java.io
Class ObjectInputStream

java.lang.Object
  java.io.InputStream
      java.io.ObjectInputStream

All Implemented Interfaces:

DataInput, ObjectInput, ObjectStreamConstants

Direct Known Subclasses:

sun.rmi.server.MarshalInputStream

public class ObjectInputStream

extends InputStream

implements ObjectInput, ObjectStreamConstants

An ObjectInputStream deserializes primitive data and objects previously written using an ObjectOutputStream.

ObjectOutputStream and ObjectInputStream can provide an application with persistent storage for graphs of objects when used with a FileOutputStream and FileInputStream respectively. ObjectInputStream is used to recover those objects previously serialized. Other uses include passing objects between hosts using a socket stream or for marshaling and unmarshaling arguments and parameters in a remote communication system.

ObjectInputStream ensures that the types of all objects in the graph created from the stream match the classes present in the Java Virtual Machine. Classes are loaded as required using the standard mechanisms.

Only objects that support the java.io.Serializable or java.io.Externalizable interface can be read from streams.

The method readObject is used to read an object from the stream. Java's safe casting should be used to get the desired type. In Java, strings and arrays are objects and are treated as objects during serialization. When read they need to be cast to the expected type.

Primitive data types can be read from the stream using the appropriate method on DataInput.

The default deserialization mechanism for objects restores the contents of each field to the value and type it had when it was written. Fields declared as transient or static are ignored by the deserialization process. References to other objects cause those objects to be read from the stream as necessary. Graphs of objects are restored correctly using a reference sharing mechanism. New objects are always allocated when deserializing, which prevents existing objects from being overwritten.

Reading an object is analogous to running the constructors of a new object. Memory is allocated for the object and initialized to zero (NULL). No-arg constructors are invoked for the non-serializable classes and then the fields of the serializable classes are restored from the stream starting with the serializable class closest to java.lang.object and finishing with the object's most specific class.

For example to read from a stream as written by the example in ObjectOutputStream:

	FileInputStream fis = new FileInputStream("t.tmp");
	ObjectInputStream ois = new ObjectInputStream(fis);

	int i = ois.readInt();
	String today = (String) ois.readObject();
	Date date = (Date) ois.readObject();

	ois.close();
 

Classes control how they are serialized by implementing either the java.io.Serializable or java.io.Externalizable interfaces.

Implementing the Serializable interface allows object serialization to save and restore the entire state of the object and it allows classes to evolve between the time the stream is written and the time it is read. It automatically traverses references between objects, saving and restoring entire graphs.

Serializable classes that require special handling during the serialization and deserialization process should implement the following methods:

 private void writeObject(java.io.ObjectOutputStream stream)
     throws IOException;
 private void readObject(java.io.ObjectInputStream stream)
     throws IOException, ClassNotFoundException; 
 private void readObjectNoData() 
     throws ObjectStreamException;
 

The readObject method is responsible for reading and restoring the state of the object for its particular class using data written to the stream by the corresponding writeObject method. The method does not need to concern itself with the state belonging to its superclasses or subclasses. State is restored by reading data from the ObjectInputStream for the individual fields and making assignments to the appropriate fields of the object. Reading primitive data types is supported by DataInput.

Any attempt to read object data which exceeds the boundaries of the custom data written by the corresponding writeObject method will cause an OptionalDataException to be thrown with an eof field value of true. Non-object reads which exceed the end of the allotted data will reflect the end of data in the same way that they would indicate the end of the stream: bytewise reads will return -1 as the byte read or number of bytes read, and primitive reads will throw EOFExceptions. If there is no corresponding writeObject method, then the end of default serialized data marks the end of the allotted data.

Primitive and object read calls issued from within a readExternal method behave in the same manner--if the stream is already positioned at the end of data written by the corresponding writeExternal method, object reads will throw OptionalDataExceptions with eof set to true, bytewise reads will return -1, and primitive reads will throw EOFExceptions. Note that this behavior does not hold for streams written with the old ObjectStreamConstants.PROTOCOL_VERSION_1 protocol, in which the end of data written by writeExternal methods is not demarcated, and hence cannot be detected.

The readObjectNoData method is responsible for initializing the state of the object for its particular class in the event that the serialization stream does not list the given class as a superclass of the object being deserialized. This may occur in cases where the receiving party uses a different version of the deserialized instance's class than the sending party, and the receiver's version extends classes that are not extended by the sender's version. This may also occur if the serialization stream has been tampered; hence, readObjectNoData is useful for initializing deserialized objects properly despite a "hostile" or incomplete source stream.

Serialization does not read or assign values to the fields of any object that does not implement the java.io.Serializable interface. Subclasses of Objects that are not serializable can be serializable. In this case the non-serializable class must have a no-arg constructor to allow its fields to be initialized. In this case it is the responsibility of the subclass to save and restore the state of the non-serializable class. It is frequently the case that the fields of that class are accessible (public, package, or protected) or that there are get and set methods that can be used to restore the state.

