Package java.io

Class ObjectInputStream

java.lang.Object
java.io.InputStream
java.io.ObjectInputStream
All Implemented Interfaces:
Closeable, DataInput, ObjectInput, ObjectStreamConstants, AutoCloseable
public class ObjectInputStream
extends InputStream
implements ObjectInput, ObjectStreamConstants
A specialized InputStream that is able to read (deserialize) Java objects as well as primitive data types (int, byte, char etc.). The data has typically been saved using an ObjectOutputStream.
See Also:
ObjectOutputStream, ObjectInput, Serializable, Externalizable

  • Constructor Details

    • ObjectInputStream

      protected ObjectInputStream() throws IOException
      Constructs a new ObjectInputStream. This default constructor can be used by subclasses that do not want to use the public constructor if it allocates unneeded data.
      Throws:
      IOException - if an error occurs when creating this stream.

    • ObjectInputStream

      public ObjectInputStream​(InputStream input) throws StreamCorruptedException, IOException
      Constructs a new ObjectInputStream that reads from the InputStream input.
      Parameters:
      input - the non-null source InputStream to filter reads on.
      Throws:
      IOException - if an error occurs while reading the stream header.
      StreamCorruptedException - if the source stream does not contain serialized objects that can be read.

  • Method Details

    • available

      public int available() throws IOException
      Description copied from class: InputStream
      Returns an estimated number of bytes that can be read or skipped without blocking for more input.

      Note that this method provides such a weak guarantee that it is not very useful in practice.

      Firstly, the guarantee is "without blocking for more input" rather than "without blocking": a read may still block waiting for I/O to complete — the guarantee is merely that it won't have to wait indefinitely for data to be written. The result of this method should not be used as a license to do I/O on a thread that shouldn't be blocked.

      Secondly, the result is a conservative estimate and may be significantly smaller than the actual number of bytes available. In particular, an implementation that always returns 0 would be correct. In general, callers should only use this method if they'd be satisfied with treating the result as a boolean yes or no answer to the question "is there definitely data ready?".

      Thirdly, the fact that a given number of bytes is "available" does not guarantee that a read or skip will actually read or skip that many bytes: they may read or skip fewer.

      It is particularly important to realize that you must not use this method to size a container and assume that you can read the entirety of the stream without needing to resize the container. Such callers should probably write everything they read to a ByteArrayOutputStream and convert that to a byte array. Alternatively, if you're reading from a file, File.length() returns the current length of the file (though assuming the file's length can't change may be incorrect, reading a file is inherently racy).

      The default implementation of this method in InputStream always returns 0. Subclasses should override this method if they are able to indicate the number of bytes available.

      Specified by:
      available in interface ObjectInput
      Overrides:
      available in class InputStream
      Returns:
      the estimated number of bytes available
      Throws:
      IOException - if this stream is closed or an error occurs

    • close

      public void close() throws IOException
      Closes this stream. This implementation closes the source stream.
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Specified by:
      close in interface ObjectInput
      Overrides:
      close in class InputStream
      Throws:
      IOException - if an error occurs while closing this stream.

    • defaultReadObject

      public void defaultReadObject() throws IOException, ClassNotFoundException, NotActiveException
      Default method to read objects from this stream. Serializable fields defined in the object's class and superclasses are read from the source stream.
      Throws:
      ClassNotFoundException - if the object's class cannot be found.
      IOException - if an I/O error occurs while reading the object data.
      NotActiveException - if this method is not called from readObject().
      See Also:
      ObjectOutputStream.defaultWriteObject()

    • enableResolveObject

      protected boolean enableResolveObject​(boolean enable)
      Enables object replacement for this stream. By default this is not enabled. Only trusted subclasses (loaded with system class loader) are allowed to change this status.
      Parameters:
      enable - true to enable object replacement; false to disable it.
      Returns:
      the previous setting.
      See Also:
      resolveObject(java.lang.Object), ObjectOutputStream.enableReplaceObject(boolean)

    • read

      public int read() throws IOException
      Reads a single byte from the source stream and returns it as an integer in the range from 0 to 255. Returns -1 if the end of the source stream has been reached. Blocks 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 source stream has been reached.
      Throws:
      IOException - if an error occurs while reading from this stream.

