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Java Socket编程实例:http://donald-draper.iteye.com/blog/2356695
java Socket读写缓存区Writer和Reader:http://donald-draper.iteye.com/blog/2356885
Java NIO ByteBuffer详解:http://donald-draper.iteye.com/blog/2357084
Java序列化与反序列化实例分析:http://donald-draper.iteye.com/blog/2357515
Java序列化与反序列化详解:http://donald-draper.iteye.com/blog/2357540
在上一篇文章中,我们讲了java序列化的过程,今天有时间,我们来看一下反序列化过程,在看之前先回顾一下,序列
化:
ObjectOutputStream的构造,主要是构造对象,对象输出流BlockDataOutputStream
,BlockDataOutputStream主要是写序列化的流数据,BlockDataOutputStream中有一个存放序列化数据的缓存区,头部数据缓冲区,原始类型数据缓冲区,其中关联一个原始类型输出流DataOutputStream,(DataOutput)主要用于写原始类型数据,int,float,String,double等;同时写流版本号和流魔数。然后,写类流对象描述,主要写类名,序列版本号,类型,属性个数,属性描述;然后写对象属性值,当对象父接口是Serializable,如果Serializable实现了WriteObject方法,则直接调用WriteObject序列化属性值,否则,通过反射获取对象属性的值,写到缓存中,如果对象父接口Externalizable,则直接调用对象writeExternal方法序列化对象。
下面我们来看反序列化过程:

从下面这段代码看起:
ObjectInputStream objectInputStream  = null;
try {
	objectInputStream = new ObjectInputStream(inFile);
} catch (IOException e) {
	e.printStackTrace();
}
PersonX getPerson = null;
try {
	getPerson = (PersonX) objectInputStream.readObject();
	int int0 = objectInputStream.readInt();
	System.out.println("=======read int after read object persion:"+int0);
	String str = objectInputStream.readUTF();
	System.out.println("=======read UTF after read object persion and int:"+str);
	objectInputStream.close();
} catch (ClassNotFoundException e) {
	e.printStackTrace();
} catch (IOException e) {
	e.printStackTrace();
}

先看一下构造:
//ObjectInputStream
public class ObjectInputStream
    extends InputStream implements ObjectInput, ObjectStreamConstants
{
/** filter stream for handling block data conversion */
    private final BlockDataInputStream bin;//数据输入流
    /** validation callback list */
    private final ValidationList vlist;
    /** recursion depth */
    private int depth;
    /** whether stream is closed */
    private boolean closed;

    /** wire handle -> obj/exception map */
    private final HandleTable handles;
    /** scratch field for passing handle values up/down call stack */
    private int passHandle = NULL_HANDLE;
    /** flag set when at end of field value block with no TC_ENDBLOCKDATA */
    private boolean defaultDataEnd = false;

    /** buffer for reading primitive field values */
    private byte[] primVals;//原始类型变量幻从去

    /** if true, invoke readObjectOverride() instead of readObject() */
    private final boolean enableOverride;
    /** if true, invoke resolveObject() */
    private boolean enableResolve;

    /**
     * Context during upcalls to class-defined readObject methods; holds
     * object currently being deserialized and descriptor for current class.
     * Null when not during readObject upcall.
     */
    private SerialCallbackContext curContext;
    public ObjectInputStream(InputStream in) throws IOException {
        verifySubclass();
	//构造BlockDataInputStream
        bin = new BlockDataInputStream(in);
        handles = new HandleTable(10);
        vlist = new ValidationList();
        enableOverride = false;
        //读取流魔数与版本号
        readStreamHeader();
        bin.setBlockDataMode(true);
    }
     //读取流魔数与版本号
     protected void readStreamHeader()
        throws IOException, StreamCorruptedException
    {
        short s0 = bin.readShort();
        short s1 = bin.readShort();
        if (s0 != STREAM_MAGIC || s1 != STREAM_VERSION) {
            throw new StreamCorruptedException(
                String.format("invalid stream header: %04X%04X", s0, s1));
        }
    }
 }


再来看BlockDataInputStream
 // BlockDataInputStream
 private class BlockDataInputStream
        extends InputStream implements DataInput
    {
        /** maximum data block length */
        private static final int MAX_BLOCK_SIZE = 1024;
        /** maximum data block header length */
        private static final int MAX_HEADER_SIZE = 5;
        /** (tunable) length of char buffer (for reading strings) */
        private static final int CHAR_BUF_SIZE = 256;
        /** readBlockHeader() return value indicating header read may block */
        private static final int HEADER_BLOCKED = -2;

        /** buffer for reading general/block data */
        private final byte[] buf = new byte[MAX_BLOCK_SIZE];//输入流缓存
        /** buffer for reading block data headers */
        private final byte[] hbuf = new byte[MAX_HEADER_SIZE];//头部缓存
        /** char buffer for fast string reads */
        private final char[] cbuf = new char[CHAR_BUF_SIZE];//字符缓存

        /** block data mode */
        private boolean blkmode = false;

        // block data state fields; values meaningful only when blkmode true
        /** current offset into buf */
        private int pos = 0;//缓存读取位置
        /** end offset of valid data in buf, or -1 if no more block data */
        private int end = -1;
        /** number of bytes in current block yet to be read from stream */
        private int unread = 0;//缓存中还有,多少数据未读取