Any exception that occurs while deserializing an object will be caught by the ObjectInputStream and abort the reading process.

Implementing the Externalizable interface allows the object to assume complete control over the contents and format of the object's serialized form. The methods of the Externalizable interface, writeExternal and readExternal, are called to save and restore the objects state. When implemented by a class they can write and read their own state using all of the methods of ObjectOutput and ObjectInput. It is the responsibility of the objects to handle any versioning that occurs.

Since:

JDK1.1

Author:

Mike Warres, Roger Riggs

See Also:

DataInput, ObjectOutputStream, Serializable, Object Serialization Specification, Section 3, Object Input Classes

Nested Class Summary

private class	ObjectInputStream.BlockDataInputStream Input stream with two modes: in default mode, inputs data written in the same format as DataOutputStream; in "block data" mode, inputs data bracketed by block data markers (see object serialization specification for details).
static class	ObjectInputStream.GetField Provide access to the persistent fields read from the input stream.
private class	ObjectInputStream.GetFieldImpl Default GetField implementation.
private static class	ObjectInputStream.HandleTable Unsynchronized table which tracks wire handle to object mappings, as well as ClassNotFoundExceptions associated with deserialized objects.
private static class	ObjectInputStream.PeekInputStream Input stream supporting single-byte peek operations.
private static class	ObjectInputStream.ValidationList Prioritized list of callbacks to be performed once object graph has been completely deserialized.

Field Summary

private ObjectInputStream.BlockDataInputStream	bin filter stream for handling block data conversion
private boolean	closed whether stream is closed
private ObjectStreamClass	curDesc descriptor for current class (null if in readExternal())
private ObjectInputStream.GetFieldImpl	curGet current GetField object
private Object	curObj object currently being deserialized
private boolean	defaultDataEnd flag set when at end of field value block with no TC_ENDBLOCKDATA
private int	depth recursion depth
private boolean	enableOverride if true, invoke readObjectOverride() instead of readObject()
private boolean	enableResolve if true, invoke resolveObject()
private ObjectInputStream.HandleTable	handles wire handle -> obj/exception map
private static int	NULL_HANDLE handle value representing null
private int	passHandle scratch field for passing handle values up/down call stack
private static HashMap	primClasses table mapping primitive type names to corresponding class objects
private byte[]	primVals buffer for reading primitive field values
private static sun.misc.SoftCache	subclassAudits cache of subclass security audit results
private static Object	unsharedMarker marker for unshared objects in internal handle table
private ObjectInputStream.ValidationList	vlist validation callback list

Fields inherited from class java.io.InputStream

Fields inherited from interface java.io.ObjectStreamConstants

baseWireHandle, PROTOCOL_VERSION_1, PROTOCOL_VERSION_2, SC_BLOCK_DATA, SC_EXTERNALIZABLE, SC_SERIALIZABLE, SC_WRITE_METHOD, STREAM_MAGIC, STREAM_VERSION, SUBCLASS_IMPLEMENTATION_PERMISSION, SUBSTITUTION_PERMISSION, TC_ARRAY, TC_BASE, TC_BLOCKDATA, TC_BLOCKDATALONG, TC_CLASS, TC_CLASSDESC, TC_ENDBLOCKDATA, TC_EXCEPTION, TC_LONGSTRING, TC_MAX, TC_NULL, TC_OBJECT, TC_PROXYCLASSDESC, TC_REFERENCE, TC_RESET, TC_STRING

Constructor Summary

protected	ObjectInputStream() Provide a way for subclasses that are completely reimplementing ObjectInputStream to not have to allocate private data just used by this implementation of ObjectInputStream.
	ObjectInputStream(InputStream in) Creates an ObjectInputStream that reads from the specified InputStream.

