jsprun中的一个类看不懂

 package cn.jsprun.utils;


import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

public class Serializer {
    private static final byte __Quote = 34;
    private static final byte __0 = 48;
    private static final byte __1 = 49;
    private static final byte __Colon = 58;
    private static final byte __Semicolon = 59;
    private static final byte __N = 78;
    private static final byte __U = 85;
    private static final byte __Slash = 92;
    private static final byte __a = 97;
    private static final byte __b = 98;
    private static final byte __d = 100;
    private static final byte __i = 105;
    private static final byte __s = 115;
    private static final byte __LeftB = 123;
    private static final byte __RightB = 125;
    private static final String __NAN = "NAN";
    private static final String __INF = "INF";
    private static final String __NINF = "-INF";
    private static final String charset="GBK";

    public static String serialize(Object obj) {
        return serialize(obj, charset);
    }

    @SuppressWarnings("unchecked")
	public static String serialize(Object obj, String charset) {
        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        serialize(stream, obj, charset);
        String result=null;
        try {
        	result = stream.toString(charset);
        } catch (Exception e) {
        	e.printStackTrace();
        }
        return result;
    }

    @SuppressWarnings("unchecked")
	private static void serialize(ByteArrayOutputStream stream, Object obj, String charset) {
    	if (obj == null) {
    		writeNull(stream);
    	} else if (obj instanceof Boolean) {
    		writeBoolean(stream, ((Boolean) obj).booleanValue() ? __1 : __0);
    	} else if ((obj instanceof Byte) || (obj instanceof Short) || (obj instanceof Integer)) {
    		writeInteger(stream, getAsciiBytes(obj));
    	} else if (obj instanceof Long) {
    		writeDouble(stream, getAsciiBytes(obj));
    	} else if (obj instanceof Float) {
    		Float f = (Float) obj;
    		obj = f.isNaN() ? __NAN : (!f.isInfinite() ? obj : (f.floatValue() > 0 ? __INF : __NINF));
    		writeDouble(stream, getAsciiBytes(obj));
    	} else if (obj instanceof Double) {
    		Double d = (Double) obj;
    		obj = d.isNaN() ? __NAN : (!d.isInfinite() ? obj : (d.doubleValue() > 0 ? __INF : __NINF));
    		writeDouble(stream, getAsciiBytes(obj));
    	} else if ((obj instanceof Character) || (obj instanceof String)) {
    		writeString(stream, getBytes(obj, charset));
    	} else if (obj instanceof Map) {
    		writeMap(stream, (Map) obj, charset);
    	} else if (obj instanceof List) {
    		writeList(stream, (List) obj, charset);
    	} else {
    		System.out.println("Serializer.serialize: The DataType is invalid");
    	}
    }

    private static void writeNull(ByteArrayOutputStream stream) {
        stream.write(__N);
        stream.write(__Semicolon);
    }

    private static void writeBoolean(ByteArrayOutputStream stream, byte b) {
        stream.write(__b);
        stream.write(__Colon);
        stream.write(b);
        stream.write(__Semicolon);
    }

    private static void writeInteger(ByteArrayOutputStream stream, byte[] i) {
        stream.write(__i);
        stream.write(__Colon);
        stream.write(i, 0, i.length);
        stream.write(__Semicolon);
    }

    private static void writeDouble(ByteArrayOutputStream stream, byte[] d) {
        stream.write(__d);
        stream.write(__Colon);
        stream.write(d, 0, d.length);
        stream.write(__Semicolon);
    }

    private static void writeString(ByteArrayOutputStream stream, byte[] s) {
    	byte[] slen = getAsciiBytes(new Integer(s.length));
        stream.write(__s);
        stream.write(__Colon);
        stream.write(slen, 0, slen.length);
        stream.write(__Colon);
        stream.write(__Quote);
        stream.write(s, 0, s.length);
        stream.write(__Quote);
        stream.write(__Semicolon);
    }

	@SuppressWarnings("unchecked")
	private static void writeList(ByteArrayOutputStream stream, List a, String charset) {
    	int len = a.size();
        byte[] alen = getAsciiBytes(new Integer(len));
        stream.write(__a);
        stream.write(__Colon);
        stream.write(alen, 0, alen.length);
        stream.write(__Colon);
        stream.write(__LeftB);
        for (int i = 0; i < len; i++) {
            writeInteger(stream, getAsciiBytes(new Integer(i)));
            serialize(stream, a.get(i), charset);
        }
        stream.write(__RightB);
    }

    @SuppressWarnings("unchecked")
	private static void writeMap(ByteArrayOutputStream stream, Map h,String charset) {
		int len = h.size();
		byte[] hlen = getAsciiBytes(new Integer(len));
		stream.write(__a);
		stream.write(__Colon);
		stream.write(hlen, 0, hlen.length);
		stream.write(__Colon);
		stream.write(__LeftB);
		for (Iterator keys = h.keySet().iterator(); keys.hasNext();) {
		    Object key = keys.next();
		    if ((key instanceof Byte) || (key instanceof Short) || (key instanceof Integer)) {
		        writeInteger(stream, getAsciiBytes(key));
		    } else if (key instanceof Boolean) {
		        writeInteger(stream, new byte[] { ((Boolean) key).booleanValue() ? __1 : __0 });
		    } else {
		        writeString(stream, getBytes(key,charset));
		    }
		    serialize(stream, h.get(key),charset);
		}
		stream.write(__RightB);
    }
    
    private static byte[] getAsciiBytes(Object obj) {
        try {
            return obj.toString().getBytes("US-ASCII");
        }
        catch (Exception e) {
            return null;
        }
    }

    private static byte[] getBytes(Object obj, String charset) {
        try {
            return obj.toString().getBytes(charset);
        } catch (Exception e) {
            return obj.toString().getBytes();
        }
    }

    public static Object unserialize(String ss,int state){
        return unserialize(ss, charset, state);
    }