        /** underlying stream (wrapped in peekable filter stream) */
        private final PeekInputStream in;//从缓冲中取数据辅助流
        /** loopback stream (for data reads that span data blocks) */
        private final DataInputStream din;//原始类型解析辅助流

        /**
         * Creates new BlockDataInputStream on top of given underlying stream.
         * Block data mode is turned off by default.
         */
        BlockDataInputStream(InputStream in) {
            this.in = new PeekInputStream(in);
            din = new DataInputStream(this);
        }
}

//PeekInputStream,主要是从缓冲中去取字节流数据
/**
     * Input stream supporting single-byte peek operations.
     */
    private static class PeekInputStream extends InputStream {

        /** underlying stream */
        private final InputStream in;
        /** peeked byte */
        private int peekb = -1;

        /**
         * Creates new PeekInputStream on top of given underlying stream.
         */
        PeekInputStream(InputStream in) {
            this.in = in;
        }

        /**
         * Peeks at next byte value in stream.  Similar to read(), except
         * that it does not consume the read value.
         */
        int peek() throws IOException {
            return (peekb >= 0) ? peekb : (peekb = in.read());
        }

        public int read() throws IOException {
            if (peekb >= 0) {
                int v = peekb;
                peekb = -1;
                return v;
            } else {
                return in.read();
            }
        }

        public int read(byte[] b, int off, int len) throws IOException {
            if (len == 0) {
                return 0;
            } else if (peekb < 0) {
                return in.read(b, off, len);
            } else {
                b[off++] = (byte) peekb;
                len--;
                peekb = -1;
                int n = in.read(b, off, len);
                return (n >= 0) ? (n + 1) : 1;
            }
        }

        void readFully(byte[] b, int off, int len) throws IOException {
            int n = 0;
            while (n < len) {
                int count = read(b, off + n, len - n);
                if (count < 0) {
                    throw new EOFException();
                }
                n += count;
            }
        }

        public long skip(long n) throws IOException {
            if (n <= 0) {
                return 0;
            }
            int skipped = 0;
            if (peekb >= 0) {
                peekb = -1;
                skipped++;
                n--;
            }
            return skipped + skip(n);
        }

        public int available() throws IOException {
            return in.available() + ((peekb >= 0) ? 1 : 0);
        }

        public void close() throws IOException {
            in.close();
        }
    }

从上面可以看出,ObjectInputStream初始化主要是,构造BlockDataInputStream,
从缓冲中读取数据,然后读取流魔数与版本号;
再来关键反序列化过程:
//从缓冲中,反序列化对象
public final Object readObject()
        throws IOException, ClassNotFoundException
    {
        if (enableOverride) {
            return readObjectOverride();
        }
        // if nested read, passHandle contains handle of enclosing object
        int outerHandle = passHandle;
        try {
	   //委托给readObject0
            Object obj = readObject0(false);
            ...
            return obj;
        } finally {
            passHandle = outerHandle;
            if (closed && depth == 0) {
                clear();
            }
        }
    }

//根据反序列化对象类型,够到对象
private Object readObject0(boolean unshared) throws IOException {
        boolean oldMode = bin.getBlockDataMode();
        if (oldMode) {
            int remain = bin.currentBlockRemaining();
            if (remain > 0) {
                throw new OptionalDataException(remain);
            } else if (defaultDataEnd) {
                /*
                 * Fix for 4360508: stream is currently at the end of a field
                 * value block written via default serialization; since there
                 * is no terminating TC_ENDBLOCKDATA tag, simulate
                 * end-of-custom-data behavior explicitly.
                 */
                throw new OptionalDataException(true);
            }
            bin.setBlockDataMode(false);
        }

        byte tc;
	//读取反序列化对象类型
        while ((tc = bin.peekByte()) == TC_RESET) {
            bin.readByte();
            handleReset();
        }

        depth++;
        try {
	    //根据反序列化对象类型,够到对象
            switch (tc) {
                case TC_NULL:
                    return readNull();

                case TC_REFERENCE:
                    return readHandle(unshared);

                case TC_CLASS:
		   //反序列化Class对象
                    return readClass(unshared);

                case TC_CLASSDESC:
                case TC_PROXYCLASSDESC:
                    return readClassDesc(unshared);

                case TC_STRING:
                case TC_LONGSTRING:
                    return checkResolve(readString(unshared));

                case TC_ARRAY:
                    return checkResolve(readArray(unshared));

                case TC_ENUM:
                    return checkResolve(readEnum(unshared));

                case TC_OBJECT:
		   //读取Object信息
                    return checkResolve(readOrdinaryObject(unshared));

                case TC_EXCEPTION:
                    IOException ex = readFatalException();
                    throw new WriteAbortedException("writing aborted", ex);

                case TC_BLOCKDATA:
                case TC_BLOCKDATALONG:
                    if (oldMode) {
                        bin.setBlockDataMode(true);
                        bin.peek();             // force header read
                        throw new OptionalDataException(
                            bin.currentBlockRemaining());
                    } else {
                        throw new StreamCorruptedException(
                            "unexpected block data");
                    }

                case TC_ENDBLOCKDATA:
                    if (oldMode) {
                        throw new OptionalDataException(true);
                    } else {
                        throw new StreamCorruptedException(
                            "unexpected end of block data");
                    }

                default:
                    throw new StreamCorruptedException(
                        String.format("invalid type code: %02X", tc));
            }
        } finally {
            depth--;
            bin.setBlockDataMode(oldMode);
        }
    }