Method Summary

private static boolean	auditSubclass(Class subcl) Performs reflective checks on given subclass to verify that it doesn't override security-sensitive non-final methods.
int	available() Returns the number of bytes that can be read without blocking.
private static void	bytesToDoubles(byte[] src, int srcpos, double[] dst, int dstpos, int ndoubles) Converts specified span of bytes into double values.
private static void	bytesToFloats(byte[] src, int srcpos, float[] dst, int dstpos, int nfloats) Converts specified span of bytes into float values.
private Object	checkResolve(Object obj) If resolveObject has been enabled and given object does not have an exception associated with it, calls resolveObject to determine replacement for object, and updates handle table accordingly.
private void	clear() Clears internal data structures.
void	close() Closes the input stream.
private void	defaultReadFields(Object obj, ObjectStreamClass desc) Reads in values of serializable fields declared by given class descriptor.
void	defaultReadObject() Read the non-static and non-transient fields of the current class from this stream.
protected boolean	enableResolveObject(boolean enable) Enable the stream to allow objects read from the stream to be replaced.
private void	handleReset() If recursion depth is 0, clears internal data structures; otherwise, throws a StreamCorruptedException.
private static ClassLoader	latestUserDefinedLoader() Returns the first non-null class loader (not counting class loaders of generated reflection implementation classes) up the execution stack, or null if only code from the null class loader is on the stack.
int	read() Reads a byte of data.
int	read(byte[] buf, int off, int len) Reads into an array of bytes.
private Object	readArray(boolean unshared) Reads in and returns array object, or null if array class is unresolvable.
boolean	readBoolean() Reads in a boolean.
byte	readByte() Reads an 8 bit byte.
char	readChar() Reads a 16 bit char.
private Class	readClass(boolean unshared) Reads in and returns class object.
private ObjectStreamClass	readClassDesc(boolean unshared) Reads in and returns (possibly null) class descriptor.
protected ObjectStreamClass	readClassDescriptor() Read a class descriptor from the serialization stream.
double	readDouble() Reads a 64 bit double.
private void	readExternalData(Externalizable obj, ObjectStreamClass desc) If obj is non-null, reads externalizable data by invoking readExternal() method of obj; otherwise, attempts to skip over externalizable data.
private IOException	readFatalException() Reads in and returns IOException that caused serialization to abort.
ObjectInputStream.GetField	readFields() Reads the persistent fields from the stream and makes them available by name.
float	readFloat() Reads a 32 bit float.
void	readFully(byte[] buf) Reads bytes, blocking until all bytes are read.
void	readFully(byte[] buf, int off, int len) Reads bytes, blocking until all bytes are read.
private Object	readHandle(boolean unshared) Reads in object handle, sets passHandle to the read handle, and returns object associated with the handle.
int	readInt() Reads a 32 bit int.
String	readLine() Deprecated. This method does not properly convert bytes to characters. see DataInputStream for the details and alternatives.
long	readLong() Reads a 64 bit long.
private ObjectStreamClass	readNonProxyDesc(boolean unshared) Reads in and returns class descriptor for a class that is not a dynamic proxy class.
private Object	readNull() Reads in null code, sets passHandle to NULL_HANDLE and returns null.
Object	readObject() Read an object from the ObjectInputStream.
private Object	readObject0(boolean unshared) Underlying readObject implementation.
protected Object	readObjectOverride() This method is called by trusted subclasses of ObjectOutputStream that constructed ObjectOutputStream using the protected no-arg constructor.
private Object	readOrdinaryObject(boolean unshared) Reads and returns "ordinary" (i.e., not a String, Class, ObjectStreamClass or array) object, or null if object's class is unresolvable (in which case a ClassNotFoundException will be associated with object's handle).
private ObjectStreamClass	readProxyDesc(boolean unshared) Reads in and returns class descriptor for a dynamic proxy class.
private void	readSerialData(Object obj, ObjectStreamClass 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.
short	readShort() Reads a 16 bit short.
protected void	readStreamHeader() The readStreamHeader method is provided to allow subclasses to read and verify their own stream headers.
private String	readString(boolean unshared) Reads in and returns new string.
(package private) String	readTypeString() Reads string without allowing it to be replaced in stream.
Object	readUnshared() Reads an "unshared" object from the ObjectInputStream.
int	readUnsignedByte() Reads an unsigned 8 bit byte.
int	readUnsignedShort() Reads an unsigned 16 bit short.
String	readUTF() Reads a UTF format String.
void	registerValidation(ObjectInputValidation obj, int prio) Register an object to be validated before the graph is returned.
protected Class	resolveClass(ObjectStreamClass desc) Load the local class equivalent of the specified stream class description.
protected Object	resolveObject(Object obj) This method will allow trusted subclasses of ObjectInputStream to substitute one object for another during deserialization.
protected Class	resolveProxyClass(String[] interfaces) Returns a proxy class that implements the interfaces named in a proxy class descriptor; subclasses may implement this method to read custom data from the stream along with the descriptors for dynamic proxy classes, allowing them to use an alternate loading mechanism for the interfaces and the proxy class.
int	skipBytes(int len) Skips bytes, block until all bytes are skipped.
private void	skipCustomData() Skips over all block data and objects until TC_ENDBLOCKDATA is encountered.
private void	verifySubclass() Verifies that this (possibly subclass) instance can be constructed without violating security constraints: the subclass must not override security-sensitive non-final methods, or else the "enableSubclassImplementation" SerializablePermission is checked.

