Java.io.ObjectInputStream Class in Java

Java.io.ObjectInputStream Class in Java | Set 1
Note :
Java codes mentioned in this article won’t run on Online IDE as the file used in the code doesn’t exists online. So, to verify the working of the codes, you can copy them to your System and can run it over there.
More Methods of ObjectInputStream Class :

defaultReadObject() : java.io.ObjectInputStream.defaultReadObject() reads the non-static field of the current class from the Input Stream. We use readObject() method of the serialized class to call this method.
Syntax :

public void defaultReadObject()
Parameters : 
-----------
Return : 
void
Exception :
-> IOException : in case of any IO error occurs.
-> ClassNotFoundException : if the class of Object(being serialized) is not found
-> NotActiveException : if the Stream is not reading.

readObject() : java.io.ObjectInputStream.readObject() reads an object from the serialized class. This method is used to call the defaultReadObject. If the class is deserialized by defaut, then it can be overridden using the readObject and writeObject methods.
Syntax :

public void defaultReadObject()
Parameters : 
public final Object readObject()
Return : 
void
Exception :
-> IOException : in case of any IO error occurs.
-> ClassNotFoundException : if the class of Object(being serialized) is not found
-> OptionalDataException : if instead of object, primitive data is found.
-> InvalidClassException : is there is something wrong with serialized class

// Java program explaining the working of 
// readObject() and defaultReadObject()  
  
import java.io.*; 
  
public class NewClass 
{ 
    public static void main(String[] args) throws IOException, ClassNotFoundException 
    { 
        // create a new file with an ObjectOutputStream and ObjectInputStream 
        FileOutputStream geek_out = new FileOutputStream("GEEKS.txt"); 
        ObjectOutputStream geek_outStream = new ObjectOutputStream(geek_out); 
  
        ObjectInputStream Geek_inStream  
            = new ObjectInputStream(new FileInputStream("GEEKS.txt")); 
  
        // These are ObjectOutputStream methods, Don't bother about these methods 
        // As they are covered in other articles you can refer them 
        geek_outStream.writeObject(new Geek()); 
        geek_outStream.flush(); 
  
          
  
        // Use of readObject() : 
        Geek a = (Geek) Geek_inStream.readObject(); 
  
        // Using both readObject and defaultReadObject(); 
        System.out.println("Using defaultReadObject by readObject : "+ a.s); 
  
    } 
      
    static class Geek implements Serializable 
    { 
  
        String s = "GeeksForGeeks"; 
        private void readObject(ObjectInputStream test)throws 
                                    IOException, ClassNotFoundException 
        { 
            // Use of defaultReadObject() : 
            test.defaultReadObject(); 
        } 
    } 
} 

output :

Using defaultReadObject by readObject : GeeksForGeeks

available() : java.io.ObjectInputStream.available() tells the no. of bytes of that can be read without being blocked
Syntax :

public int available()
Parameters : 
-----------
Return : 
no. of bytes of that can be read without being blocked
Exception :
-> IOException : in case of any IO error occurs.

close() : java.io.ObjectInputStream.close() closes the Input Stream and releases all the resources allocated to the Stream
Syntax :

public void close()
Parameters : 
-----------
Return : 
void
Exception :
-> IOException : in case of any IO error occurs.

readShort() : java.io.ObjectInputStream.readShort()reads 16 bit short.
Syntax :

public short readShort()
Parameters : 
public final Object readObject()
Return : 
reads 16 bit short.
Exception :
-> IOException : in case of any IO error occurs.
-> EOFException : if End of stream is reached

// Java program explaining the working of 
// available(), readShort(),close() 
  
import java.io.*; 
  
public class NewClass 
{ 
    public static void main(String[] args) throws IOException, ClassNotFoundException 
    { 
        // create a new file with an ObjectOutputStream and ObjectInputStream 
        FileOutputStream geek_out = new FileOutputStream("GEEKS.txt"); 
        ObjectOutputStream geek_outStream = new ObjectOutputStream(geek_out); 
  
        ObjectInputStream Geek_inStream  
                    = new ObjectInputStream(new FileInputStream("GEEKS.txt")); 
  
        // These are ObjectOutputStream methods, Don't bother about these methods 
        // As they are covered in other articles you can refer them 
        geek_outStream.writeShort(3050); 
        geek_outStream.writeUTF("gEEKSArehERE"); 
  
        geek_outStream.flush(); 
  