反序列化Object对象


    /**
     * Reads and returns "ordinary" (i.e., not a String, Class,
     * ObjectStreamClass, array, or enum constant) object, or null if object's
     * class is unresolvable (in which case a ClassNotFoundException will be
     * associated with object's handle).  Sets passHandle to object's assigned
     * handle.
     */
    private Object readOrdinaryObject(boolean unshared)
        throws IOException
    {
        
        if (bin.readByte() != TC_OBJECT) {
	    //如果非Object对象,抛出异常
            throw new InternalError();
        }
        //获取对象类型描述信息
        ObjectStreamClass desc = readClassDesc(false);
        desc.checkDeserialize();
        //加载Class
        Class<?> cl = desc.forClass();
        if (cl == String.class || cl == Class.class
                || cl == ObjectStreamClass.class) {
            throw new InvalidClassException("invalid class descriptor");
        }

        Object obj;
        try {
            obj = desc.isInstantiable() ? desc.newInstance() : null;
        } catch (Exception ex) {
            throw (IOException) new InvalidClassException(
                desc.forClass().getName(),
                "unable to create instance").initCause(ex);
        }

        passHandle = handles.assign(unshared ? unsharedMarker : obj);
        ClassNotFoundException resolveEx = desc.getResolveException();
        if (resolveEx != null) {
            handles.markException(passHandle, resolveEx);
        }
        //如果是Externalizable
        if (desc.isExternalizable()) {
            readExternalData((Externalizable) obj, desc);
        } else {
	   //如果是Serializable
            readSerialData(obj, desc);
        }

        handles.finish(passHandle);

        if (obj != null &&
            handles.lookupException(passHandle) == null &&
            desc.hasReadResolveMethod())
        {
	    //如果对象有readResolve,则调用readResolve方法
            Object rep = desc.invokeReadResolve(obj);
            if (unshared && rep.getClass().isArray()) {
                rep = cloneArray(rep);
            }
            if (rep != obj) {
                handles.setObject(passHandle, obj = rep);
            }
        }

        return obj;
    }




先看
//获取对象类描述信息
ObjectStreamClass desc = readClassDesc(false);


private ObjectStreamClass readClassDesc(boolean unshared)
        throws IOException
    {
        byte tc = bin.peekByte();
        switch (tc) {
            case TC_NULL:
                return (ObjectStreamClass) readNull();

            case TC_REFERENCE:
                return (ObjectStreamClass) readHandle(unshared);

            case TC_PROXYCLASSDESC:
	        //读取代理对象的信息
                return readProxyDesc(unshared);

            case TC_CLASSDESC:
	        //读取非代理对象的信息
                return readNonProxyDesc(unshared);

            default:
                throw new StreamCorruptedException(
                    String.format("invalid type code: %02X", tc));
        }
    }



/**
     * Reads in and returns class descriptor for a class that is not a dynamic
     * proxy class.  Sets passHandle to class descriptor's assigned handle.  If
     * class descriptor cannot be resolved to a class in the local VM, a
     * ClassNotFoundException is associated with the descriptor's handle.
     */
    private ObjectStreamClass readNonProxyDesc(boolean unshared)
        throws IOException
    {
        if (bin.readByte() != TC_CLASSDESC) {
	    //非对象流描述类,则抛出异常
            throw new InternalError();
        }

        ObjectStreamClass desc = new ObjectStreamClass();
        int descHandle = handles.assign(unshared ? unsharedMarker : desc);
        passHandle = NULL_HANDLE;

        ObjectStreamClass readDesc = null;
        try {
	    //读取对象描述信息
            readDesc = readClassDescriptor();
        } catch (ClassNotFoundException ex) {
            throw (IOException) new InvalidClassException(
                "failed to read class descriptor").initCause(ex);
        }

        Class cl = null;
        ClassNotFoundException resolveEx = null;
        bin.setBlockDataMode(true);
        try {
	    //先调用序列化类的resolveClass
            if ((cl = resolveClass(readDesc)) == null) {
                resolveEx = new ClassNotFoundException("null class");
            }
        } catch (ClassNotFoundException ex) {
            resolveEx = ex;
        }
	//跳过非必要数据
        skipCustomData();
        //初始化对象
        desc.initNonProxy(readDesc, cl, resolveEx, readClassDesc(false));

        handles.finish(descHandle);
        passHandle = descHandle;
        return desc;
    }

来看读取对象描述信息
//读取对象描述信息
readDesc = readClassDescriptor();



 protected ObjectStreamClass readClassDescriptor()
        throws IOException, ClassNotFoundException
    {
        ObjectStreamClass desc = new ObjectStreamClass();
	//委托给ObjectStreamClass的readNonProxy方法
        desc.readNonProxy(this);
        return desc;
    }