Methods inherited from class java.io.InputStream

mark, markSupported, read, reset, skip

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.io.ObjectInput

read, skip

Field Detail

NULL_HANDLE

private static final int NULL_HANDLE

handle value representing null

See Also:

Constant Field Values

unsharedMarker

private static final Object unsharedMarker

marker for unshared objects in internal handle table

primClasses

private static final HashMap primClasses

table mapping primitive type names to corresponding class objects

subclassAudits

private static final sun.misc.SoftCache subclassAudits

cache of subclass security audit results

bin

private final ObjectInputStream.BlockDataInputStream bin

filter stream for handling block data conversion

vlist

private final ObjectInputStream.ValidationList vlist

validation callback list

depth

private int depth

recursion depth

closed

private boolean closed

whether stream is closed

handles

private final ObjectInputStream.HandleTable handles

wire handle -> obj/exception map

passHandle

private int passHandle

scratch field for passing handle values up/down call stack

defaultDataEnd

private boolean defaultDataEnd

flag set when at end of field value block with no TC_ENDBLOCKDATA

primVals

private byte[] primVals

buffer for reading primitive field values

enableOverride

private final boolean enableOverride

if true, invoke readObjectOverride() instead of readObject()

enableResolve

private boolean enableResolve

if true, invoke resolveObject()

curObj

private Object curObj

object currently being deserialized

curDesc

private ObjectStreamClass curDesc

descriptor for current class (null if in readExternal())

curGet

private ObjectInputStream.GetFieldImpl curGet

current GetField object

Constructor Detail

ObjectInputStream

public ObjectInputStream(InputStream in)
                  throws IOException

Creates an ObjectInputStream that reads from the specified InputStream. A serialization stream header is read from the stream and verified. This constructor will block until the corresponding ObjectOutputStream has written and flushed the header.

If a security manager is installed, this constructor will check for the "enableSubclassImplementation" SerializablePermission when invoked directly or indirectly by the constructor of a subclass which overrides the ObjectInputStream.readFields or ObjectInputStream.readUnshared methods.

Parameters:

in - input stream to read from

Throws:

StreamCorruptedException - if the stream header is incorrect

IOException - if an I/O error occurs while reading stream header

SecurityException - if untrusted subclass illegally overrides security-sensitive methods

NullPointerException - if in is null

See Also:

ObjectInputStream(), readFields(), ObjectOutputStream.ObjectOutputStream(OutputStream)

ObjectInputStream

protected ObjectInputStream()
                     throws IOException,
                            SecurityException

Provide a way for subclasses that are completely reimplementing ObjectInputStream to not have to allocate private data just used by this implementation of ObjectInputStream.

If there is a security manager installed, this method first calls the security manager's checkPermission method with the SerializablePermission("enableSubclassImplementation") permission to ensure it's ok to enable subclassing.

Throws:

SecurityException - if a security manager exists and its checkPermission method denies enabling subclassing.

IOException

See Also:

SecurityManager.checkPermission(java.security.Permission), SerializablePermission

Method Detail

readObject

public final Object readObject()
                        throws IOException,
                               ClassNotFoundException

Read an object from the ObjectInputStream. The class of the object, the signature of the class, and the values of the non-transient and non-static fields of the class and all of its supertypes are read. Default deserializing for a class can be overriden using the writeObject and readObject methods. Objects referenced by this object are read transitively so that a complete equivalent graph of objects is reconstructed by readObject.

The root object is completly restored when all of its fields and the objects it references are completely restored. At this point the object validation callbacks are executed in order based on their registered priorities. The callbacks are registered by objects (in the readObject special methods) as they are individually restored.

Exceptions are thrown for problems with the InputStream and for classes that should not be deserialized. All exceptions are fatal to the InputStream and leave it in an indeterminate state; it is up to the caller to ignore or recover the stream state.

Specified by:

readObject in interface ObjectInput

Returns:

the object read from the stream

Throws:

ClassNotFoundException - Class of a serialized object cannot be found.

InvalidClassException - Something is wrong with a class used by serialization.

StreamCorruptedException - Control information in the stream is inconsistent.

OptionalDataException - Primitive data was found in the stream instead of objects.

IOException - Any of the usual Input/Output related exceptions.

readObjectOverride

protected Object readObjectOverride()
                             throws IOException,
                                    ClassNotFoundException

This method is called by trusted subclasses of ObjectOutputStream that constructed ObjectOutputStream using the protected no-arg constructor. The subclass is expected to provide an override method with the modifier "final".

Returns:

the Object read from the stream.

Throws:

ClassNotFoundException - Class definition of a serialized object cannot be found.

OptionalDataException - Primitive data was found in the stream instead of objects.

IOException - if I/O errors occurred while reading from the underlying stream

Since:

1.2

See Also:

ObjectInputStream(), readObject()

readUnshared

public Object readUnshared()
                    throws IOException,
                           ClassNotFoundException

Reads an "unshared" object from the ObjectInputStream. This method is identical to readObject, except that it prevents subsequent calls to readObject and readUnshared from returning additional references to the deserialized instance obtained via this call. Specifically:

• If readUnshared is called to deserialize a back-reference (the stream representation of an object which has been written previously to the stream), an ObjectStreamException will be thrown.
• If readUnshared returns successfully, then any subsequent attempts to deserialize back-references to the stream handle deserialized by readUnshared will cause an ObjectStreamException to be thrown.