    • read

      public int read​(byte[] buffer, int byteOffset, int byteCount) throws IOException
      Description copied from class: InputStream
      Reads up to byteCount bytes from this stream and stores them in the byte array buffer starting at byteOffset. Returns the number of bytes actually read or -1 if the end of the stream has been reached.
      Specified by:
      read in interface ObjectInput
      Overrides:
      read in class InputStream
      Throws:
      IOException - if the stream is closed or another IOException occurs.

    • readBoolean

      public boolean readBoolean() throws IOException
      Reads a boolean from the source stream.
      Specified by:
      readBoolean in interface DataInput
      Returns:
      the boolean value read from the source stream.
      Throws:
      EOFException - if the end of the input is reached before the read request can be satisfied.
      IOException - if an error occurs while reading from the source stream.
      See Also:
      DataOutput.writeBoolean(boolean)

    • readByte

      public byte readByte() throws IOException
      Reads a byte (8 bit) from the source stream.
      Specified by:
      readByte in interface DataInput
      Returns:
      the byte value read from the source stream.
      Throws:
      EOFException - if the end of the input is reached before the read request can be satisfied.
      IOException - if an error occurs while reading from the source stream.
      See Also:
      DataOutput.writeByte(int)

    • readChar

      public char readChar() throws IOException
      Reads a character (16 bit) from the source stream.
      Specified by:
      readChar in interface DataInput
      Returns:
      the char value read from the source stream.
      Throws:
      EOFException - if the end of the input is reached before the read request can be satisfied.
      IOException - if an error occurs while reading from the source stream.
      See Also:
      DataOutput.writeChar(int)

    • readDouble

      public double readDouble() throws IOException
      Reads a double (64 bit) from the source stream.
      Specified by:
      readDouble in interface DataInput
      Returns:
      the double value read from the source stream.
      Throws:
      EOFException - if the end of the input is reached before the read request can be satisfied.
      IOException - if an error occurs while reading from the source stream.
      See Also:
      DataOutput.writeDouble(double)

    • readFields

      public ObjectInputStream.GetField readFields() throws IOException, ClassNotFoundException, NotActiveException
      Reads the persistent fields of the object that is currently being read from the source stream. The values read are stored in a GetField object that provides access to the persistent fields. This GetField object is then returned.
      Returns:
      the GetField object from which persistent fields can be accessed by name.
      Throws:
      ClassNotFoundException - if the class of an object being deserialized can not be found.
      IOException - if an error occurs while reading from this stream.
      NotActiveException - if this stream is currently not reading an object.

    • readFloat

      public float readFloat() throws IOException
      Reads a float (32 bit) from the source stream.
      Specified by:
      readFloat in interface DataInput
      Returns:
      the float value read from the source stream.
      Throws:
      EOFException - if the end of the input is reached before the read request can be satisfied.
      IOException - if an error occurs while reading from the source stream.
      See Also:
      DataOutput.writeFloat(float)

    • readFully

      public void readFully​(byte[] dst) throws IOException
      Reads bytes from the source stream into the byte array dst. This method will block until dst.length bytes have been read.
      Specified by:
      readFully in interface DataInput
      Parameters:
      dst - the array in which to store the bytes read.
      Throws:
      EOFException - if the end of the input is reached before the read request can be satisfied.
      IOException - if an error occurs while reading from the source stream.

    • readFully

      public void readFully​(byte[] dst, int offset, int byteCount) throws IOException
      Reads byteCount bytes from the source stream into the byte array dst.
      Specified by:
      readFully in interface DataInput
      Parameters:
      dst - the byte array in which to store the bytes read.
      offset - the initial position in dst to store the bytes read from the source stream.
      byteCount - the number of bytes to read.
      Throws:
      EOFException - if the end of the input is reached before the read request can be satisfied.
      IOException - if an error occurs while reading from the source stream.

