Streams.java

package com.google.gson.internal;

import com.google.gson.JsonElement;
import com.google.gson.JsonIOException;
import com.google.gson.JsonNull;
import com.google.gson.JsonParseException;
import com.google.gson.JsonSyntaxException;
import com.google.gson.internal.bind.TypeAdapters;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;
import com.google.gson.stream.MalformedJsonException;
import java.io.EOFException;
import java.io.IOException;
import java.io.Writer;

/**
 * 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 TypeAdapters.JSON_ELEMENT.read(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;
            }
            // The stream ended prematurely so it is likely a syntax error.
            throw new JsonSyntaxException(e);
        } catch (MalformedJsonException e) {
            throw new JsonSyntaxException(e);
        } catch (IOException e) {
            throw new JsonIOException(e);
        } catch (NumberFormatException e) {
            throw new JsonSyntaxException(e);
        }
    }

    /**
     * Writes the JSON element to the writer, recursively.
     */
    public static void write(JsonElement element, JsonWriter writer) throws IOException {
        TypeAdapters.JSON_ELEMENT.write(writer, element);
    }

    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;

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

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

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

}