    @SuppressWarnings("unchecked")
	public static Object unserialize(String ss, String charset,int state){
    	ByteArrayInputStream stream =null;
		try {
			stream = new ByteArrayInputStream(ss.getBytes(charset));
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
		}
        Object result = unserialize(stream, charset, state);
        return result;
    }

    @SuppressWarnings("unchecked")
	private static Object unserialize(ByteArrayInputStream stream, String charset,int state) {
    	switch (stream.read()) {
	    	case __N:
	    		return readNull(stream);
	    	case __b:
	    		return readBoolean(stream);
	    	case __i:
	    		return readInteger(stream);
	    	case __d:
	    		return readDouble(stream);
	    	case __s:
	    		return readString(stream, charset);
	    	case __U:
	    		return readUnicodeString(stream);
	    	case __a:
	    		return readArray(stream, charset, state);
	    	default:
	    		System.out.println("Serializer.unserialize: The DataType Is invalid,state="+state);
	    		return null;
    	}
    }

    private static String readNumber(ByteArrayInputStream stream) {
    	 StringBuffer sb = new StringBuffer();
         int i = stream.read();
         while ((i != __Semicolon) && (i != __Colon)) {
             sb.append((char) i);
             i = stream.read();
         }
         return sb.toString();
    }

    private static Object readNull(ByteArrayInputStream stream) {
        stream.skip(1);
        return null;
    }

    private static Boolean readBoolean(ByteArrayInputStream stream) {
    	 stream.skip(1);
         boolean b = stream.read() == __1;
         stream.skip(1);
         return b;
    }
    private static Number readInteger(ByteArrayInputStream stream) {
        stream.skip(1);
        String i = readNumber(stream);
        return Integer.parseInt(i);
    }

    private static Number readDouble(ByteArrayInputStream stream) {
    	stream.skip(1);
        String d = readNumber(stream);
        if (d.equals(__NAN)) {
            return new Double(Double.NaN);
        }
        if (d.equals(__INF)) {
            return new Double(Double.POSITIVE_INFINITY);
        }
        if (d.equals(__NINF)) {
            return new Double(Double.NEGATIVE_INFINITY);
        }
        if ((d.indexOf('.') > 0) || (d.indexOf('e') > 0) || (d.indexOf('E') > 0)) {
            return new Double(d);
        }
        int len = d.length();
        char c = d.charAt(0);
        if ((len < 19) || ((c == '-') && (len < 20))) {
            return new Long(d);
        }
        if ((len > 20) || ((c != '-') && (len > 19))) {
            return new Double(d);
        }
        try {
            return new Long(d);
        }
        catch (Exception e) {
            return new Double(d);
        }
    }

    private static String readString(ByteArrayInputStream stream, String charset) {
        stream.skip(1);
        int len = Integer.parseInt(readNumber(stream));
        stream.skip(1);
        byte[] buf = new byte[len];
        stream.read(buf, 0, len);
        stream.skip(2);
        try {
            return new String(buf, charset);
        } catch (Exception e) {
            return new String(buf);
        }
    }

    private static String readUnicodeString(ByteArrayInputStream stream) {
    	stream.skip(1);
        int len = Integer.parseInt(readNumber(stream));
        stream.skip(1);
        StringBuffer sb = new StringBuffer(len);
        int c;
        for (int i = 0; i < len; i++) {
            if ((c = stream.read()) == __Slash) {
            	char[] chs=new char[4];
            	chs[0] = (char) stream.read();
            	chs[1] = (char) stream.read();
            	chs[2] = (char) stream.read();
            	chs[3] = (char) stream.read();
                sb.append((char) (Integer.parseInt(new String(chs), 16)));
            }
            else {
                sb.append((char) c);
            }
        }
        stream.skip(2);
        return sb.toString();
    }

    @SuppressWarnings("unchecked")
	private static Object readArray(ByteArrayInputStream stream, String charset,int state) {
        stream.skip(1);
        int n = Integer.parseInt(readNumber(stream));
        stream.skip(1);
        Map map = null;
        List list = null;
        if(state==0){
        	list=new ArrayList(n);
        	state=-1;
        }else if(state==1){
        	map=new TreeMap();
        }else {
        	map=new HashMap(n);
        }

        for (int i = 0; i < n; i++) {
            Object key;
            switch (stream.read()) {
            case __i:
                key = readInteger(stream);
                break;
            case __s:
                key = readString(stream, charset);
                break;
            case __U:
                key = readUnicodeString(stream);
                break;
            default:
                return null;
            }
            Object result = unserialize(stream, charset, state);
            if (list != null) {
                if ((key instanceof Integer) && (((Integer) key).intValue() == i)) {
                	list.add(result);
                } else {
                	list = null;
                }
            }else{
            	map.put(key, result);
            }
        }
        stream.skip(1);
        if (list != null) {
        	return list;
        }else{
        	return map;
        }
    }
}