    • readInt

      public int readInt() throws IOException
      Reads an integer (32 bit) from the source stream.
      Specified by:
      readInt in interface DataInput
      Returns:
      the integer value read from the source stream.
      Throws:
      EOFException - if the end of the input is reached before the read request can be satisfied.
      IOException - if an error occurs while reading from the source stream.
      See Also:
      DataOutput.writeInt(int)

    • readLine

      @Deprecated public String readLine() throws IOException
      Deprecated.
      Use BufferedReader instead.
      Reads the next line from the source stream. Lines are terminated by '\r', '\n', "\r\n" or an EOF.
      Specified by:
      readLine in interface DataInput
      Returns:
      the string read from the source stream.
      Throws:
      IOException - if an error occurs while reading from the source stream.

    • readLong

      public long readLong() throws IOException
      Reads a long (64 bit) from the source stream.
      Specified by:
      readLong in interface DataInput
      Returns:
      the long value read from the source stream.
      Throws:
      EOFException - if the end of the input is reached before the read request can be satisfied.
      IOException - if an error occurs while reading from the source stream.
      See Also:
      DataOutput.writeLong(long)

    • readClassDescriptor

      protected ObjectStreamClass readClassDescriptor() throws IOException, ClassNotFoundException
      Reads a class descriptor from the source stream.
      Returns:
      the class descriptor read from the source stream.
      Throws:
      ClassNotFoundException - if a class for one of the objects cannot be found.
      IOException - if an error occurs while reading from the source stream.

    • resolveProxyClass

      protected Class<?> resolveProxyClass​(String[] interfaceNames) throws IOException, ClassNotFoundException
      Creates the proxy class that implements the interfaces specified in interfaceNames.
      Parameters:
      interfaceNames - the interfaces used to create the proxy class.
      Returns:
      the proxy class.
      Throws:
      ClassNotFoundException - if the proxy class or any of the specified interfaces cannot be created.
      IOException - if an error occurs while reading from the source stream.
      See Also:
      ObjectOutputStream.annotateProxyClass(Class)

    • readObject

      public final Object readObject() throws OptionalDataException, ClassNotFoundException, IOException
      Reads the next object from the source stream.
      Specified by:
      readObject in interface ObjectInput
      Returns:
      the object read from the source stream.
      Throws:
      ClassNotFoundException - if the class of one of the objects in the object graph cannot be found.
      IOException - if an error occurs while reading from the source stream.
      OptionalDataException - if primitive data types were found instead of an object.
      See Also:
      ObjectOutputStream.writeObject(Object)

    • readUnshared

      public Object readUnshared() throws IOException, ClassNotFoundException
      Reads the next unshared object from the source stream.
      Returns:
      the new object read.
      Throws:
      ClassNotFoundException - if the class of one of the objects in the object graph cannot be found.
      IOException - if an error occurs while reading from the source stream.
      See Also:
      ObjectOutputStream.writeUnshared(java.lang.Object)

    • readObjectOverride

      protected Object readObjectOverride() throws OptionalDataException, ClassNotFoundException, IOException
      Method to be overridden by subclasses to read the next object from the source stream.
      Returns:
      the object read from the source stream.
      Throws:
      ClassNotFoundException - if the class of one of the objects in the object graph cannot be found.
      IOException - if an error occurs while reading from the source stream.
      OptionalDataException - if primitive data types were found instead of an object.
      See Also:
      ObjectOutputStream.writeObjectOverride(java.lang.Object)

    • readShort

      public short readShort() throws IOException
      Reads a short (16 bit) from the source stream.
      Specified by:
      readShort in interface DataInput
      Returns:
      the short value read from the source stream.
      Throws:
      IOException - if an error occurs while reading from the source stream.
      See Also:
      DataOutput.writeShort(int)

    • readStreamHeader

      protected void readStreamHeader() throws IOException, StreamCorruptedException
      Reads and validates the ObjectInputStream header from the source stream.
      Throws:
      IOException - if an error occurs while reading from the source stream.
      StreamCorruptedException - if the source stream does not contain readable serialized objects.