        // Use of available() method : 
        System.out.println("Use of available() : " + Geek_inStream.available()); 
  
        // Use of readShort() method : 
        System.out.println("Use of readShort() : " + Geek_inStream.readShort()); 
  
  
  
        // Use of close() method : to release the resources assigned to Geek_inStream 
        System.out.println("Closing the stream"); 
        Geek_inStream.close(); 
  
    } 
} 

Output :

Use of available() : 16
Use of readShort() : 3050
Closing the stream

readUTF() : java.io.ObjectInputStream.readUTF()reads String in modified UTF-8 (Unicode Transformation Format) format. UTF -8 means it uses 8-bit blocks to represent a character.
Syntax :

public String readUTF()
Parameters : 
public final Object readObject()
Return : 
reads String in modified UTF-8 (Unicode Transformation Format) format
Exception :
-> IOException : in case of any IO error occurs.

// Java program explaining the working of readUTF() 
  
import java.io.*; 
  
public class NewClass 
{ 
    public static void main(String[] args) throws IOException, ClassNotFoundException 
    { 
        // create a new file with an ObjectOutputStream and ObjectInputStream 
        FileOutputStream geek_out = new FileOutputStream("GEEKS.txt"); 
        ObjectOutputStream geek_outStream = new ObjectOutputStream(geek_out); 
  
        ObjectInputStream Geek_inStream  
            = new ObjectInputStream(new FileInputStream("GEEKS.txt")); 
  
        // These are ObjectOutputStream methods, Don't bother about these methods 
        // As they are covered in other articles you can refer them 
        geek_outStream.writeUTF("gEEKSArehERE"); 
        geek_outStream.flush(); 
  
          
          
        // Use of readUTF() method : 
        System.out.println("Use of readUTF() : " + Geek_inStream.readUTF()); 
    } 
} 

Output :

Use of readUTF() : gEEKSArehERE

skipBytes(int maxlen) : java.io.ObjectInputStream.skipBytes(int maxlen)skips ‘maxlen’ no. of bytes while reading.
Syntax :

public int skipBytes(int maxlen)
Parameters : 
maxlen : max. no. of bytes to be skipped
Return : 
no. of bytes to be skipped
Exception :
-> IOException : in case of any IO error occurs.

// Java program explaining the working of skipBytes() 
  
import java.io.*; 
  
public class NewClass 
{ 
    public static void main(String[] args) throws IOException, ClassNotFoundException 
    { 
        // create a new file with an ObjectOutputStream and ObjectInputStream 
        FileOutputStream geek_out = new FileOutputStream("GEEKS.txt"); 
        ObjectOutputStream geek_outStream = new ObjectOutputStream(geek_out); 
  
        ObjectInputStream Geek_inStream  
                    = new ObjectInputStream(new FileInputStream("GEEKS.txt")); 
  
        // These are ObjectOutputStream methods, Don't bother about these methods 
        // As they are covered in other articles you can refer them 
        geek_outStream.writeUTF("gEEKSArehERE"); 
        geek_outStream.flush(); 
  
          
          
        // Use of skipBytes() :  
        Geek_inStream.skipBytes(7); 
          
        for (int i = 2; i < Geek_inStream.available(); i++)  
        { 
            System.out.print((char) Geek_inStream.readByte()); 
        } 
    } 
} 

Output :

Are

readFully(byte[] destination) : java.io.ObjectInputStream.readFully(byte[] destination)reads all the bytes from source to the destination array.
Syntax :

public void readFully(byte[] destination)
Parameters : 
destination : the buffer in which the data is to be read
Return : 
returns the 32 bit float read
Exception :
-> IOException : in case of any IO error occurs.
-> EOFException : if End of stream is reached

// Java program explaining the working of readFully() 
  
import java.io.*; 
  
public class NewClass 
{ 
    public static void main(String[] args) throws IOException, ClassNotFoundException 
    { 
        // create a new file with an ObjectOutputStream and ObjectInputStream 
        FileOutputStream geek_out = new FileOutputStream("GEEKS.txt"); 
        ObjectOutputStream geek_outStream = new ObjectOutputStream(geek_out); 
  
        ObjectInputStream Geek_inStream 
                        = new ObjectInputStream(new FileInputStream("GEEKS.txt")); 
  
