Serialization is a process that allows you to save and retrieve Java objects. You need to master serialization and file i/o to save objects to a hard drive, a USB drive, or share objects over a network. Here is what you need to know about Java file i/o and serialization.
Java Objects and Serialization
In Java, an object is an element with a value. You can invoke it with an identifier at any point in your code. Objects can be functions, methods, data structures, or variables.
Objects are organized in classes. The purpose of a class is to define which parameters the object contains and how it should behave.
When invoking an object, a specific method or function will be executed. Serialization allows for the behavior of an object to be preserved when it is saved or shared.
Objects need to be saved as a stream of bytes. This stream contains type information, the type of data content associated with the object, and the values associated with the object. This information is serialized in a stream of bytes, saved to a device or sent over a network, and the object is recreated through a process called deserialization.
In a way, serialization prepares data so it can be shared thanks to the I/O mechanism. The I/O mechanism in itself allows you to generate data streams between programs and machines, but this data would be useless if it weren’t correctly formatted during the serialization process.
What Is File I/O in Java?
I/O stands for input/output. The file I/O refers to the input and output streams programmers can use to read and write data when working with Java.
These streams are often used to share data between programs run on the same machine, to send data over a network, or to simply save files to I/O devices. It is important to choose the right type of data streams depending on the size of the data packets and on the CPU memory available for this action.
These streams belong to the java.io package. This package contains the classes needed to share data between applications and save data to an I/O device. An I/O device can be a hard drive, a USB key, a CD-ROM, etc.
In Java programming, a stream is an object that allows a flow of data to be shared. This flow of data can either go to a device or be shared between programs. The purpose of an input stream is to read data while an output stream writes data.
There are different types of I/O streams. Java Byte streams are used to share data in 8-bit format while Java Character streams allow you to save and share 16-bit Unicode. You would need to use a character stream to save or share a text file, while a bite stream would be more convenient if you are working with binary files.
In Java, data is stored in binary form. Integers are stored in a 4-byte format, while strings are stored in a 16-bit format. Using binary forms makes Java code files smaller than text files saved in ASCII formats. However, it means you need to use a method known as serialization to save and share this data.
These are the different I/O streams you need to know about.
The two Byte streams are called ObjectInputStream and ObjectOutputStream. The methods known as readObject and writeObject are associated with these streams.
Using a Byte stream is suitable when you are working with raw data. However, these streams won’t work if the data isn’t binary.
FileInputStream and FileOutputStream are the streams used for 16-bit Unicode. The FileReader and FileWriter classes are associated with these streams.
These are the streams you will use for most applications since they aren’t limited to raw binary data.
The java.io package includes other streams you might have to use. System.in is a stream used to send data to a program. A keyboard is used to input the data.
System.out is the stream that generates a data output from a program and sends this data to the computer monitor.
System.err is the stream that outputs error data to the computer monitor. The system.out and system.err streams include a built-in method known as printIn(). You can use this method to add data to these streams.
There are two I/O streams that are designed to use more CPU than other streams. The BufferedReader and BufferedWriter classes use less buff memory and will help you save time.
On the other end, the streams that rely on large quantities of buffer memory need to convert each invocation of a method into bytes. The information is written to a file once everything has been processed.
Using these streams can make a difference when working with large files.
How Does Serialization Work?
Serialization is a standard practice. It is a convenient way to store and retrieve data when programming with Java. Without serialization, data streams wouldn’t be able to preserve the parameters associated with each object when data is saved or shared.
This is the approach used to share a message over a network or save information in a database. The main advantage of serialization is that this approach allows you to save an object’s state and retrieve it at a later time.
Each object tagged for serialization is processed, shared via a data stream, and reconstructed by the machine or program that receives it.
Without serialization, you would end up with values that aren’t associated with an integer or a string. Separators would disappear, and it would be impossible to correctly reproduce a Java object once it has been saved or sent over a network.
Note that you can’t use this method if you don’t have access to a serializable interface. You need to add a marker to a class header to indicate that the class is associated with a serializable interface. All you have to do is add implements Serializable in the class header line.
Once this marker has been added, your code compiler will know that objects within this class are ready to be written or read depending on the stream you use. A Java Virtual Machine can only read and write serialized objects.
The Java Virtual Machine turns each object inside of the serializable class into bytes. The byte stream contains the object values and the type of information associated with the object.
The Virtual Machine works by discovering objects that the Virtual Machine can serialize in your code. Reflection is the default mechanism to identify all the items the Virtual Machine needs to serialize. If the reflection is used, each data stream will include a class description, the instance data associated with the class, and the description of serializable superclasses associated with the class.
If you want to reduce the size of the data stream, switch to Externalization. With this method, the data stream will carry a lot less information. It will only include details about the class hierarchy, the superclass structure, and the identity of the class.
Class attributes are another thing that can cause serialization to take longer. Each serializable class should have a version number. This parameter is called a serialVersionUID. If you don’t create it manually, the Virtual Machine will calculate it for each class that needs to be serialized.
Some instance variables can’t be serialized. You need to mark these variables as transient so the Java Virtual Machine won’t serialize them while processing other valid objects in the same class. You can mark any variable as transient if you want them to be ignored during the serialization process.
Note that it is possible to use serialization with arrays and primitive variables. However, you won’t be able to use serialization if you are working with reference types.
You might run into errors when using the I/O mechanism. The purpose of the catch block is to detect these errors and do what is most relevant. You will need to configure your catch block to determine what it should do when an error is found.
If you are expecting to encounter different types of errors while using the I/O mechanism, you will need to create a catch block for each type of error.
You can then tell each catch block what to do when an error is detected by adding a final block.
You don’t have to use catch and finally blocks. If you decide not to use blocks, add a throws clause inside of your file header. This marker will indicate that errors can happen when called by a method. You can also add throws clauses inside of each method header if you want to associate other methods with a specific catch block.
Using the file I/O mechanism and serialization is crucial for saving and retrieving data generated with Java files. Without these mechanisms, it would be impossible to store data in a database or to share messages over networks.