//ObjectStreamClass

void readNonProxy(ObjectInputStream in)
        throws IOException, ClassNotFoundException
    {
       //读取类名
        name = in.readUTF();
	//读取类型序列号
        suid = Long.valueOf(in.readLong());
        isProxy = false;
        //读取对象序列化的方式,writeObject方法,Serializable,Externalizable,还是SC_BLOCK_DATA
        byte flags = in.readByte();
        hasWriteObjectData =
            ((flags & ObjectStreamConstants.SC_WRITE_METHOD) != 0);
        hasBlockExternalData =
            ((flags & ObjectStreamConstants.SC_BLOCK_DATA) != 0);
        externalizable =
            ((flags & ObjectStreamConstants.SC_EXTERNALIZABLE) != 0);
        boolean sflag =
            ((flags & ObjectStreamConstants.SC_SERIALIZABLE) != 0);
        if (externalizable && sflag) {
            throw new InvalidClassException(
                name, "serializable and externalizable flags conflict");
        }
        serializable = externalizable || sflag;
        isEnum = ((flags & ObjectStreamConstants.SC_ENUM) != 0);
        if (isEnum && suid.longValue() != 0L) {
            throw new InvalidClassException(name,
                "enum descriptor has non-zero serialVersionUID: " + suid);
        }
        //读取对象属性个数
        int numFields = in.readShort();
        if (isEnum && numFields != 0) {
            throw new InvalidClassException(name,
                "enum descriptor has non-zero field count: " + numFields);
        }
        fields = (numFields > 0) ?
            new ObjectStreamField[numFields] : NO_FIELDS;
	//读取对象属性类型,及name
        for (int i = 0; i < numFields; i++) {
	    //读取对象属性,类型编码
            char tcode = (char) in.readByte();
	    //读取对象属性名
            String fname = in.readUTF();
            String signature = ((tcode == 'L') || (tcode == '[')) ?
                in.readTypeString() : new String(new char[] { tcode });
            try {
                fields[i] = new ObjectStreamField(fname, signature, false);
            } catch (RuntimeException e) {
                throw (IOException) new InvalidClassException(name,
                    "invalid descriptor for field " + fname).initCause(e);
            }
        }
        //根据属性类型,初始化属性读取的缓存位置
        computeFieldOffsets();
    }

//ObjectStreamField
ObjectStreamField(String name, String signature, boolean unshared) {
        if (name == null) {
            throw new NullPointerException();
        }
        this.name = name;
        this.signature = signature.intern();
        this.unshared = unshared;
        field = null;

        switch (signature.charAt(0)) {
            case 'Z': type = Boolean.TYPE; break;
            case 'B': type = Byte.TYPE; break;
            case 'C': type = Character.TYPE; break;
            case 'S': type = Short.TYPE; break;
            case 'I': type = Integer.TYPE; break;
            case 'J': type = Long.TYPE; break;
            case 'F': type = Float.TYPE; break;
            case 'D': type = Double.TYPE; break;
            case 'L':
            case '[': type = Object.class; break;
            default: throw new IllegalArgumentException("illegal signature");
        }
    }

//根据属性类型,初始化属性读取的缓存位置
private void computeFieldOffsets() throws InvalidClassException {
        primDataSize = 0;
        numObjFields = 0;
        int firstObjIndex = -1;
        //根据属性类型,初始化属性读取的缓存位置
        for (int i = 0; i < fields.length; i++) {
            ObjectStreamField f = fields[i];
            switch (f.getTypeCode()) {
	        //boolean,byte类型一个字节
                case 'Z':
                case 'B':
                    f.setOffset(primDataSize++);
                    break;
                //char,short类型2个字节
                case 'C':
                case 'S':
                    f.setOffset(primDataSize);
                    primDataSize += 2;
                    break;
                //int,float类型4个字节
                case 'I':
                case 'F':
                    f.setOffset(primDataSize);
                    primDataSize += 4;
                    break;
                //long,double类型8个字节
                case 'J':
                case 'D':
                    f.setOffset(primDataSize);
                    primDataSize += 8;
                    break;

                case '[':
                case 'L':
                    f.setOffset(numObjFields++);
                    if (firstObjIndex == -1) {
                        firstObjIndex = i;
                    }
                    break;

                default:
                    throw new InternalError();
            }
        }
        if (firstObjIndex != -1 &&
            firstObjIndex + numObjFields != fields.length)
        {
            throw new InvalidClassException(name, "illegal field order");
        }
    }

回到readNonProxyDesc的方法这一句:
//加载类
if ((cl = resolveClass(readDesc)) == null) {
                resolveEx = new ClassNotFoundException("null class");
}

 protected Class<?> resolveClass(ObjectStreamClass desc)
        throws IOException, ClassNotFoundException
    {
        String name = desc.getName();
        try {
            return Class.forName(name, false, latestUserDefinedLoader());
        } catch (ClassNotFoundException ex) {
	   //如果非class类,从原始类型Map中获取
            Class<?> cl = primClasses.get(name);
            if (cl != null) {
                return cl;
            } else {
                throw ex;
            }
        }
    }

//ObjectInputStream
public class ObjectInputStream
    extends InputStream implements ObjectInput, ObjectStreamConstants
{
    /** handle value representing null */
    private static final int NULL_HANDLE = -1;

    /** marker for unshared objects in internal handle table */
    private static final Object unsharedMarker = new Object();

