Reading and writing Serializable objects

http://www.javapractices.com/topic/TopicAction.do?Id=57

Reading and writing Serializable objects
is very similar to reading and writing text:

it' almost always a good idea to use buffering (default size is 8K)
it's often possible to use abstract base class references, instead of references to concrete classes
there's always a need to pay attention to exceptions; in particular, IOException and ClassNotFoundException

Example

Here, a List of String objects is serialized and then deserialized.

import java.io.*;
import java.util.*;
import java.util.logging.*;

/**
Uses buffering, and abstract base classes.
JDK 7+.
*/
public class ExerciseSerializableNew {

public static void main(String... aArguments) {
//create a Serializable List
List<String> quarks = Arrays.asList(
"up", "down", "strange", "charm", "top", "bottom"
);

//serialize the List
try (
OutputStream file = new FileOutputStream("quarks.ser");
OutputStream buffer = new BufferedOutputStream(file);
ObjectOutput output = new ObjectOutputStream(buffer);
){
output.writeObject(quarks);
}
catch(IOException ex){
fLogger.log(Level.SEVERE, "Cannot perform output.", ex);
}

//deserialize the quarks.ser file
try(
InputStream file = new FileInputStream("quarks.ser");
InputStream buffer = new BufferedInputStream(file);
ObjectInput input = new ObjectInputStream (buffer);
){
//deserialize the List
List<String> recoveredQuarks = (List<String>)input.readObject();
//display its data
for(String quark: recoveredQuarks){
System.out.println("Recovered Quark: " + quark);
}
}
catch(ClassNotFoundException ex){
fLogger.log(Level.SEVERE, "Cannot perform input. Class not found.", ex);
}
catch(IOException ex){
fLogger.log(Level.SEVERE, "Cannot perform input.", ex);
}
}

// PRIVATE

private static final Logger fLogger =
Logger.getLogger(ExerciseSerializableNew.class.getPackage().getName())
;
}

Example - JDK 6-

If try-with-resources is not available (JDK 6-), then you must be careful with the close method:

it always needs to be called, or else resources will leak
it will automatically flush the stream, if necessary
calling close on a "wrapper" stream will automatically call close on its underlying stream
closing a stream a second time has no consequence

Example

Here's the same example as above, but using JDK 6-.

import java.io.*;
import java.util.*;
import java.util.logging.*;

/** JDK before version 7. */
public class ExerciseSerializable {

public static void main(String... aArguments) {
//create a Serializable List
List<String> quarks = Arrays.asList(
"up", "down", "strange", "charm", "top", "bottom"
);

//serialize the List
//note the use of abstract base class references

try{
//use buffering
OutputStream file = new FileOutputStream("quarks.ser");
OutputStream buffer = new BufferedOutputStream(file);
ObjectOutput output = new ObjectOutputStream(buffer);
try{
output.writeObject(quarks);
}
finally{
output.close();
}
}
catch(IOException ex){
fLogger.log(Level.SEVERE, "Cannot perform output.", ex);
}

//deserialize the quarks.ser file
//note the use of abstract base class references

try{
//use buffering
InputStream file = new FileInputStream("quarks.ser");
InputStream buffer = new BufferedInputStream(file);
ObjectInput input = new ObjectInputStream (buffer);
try{
//deserialize the List
List<String> recoveredQuarks = (List<String>)input.readObject();
//display its data
for(String quark: recoveredQuarks){
System.out.println("Recovered Quark: " + quark);
}
}
finally{
input.close();
}
}
catch(ClassNotFoundException ex){
fLogger.log(Level.SEVERE, "Cannot perform input. Class not found.", ex);
}
catch(IOException ex){
fLogger.log(Level.SEVERE, "Cannot perform input.", ex);
}
}

// PRIVATE

//Use Java's logging facilities to record exceptions.
//The behavior of the logger can be configured through a
//text file, or programmatically through the logging API.
private static final Logger fLogger =
Logger.getLogger(ExerciseSerializable.class.getPackage().getName())
;
}