java原生序列化中反序列化时，是如何创建对象的

看一下源代码

生成对象的

private Object readOrdinaryObject(boolean unshared)
        throws IOException
    {
       		...
            obj = desc.isInstantiable() ? desc.newInstance() : null;
       		...
        return obj;
    }


Object newInstance()
        throws InstantiationException, InvocationTargetException,
               UnsupportedOperationException
    {
        requireInitialized();
        if (cons != null) {
            try {
                return cons.newInstance();//走到这里 cons是对象obj所属类父类class java.lang.Object的无参构造函数
            } catch (IllegalAccessException ex) {
                // should not occur, as access checks have been suppressed
                throw new InternalError(ex);
            }
        } else {
            throw new UnsupportedOperationException();
        }
    }

生成构造函数cons源码如下

private Object readOrdinaryObject(boolean unshared)
        throws IOException
    {
    		...
      		ObjectStreamClass desc = readClassDesc(false);//这里
       		...
            obj = desc.isInstantiable() ? desc.newInstance() : null;
       		...
        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_CLASSDESC:
                descriptor = readNonProxyDesc(unshared);// 走到这里
                break;
            default:
                throw new StreamCorruptedException(
                    String.format("invalid type code: %02X", tc));
        }
        if (descriptor != null) {
            validateDescriptor(descriptor);
        }
        return descriptor;
    }

private ObjectStreamClass readNonProxyDesc(boolean unshared)
        throws IOException
    {
       ......
        desc.initNonProxy(readDesc, cl, resolveEx, readClassDesc(false));
       ......
        return desc;
    }

void initNonProxy(ObjectStreamClass model,
                      Class<?> cl,
                      ClassNotFoundException resolveEx,
                      ObjectStreamClass superDesc)
        throws InvalidClassException
    {
       .......
        if (cl != null) {
            osc = lookup(cl, true);
       ......
    }

static ObjectStreamClass lookup(Class<?> cl, boolean all) {
      	......
        if (entry == null) {
           ......
                entry = new ObjectStreamClass(cl);
           ......
        }
    }

 private ObjectStreamClass(final Class<?> cl) {
        this.cl = cl;
        name = cl.getName();
        isProxy = Proxy.isProxyClass(cl);
        isEnum = Enum.class.isAssignableFrom(cl);
        serializable = Serializable.class.isAssignableFrom(cl);
        externalizable = Externalizable.class.isAssignableFrom(cl);

        Class<?> superCl = cl.getSuperclass();
        superDesc = (superCl != null) ? lookup(superCl, false) : null;
        localDesc = this;

        if (serializable) {
            AccessController.doPrivileged(new PrivilegedAction<Void>() {
                public Void run() {
                    if (isEnum) {
                        suid = Long.valueOf(0);
                        fields = NO_FIELDS;
                        return null;
                    }
                    if (cl.isArray()) {
                        fields = NO_FIELDS;
                        return null;
                    }

                    suid = getDeclaredSUID(cl);
                    try {
                        fields = getSerialFields(cl);
                        computeFieldOffsets();
                    } catch (InvalidClassException e) {
                        serializeEx = deserializeEx =
                            new ExceptionInfo(e.classname, e.getMessage());
                        fields = NO_FIELDS;
                    }

                    if (externalizable) {
                        cons = getExternalizableConstructor(cl);
                    } else {
                        cons = getSerializableConstructor(cl);//这里是重点，真正的获取构造函数的地方
                        writeObjectMethod = getPrivateMethod(cl, "writeObject",
                            new Class<?>[] { ObjectOutputStream.class },
                            Void.TYPE);
                        readObjectMethod = getPrivateMethod(cl, "readObject",
                            new Class<?>[] { ObjectInputStream.class },
                            Void.TYPE);
                        readObjectNoDataMethod = getPrivateMethod(
                            cl, "readObjectNoData", null, Void.TYPE);
                        hasWriteObjectData = (writeObjectMethod != null);
                    }
                    writeReplaceMethod = getInheritableMethod(
                        cl, "writeReplace", null, Object.class);
                    readResolveMethod = getInheritableMethod(
                        cl, "readResolve", null, Object.class);
                    return null;
                }
            });
        } else {
            suid = Long.valueOf(0);
            fields = NO_FIELDS;
        }

        try {
            fieldRefl = getReflector(fields, this);
        } catch (InvalidClassException ex) {
            // field mismatches impossible when matching local fields vs. self
            throw new InternalError(ex);
        }

        if (deserializeEx == null) {
            if (isEnum) {
                deserializeEx = new ExceptionInfo(name, "enum type");
            } else if (cons == null) {
                deserializeEx = new ExceptionInfo(name, "no valid constructor");
            }
        }
        for (int i = 0; i < fields.length; i++) {
            if (fields[i].getField() == null) {
                defaultSerializeEx = new ExceptionInfo(
                    name, "unmatched serializable field(s) declared");
            }
        }
        initialized = true;
    }

//获取构造函数
 private static Constructor<?> getSerializableConstructor(Class<?> cl) {
        Class<?> initCl = cl;
        while (Serializable.class.isAssignableFrom(initCl)) {
            if ((initCl = initCl.getSuperclass()) == null) { // 看这里，获取的是基类的构造函数
                return null;
            }
        }
        try {
            Constructor<?> cons = initCl.getDeclaredConstructor((Class<?>[]) null);
            int mods = cons.getModifiers();
            if ((mods & Modifier.PRIVATE) != 0 ||
                ((mods & (Modifier.PUBLIC | Modifier.PROTECTED)) == 0 &&
                 !packageEquals(cl, initCl)))
            {
                return null;
            }
            cons = reflFactory.newConstructorForSerialization(cl, cons);
            cons.setAccessible(true);
            return cons;
        } catch (NoSuchMethodException ex) {
            return null;
        }
    }