    /** table mapping primitive type names to corresponding class objects */
    private static final HashMap<String, Class<?>> primClasses
        = new HashMap<>(8, 1.0F);
    static {
        primClasses.put("boolean", boolean.class);
        primClasses.put("byte", byte.class);
        primClasses.put("char", char.class);
        primClasses.put("short", short.class);
        primClasses.put("int", int.class);
        primClasses.put("long", long.class);
        primClasses.put("float", float.class);
        primClasses.put("double", double.class);
        primClasses.put("void", void.class);
    }
}
回到readNonProxyDesc的方法这一句:
skipCustomData();

/**
     * Skips over all block data and objects until TC_ENDBLOCKDATA is
     * encountered.
     */
    private void skipCustomData() throws IOException {
        int oldHandle = passHandle;
        for (;;) {
            if (bin.getBlockDataMode()) {
                bin.skipBlockData();
                bin.setBlockDataMode(false);
            }
            switch (bin.peekByte()) {
                case TC_BLOCKDATA:
                case TC_BLOCKDATALONG:
                    bin.setBlockDataMode(true);
                    break;

                case TC_ENDBLOCKDATA:
                    bin.readByte();
                    passHandle = oldHandle;
                    return;

                default:
                    readObject0(false);
                    break;
            }
        }
    }

回到readNonProxyDesc的方法这一句:
desc.initNonProxy(readDesc, cl, resolveEx, readClassDesc(false));

//ObjectStreamClass
/**
     * Initializes class descriptor representing a non-proxy class.
     */
    void initNonProxy(ObjectStreamClass model,
                      Class<?> cl,
                      ClassNotFoundException resolveEx,
                      ObjectStreamClass superDesc)
        throws InvalidClassException
    {
        this.cl = cl;
        this.resolveEx = resolveEx;
        this.superDesc = superDesc;
	//类名
        name = model.name;
	//序列号
        suid = Long.valueOf(model.getSerialVersionUID());
        isProxy = false;
	//是否为Enum
        isEnum = model.isEnum;
	//父接口类型serializable、externalizable
        serializable = model.serializable;
        externalizable = model.externalizable;
        hasBlockExternalData = model.hasBlockExternalData;
	//对象是否有WriteObject方法
        hasWriteObjectData = model.hasWriteObjectData;
	//属性
        fields = model.fields;
	//原始类型数据大小
        primDataSize = model.primDataSize;
	//属性书量
        numObjFields = model.numObjFields;

        if (cl != null) {
            localDesc = lookup(cl, true);
            if (localDesc.isProxy) {
                throw new InvalidClassException(
                    "cannot bind non-proxy descriptor to a proxy class");
            }
            if (isEnum != localDesc.isEnum) {
                throw new InvalidClassException(isEnum ?
                    "cannot bind enum descriptor to a non-enum class" :
                    "cannot bind non-enum descriptor to an enum class");
            }

            if (serializable == localDesc.serializable &&
                !cl.isArray() &&
                suid.longValue() != localDesc.getSerialVersionUID())
            {
                throw new InvalidClassException(localDesc.name,
                    "local class incompatible: " +
                    "stream classdesc serialVersionUID = " + suid +
                    ", local class serialVersionUID = " +
                    localDesc.getSerialVersionUID());
            }

            if (!classNamesEqual(name, localDesc.name)) {
                throw new InvalidClassException(localDesc.name,
                    "local class name incompatible with stream class " +
                    "name \"" + name + "\"");
            }

            if (!isEnum) {
                if ((serializable == localDesc.serializable) &&
                    (externalizable != localDesc.externalizable))
                {
                    throw new InvalidClassException(localDesc.name,
                        "Serializable incompatible with Externalizable");
                }

                if ((serializable != localDesc.serializable) ||
                    (externalizable != localDesc.externalizable) ||
                    !(serializable || externalizable))
                {
                    deserializeEx = new ExceptionInfo(
                        localDesc.name, "class invalid for deserialization");
                }
            }

            cons = localDesc.cons;
	    //初始化writeObjectMethod,readObjectMethod,readResolveMethod
            writeObjectMethod = localDesc.writeObjectMethod;
            readObjectMethod = localDesc.readObjectMethod;
            readObjectNoDataMethod = localDesc.readObjectNoDataMethod;
            writeReplaceMethod = localDesc.writeReplaceMethod;
            readResolveMethod = localDesc.readResolveMethod;
            if (deserializeEx == null) {
                deserializeEx = localDesc.deserializeEx;
            }
        }
	//获取对象属性反射器,这段我们在上一篇已将看过
        fieldRefl = getReflector(fields, localDesc);

        // reassign to matched fields so as to reflect local unshared settings
        fields = fieldRefl.getFields();
    }
}

