File Handling in Java with CRUD operations

So far the operations using Java programs are done on a prompt/terminal which is not stored anywhere. But in the software industry, most of the programs are written to store the information fetched from the program. One such way is to store the fetched information in a file.

What is File Handling in Java?

A file is a container that is used to store various types of information. Data is permanently stored in secondary memory by creating a file with a unique name. A file may consist of text, image or any other document. 

Different operations that can be performed on a file are: 

1. Creation of a new file
2. Opening an existing file
3. Reading from file
4. Writing to a file
5. Moving to a specific location in a file
6. Closing a file

Different classes that can be used in Java for File Handling: 

1. InputStream
2. OutputStream
3. FilterOutputStream
4. FileOutputStream
5. ByteArrayOutputStream
6. ByteArrayInputStream
7. FileInputStream
8. FilterInputStream
9. StringBufferInputStream
10. SequenceInputStream
11. BufferedOutputStream
12. StringBufferInputStream
13. DataOutputStream
14. PrintStream
15. BufferedInputStream
16. DataInputStream
17. PushbackInputStream

In this article, we will learn how Java ByteStreams are used to perform input and output of 8-bits(1 byte) using class RandomAccessFile which consists of method writeBytes() and readBytes() to write and read the data in the form of bytes.

Various Methods used to perform File operation:  

• writeBytes(String s): