java.io.ObjectOutputStream Maven / Gradle / Ivy
/*
This is not an official specification document, and usage is restricted.
NOTICE
(c) 2005-2007 Sun Microsystems, Inc. All Rights Reserved.
Neither this file nor any files generated from it describe a complete
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example, no permission is given for you to incorporate this file, in
whole or in part, in an implementation of a Java specification.
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to you for informative, as opposed to normative, use. The file and any
files generated from it may be used to generate other informative
documentation, such as a unified set of documents of API signatures for
a platform that includes technologies expressed as Java APIs. The file
may also be used to produce "compilation stubs," which allow
applications to be compiled and validated for such platforms.
Any work generated from this file, such as unified javadocs or compiled
stub files, must be accompanied by this notice in its entirety.
This work corresponds to the API signatures of JSR 219: Foundation
Profile 1.1. In the event of a discrepency between this work and the
JSR 219 specification, which is available at
http://www.jcp.org/en/jsr/detail?id=219, the latter takes precedence.
*/
package java.io;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Arrays;
/**
* An ObjectOutputStream writes primitive data types and graphs of Java objects
* to an OutputStream. The objects can be read (reconstituted) using an
* ObjectInputStream. Persistent storage of objects can be accomplished by
* using a file for the stream. If the stream is a network socket stream, the
* objects can be reconsituted on another host or in another process.
*
*
Only objects that support the java.io.Serializable interface can be
* written to streams. The class of each serializable object is encoded
* including the class name and signature of the class, the values of the
* object's fields and arrays, and the closure of any other objects referenced
* from the initial objects.
*
*
The method writeObject is used to write an object to the stream. Any
* object, including Strings and arrays, is written with writeObject. Multiple
* objects or primitives can be written to the stream. The objects must be
* read back from the corresponding ObjectInputstream with the same types and
* in the same order as they were written.
*
*
Primitive data types can also be written to the stream using the
* appropriate methods from DataOutput. Strings can also be written using the
* writeUTF method.
*
*
The default serialization mechanism for an object writes the class of the
* object, the class signature, and the values of all non-transient and
* non-static fields. References to other objects (except in transient or
* static fields) cause those objects to be written also. Multiple references
* to a single object are encoded using a reference sharing mechanism so that
* graphs of objects can be restored to the same shape as when the original was
* written.
*
*
For example to write an object that can be read by the example in
* ObjectInputStream:
*
*
* FileOutputStream fos = new FileOutputStream("t.tmp");
* ObjectOutputStream oos = new ObjectOutputStream(fos);
*
* oos.writeInt(12345);
* oos.writeObject("Today");
* oos.writeObject(new Date());
*
* oos.close();
*
*
* Classes that require special handling during the serialization and
* deserialization process must implement special methods with these exact
* signatures:
*
*
* private void readObject(java.io.ObjectInputStream stream)
* throws IOException, ClassNotFoundException;
* private void writeObject(java.io.ObjectOutputStream stream)
* throws IOException
*
*
* The writeObject method is responsible for writing the state of the object
* for its particular class so that the corresponding readObject method can
* restore it. The method does not need to concern itself with the state
* belonging to the object's superclasses or subclasses. State is saved by
* writing the individual fields to the ObjectOutputStream using the
* writeObject method or by using the methods for primitive data types
* supported by DataOutput.
*
*
Serialization does not write out 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.
*
*
Serialization of an object can be prevented by implementing writeObject
* and readObject methods that throw the NotSerializableException.
* The exception will be caught by the ObjectOutputStream and abort the
* serialization 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.
*
*
Primitive data, excluding serializable fields and externalizable data, is
* written to the ObjectOutputStream in block-data records. A block data record
* is composed of a header and data. The block data header consists of a marker
* and the number of bytes to follow the header. Consecutive primitive data
* writes are merged into one block-data record. The blocking factor used for
* a block-data record will be 1024 bytes. Each block-data record will be
* filled up to 1024 bytes, or be written whenever there is a termination of
* block-data mode. Calls to the ObjectOutputStream methods writeObject,
* defaultWriteObject and writeFields initially terminate any existing
* block-data record.
*
* @author Mike Warres
* @author Roger Riggs
* @version 1.105, 08/09/01
* @see java.io.DataOutput
* @see java.io.ObjectInputStream
* @see java.io.Serializable
* @see java.io.Externalizable
* @see Object Serialization Specification, Section 2, Object Output Classes
* @since JDK1.1
*/
public class ObjectOutputStream extends OutputStream
implements ObjectOutput, ObjectStreamConstants
{
/**
* Creates an ObjectOutputStream that writes to the specified OutputStream.
* This constructor writes the serialization stream header to the
* underlying stream; callers may wish to flush the stream immediately to
* ensure that constructors for receiving ObjectInputStreams will not block
* when reading 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 ObjectOutputStream.putFields or ObjectOutputStream.writeUnshared
* methods.
*
* @param out output stream to write to
* @throws IOException if an I/O error occurs while writing stream header
* @throws SecurityException if untrusted subclass illegally overrides
* security-sensitive methods
* @throws NullPointerException if out is null
* @see ObjectOutputStream#ObjectOutputStream()
* @see ObjectOutputStream#putFields()
* @see ObjectInputStream#ObjectInputStream(InputStream)
*/
public ObjectOutputStream(OutputStream out) throws IOException { }
/**
* Provide a way for subclasses that are completely reimplementing
* ObjectOutputStream to not have to allocate private data just used by
* this implementation of ObjectOutputStream.
*
*
If there is a security manager installed, this method first calls the
* security manager's checkPermission method with a
* SerializablePermission("enableSubclassImplementation")
* permission to ensure it's ok to enable subclassing.
*
* @exception IOException Thrown if not called by a subclass.
*
* @throws SecurityException
* if a security manager exists and its
* checkPermission method denies
* enabling subclassing.
*
* @see SecurityManager#checkPermission
* @see java.io.SerializablePermission
*/
protected ObjectOutputStream() throws IOException, SecurityException { }
/**
* Specify stream protocol version to use when writing the stream.
*
*
This routine provides a hook to enable the current version of
* Serialization to write in a format that is backwards compatible to a
* previous version of the stream format.
*
*
Every effort will be made to avoid introducing additional
* backwards incompatibilities; however, sometimes there is no
* other alternative.
*
* @param version use ProtocolVersion from java.io.ObjectStreamConstants.
* @throws IllegalStateException if called after any objects
* have been serialized.
* @throws IllegalArgumentException if invalid version is passed in.
* @throws IOException if I/O errors occur
* @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_1
* @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_2
* @since 1.2
*/
public void useProtocolVersion(int version) throws IOException { }
/**
* Write the specified object to the ObjectOutputStream. 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
* written. Default serialization for a class can be overridden using the
* writeObject and the readObject methods. Objects referenced by this
* object are written transitively so that a complete equivalent graph of
* objects can be reconstructed by an ObjectInputStream.
*
*
Exceptions are thrown for problems with the OutputStream and for
* classes that should not be serialized. All exceptions are fatal to the
* OutputStream, which is left in an indeterminate state, and it is up to
* the caller to ignore or recover the stream state.
*
* @throws InvalidClassException Something is wrong with a class used by
* serialization.
* @throws NotSerializableException Some object to be serialized does not
* implement the java.io.Serializable interface.
* @throws IOException Any exception thrown by the underlying
* OutputStream.
*/
public final void writeObject(Object obj) throws IOException { }
/**
* Method used by subclasses to override the default writeObject method.
* This method is called by trusted subclasses of ObjectInputStream
* that constructed ObjectInputStream using the
* protected no-arg constructor. The subclass is expected to provide
* an override method with the modifier "final".
*
* @param obj object to be written to the underlying stream
* @throws IOException if there are I/O errors while writing to the
* underlying stream
* @see #ObjectOutputStream()
* @see #writeObject(Object)
* @since 1.2
*/
protected void writeObjectOverride(Object obj) throws IOException { }
/**
* Writes an "unshared" object to the ObjectOutputStream. This method is
* identical to writeObject, except that it always writes the given object
* as a new, unique object in the stream (as opposed to a back-reference
* pointing to a previously serialized instance). Specifically:
*
* - An object written via writeUnshared is always serialized in the
* same manner as a newly appearing object (an object that has not
* been written to the stream yet), regardless of whether or not the
* object has been written previously.
*
*
- If writeObject is used to write an object that has been previously
* written with writeUnshared, the previous writeUnshared operation
* is treated as if it were a write of a separate object. In other
* words, ObjectOutputStream will never generate back-references to
* object data written by calls to writeUnshared.
*
* While writing an object via writeUnshared does not in itself guarantee a
* unique reference to the object when it is deserialized, it allows a
* single object to be defined multiple times in a stream, so that multiple
* calls to readUnshared by the receiver will not conflict. Note that the
* rules described above only apply to the base-level object written with
* writeUnshared, and not to any transitively referenced sub-objects in the
* object graph to be serialized.
*
* ObjectOutputStream 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.
*
* @param obj object to write to stream
* @throws NotSerializableException if an object in the graph to be
* serialized does not implement the Serializable interface
* @throws InvalidClassException if a problem exists with the class of an
* object to be serialized
* @throws IOException if an I/O error occurs during serialization
*
*/
public void writeUnshared(Object obj) throws IOException { }
/**
* Write the non-static and non-transient fields of the current class
* to this stream. This may only be called from the writeObject method
* of the class being serialized. It will throw the NotActiveException
* if it is called otherwise.
*
* @throws IOException if I/O errors occur while writing to the underlying
* OutputStream
*/
public void defaultWriteObject() throws IOException { }
/**
* Retrieve the object used to buffer persistent fields to be written to
* the stream. The fields will be written to the stream when writeFields
* method is called.
*
* @return an instance of the class Putfield that holds the serializable
* fields
* @throws IOException if I/O errors occur
* @since 1.2
*/
public java.io.ObjectOutputStream.PutField putFields() throws IOException {
return null;
}
/**
* Write the buffered fields to the stream.
*
* @throws IOException if I/O errors occur while writing to the underlying
* stream
* @throws NotActiveException Called when a classes writeObject
* method was not called to write the state of the object.
* @since 1.2
*/
public void writeFields() throws IOException { }
/**
* Reset will disregard the state of any objects already written
* to the stream. The state is reset to be the same as a new
* ObjectOutputStream. The current point in the stream is marked
* as reset so the corresponding ObjectInputStream will be reset
* at the same point. Objects previously written to the stream
* will not be refered to as already being in the stream. They
* will be written to the stream again.
*
* @throws IOException if reset() is invoked while serializing an object.
*/
public void reset() throws IOException { }
/**
* Subclasses may implement this method to allow class data to be stored in
* the stream. By default this method does nothing. The corresponding
* method in ObjectInputStream is resolveClass. This method is called
* exactly once for each unique class in the stream. The class name and
* signature will have already been written to the stream. This method may
* make free use of the ObjectOutputStream to save any representation of
* the class it deems suitable (for example, the bytes of the class file).
* The resolveClass method in the corresponding subclass of
* ObjectInputStream must read and use any data or objects written by
* annotateClass.
*
* @param cl the class to annotate custom data for
* @throws IOException Any exception thrown by the underlying
* OutputStream.
*/
protected void annotateClass(Class cl) throws IOException { }
/**
* Subclasses may implement this method to store custom data in the
* stream along with descriptors for dynamic proxy classes.
*
*
This method is called exactly once for each unique proxy class
* descriptor in the stream. The default implementation of this
* method in ObjectOutputStream does nothing.
*
*
The corresponding method in ObjectInputStream is
* resolveProxyClass. For a given subclass of
* ObjectOutputStream that overrides this method, the
* resolveProxyClass method in the corresponding
* subclass of ObjectInputStream must read any data or
* objects writtem by annotateProxyClass.
*
* @param cl the proxy class to annotate custom data for
* @throws IOException any exception thrown by the underlying
* OutputStream
* @see ObjectInputStream#resolveProxyClass(String[])
* @since 1.3
*/
protected void annotateProxyClass(Class cl) throws IOException { }
/**
* This method will allow trusted subclasses of ObjectOutputStream to
* substitute one object for another during serialization. Replacing
* objects is disabled until enableReplaceObject is called. The
* enableReplaceObject method checks that the stream requesting to do
* replacment can be trusted. The first occurrence of each object written
* into the serialization stream is passed to replaceObject. Subsequent
* references to the object are replaced by the object returned by the
* original call to replaceObject. To ensure that the private state of
* objects is not unintentionally exposed, only trusted streams may use
* replaceObject.
*
*
The ObjectOutputStream.writeObject method takes a parameter of type
* Object (as opposed to type Serializable) to allow for cases where
* non-serializable objects are replaced by serializable ones.
