Java.io.ObjectOutputStream Class in Java | Set 2

Java.io.ObjectOutputStream Class in Java | Set 1

More Methods:

  • void write(byte[] buf) : Writes an array of bytes. This method will block until the byte is actually written.
    Syntax :public void write(byte[] buf)
               throws IOException
    Parameters:
    buf - the data to be written
    Throws:
    IOException 
    
  • void write(byte[] buf, int off, int len) : Writes a sub array of bytes.
    Syntax :public void write(byte[] buf,
             int off,
             int len)
               throws IOException
    Parameters:
    buf - the data to be written
    off - the start offset in the data
    len - the number of bytes that are written
    Throws:
    IOException
  • void write(int val) : Writes a byte. This method will block until the byte is actually written.
    Syntax :public void write(int val)
               throws IOException
    Parameters:
    val - the byte to be written to the stream
    Throws:
    IOException 
  • void writeBoolean(boolean val) : Writes a boolean.
    Syntax :public void writeBoolean(boolean val)
                      throws IOException
    Parameters:
    val - the boolean to be written
    Throws:
    IOException 
  • void writeByte(int val) : Writes an 8 bit byte.
    Syntax :public void writeByte(int val)
                   throws IOException
    Parameters:
    val - the byte value to be written
    Throws:
    IOException
  • void writeBytes(String str) : Writes a String as a sequence of bytes.
    Syntax :public void writeBytes(String str)
                    throws IOException
    Parameters:
    str - the String of writeBytes to be written
    Throws:
    IOException
  • void writeChar(int val) : Writes a 16 bit char.
    Syntax :public void writeChar(int val)
                   throws IOException
    Parameters:
    val - the char value to be written
    Throws:
    IOException
  • void writeChars(String str) : Writes a String as a sequence of chars.
    Syntax :public void writeChars(String str)
                    throws IOException
    Parameters:
    str - the String of chars to be written
    Throws:
    IOException
  • protected void writeClassDescriptor(ObjectStreamClass desc) : 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.
    Syntax :protected void writeClassDescriptor(ObjectStreamClass desc)
                                 throws IOException
    Parameters:
    desc - class descriptor to write to the stream
    Throws:
    IOException
  • void writeDouble(double val) : Writes a 64 bit double.
    Syntax :public void writeDouble(double val)
                     throws IOException
    Parameters:
    val - the double value to be written
    Throws:
    IOException
  • void writeFields() : Write the buffered fields to the stream.
    Syntax :public void writeFields()
                     throws IOException
    Throws:
    IOException
    NotActiveException
  • void writeFloat(float val) : Writes a 32 bit float.
    Syntax :public void writeFloat(float val)
                    throws IOException
    Parameters:
    val - the float value to be written
    Throws:
    IOException 
  • void writeInt(int val) : Writes a 32 bit int.
    Syntax :public void writeInt(int val)
                  throws IOException
    Parameters:
    val - the integer value to be written
    Throws:
    IOException
    
  • void writeLong(long val) : Writes a 64 bit long.
    Syntax :public void writeLong(long val)
                   throws IOException
    Parameters:
    val - the long value to be written
    Throws:
    IOException 
  • void writeObject(Object obj) : 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.
    Syntax :public final void writeObject(Object obj)
                           throws IOException
    Parameters:
    obj - the object to be written
    Throws:
    InvalidClassException 
    NotSerializableException 
    IOException
  • protected void writeObjectOverride(Object obj) : 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”.
    Syntax :protected void writeObjectOverride(Object obj)
                                throws IOException
    Parameters:
    obj - object to be written to the underlying stream
    Throws:
    IOException 
  • void writeShort(int val) : Writes a 16 bit short.
    Syntax :public void writeShort(int val)
                    throws IOException
    Parameters:
    val - the short value to be written
    Throws:
    IOException
  • protected void writeStreamHeader() : 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.
    Syntax :protected void writeStreamHeader()
                              throws IOException
    Throws:
    IOException
  • void writeUnshared(Object obj) : 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.