Deserializing an object via readUnshared invalidates the stream handle associated with the returned object. Note that this in itself does not always guarantee that the reference returned by readUnshared is unique; the deserialized object may define a readResolve method which returns an object visible to other parties, or readUnshared may return a Class object obtainable elsewhere in the stream or through external means.

However, for objects which are not instances of java.lang.Class and do not define readResolve methods, readUnshared guarantees that the returned object reference is unique and cannot be obtained a second time from the ObjectInputStream that created it, even if the underlying data stream has been manipulated. This guarantee applies only to the base-level object returned by readUnshared, and not to any transitively referenced sub-objects in the returned object graph.

ObjectInputStream subclasses which override this method can only be constructed in security contexts possessing the "enableSubclassImplementation" SerializablePermission; any attempt to instantiate such a subclass without this permission will cause a SecurityException to be thrown.

Returns:

reference to deserialized object

Throws:

ClassNotFoundException - if class of an object to deserialize cannot be found

StreamCorruptedException - if control information in the stream is inconsistent

ObjectStreamException - if object to deserialize has already appeared in stream

OptionalDataException - if primitive data is next in stream

IOException - if an I/O error occurs during deserialization

defaultReadObject

public void defaultReadObject()
                       throws IOException,
                              ClassNotFoundException

Read the non-static and non-transient fields of the current class from this stream. This may only be called from the readObject method of the class being deserialized. It will throw the NotActiveException if it is called otherwise.

Throws:

ClassNotFoundException - if the class of a serialized object could not be found.

IOException - if an I/O error occurs.

NotActiveException - if the stream is not currently reading objects.

readFields

public ObjectInputStream.GetField readFields()
                                      throws IOException,
                                             ClassNotFoundException

Reads the persistent fields from the stream and makes them available by name.

Returns:

the GetField object representing the persistent fields of the object being deserialized

Throws:

ClassNotFoundException - if the class of a serialized object could not be found.

IOException - if an I/O error occurs.

NotActiveException - if the stream is not currently reading objects.

Since:

1.2

registerValidation

public void registerValidation(ObjectInputValidation obj,
                               int prio)
                        throws NotActiveException,
                               InvalidObjectException

Register an object to be validated before the graph is returned. While similar to resolveObject these validations are called after the entire graph has been reconstituted. Typically, a readObject method will register the object with the stream so that when all of the objects are restored a final set of validations can be performed.

Parameters:

obj - the object to receive the validation callback.

prio - controls the order of callbacks;zero is a good default. Use higher numbers to be called back earlier, lower numbers for later callbacks. Within a priority, callbacks are processed in no particular order.

Throws:

NotActiveException - The stream is not currently reading objects so it is invalid to register a callback.

InvalidObjectException - The validation object is null.

resolveClass

protected Class resolveClass(ObjectStreamClass desc)
                      throws IOException,
                             ClassNotFoundException

Load the local class equivalent of the specified stream class description. Subclasses may implement this method to allow classes to be fetched from an alternate source.

The corresponding method in ObjectOutputStream is annotateClass. This method will be invoked only once for each unique class in the stream. This method can be implemented by subclasses to use an alternate loading mechanism but must return a Class object. Once returned, the serialVersionUID of the class is compared to the serialVersionUID of the serialized class. If there is a mismatch, the deserialization fails and an exception is raised.

By default the class name is resolved relative to the class that called readObject.

Parameters:

desc - an instance of class ObjectStreamClass

Returns:

a Class object corresponding to desc

Throws:

IOException - any of the usual input/output exceptions

ClassNotFoundException - if class of a serialized object cannot be found

resolveProxyClass

protected Class resolveProxyClass(String[] interfaces)
                           throws IOException,
                                  ClassNotFoundException

Returns a proxy class that implements the interfaces named in a proxy class descriptor; subclasses may implement this method to read custom data from the stream along with the descriptors for dynamic proxy classes, allowing them to use an alternate loading mechanism for the interfaces and the proxy class.

This method is called exactly once for each unique proxy class descriptor in the stream.

The corresponding method in ObjectOutputStream is annotateProxyClass. For a given subclass of ObjectInputStream that overrides this method, the annotateProxyClass method in the corresponding subclass of ObjectOutputStream must write any data or objects read by this method.