*
*
When a subclass is replacing objects it must insure that either a
* complementary substitution must be made during deserialization or 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. This method should return the object to be
* substituted or the original object.
*
*
Null can be returned as the object to be substituted, but may cause
* NullReferenceException in classes that contain references to the
* original object since they may be expecting an object instead of
* null.
*
* @param obj the object to be replaced
* @return the alternate object that replaced the specified one
* @throws IOException Any exception thrown by the underlying
* OutputStream.
*/
protected Object replaceObject(Object obj) throws IOException {
return null;
}
/**
* Enable the stream to do replacement of objects in the stream.
*
*
When enabled, the replaceObject method is called for every object
* being serialized.
*
*
If enable is true, and there is a security manager installed,
* this method first calls the
* security manager's checkPermission method with a
* SerializablePermission("enableSubstitution")
* permission to ensure it's ok to
* enable the stream to do replacement of objects in the stream.
*
* @param enable boolean parameter to enable replacement of objects
* @return the previous setting before this method was invoked
* @throws SecurityException
* if a security manager exists and its
* checkPermission method denies
* enabling the stream to do replacement of objects in the stream.
*
* @see SecurityManager#checkPermission
* @see java.io.SerializablePermission
*/
protected boolean enableReplaceObject(boolean enable)
throws SecurityException
{
return false;
}
/**
* The writeStreamHeader method is provided so subclasses can
* append or prepend their own header to the stream.
* It writes the magic number and version to the stream.
*
* @throws IOException if I/O errors occur while writing to the underlying
* stream
*/
protected void writeStreamHeader() throws IOException { }
/**
* Write the specified class descriptor to the ObjectOutputStream. Class
* descriptors are used to identify the classes of objects written to the
* stream. Subclasses of ObjectOutputStream may override this method to
* customize the way in which class descriptors are written to the
* serialization stream. The corresponding method in ObjectInputStream,
* readClassDescriptor, should then be overridden to
* reconstitute the class descriptor from its custom stream representation.
* By default, this method writes class descriptors according to the format
* defined in the Object Serialization specification.
*
*
Note that this method will only be called if the ObjectOutputStream
* is not using the old serialization stream format (set by calling
* ObjectOutputStream's useProtocolVersion method). If this
* serialization stream is using the old format
* (PROTOCOL_VERSION_1), the class descriptor will be written
* internally in a manner that cannot be overridden or customized.
*
* @param desc class descriptor to write to the stream
* @throws IOException If an I/O error has occurred.
* @see java.io.ObjectInputStream#readClassDescriptor()
* @see #useProtocolVersion(int)
* @see java.io.ObjectStreamConstants#PROTOCOL_VERSION_1
* @since 1.3
*/
protected void writeClassDescriptor(ObjectStreamClass desc)
throws IOException
{ }
/**
* Writes a byte. This method will block until the byte is actually
* written.
*
* @param val the byte to be written to the stream
* @throws IOException If an I/O error has occurred.
*/
public void write(int val) throws IOException { }
/**
* Writes an array of bytes. This method will block until the bytes
* are actually written.
*
* @param buf the data to be written
* @exception IOException If an I/O error has occurred.
*/
public void write(byte[] buf) throws IOException { }
/**
* Writes a sub array of bytes.
*
* @param buf the data to be written
* @param off the start offset in the data
* @param len the number of bytes that are written
* @param copyOnWrite do not expose b to overrides of ObjectStream.write,
* copy the contents of b to a buffer before writing.
* @exception IOException If an I/O error has occurred.
*/
public void write(byte[] buf, int off, int len) throws IOException { }
/**
* Flushes the stream. This will write any buffered output bytes and flush
* through to the underlying stream.
*
* @throws IOException If an I/O error has occurred.
*/
public void flush() throws IOException { }
/**
* Drain any buffered data in ObjectOutputStream. Similar to flush but
* does not propagate the flush to the underlying stream.
*
* @throws IOException if I/O errors occur while writing to the underlying
* stream
*/
protected void drain() throws IOException { }
/**
* Closes the stream. This method must be called to release any resources
* associated with the stream.
*
* @throws IOException If an I/O error has occurred.
*/
public void close() throws IOException { }
/**
* Writes a boolean.