        // These are ObjectOutputStream methods, Don't bother about these methods 
        // As they are covered in other articles you can refer them 
        geek_outStream.writeUTF("gEEKSArehERE"); 
        geek_outStream.flush(); 
  
          
          
        // Use of readFully() :  
        byte[] destination = new byte[14]; 
        Geek_inStream.readFully(destination); 
        String str = new String(destination); 
        System.out.println("Use of readFully(destination, offset, maxlen) : "+str); 
    } 
} 

Output :

Use of readFully(destination, offset, maxlen) : gEEKSArehERE

readFully(byte[] destination, int offset, int maxlen) : java.io.ObjectInputStream.readFully(byte[] destination, int offset, int maxlen)reads some the bytes (starting from offset to maxlen position) from source to the destination array .
Syntax :

public void readFully(byte[] destination, int offset, int maxlen)
Parameters : 
destination : the buffer in which the data is to be read
offset : starting position of the buffer
maxlen : max no. of bytes to be read
Return : 
void
Exception :
-> IOException : in case of any IO error occurs.
-> EOFException : if End of stream is reached

// Java program explaining the working of  
// readFully(byte[] destination, int offset, int maxlen) 
  
import java.io.*; 
  
public class NewClass 
{ 
    public static void main(String[] args) throws IOException, ClassNotFoundException 
    { 
        // create a new file with an ObjectOutputStream and ObjectInputStream 
        FileOutputStream geek_out = new FileOutputStream("GEEKS.txt"); 
        ObjectOutputStream geek_outStream = new ObjectOutputStream(geek_out); 
  
        ObjectInputStream Geek_inStream  
                    = new ObjectInputStream(new FileInputStream("GEEKS.txt")); 
  
        // These are ObjectOutputStream methods, Don't bother about these methods 
        // As they are covered in other articles you can refer them 
        geek_outStream.writeUTF("gEEKSArehERE"); 
        geek_outStream.flush(); 
  
          
          
        // Use of readFully(byte[] destination, int offset, int maxlen) :  
        byte[] destination = new byte[14]; 
        Geek_inStream.readFully(destination, 3, 7); 
        String str = new String(destination); 
        System.out.println("Use of readFully(destination, offset, maxlen) : "+ str); 
    } 
} 

Output :

Use of readFully(destination, offset, maxlen) : geeks

readFields() : java.io.ObjectInputStream.readFields() reads the constant field from the Input Stream and indicates the name.
Syntax :

public ObjectInputStream.GetField readFields()
Parameters : 
-------
Return : 
GetField object reading the constant fields
Exception :
-> IOException : in case of any IO error occurs.
-> ClassNotFoundException : if class of serialized object is not found

resolveClass() : java.io.ObjectInputStream.resolveClass(ObjectStreamClass INS_class) loads an instance class to Specified Stream Class in place of it.
Syntax :

protected Class resolveClass(ObjectStreamClass desc)

 : means that the class object can be of any type, it is to be specified by the coder.
Parameters : 
INS_class : instance of the specified Stream Class
Return : 
Class Object equivalent to the Specified Stream Class
Exception :
-> IO Exception : if any IO exception occurs
-> ClassNotFoundException : if the argumented class is not available.

registerValidation() : java.io.ObjectInputStream.registerValidation(ObjectInputValidation object, int order) registers the object to validate it.
Syntax :

public void registerValidation(ObjectInputValidation object, int order)
Parameters : 
-------
Return : 
object : object to be validated 
order : Controls the order of callback. These are processed in no particular order
Exception :
-> NotActiveException : If IO stream is not ready to be read
-> InvalidObjectException : if the argumented object to be validated is NULL.