/**
     * Matches given set of serializable fields with serializable fields
     * described by the given local class descriptor, and returns a
     * FieldReflector instance capable of setting/getting values from the
     * subset of fields that match (non-matching fields are treated as filler,
     * for which get operations return default values and set operations
     * discard given values).  Throws InvalidClassException if unresolvable
     * type conflicts exist between the two sets of fields.
     */
//从ObjectStreamClass的获取Field对应的反射器
private static FieldReflector getReflector(ObjectStreamField[] fields,
                                               ObjectStreamClass localDesc)
        throws InvalidClassException
    {
        // class irrelevant if no fields
        Class<?> cl = (localDesc != null && fields.length > 0) ?
            localDesc.cl : null;
        processQueue(Caches.reflectorsQueue, Caches.reflectors);
        FieldReflectorKey key = new FieldReflectorKey(cl, fields,
                                                      Caches.reflectorsQueue);
        Reference<?> ref = Caches.reflectors.get(key);
        Object entry = null;
        if (ref != null) {
            entry = ref.get();
        }
        EntryFuture future = null;
        if (entry == null) {
            EntryFuture newEntry = new EntryFuture();
            Reference<?> newRef = new SoftReference<>(newEntry);
            do {
                if (ref != null) {
                    Caches.reflectors.remove(key, ref);
                }
                ref = Caches.reflectors.putIfAbsent(key, newRef);
                if (ref != null) {
                    entry = ref.get();
                }
            } while (ref != null && entry == null);
            if (entry == null) {
                future = newEntry;
            }
        }

        if (entry instanceof FieldReflector) {  // check common case first
            return (FieldReflector) entry;
        } else if (entry instanceof EntryFuture) {
            entry = ((EntryFuture) entry).get();
        } else if (entry == null) {
            try {
                entry = new FieldReflector(matchFields(fields, localDesc));
            } catch (Throwable th) {
                entry = th;
            }
            future.set(entry);
            Caches.reflectors.put(key, new SoftReference<Object>(entry));
        }

        if (entry instanceof FieldReflector) {
            return (FieldReflector) entry;
        } else if (entry instanceof InvalidClassException) {
            throw (InvalidClassException) entry;
        } else if (entry instanceof RuntimeException) {
            throw (RuntimeException) entry;
        } else if (entry instanceof Error) {
            throw (Error) entry;
        } else {
            throw new InternalError("unexpected entry: " + entry);
        }
    }



 /**
         * Returns list of ObjectStreamFields representing fields operated on
         * by this reflector.  The shared/unshared values and Field objects
         * contained by ObjectStreamFields in the list reflect their bindings
         * to locally defined serializable fields.
         */
//ObjectStreamClass
 ObjectStreamField[] getFields() {
            return fields;
        }

回到readOrdinaryObject的这一句

//加载Class
Class<?> cl = desc.forClass();


//ObjectStreamClass
  /**
     * Return the class in the local VM that this version is mapped to.  Null
     * is returned if there is no corresponding local class.
     *
     * @return  the <code>Class</code> instance that this descriptor represents
     */
    public Class<?> forClass() {
        return cl;
    }


回到readOrdinaryObject的这一句
//如果是Externalizable
       if (desc.isExternalizable()) {
            readExternalData((Externalizable) obj, desc);
        } else {
	   //如果是Serializable
            readSerialData(obj, desc);
        }


先看
readExternalData((Externalizable) obj, desc);


private void readExternalData(Externalizable obj, ObjectStreamClass desc)
        throws IOException
    {
        SerialCallbackContext oldContext = curContext;
        curContext = null;
        try {
            boolean blocked = desc.hasBlockExternalData();
            if (blocked) {
                bin.setBlockDataMode(true);
            }
            if (obj != null) {
                try {
		    //调用对象的readExternal
                    obj.readExternal(this);
                } catch (ClassNotFoundException ex) {
                    /*
                     * In most cases, the handle table has already propagated
                     * a CNFException to passHandle at this point; this mark
                     * call is included to address cases where the readExternal
                     * method has cons'ed and thrown a new CNFException of its
                     * own.
                     */
                     handles.markException(passHandle, ex);
                }
            }
            if (blocked) {
                skipCustomData();
            }
        } finally {
            curContext = oldContext;
        }

再来看
readSerialData(obj, desc);


/**
     * Reads (or attempts to skip, if obj is null or is tagged with a
     * ClassNotFoundException) instance data for each serializable class of
     * object in stream, from superclass to subclass.  Expects that passHandle
     * is set to obj's handle before this method is called.
     */
    private void readSerialData(Object obj, ObjectStreamClass desc)
        throws IOException
    {
        ObjectStreamClass.ClassDataSlot[] slots = desc.getClassDataLayout();
        for (int i = 0; i < slots.length; i++) {
            ObjectStreamClass slotDesc = slots[i].desc;

            if (slots[i].hasData) {
                if (obj != null &&
                    slotDesc.hasReadObjectMethod() &&
                    handles.lookupException(passHandle) == null)
                {
                    SerialCallbackContext oldContext = curContext;

                    try {
                        curContext = new SerialCallbackContext(obj, slotDesc);

                        bin.setBlockDataMode(true);
			//如果对象有ReadObject,则调用对象的Object方法
                        slotDesc.invokeReadObject(obj, this);
                    } catch (ClassNotFoundException ex) {
                        /*
                         * In most cases, the handle table has already
                         * propagated a CNFException to passHandle at this
                         * point; this mark call is included to address cases
                         * where the custom readObject method has cons'ed and
                         * thrown a new CNFException of its own.
                         */
                        handles.markException(passHandle, ex);
                    } finally {
                        curContext.setUsed();
                        curContext = oldContext;
                    }