The default implementation of this method in ObjectInputStream returns the result of calling Proxy.getProxyClass with the list of Class objects for the interfaces that are named in the interfaces parameter. The Class object for each interface name i is the value returned by calling

     Class.forName(i, false, loader)
 

where loader is that of the first non-null class loader up the execution stack, or null if no non-null class loaders are on the stack (the same class loader choice used by the resolveClass method). Unless any of the resolved interfaces are non-public, this same value of loader is also the class loader passed to Proxy.getProxyClass; if non-public interfaces are present, their class loader is passed instead (if more than one non-public interface class loader is encountered, an IllegalAccessError is thrown). If Proxy.getProxyClass throws an IllegalArgumentException, resolveProxyClass will throw a ClassNotFoundException containing the IllegalArgumentException.

Parameters:

interfaces - the list of interface names that were deserialized in the proxy class descriptor

Returns:

a proxy class for the specified interfaces

Throws:

IOException - any exception thrown by the underlying InputStream

ClassNotFoundException - if the proxy class or any of the named interfaces could not be found

Since:

1.3

See Also:

ObjectOutputStream.annotateProxyClass(Class)

resolveObject

protected Object resolveObject(Object obj)
                        throws IOException

This method will allow trusted subclasses of ObjectInputStream to substitute one object for another during deserialization. Replacing objects is disabled until enableResolveObject is called. The enableResolveObject method checks that the stream requesting to resolve object can be trusted. Every reference to serializable objects is passed to resolveObject. To insure that the private state of objects is not unintentionally exposed only trusted streams may use resolveObject.

This method is called after an object has been read but before it is returned from readObject. The default resolveObject method just returns the same object.

When a subclass is replacing objects it must insure that the substituted object is compatible with every field where the reference will be stored. Objects whose type is not a subclass of the type of the field or array element abort the serialization by raising an exception and the object is not be stored.

This method is called only once when each object is first encountered. All subsequent references to the object will be redirected to the new object.

Parameters:

obj - object to be substituted

Returns:

the substituted object

Throws:

IOException - Any of the usual Input/Output exceptions.

enableResolveObject

protected boolean enableResolveObject(boolean enable)
                               throws SecurityException

Enable the stream to allow objects read from the stream to be replaced. When enabled, the resolveObject method is called for every object being deserialized.

If enable is true, and there is a security manager installed, this method first calls the security manager's checkPermission method with the SerializablePermission("enableSubstitution") permission to ensure it's ok to enable the stream to allow objects read from the stream to be replaced.

Parameters:

enable - true for enabling use of resolveObject for every object being deserialized

Returns:

the previous setting before this method was invoked

Throws:

SecurityException - if a security manager exists and its checkPermission method denies enabling the stream to allow objects read from the stream to be replaced.

See Also:

SecurityManager.checkPermission(java.security.Permission), SerializablePermission

readStreamHeader

protected void readStreamHeader()
                         throws IOException,
                                StreamCorruptedException

The readStreamHeader method is provided to allow subclasses to read and verify their own stream headers. It reads and verifies the magic number and version number.

Throws:

IOException - if there are I/O errors while reading from the underlying InputStream

StreamCorruptedException - if control information in the stream is inconsistent

readClassDescriptor

protected ObjectStreamClass readClassDescriptor()
                                         throws IOException,
                                                ClassNotFoundException

Read a class descriptor from the serialization stream. This method is called when the ObjectInputStream expects a class descriptor as the next item in the serialization stream. Subclasses of ObjectInputStream may override this method to read in class descriptors that have been written in non-standard formats (by subclasses of ObjectOutputStream which have overridden the writeClassDescriptor method). By default, this method reads class descriptors according to the format defined in the Object Serialization specification.

Returns:

the class descriptor read

Throws:

IOException - If an I/O error has occurred.

ClassNotFoundException - If the Class of a serialized object used in the class descriptor representation cannot be found

Since:

1.3

See Also:

ObjectOutputStream.writeClassDescriptor(java.io.ObjectStreamClass)

read

public int read()
         throws IOException

Reads a byte of data. This method will block if no input is available.

Specified by:

read in interface ObjectInput

Specified by:

read in class InputStream

Returns:

the byte read, or -1 if the end of the stream is reached.

Throws:

IOException - If an I/O error has occurred.

read

public int read(byte[] buf,
                int off,
                int len)
         throws IOException

Reads into an array of bytes. This method will block until some input is available. Consider using java.io.DataInputStream.readFully to read exactly 'length' bytes.

Specified by:

read in interface ObjectInput

Overrides:

read in class InputStream

Parameters:

buf - the buffer into which the data is read

off - the start offset of the data

len - the maximum number of bytes read

Returns:

the actual number of bytes read, -1 is returned when the end of the stream is reached.

Throws:

IOException - If an I/O error has occurred.

See Also:

DataInputStream.readFully(byte[],int,int)

available

public int available()
              throws IOException

Returns the number of bytes that can be read without blocking.

Specified by:

available in interface ObjectInput

Overrides:

available in class InputStream

Returns:

the number of available bytes.

