Streams.java

/*
 * Copyright (C) 2010 Google Inc.
 *
 * 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 com.smartandroid.sa.json.internal;

import java.io.EOFException;
import java.io.IOException;
import java.io.Writer;
import java.util.Map;

import com.smartandroid.sa.json.JsonArray;
import com.smartandroid.sa.json.JsonElement;
import com.smartandroid.sa.json.JsonIOException;
import com.smartandroid.sa.json.JsonNull;
import com.smartandroid.sa.json.JsonObject;
import com.smartandroid.sa.json.JsonParseException;
import com.smartandroid.sa.json.JsonPrimitive;
import com.smartandroid.sa.json.JsonSyntaxException;
import com.smartandroid.sa.json.stream.JsonReader;
import com.smartandroid.sa.json.stream.JsonWriter;
import com.smartandroid.sa.json.stream.MalformedJsonException;

/**
 * Reads and writes GSON parse trees over streams.
 */
public final class Streams {

	/**
	 * Takes a reader in any state and returns the next value as a JsonElement.
	 */
	public static JsonElement parse(JsonReader reader)
			throws JsonParseException {
		boolean isEmpty = true;
		try {
			reader.peek();
			isEmpty = false;
			return parseRecursive(reader);
		} catch (EOFException e) {
			/*
			 * For compatibility with JSON 1.5 and earlier, we return a JsonNull
			 * for empty documents instead of throwing.
			 */
			if (isEmpty) {
				return JsonNull.INSTANCE;
			}
			throw new JsonIOException(e);
		} catch (MalformedJsonException e) {
			throw new JsonSyntaxException(e);
		} catch (IOException e) {
			throw new JsonIOException(e);
		} catch (NumberFormatException e) {
			throw new JsonSyntaxException(e);
		}
	}

	private static JsonElement parseRecursive(JsonReader reader)
			throws IOException {
		switch (reader.peek()) {
		case STRING:
			return new JsonPrimitive(reader.nextString());
		case NUMBER:
			String number = reader.nextString();
			return new JsonPrimitive(new LazilyParsedNumber(number));
		case BOOLEAN:
			return new JsonPrimitive(reader.nextBoolean());
		case NULL:
			reader.nextNull();
			return JsonNull.INSTANCE;
		case BEGIN_ARRAY:
			JsonArray array = new JsonArray();
			reader.beginArray();
			while (reader.hasNext()) {
				array.add(parseRecursive(reader));
			}
			reader.endArray();
			return array;
		case BEGIN_OBJECT:
			JsonObject object = new JsonObject();
			reader.beginObject();
			while (reader.hasNext()) {
				object.add(reader.nextName(), parseRecursive(reader));
			}
			reader.endObject();
			return object;
		case END_DOCUMENT:
		case NAME:
		case END_OBJECT:
		case END_ARRAY:
		default:
			throw new IllegalArgumentException();
		}
	}

	/**
	 * Writes the JSON element to the writer, recursively.
	 */
	public static void write(JsonElement element, boolean serializeNulls,
			JsonWriter writer) throws IOException {
		if (element == null || element.isJsonNull()) {
			if (serializeNulls) {
				writer.nullValue();
			}

		} else if (element.isJsonPrimitive()) {
			JsonPrimitive primitive = element.getAsJsonPrimitive();
			if (primitive.isNumber()) {
				writer.value(primitive.getAsNumber());
			} else if (primitive.isBoolean()) {
				writer.value(primitive.getAsBoolean());
			} else {
				writer.value(primitive.getAsString());
			}

		} else if (element.isJsonArray()) {
			writer.beginArray();
			for (JsonElement e : element.getAsJsonArray()) {
				/* always print null when its parent element is an array! */
				if (e.isJsonNull()) {
					writer.nullValue();
					continue;
				}
				write(e, serializeNulls, writer);
			}
			writer.endArray();

		} else if (element.isJsonObject()) {
			writer.beginObject();
			for (Map.Entry<String, JsonElement> e : element.getAsJsonObject()
					.entrySet()) {
				JsonElement value = e.getValue();
				if (!serializeNulls && value.isJsonNull()) {
					continue;
				}
				writer.name(e.getKey());
				write(value, serializeNulls, writer);
			}
			writer.endObject();

		} else {
			throw new IllegalArgumentException("Couldn't write "
					+ element.getClass());
		}
	}

	public static Writer writerForAppendable(Appendable appendable) {
		return appendable instanceof Writer ? (Writer) appendable
				: new AppendableWriter(appendable);
	}

	/**
	 * Adapts an {@link Appendable} so it can be passed anywhere a
	 * {@link Writer} is used.
	 */
	private static class AppendableWriter extends Writer {
		private final Appendable appendable;
		private final CurrentWrite currentWrite = new CurrentWrite();

		private AppendableWriter(Appendable appendable) {
			this.appendable = appendable;
		}

		@Override
		public void write(char[] chars, int offset, int length)
				throws IOException {
			currentWrite.chars = chars;
			appendable.append(currentWrite, offset, offset + length);
		}

		@Override
		public void write(int i) throws IOException {
			appendable.append((char) i);
		}

		@Override
		public void flush() {
		}

		@Override
		public void close() {
		}

		/**
		 * A mutable char sequence pointing at a single char[].
		 */
		static class CurrentWrite implements CharSequence {
			char[] chars;

			public int length() {
				return chars.length;
			}

			public char charAt(int i) {
				return chars[i];
			}

			public CharSequence subSequence(int start, int end) {
				return new String(chars, start, end - start);
			}
		}
	}
}