    Syntax :public void writeUnshared(Object obj)
                       throws IOException
    Parameters:
    obj - object to write to stream
    Throws:
    NotSerializableException
    InvalidClassException
    IOException 
  • void writeUTF(String str) : Primitive data write of this String in modified UTF-8 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.
    Syntax :public void writeUTF(String str)
                  throws IOException
    Parameters:
    str - the String to be written
    Throws:
    IOException
  • void flush() :Flushes the stream. This will write any buffered output bytes and flush through to the underlying stream.
    Syntax :public void flush()
               throws IOException
    Throws:
    IOException

Program :

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//Java program demonstrating ObjectOutputStream
//write methods
import java.io.*;
class ObjectOutputStreamDemo
{
    public static void main(String[] args) throws IOException, ClassNotFoundException 
    {
        FileOutputStream fout = new FileOutputStream("file.txt");
        ObjectOutputStream oot = new ObjectOutputStream(fout);
          
        String a = "GeeksforGeeks";
        String b = "Geek";
        byte[] be = {'A','B','C'};
  
        //illustrating write()
        oot.write(1);
  
        //illustrating writeInt(int i)
        oot.writeInt(1);
  
        //illustrating writeBoolean(boolean a)
        oot.writeBoolean(true);
  
        //illustrating writeObject(Object x)
        oot.writeObject(a);
  
        //illustrating writeByte(byte a)
        oot.writeByte(65);
  
        //illustrating writeBytes(String b)
        oot.writeBytes(b);
  
        //illustrating writeDouble(double d)
        oot.writeDouble(2.3);
  
        //illustrating writeUTF(String str)
        oot.writeUTF(a);
  
        //illustrating writeFloat(float x)
        oot.writeFloat(2.42f);
  
        //illustrating writeLone(long x)
        oot.writeLong(234342347908l);
  
        //illustrating writeChars(String a)
        oot.writeChars(a);
  
        //illustrating writeShort(int val)
        oot.writeShort(2);
  
        //illustrating write(byte[] buff)
        oot.write(be);
          
        //flushing the stream
        oot.flush();
          
        oot.close();
          
        byte c[]=new byte[4];
        char c1[]=new char[13];
          
        FileInputStream fin = new FileInputStream("file.txt");
        ObjectInputStream oit = new ObjectInputStream(fin);
          
        System.out.println(oit.read());
        System.out.println(oit.readInt());
        System.out.println(oit.readBoolean());
        System.out.println(oit.readObject());
        System.out.println(oit.readByte());
        oit.read(c);
          
        for (int i = 0; i  < 4 ; i++) 
        {
            System.out.print((char)c[i]);
        }
          
        System.out.println();
        System.out.println(oit.readDouble());
        System.out.println(oit.readUTF());
        System.out.println(oit.readFloat());
        System.out.println(oit.readLong());
          
        for (int i = 0; i < 13 ; i++)
        {
            System.out.print(oit.readChar());
        }
          
        System.out.println();
        System.out.println(oit.readShort());
        oit.readFully(be);
          
        for (int i = 0; i < 3 ; i++) 
        {
            System.out.print((char)be[i]);
        }
        oit.close();
    }
}

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Output :

1
1
true
GeeksforGeeks
65
Geek
2.3
GeeksforGeeks
2.42
234342347908
GeeksforGeeks
2
ABC

Program 2:

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//Java program illustrating ObjectOutputStream
//write methods
import java.io.*;
class ObjectOutputStreamDemo
{
    public static void main(String[] args) throws IOException,
            ClassNotFoundException
    {
            FileOutputStream out = new FileOutputStream("file.txt");
            ObjectOutputStream oout = new ObjectOutputStream(out);
            oout.writeObject(new demo());
              
            //illustrating writeUnshared()
            //Writes an "unshared" object to the ObjectOutputStream.
            oout.writeUnshared(14);
              
            //flush the stream
            oout.flush();
              
            oout.close();
  
            FileInputStream fin=new FileInputStream("file.txt");
            ObjectInputStream ois=new ObjectInputStream(fin);
  
            // read an object from the stream and cast it to demo
            demo obj = (demo)ois.readObject();
              
            System.out.println( obj.var);
            System.out.println(ois.readUnshared());
    }
}
class demo implements Serializable
{
    static int var = 25;
          
    // assign a new serialPersistentFields
    private static final ObjectStreamField[] serialPersistentFields = 
    {
        new ObjectStreamField("var", Integer.TYPE)
    };
  
    private void readObject(ObjectInputStream in)
    throws IOException, ClassNotFoundException
    {
        // makes them available by name.
        ObjectInputStream.GetField fields = in.readFields();
              
        //Get the value of the named int field from the persistent field.
        var = fields.get("var", 0);
    }
  
    private void writeObject(ObjectOutputStream out)
                throws IOException
    {
        // write into the ObjectStreamField array the variable string
        ObjectOutputStream.PutField fields = out.putFields();
        fields.put("var", var);
              
        //Write the buffered fields to the stream
        out.writeFields();
  
    }
}

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Output :

25
14

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