Throws:

IOException - if there are I/O errors while reading from the underlying InputStream

close

public void close()
           throws IOException

Closes the input stream. Must be called to release any resources associated with the stream.

Specified by:

close in interface ObjectInput

Overrides:

close in class InputStream

Throws:

IOException - If an I/O error has occurred.

readBoolean

public boolean readBoolean()
                    throws IOException

Reads in a boolean.

Specified by:

readBoolean in interface DataInput

Returns:

the boolean read.

Throws:

EOFException - If end of file is reached.

IOException - If other I/O error has occurred.

readByte

public byte readByte()
              throws IOException

Reads an 8 bit byte.

Specified by:

readByte in interface DataInput

Returns:

the 8 bit byte read.

Throws:

EOFException - If end of file is reached.

IOException - If other I/O error has occurred.

readUnsignedByte

public int readUnsignedByte()
                     throws IOException

Reads an unsigned 8 bit byte.

Specified by:

readUnsignedByte in interface DataInput

Returns:

the 8 bit byte read.

Throws:

EOFException - If end of file is reached.

IOException - If other I/O error has occurred.

readChar

public char readChar()
              throws IOException

Reads a 16 bit char.

Specified by:

readChar in interface DataInput

Returns:

the 16 bit char read.

Throws:

EOFException - If end of file is reached.

IOException - If other I/O error has occurred.

readShort

public short readShort()
                throws IOException

Reads a 16 bit short.

Specified by:

readShort in interface DataInput

Returns:

the 16 bit short read.

Throws:

EOFException - If end of file is reached.

IOException - If other I/O error has occurred.

readUnsignedShort

public int readUnsignedShort()
                      throws IOException

Reads an unsigned 16 bit short.

Specified by:

readUnsignedShort in interface DataInput

Returns:

the 16 bit short read.

Throws:

EOFException - If end of file is reached.

IOException - If other I/O error has occurred.

readInt

public int readInt()
            throws IOException

Reads a 32 bit int.

Specified by:

readInt in interface DataInput

Returns:

the 32 bit integer read.

Throws:

EOFException - If end of file is reached.

IOException - If other I/O error has occurred.

readLong

public long readLong()
              throws IOException

Reads a 64 bit long.

Specified by:

readLong in interface DataInput

Returns:

the read 64 bit long.

Throws:

EOFException - If end of file is reached.

IOException - If other I/O error has occurred.

readFloat

public float readFloat()
                throws IOException

Reads a 32 bit float.

Specified by:

readFloat in interface DataInput

Returns:

the 32 bit float read.

Throws:

EOFException - If end of file is reached.

IOException - If other I/O error has occurred.

readDouble

public double readDouble()
                  throws IOException

Reads a 64 bit double.

Specified by:

readDouble in interface DataInput

Returns:

the 64 bit double read.

Throws:

EOFException - If end of file is reached.

IOException - If other I/O error has occurred.

readFully

public void readFully(byte[] buf)
               throws IOException

Reads bytes, blocking until all bytes are read.

Specified by:

readFully in interface DataInput

Parameters:

buf - the buffer into which the data is read

Throws:

EOFException - If end of file is reached.

IOException - If other I/O error has occurred.

readFully

public void readFully(byte[] buf,
                      int off,
                      int len)
               throws IOException

Reads bytes, blocking until all bytes are read.

Specified by:

readFully in interface DataInput

Parameters:

buf - the buffer into which the data is read

off - the start offset of the data

len - the maximum number of bytes to read

Throws:

EOFException - If end of file is reached.

IOException - If other I/O error has occurred.

skipBytes

public int skipBytes(int len)
              throws IOException

Skips bytes, block until all bytes are skipped.

Specified by:

skipBytes in interface DataInput

Parameters:

len - the number of bytes to be skipped

Returns:

the actual number of bytes skipped.

Throws:

EOFException - If end of file is reached.

IOException - If other I/O error has occurred.

readLine

public String readLine()
                throws IOException

Deprecated. This method does not properly convert bytes to characters. see DataInputStream for the details and alternatives.

Reads in a line that has been terminated by a \n, \r, \r\n or EOF.

Specified by:

readLine in interface DataInput

Returns:

a String copy of the line.

Throws:

IOException - if there are I/O errors while reading from the underlying InputStream

readUTF

public String readUTF()
               throws IOException

Reads a UTF format String.

Specified by:

readUTF in interface DataInput

Returns:

the String.

Throws:

IOException - if there are I/O errors while reading from the underlying InputStream

UTFDataFormatException - if read bytes do not represent a valid UTF-8 encoding of a string

verifySubclass

private void verifySubclass()

Verifies that this (possibly subclass) instance can be constructed without violating security constraints: the subclass must not override security-sensitive non-final methods, or else the "enableSubclassImplementation" SerializablePermission is checked.

auditSubclass

private static boolean auditSubclass(Class subcl)

Performs reflective checks on given subclass to verify that it doesn't override security-sensitive non-final methods. Returns true if subclass is "safe", false otherwise.

clear

private void clear()

Clears internal data structures.

readObject0

private Object readObject0(boolean unshared)
                    throws IOException

Underlying readObject implementation.