resolveObject(Object o) : java.io.ObjectInputStream.resolveObject(Object o) substitutes an object to ObjectInputStream from another trusted subclass. We can’t replace object until
enableResolveObject is called. It is called after an object has been read.
Syntax :
```
protected Object resolveObject(Object o)
Parameters : 
o : object we want to substitue
Return : 
---------
Exception :
-> IOException : If IO error occurs.
```
enableResolveObject() : java.io.ObjectInputStream.enableResolveObject(boolean check) allows resolveObject method to substitute an object to the ObjectInputStream from another trusted class.
enableResolveObject is called. It is called after an object has been read.
Syntax :
```
protected boolean enableResolveObject(boolean enable)
Parameters : 
check : "true" to allow resolveObject() method
Return : 
----
```
readClassDescriptor() : java.io.ObjectInputStream.readClassDescriptor() reads class descriptor from the serialized stream, this method is called if descriptor is accepted by the ObjectInputStream. By default, descriptor is called by readClassDescriptor() method acc. to the format defined in Object Serialization
Syntax :
```
protected ObjectStreamClass readClassDescriptor()
Parameters : 
-------
Return : 
reads class descriptor
```
readObjectOverride() : java.io.ObjectInputStream.readObjectOverride() reads object from the ObjectOutputStream using protected no-argument constructor
Syntax :
```
protected Object readObjectOverride()
Parameters : 
-------
Return : 
reads object from the Stream
```
readStreamHeader() : java.io.ObjectInputStream.readStreamHeader() allows subclass to read and verify their header and verifying the version number
Syntax :
```
protected void readStreamHeader()
Parameters : 
-------
Return : 
void
```
resolveProxyClass(String[] in_list) : java.io.resolveProxyClass(String[] in_list) returns a proxy class implementing those interfaces which are named in Proxy Class Descriptor. Using this method, we can read descriptors from the dynamic proxy classes
Syntax :
```
protected Class resolveProxyClass(String[] in_list)
Parameters : 
in_List : interface names list, deserialized in the proxy class descriptor
Return : 
Proxy class for specific Interface mentioned in the list
```

// Java Program explaining working of ObjectInputStream class methods 
  
import java.io.*; 
  
public class ObjectInputStreamDemo extends ObjectInputStream 
{ 
  
    public ObjectInputStreamDemo(InputStream in) throws IOException 
    { 
        super(in); 
    } 
} 
public class NewClass 
{ 
    public static void main(String[] args) 
    { 
        String str = "Geeks"; 
        try
        { 
            // create a new file with an ObjectOutputStream and ObjectInputStream 
            FileOutputStream geek_out = new FileOutputStream("test.txt"); 
            ObjectOutputStream geek_in = new ObjectOutputStream(geek_out); 
  
            ObjectInputStream geek_InStream  
                        = new ObjectInputStream(new FileInputStream("test.txt")); 
  
  
            // These are ObjectOutputStream methods, Don't bother about these methods 
            // As they are covered in other articles you can refer them 
            geek_in.writeObject(new Test()); 
            geek_in.writeUTF(str); 
            geek_in.flush(); 
  
            // Gvivg true to the resove Object to enable it 
            geek_InStream.enableResolveObject(true); 
  
            // Using resolveObject() : 
            System.out.println("resoveObject() : " 
                        + geek_InStream.resolveObject(geek_InStream.readUTF())); 
  
            // read the object and print the string 
            Test a = (Test) geek_InStream.readObject(); 
  
            // String value using readFields() methods : 
            System.out.println("Using readFields() : " + a.geek); 
  
            // Checking th use of registerValidation 
            System.out.println("Testing the valiations : : : "); 
            if (Test.geek.equals("Geeks For Geeks")) 
            { 
                System.out.println("\t\t\t\tWorking Perfect "); 
            } 
            else
            { 
                System.out.println("Something wrong with the validations : "); 
            } 
        } 
  
        catch (Exception excpt) 
        { 
            System.out.println("Error"); 
            excpt.printStackTrace(); 
        } 
    } 
  
    static class Test implements Serializable, ObjectInputValidation 
    { 
        static String geek = "Geeks For Geeks"; 
        private String readObject(ObjectInputStream in) 
        throws IOException, ClassNotFoundException 
        { 
  
            // use of readFields() method : 
            ObjectInputStream.GetField getfield = in.readFields(); 
  
            // USe of registerValidation() method : 
            in.registerValidation(this, 0); 
  
            // Returning String "geek" to the main 
            return (String) getfield.get("geek", null); 
        } 
  
        @Override
        public void validateObject() throws InvalidObjectException 
        { 
            throw new UnsupportedOperationException("Not supported yet."); 
        } 
    } 
} 

Output :

Using resoveObject() : Geeks
Using readFields() : Geeks For Geeks
Testing the valiations : : :  
				Working Perfect

This article is contributed by Mohit Gupta 🙂. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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My Personal Notes

Java.io.ObjectInputStream Class in Java | Set 2

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