jdk源碼解析八之序列化

package org.example.io;

import java.io.Serializable;

//類通過實現 java.io.Serializable 接口以啓用其序列化功能。
public class Person implements Serializable {
    //通過id來判斷類是否改變
    private static final long serialVersionUID = 3;
    private transient  String name;
    //不需要序列化的成員變量
    private  int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    @Override
    public String toString() {
        return "Person [name=" + name + ", age=" + age + "]";
    }

}

0xACED:根據協議文檔的約定,由於所有二進制流(文件)都需要在流的頭部約定魔數(magic number=STREAM_MAGIC),既java object 序列化後的流的魔數約定爲ACED;

0x0005:然後是流協議版本是short類型(2字節)並且值爲5,則十六進制值爲0005;

java byte型長度爲1字節,所以0x73 0x72直接對應到字節流上,0x73(TC_OBJECT)代表這是一個對象,0x72(TC_CLASSDESC)代表這個之後開始是對類的描述.

接着類長度,我也不知道爲啥是15
類全限定名
序列化id
0x02:表示可以序列化
0001:表示只有一個字段
49:表示int類型
0003:字段名長度
接着字段名
0x78:該塊定義的序列化流結束了
0x70是NULL,沒有超類了.
00000002:表示字段值

ObjectInputStream

    public ObjectInputStream(InputStream in) throws IOException {
        //校驗是否是子類
        verifySubclass();
        bin = new BlockDataInputStream(in);
        handles = new HandleTable(10);
        vlist = new ValidationList();
        serialFilter = ObjectInputFilter.Config.getSerialFilter();
        enableOverride = false;
        //驗證魔數和版本號
        readStreamHeader();
        bin.setBlockDataMode(true);
    }

    protected void readStreamHeader()
        throws IOException, StreamCorruptedException
    {
        short s0 = bin.readShort();
        short s1 = bin.readShort();
        //魔數,用來描述這個文件到底啥類型,ACED
        if (s0 != STREAM_MAGIC ||
                //class版本號,0005
                s1 != STREAM_VERSION) {
            throw new StreamCorruptedException(
                String.format("invalid stream header: %04X%04X", s0, s1));
        }
    }

反序列化

 //讀取輸入流數據,返回一個對象
    public final Object readObject()
        throws IOException, ClassNotFoundException
    {
        //爲true,則調用readObjectOverride(),調用子類覆蓋方法
        if (enableOverride) {
            return readObjectOverride();
        }

        // if nested read, passHandle contains handle of enclosing object
        int outerHandle = passHandle;
        try {
            //加載對象
            Object obj = readObject0(false);
            handles.markDependency(outerHandle, passHandle);
            ClassNotFoundException ex = handles.lookupException(passHandle);
            if (ex != null) {
                throw ex;
            }
            if (depth == 0) {
                vlist.doCallbacks();
            }
            return obj;
        } finally {
            passHandle = outerHandle;
            if (closed && depth == 0) {
                clear();
            }
        }
    }

    protected Object readObjectOverride()
        throws IOException, ClassNotFoundException
    {
        return null;
    }

 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;
        while ((tc = bin.peekByte()) == TC_RESET) {
            bin.readByte();
            handleReset();
        }

        depth++;
        totalObjectRefs++;
        try {
            switch (tc) {
                case TC_NULL:
                    return readNull();

                case TC_REFERENCE:
                    return readHandle(unshared);

                case TC_CLASS:
                    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));

                    //0x73 則新建對象
                case TC_OBJECT:
                    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);
        }
    }

 private Object readOrdinaryObject(boolean unshared)
        throws IOException
    {
        if (bin.readByte() != TC_OBJECT) {
            throw new InternalError();
        }

        //獲取類的描述
        ObjectStreamClass desc = readClassDesc(false);
        desc.checkDeserialize();

        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);
        }

        if (desc.isExternalizable()) {
            readExternalData((Externalizable) obj, desc);
        } else {
            //填充字段數據
            readSerialData(obj, desc);
        }

        handles.finish(passHandle);

        if (obj != null &&
            handles.lookupException(passHandle) == null &&
            desc.hasReadResolveMethod())
        {
            Object rep = desc.invokeReadResolve(obj);
            if (unshared && rep.getClass().isArray()) {
                rep = cloneArray(rep);
            }
            if (rep != obj) {
                // Filter the replacement object
                if (rep != null) {
                    if (rep.getClass().isArray()) {
                        filterCheck(rep.getClass(), Array.getLength(rep));
                    } else {
                        filterCheck(rep.getClass(), -1);
                    }
                }
                handles.setObject(passHandle, obj = rep);
            }
        }