                    /*
                     * defaultDataEnd may have been set indirectly by custom
                     * readObject() method when calling defaultReadObject() or
                     * readFields(); clear it to restore normal read behavior.
                     */
                    defaultDataEnd = false;
                } else {
		    //否则读取属性
                    defaultReadFields(obj, slotDesc);
                }
                if (slotDesc.hasWriteObjectData()) {
                    skipCustomData();
                } else {
                    bin.setBlockDataMode(false);
                }
            } else {
                if (obj != null &&
                    slotDesc.hasReadObjectNoDataMethod() &&
                    handles.lookupException(passHandle) == null)
                {
                    slotDesc.invokeReadObjectNoData(obj);
                }
            }
        }
    }

//否则读取属性
 defaultReadFields(obj, slotDesc);


  /**
     * Reads in values of serializable fields declared by given class
     * descriptor.  If obj is non-null, sets field values in obj.  Expects that
     * passHandle is set to obj's handle before this method is called.
     */
    private void defaultReadFields(Object obj, ObjectStreamClass desc)
        throws IOException
    {
        // REMIND: is isInstance check necessary?
        Class cl = desc.forClass();
        if (cl != null && obj != null && !cl.isInstance(obj)) {
            throw new ClassCastException();
        }
        //获取原始类型个数
        int primDataSize = desc.getPrimDataSize();
        if (primVals == null || primVals.length < primDataSize) {
            primVals = new byte[primDataSize];
        }
	//从缓冲区,读取所有属性数据
        bin.readFully(primVals, 0, primDataSize, false);
        if (obj != null) {
	    //设置对象原始类型属性数据
            desc.setPrimFieldValues(obj, primVals);
        }

        int objHandle = passHandle;
        ObjectStreamField[] fields = desc.getFields(false);
        Object[] objVals = new Object[desc.getNumObjFields()];
        int numPrimFields = fields.length - objVals.length;
	//遍历所有Field,并读取属性值
        for (int i = 0; i < objVals.length; i++) {
            ObjectStreamField f = fields[numPrimFields + i];
            objVals[i] = readObject0(f.isUnshared());
            if (f.getField() != null) {
                handles.markDependency(objHandle, passHandle);
            }
        }
        if (obj != null) {
	    //设置所有属性值
            desc.setObjFieldValues(obj, objVals);
        }
        passHandle = objHandle;
    }

//ObjectStreamClass
/**
     * Sets the serializable object fields of object obj using values from
     * array vals starting at offset 0.  It is the responsibility of the caller
     * to ensure that obj is of the proper type if non-null.
     */
    void setObjFieldValues(Object obj, Object[] vals) {
        fieldRefl.setObjFieldValues(obj, vals);
    }

     /**
     * Invokes the readObject method of the represented serializable class.
     * Throws UnsupportedOperationException if this class descriptor is not
     * associated with a class, or if the class is externalizable,
     * non-serializable or does not define readObject.
     */
    void invokeReadObject(Object obj, ObjectInputStream in)
        throws ClassNotFoundException, IOException,
               UnsupportedOperationException
    {
        if (readObjectMethod != null) {
            try {
                readObjectMethod.invoke(obj, new Object[]{ in });
        } else {
            throw new UnsupportedOperationException();
        }
    }

回到readOrdinaryObject的这一句
//如果对象有readResolve,则调用readResolve方法
Object rep = desc.invokeReadResolve(obj);


//ObjectStreamClass
 /**
     * Invokes the writeReplace method of the represented serializable class and
     * returns the result.  Throws UnsupportedOperationException if this class
     * descriptor is not associated with a class, or if the class is
     * non-serializable or does not define writeReplace.
     */
    Object invokeWriteReplace(Object obj)
        throws IOException, UnsupportedOperationException
    {
        if (writeReplaceMethod != null) {
            try {
                return writeReplaceMethod.invoke(obj, (Object[]) null);
            } 
   }

总结:
ObjectInputStream初始化主要是,构造BlockDataInputStream,从缓冲中读取数据,然后读取流魔数与版本号;然后从缓冲中读取对象流描述信息,包括类型,属性名,及每个属性对应的读取位置;在加载流对象描述信息类;如果是Externalizable,则调用对象的readExternal的方法,如果是Serializable,有ReadObject,则通过反射调用ReadObject方法,没有从缓冲中读取属性数据,并给属性赋值;如果对象中有readResolve方法,则调用readResolve,并返回。

来看一个readint
//ObjectInputStream
public int readInt()  throws IOException {
        return bin.readInt();
    }

//BlockDataInputStream
 
   public int readInt() throws IOException {
            if (!blkmode) {
                pos = 0;
                in.readFully(buf, 0, 4);
            } else if (end - pos < 4) {
                return din.readInt();
            }
            int v = Bits.getInt(buf, pos);
            pos += 4;
            return v;
        }


//Double
public final class Double extends Number implements Comparable<Double> {
/**
     * The {@code Class} instance representing the primitive type
     * {@code double}.
     *
     * @since JDK1.1
     */
    public static final Class<Double>   TYPE = (Class<Double>) Class.getPrimitiveClass("double");
}


//ObjectStreamConstants
package java.io;

/**
 * Constants written into the Object Serialization Stream.
 *
 * @author  unascribed
 * @since JDK 1.1
 */
public interface ObjectStreamConstants {

    /**
     * Magic number that is written to the stream header.
     */
    final static short STREAM_MAGIC = (short)0xaced;