*
* @param val the boolean to be written
* @throws IOException if I/O errors occur while writing to the underlying
* stream
*/
public void writeBoolean(boolean val) throws IOException { }
/**
* Writes an 8 bit byte.
*
* @param val the byte value to be written
* @throws IOException if I/O errors occur while writing to the underlying
* stream
*/
public void writeByte(int val) throws IOException { }
/**
* Writes a 16 bit short.
*
* @param val the short value to be written
* @throws IOException if I/O errors occur while writing to the underlying
* stream
*/
public void writeShort(int val) throws IOException { }
/**
* Writes a 16 bit char.
*
* @param val the char value to be written
* @throws IOException if I/O errors occur while writing to the underlying
* stream
*/
public void writeChar(int val) throws IOException { }
/**
* Writes a 32 bit int.
*
* @param val the integer value to be written
* @throws IOException if I/O errors occur while writing to the underlying
* stream
*/
public void writeInt(int val) throws IOException { }
/**
* Writes a 64 bit long.
*
* @param val the long value to be written
* @throws IOException if I/O errors occur while writing to the underlying
* stream
*/
public void writeLong(long val) throws IOException { }
/**
* Writes a 32 bit float.
*
* @param val the float value to be written
* @throws IOException if I/O errors occur while writing to the underlying
* stream
*/
public void writeFloat(float val) throws IOException { }
/**
* Writes a 64 bit double.
*
* @param val the double value to be written
* @throws IOException if I/O errors occur while writing to the underlying
* stream
*/
public void writeDouble(double val) throws IOException { }
/**
* Writes a String as a sequence of bytes.
*
* @param str the String of bytes to be written
* @throws IOException if I/O errors occur while writing to the underlying
* stream
*/
public void writeBytes(String str) throws IOException { }
/**
* Writes a String as a sequence of chars.
*
* @param str the String of chars to be written
* @throws IOException if I/O errors occur while writing to the underlying
* stream
*/
public void writeChars(String str) throws IOException { }
/**
* Primitive data write of this String in UTF format.
*
* Note that there is a significant difference between
* writing a String into the stream as primitive data or
* as an Object. A String instance written by writeObject
* is written into the stream as a String initially. Future
* writeObject() calls write references to the string into
* the stream.
*
* @param str the String in UTF format
* @throws IOException if I/O errors occur while writing to the underlying
* stream
*/
public void writeUTF(String str) throws IOException { }
/**
* Provide programatic access to the persistent fields to be written
* to ObjectOutput.
*
* @since 1.2
*/
public abstract static class PutField
{
public PutField() { }
/**
* Put the value of the named boolean field into the persistent field.
*
* @param name the name of the serializable field
* @param val the value to assign to the field
*/
public abstract void put(String name, boolean val);
/**
* Put the value of the named byte field into the persistent field.
*
* @param name the name of the serializable field
* @param val the value to assign to the field
*/
public abstract void put(String name, byte val);
/**
* Put the value of the named char field into the persistent field.
*
* @param name the name of the serializable field
* @param val the value to assign to the field
*/
public abstract void put(String name, char val);
/**
* Put the value of the named short field into the persistent field.
*
* @param name the name of the serializable field
* @param val the value to assign to the field
*/
public abstract void put(String name, short val);
/**
* Put the value of the named int field into the persistent field.
*
* @param name the name of the serializable field
* @param val the value to assign to the field
*/
public abstract void put(String name, int val);
/**
* Put the value of the named long field into the persistent field.
*
* @param name the name of the serializable field
* @param val the value to assign to the field
*/
public abstract void put(String name, long val);
/**
* Put the value of the named float field into the persistent field.
*
* @param name the name of the serializable field
* @param val the value to assign to the field
*/
public abstract void put(String name, float val);
/**
* Put the value of the named double field into the persistent field.
*
* @param name the name of the serializable field
* @param val the value to assign to the field
*/
public abstract void put(String name, double val);
/**
* Put the value of the named Object field into the persistent field.
*
* @param name the name of the serializable field
* @param val the value to assign to the field
*/
public abstract void put(String name, Object val);
/**
* Write the data and fields to the specified ObjectOutput stream.
*
* @param out the stream to write the data and fields to
* @throws IOException if I/O errors occur while writing to the
* underlying stream
*/
public abstract void write(ObjectOutput out) throws IOException;
}
}