        return obj;
    }

private ObjectStreamClass readClassDesc(boolean unshared)
        throws IOException
    {
        byte tc = bin.peekByte();
        ObjectStreamClass descriptor;
        switch (tc) {
            case TC_NULL:
                descriptor = (ObjectStreamClass) readNull();
                break;
            case TC_REFERENCE:
                descriptor = (ObjectStreamClass) readHandle(unshared);
                break;
            case TC_PROXYCLASSDESC:
                descriptor = readProxyDesc(unshared);
                break;
                //0x72 對類的描述
            case TC_CLASSDESC:
                descriptor = readNonProxyDesc(unshared);
                break;
            default:
                throw new StreamCorruptedException(
                    String.format("invalid type code: %02X", tc));
        }
        return descriptor;
    }

private ObjectStreamClass readNonProxyDesc(boolean unshared)
        throws IOException
    {
        if (bin.readByte() != TC_CLASSDESC) {
            throw new InternalError();
        }

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

        ObjectStreamClass readDesc = null;
        try {
            //讀取類的說明
            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);
        final boolean checksRequired = isCustomSubclass();
        try {
            if ((cl = resolveClass(readDesc)) == null) {
                resolveEx = new ClassNotFoundException("null class");
            } else if (checksRequired) {
                ReflectUtil.checkPackageAccess(cl);
            }
        } catch (ClassNotFoundException ex) {
            resolveEx = ex;
        }

        // Call filterCheck on the class before reading anything else
        filterCheck(cl, -1);

        skipCustomData();

        try {
            totalObjectRefs++;
            depth++;
            desc.initNonProxy(readDesc, cl, resolveEx, readClassDesc(false));
        } finally {
            depth--;
        }

        handles.finish(descHandle);
        passHandle = descHandle;

        return desc;
    }

    protected ObjectStreamClass readClassDescriptor()
        throws IOException, ClassNotFoundException
    {
        ObjectStreamClass desc = new ObjectStreamClass();
        desc.readNonProxy(this);
        return desc;
    }

填充字段值

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 || handles.lookupException(passHandle) != null) {
                    defaultReadFields(null, slotDesc); // skip field values
                } else if (slotDesc.hasReadObjectMethod()) {
                    ThreadDeath t = null;
                    boolean reset = false;
                    SerialCallbackContext oldContext = curContext;
                    if (oldContext != null)
                        oldContext.check();
                    try {
                        curContext = new SerialCallbackContext(obj, slotDesc);

                        bin.setBlockDataMode(true);
                        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 {
                        do {
                            try {
                                curContext.setUsed();
                                if (oldContext!= null)
                                    oldContext.check();
                                curContext = oldContext;
                                reset = true;
                            } catch (ThreadDeath x) {
                                t = x;  // defer until reset is true
                            }
                        } while (!reset);
                        if (t != null)
                            throw t;
                    }

                    /*
                     * 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 {
                    //填充值
                    defaultReadFields(obj, slotDesc);
                    }

                if (slotDesc.hasWriteObjectData()) {
                    skipCustomData();
                } else {
                    bin.setBlockDataMode(false);
                }
            } else {
                if (obj != null &&
                    slotDesc.hasReadObjectNoDataMethod() &&
                    handles.lookupException(passHandle) == null)
                {
                    slotDesc.invokeReadObjectNoData(obj);
                }
            }
        }
            }


  private void defaultReadFields(Object obj, ObjectStreamClass desc)
        throws IOException
    {
        Class<?> cl = desc.forClass();
        if (cl != null && obj != null && !cl.isInstance(obj)) {
            throw new ClassCastException();
        }

        //獲取讀取數據長度
        int primDataSize = desc.getPrimDataSize();
        if (primVals == null || primVals.length < primDataSize) {
            primVals = new byte[primDataSize];
        }
        //讀取數據
            bin.readFully(primVals, 0, primDataSize, false);
        //賦值
        if (obj != null) {
            desc.setPrimFieldValues(obj, primVals);
        }

        int objHandle = passHandle;
        ObjectStreamField[] fields = desc.getFields(false);
        Object[] objVals = new Object[desc.getNumObjFields()];
        int numPrimFields = fields.length - objVals.length;
        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) {
            desc.setObjFieldValues(obj, objVals);
        }
        passHandle = objHandle;
    }

讀取類描述以及屬性

void readNonProxy(ObjectInputStream in)
        throws IOException, ClassNotFoundException
    {
        //獲取類全限定名
        name = in.readUTF();
        //讀取之後8個字節,獲取序列化id
        suid = Long.valueOf(in.readLong());
        isProxy = false;

        //0002:表示可序列化
        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);
        }

        //讀取2個字節,代表了類中域的個數
        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;
        //遍歷序列化字段
        for (int i = 0; i < numFields; i++) {
            //讀取字段類型
            char tcode = (char) in.readByte();
            //獲取字段名,內部會先讀取字段的長度,然後讀取長度的字節也就是字段名稱了
            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);
            }
        }
        computeFieldOffsets();
    }

ObjectOutputStream