Using java collections instead of JsonBuilder

RecurseiveParsingWithCollections.java

package net.jhorstmann.jsonp;

import java.io.IOException;
import java.io.PushbackReader;
import java.io.StringReader;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

/**
 * Trying to get familiar with the proposed API of JSR353,
 * this code uses the Java collection classes instead of JsonBuilder.
 */
public class RecurseiveParsingWithCollections {

    public static void readObject(PushbackReader reader, Map object) throws IOException {
        int ch = reader.read();
        if (ch == -1) {
            throw new IOException("unexpected eof");
        } else if (ch != '}') {
            reader.unread(ch);
            while (true) {
                ch = reader.read();
                if (ch >= 'a' || ch <= '9') {
                    String key = "" + (char) ch;
                    ch = reader.read();
                    if (ch == -1) {
                        throw new IOException("unexpected eof");
                    } else if (ch != ':') {
                        throw new IOException("unexpected char " + (char) ch);
                    } else {
                        ch = reader.read();
                        if (ch == -1) {
                            throw new IOException("unexpected eof");
                        } else if (ch == '[') {
                            List child = new ArrayList();
                            object.put(key, child);
                            readArray(reader, child);
                        } else if (ch == '{') {
                            Map child = new LinkedHashMap();
                            object.put(key, child);
                            readObject(reader, child);
                        } else if (ch >= '0' && ch <= '9') {
                            object.put(key, ch - '0');
                        } else {
                            throw new IOException("unexpected char " + (char) ch);
                        }
                    }
                } else if (ch == -1) {
                    throw new IOException("unexpected eof");
                }

                ch = reader.read();
                if (ch == '}') {
                    break;
                } else if (ch == -1) {
                    throw new IOException("unexpected eof");
                } else if (ch != ',') {
                    throw new IOException("unexpected char " + (char) ch);
                }
            }
        }
    }

    public static void readArray(PushbackReader reader, List list) throws IOException {
        int ch = reader.read();
        if (ch == -1) {
            throw new IOException("unexpected eof");
        } else if (ch != ']') {
            reader.unread(ch);
            while (true) {
                ch = reader.read();
                if (ch == '[') {
                    List child = new ArrayList();
                    list.add(child);
                    readArray(reader, child);
                } else if (ch == '{') {
                    Map child = new LinkedHashMap();
                    list.add(child);
                    readObject(reader, child);
                } else if (ch >= '0' && ch <= '9') {
                    list.add(ch - '0');
                } else if (ch == -1) {
                    throw new IOException("unexpected eof");
                } else {
                    throw new IOException("unexpected char " + (char) ch);
                }

                ch = reader.read();
                if (ch == ']') {
                    break;
                } else if (ch == -1) {
                    throw new IOException("unexpected eof");
                } else if (ch != ',') {
                    throw new IOException("unexpected char " + (char) ch);
                }
            }
        }
    }

    /*
     * Parses the root element, either an object or an array.
     */
    public static Object readRoot(PushbackReader reader) throws IOException {
        int ch = reader.read();
        if (ch == '[') {
            List result = new ArrayList();
            readArray(reader, result);
            return result;
        } else if (ch == '{') {
            Map result = new LinkedHashMap();
            readObject(reader, result);
            return result;
        } else {
            throw new IOException("unexpected char " + (char) ch);
        }
    }

    public static Object readRoot(String data) throws IOException {
        PushbackReader reader = new PushbackReader(new StringReader(data));
        return readRoot(reader);
    }

    public static void main(String[] args) throws IOException {
        System.out.println(readRoot("[1,2,3,[4],{a:1,b:2,c:{},d:[]},[5,6,{}]]"));
        System.out.println(readRoot("{a:[1,2,3,[4],{a:1,b:2,c:{},d:[]},[5,6,{}]]}"));
    }
}