Throws:

IOException

checkResolve

private Object checkResolve(Object obj)
                     throws IOException

If resolveObject has been enabled and given object does not have an exception associated with it, calls resolveObject to determine replacement for object, and updates handle table accordingly. Returns replacement object, or echoes provided object if no replacement occurred. Expects that passHandle is set to given object's handle prior to calling this method.

Throws:

IOException

readTypeString

String readTypeString()
                throws IOException

Reads string without allowing it to be replaced in stream. Called from within ObjectStreamClass.read().

Throws:

IOException

readNull

private Object readNull()
                 throws IOException

Reads in null code, sets passHandle to NULL_HANDLE and returns null.

Throws:

IOException

readHandle

private Object readHandle(boolean unshared)
                   throws IOException

Reads in object handle, sets passHandle to the read handle, and returns object associated with the handle.

Throws:

IOException

readClass

private Class readClass(boolean unshared)
                 throws IOException

Reads in and returns class object. Sets passHandle to class object's assigned handle. Returns null if class is unresolvable (in which case a ClassNotFoundException will be associated with the class' handle in the handle table).

Throws:

IOException

readClassDesc

private ObjectStreamClass readClassDesc(boolean unshared)
                                 throws IOException

Reads in and returns (possibly null) class descriptor. 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 class descriptor's handle.

Throws:

IOException

readProxyDesc

private ObjectStreamClass readProxyDesc(boolean unshared)
                                 throws IOException

Reads in and returns class descriptor for a dynamic proxy class. Sets passHandle to proxy class descriptor's assigned handle. If proxy class descriptor cannot be resolved to a class in the local VM, a ClassNotFoundException is associated with the descriptor's handle.

Throws:

IOException

readNonProxyDesc

private ObjectStreamClass readNonProxyDesc(boolean unshared)
                                    throws IOException

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.

Throws:

IOException

readString

private String readString(boolean unshared)
                   throws IOException

Reads in and returns new string. Sets passHandle to new string's assigned handle.

Throws:

IOException

readArray

private Object readArray(boolean unshared)
                  throws IOException

Reads in and returns array object, or null if array class is unresolvable. Sets passHandle to array's assigned handle.

Throws:

IOException

readOrdinaryObject

private Object readOrdinaryObject(boolean unshared)
                           throws IOException

Reads and returns "ordinary" (i.e., not a String, Class, ObjectStreamClass or array) 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.

Throws:

IOException

readExternalData

private void readExternalData(Externalizable obj,
                              ObjectStreamClass desc)
                       throws IOException

If obj is non-null, reads externalizable data by invoking readExternal() method of obj; otherwise, attempts to skip over externalizable data. Expects that passHandle is set to obj's handle before this method is called.

Throws:

IOException

readSerialData

private void readSerialData(Object obj,
                            ObjectStreamClass desc)
                     throws IOException

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.

Throws:

IOException

skipCustomData

private void skipCustomData()
                     throws IOException

Skips over all block data and objects until TC_ENDBLOCKDATA is encountered.

Throws:

IOException

defaultReadFields

private void defaultReadFields(Object obj,
                               ObjectStreamClass desc)
                        throws IOException

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.

Throws:

IOException

readFatalException

private IOException readFatalException()
                                throws IOException

Reads in and returns IOException that caused serialization to abort. All stream state is discarded prior to reading in fatal exception. Sets passHandle to fatal exception's handle.

Throws:

IOException

handleReset

private void handleReset()
                  throws StreamCorruptedException

If recursion depth is 0, clears internal data structures; otherwise, throws a StreamCorruptedException. This method is called when a TC_RESET typecode is encountered.

Throws:

StreamCorruptedException

bytesToFloats

private static void bytesToFloats(byte[] src,
                                  int srcpos,
                                  float[] dst,
                                  int dstpos,
                                  int nfloats)

Converts specified span of bytes into float values.

bytesToDoubles

private static void bytesToDoubles(byte[] src,
                                   int srcpos,
                                   double[] dst,
                                   int dstpos,
                                   int ndoubles)

Converts specified span of bytes into double values.

latestUserDefinedLoader

private static ClassLoader latestUserDefinedLoader()

Returns the first non-null class loader (not counting class loaders of generated reflection implementation classes) up the execution stack, or null if only code from the null class loader is on the stack. This method is also called via reflection by the following RMI-IIOP class: com.sun.corba.se.internal.util.JDKClassLoader This method should not be removed or its signature changed without corresponding modifications to the above class.