    • readUnsignedByte

      public int readUnsignedByte() throws IOException
      Reads an unsigned byte (8 bit) from the source stream.
      Specified by:
      readUnsignedByte in interface DataInput
      Returns:
      the unsigned byte value read from the source stream packaged in an integer.
      Throws:
      EOFException - if the end of the input is reached before the read request can be satisfied.
      IOException - if an error occurs while reading from the source stream.
      See Also:
      DataOutput.writeByte(int)

    • readUnsignedShort

      public int readUnsignedShort() throws IOException
      Reads an unsigned short (16 bit) from the source stream.
      Specified by:
      readUnsignedShort in interface DataInput
      Returns:
      the unsigned short value read from the source stream packaged in an integer.
      Throws:
      EOFException - if the end of the input is reached before the read request can be satisfied.
      IOException - if an error occurs while reading from the source stream.
      See Also:
      DataOutput.writeShort(int)

    • readUTF

      public String readUTF() throws IOException
      Reads a string encoded in modified UTF-8 from the source stream.
      Specified by:
      readUTF in interface DataInput
      Returns:
      the string encoded in modified UTF-8 read from the source stream.
      Throws:
      EOFException - if the end of the input is reached before the read request can be satisfied.
      IOException - if an error occurs while reading from the source stream.
      See Also:
      DataOutput.writeUTF(java.lang.String)

    • registerValidation

      public void registerValidation​(ObjectInputValidation object, int priority) throws NotActiveException, InvalidObjectException
      Registers a callback for post-deserialization validation of objects. It allows to perform additional consistency checks before the readObject() method of this class returns its result to the caller. This method can only be called from within the readObject() method of a class that implements "special" deserialization rules. It can be called multiple times. Validation callbacks are then done in order of decreasing priority, defined by priority.
      Parameters:
      object - an object that can validate itself by receiving a callback.
      priority - the validator's priority.
      Throws:
      InvalidObjectException - if object is null.
      NotActiveException - if this stream is currently not reading objects. In that case, calling this method is not allowed.
      See Also:
      ObjectInputValidation.validateObject()

    • resolveClass

      protected Class<?> resolveClass​(ObjectStreamClass osClass) throws IOException, ClassNotFoundException
      Loads the Java class corresponding to the class descriptor osClass that has just been read from the source stream.
      Parameters:
      osClass - an ObjectStreamClass read from the source stream.
      Returns:
      a Class corresponding to the descriptor osClass.
      Throws:
      ClassNotFoundException - if the class for an object cannot be found.
      IOException - if an I/O error occurs while creating the class.
      See Also:
      ObjectOutputStream.annotateClass(Class)

    • resolveObject

      protected Object resolveObject​(Object object) throws IOException
      Allows trusted subclasses to substitute the specified original object with a new object. Object substitution has to be activated first with calling enableResolveObject(true). This implementation just returns object.
      Parameters:
      object - the original object for which a replacement may be defined.
      Returns:
      the replacement object for object.
      Throws:
      IOException - if any I/O error occurs while creating the replacement object.
      See Also:
      enableResolveObject(boolean), ObjectOutputStream.enableReplaceObject(boolean), ObjectOutputStream.replaceObject(java.lang.Object)

    • skipBytes

      public int skipBytes​(int length) throws IOException
      Skips length bytes on the source stream. This method should not be used to skip bytes at any arbitrary position, just when reading primitive data types (int, char etc).
      Specified by:
      skipBytes in interface DataInput
      Parameters:
      length - the number of bytes to skip.
      Returns:
      the number of bytes actually skipped.
      Throws:
      IOException - if an error occurs while skipping bytes on the source stream.
      NullPointerException - if the source stream is null.