @return A reference to this object. + */ + public JsonObjectBuilder appendNull(String key) { + appendFieldUnescaped(key, "null"); + return this; + } + + /** + * Appends a string field to the JSON. + * + * @param key The key of the field. + * @param value The value of the field. + * @return A reference to this object. + */ + public JsonObjectBuilder appendField(String key, String value) { + if (value == null) { + throw new IllegalArgumentException("JSON value must not be null"); + } + appendFieldUnescaped(key, "\"" + escape(value) + "\""); + return this; + } + + /** + * Appends an integer field to the JSON. + * + * @param key The key of the field. + * @param value The value of the field. + * @return A reference to this object. + */ + public JsonObjectBuilder appendField(String key, int value) { + appendFieldUnescaped(key, String.valueOf(value)); + return this; + } + + /** + * Appends an object to the JSON. + * + * @param key The key of the field. + * @param object The object. + * @return A reference to this object. + */ + public JsonObjectBuilder appendField(String key, JsonObject object) { + if (object == null) { + throw new IllegalArgumentException("JSON object must not be null"); + } + appendFieldUnescaped(key, object.toString()); + return this; + } + + /** + * Appends a string array to the JSON. + * + * @param key The key of the field. + * @param values The string array. + * @return A reference to this object. + */ + public JsonObjectBuilder appendField(String key, String[] values) { + if (values == null) { + throw new IllegalArgumentException("JSON values must not be null"); + } + String escapedValues = + Arrays.stream(values) + .map(value -> "\"" + escape(value) + "\"") + .collect(Collectors.joining(",")); + appendFieldUnescaped(key, "[" + escapedValues + "]"); + return this; + } + + /** + * Appends an integer array to the JSON. + * + * @param key The key of the field. + * @param values The integer array. + * @return A reference to this object. + */ + public JsonObjectBuilder appendField(String key, int[] values) { + if (values == null) { + throw new IllegalArgumentException("JSON values must not be null"); + } + String escapedValues = + Arrays.stream(values).mapToObj(String::valueOf).collect(Collectors.joining(",")); + appendFieldUnescaped(key, "[" + escapedValues + "]"); + return this; + } + + /** + * Appends an object array to the JSON. + * + * @param key The key of the field. + * @param values The integer array. + * @return A reference to this object. + */ + public JsonObjectBuilder appendField(String key, JsonObject[] values) { + if (values == null) { + throw new IllegalArgumentException("JSON values must not be null"); + } + String escapedValues = + Arrays.stream(values).map(JsonObject::toString).collect(Collectors.joining(",")); + appendFieldUnescaped(key, "[" + escapedValues + "]"); + return this; + } + + /** + * Appends a field to the object. + * + * @param key The key of the field. + * @param escapedValue The escaped value of the field. + */ + private void appendFieldUnescaped(String key, String escapedValue) { + if (builder == null) { + throw new IllegalStateException("JSON has already been built"); + } + if (key == null) { + throw new IllegalArgumentException("JSON key must not be null"); + } + if (hasAtLeastOneField) { + builder.append(","); + } + builder.append("\"").append(escape(key)).append("\":").append(escapedValue); + hasAtLeastOneField = true; + } + + /** + * Builds the JSON string and invalidates this builder. + * + * @return The built JSON string. + */ + public JsonObject build() { + if (builder == null) { + throw new IllegalStateException("JSON has already been built"); + } + JsonObject object = new JsonObject(builder.append("}").toString()); + builder = null; + return object; + } + + /** + * Escapes the given string like stated in https://www.ietf.org/rfc/rfc4627.txt. + * + *
This method escapes only the necessary characters '"', '\'. and '\u0000' - '\u001F'. + * Compact escapes are not used (e.g., '\n' is escaped as "\u000a" and not as "\n"). + * + * @param value The value to escape. + * @return The escaped value. + */ + private static String escape(String value) { + final StringBuilder builder = new StringBuilder(); + for (int i = 0; i < value.length(); i++) { + char c = value.charAt(i); + if (c == '"') { + builder.append("\\\""); + } else if (c == '\\') { + builder.append("\\\\"); + } else if (c <= '\u000F') { + builder.append("\\u000").append(Integer.toHexString(c)); + } else if (c <= '\u001F') { + builder.append("\\u00").append(Integer.toHexString(c)); + } else { + builder.append(c); + } + } + return builder.toString(); + } + + /** + * A super simple representation of a JSON object. + * + *
This class only exists to make methods of the {@link JsonObjectBuilder} type-safe and not + * allow a raw string inputs for methods like {@link JsonObjectBuilder#appendField(String, + * JsonObject)}. + */ + public static class JsonObject { + + private final String value; + + private JsonObject(String value) { + this.value = value; + } + + @Override + public String toString() { + return value; + } + } + } +}