Java序列化与反序列化详解后续

Java Socket编程实例:[url]http://donald-draper.iteye.com/blog/2356695[/url]
java Socket读写缓存区Writer和Reader：[url]http://donald-draper.iteye.com/blog/2356885[/url]
Java NIO ByteBuffer详解：[url]http://donald-draper.iteye.com/blog/2357084[/url]
Java序列化与反序列化实例分析：[url]http://donald-draper.iteye.com/blog/2357515[/url]
Java序列化与反序列化详解：[url]http://donald-draper.iteye.com/blog/2357540[/url]
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> 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