    /**
     * Version number that is written to the stream header.
     */
    final static short STREAM_VERSION = 5;

    /* Each item in the stream is preceded by a tag
     */

    /**
     * First tag value.
     */
    final static byte TC_BASE = 0x70;

    /**
     * Null object reference.
     */
    final static byte TC_NULL =         (byte)0x70;

    /**
     * Reference to an object already written into the stream.
     */
    final static byte TC_REFERENCE =    (byte)0x71;

    /**
     * new Class Descriptor.
     */
    final static byte TC_CLASSDESC =    (byte)0x72;

    /**
     * new Object.
     */
    final static byte TC_OBJECT =       (byte)0x73;

    /**
     * new String.
     */
    final static byte TC_STRING =       (byte)0x74;

    /**
     * new Array.
     */
    final static byte TC_ARRAY =        (byte)0x75;

    /**
     * Reference to Class.
     */
    final static byte TC_CLASS =        (byte)0x76;

    /**
     * Block of optional data. Byte following tag indicates number
     * of bytes in this block data.
     */
    final static byte TC_BLOCKDATA =    (byte)0x77;

    /**
     * End of optional block data blocks for an object.
     */
    final static byte TC_ENDBLOCKDATA = (byte)0x78;

    /**
     * Reset stream context. All handles written into stream are reset.
     */
    final static byte TC_RESET =        (byte)0x79;

    /**
     * long Block data. The long following the tag indicates the
     * number of bytes in this block data.
     */
    final static byte TC_BLOCKDATALONG= (byte)0x7A;

    /**
     * Exception during write.
     */
    final static byte TC_EXCEPTION =    (byte)0x7B;

    /**
     * Long string.
     */
    final static byte TC_LONGSTRING =   (byte)0x7C;

    /**
     * new Proxy Class Descriptor.
     */
    final static byte TC_PROXYCLASSDESC =       (byte)0x7D;

    /**
     * new Enum constant.
     * @since 1.5
     */
    final static byte TC_ENUM =         (byte)0x7E;

    /**
     * Last tag value.
     */
    final static byte TC_MAX =          (byte)0x7E;

    /**
     * First wire handle to be assigned.
     */
    final static int baseWireHandle = 0x7e0000;


    /******************************************************/
    /* Bit masks for ObjectStreamClass flag.*/

    /**
     * Bit mask for ObjectStreamClass flag. Indicates a Serializable class
     * defines its own writeObject method.
     */
    final static byte SC_WRITE_METHOD = 0x01;

    /**
     * Bit mask for ObjectStreamClass flag. Indicates Externalizable data
     * written in Block Data mode.
     * Added for PROTOCOL_VERSION_2.
     *
     * @see #PROTOCOL_VERSION_2
     * @since 1.2
     */
    final static byte SC_BLOCK_DATA = 0x08;

    /**
     * Bit mask for ObjectStreamClass flag. Indicates class is Serializable.
     */
    final static byte SC_SERIALIZABLE = 0x02;

    /**
     * Bit mask for ObjectStreamClass flag. Indicates class is Externalizable.
     */
    final static byte SC_EXTERNALIZABLE = 0x04;

    /**
     * Bit mask for ObjectStreamClass flag. Indicates class is an enum type.
     * @since 1.5
     */
    final static byte SC_ENUM = 0x10;


    /* *******************************************************************/
    /* Security permissions */

    /**
     * Enable substitution of one object for another during
     * serialization/deserialization.
     *
     * @see java.io.ObjectOutputStream#enableReplaceObject(boolean)
     * @see java.io.ObjectInputStream#enableResolveObject(boolean)
     * @since 1.2
     */
    final static SerializablePermission SUBSTITUTION_PERMISSION =
                           new SerializablePermission("enableSubstitution");

    /**
     * Enable overriding of readObject and writeObject.
     *
     * @see java.io.ObjectOutputStream#writeObjectOverride(Object)
     * @see java.io.ObjectInputStream#readObjectOverride()
     * @since 1.2
     */
    final static SerializablePermission SUBCLASS_IMPLEMENTATION_PERMISSION =
                    new SerializablePermission("enableSubclassImplementation");
   /**
    * A Stream Protocol Version. <p>
    *
    * All externalizable data is written in JDK 1.1 external data
    * format after calling this method. This version is needed to write
    * streams containing Externalizable data that can be read by
    * pre-JDK 1.1.6 JVMs.
    *
    * @see java.io.ObjectOutputStream#useProtocolVersion(int)
    * @since 1.2
    */
    public final static int PROTOCOL_VERSION_1 = 1;


   /**
    * A Stream Protocol Version. <p>
    *
    * This protocol is written by JVM 1.2.
    *
    * Externalizable data is written in block data mode and is
    * terminated with TC_ENDBLOCKDATA. Externalizable classdescriptor
    * flags has SC_BLOCK_DATA enabled. JVM 1.1.6 and greater can
    * read this format change.
    *
    * Enables writing a nonSerializable class descriptor into the
    * stream. The serialVersionUID of a nonSerializable class is
    * set to 0L.
    *
    * @see java.io.ObjectOutputStream#useProtocolVersion(int)
    * @see #SC_BLOCK_DATA
    * @since 1.2
    */
    public final static int PROTOCOL_VERSION_2 = 2;
}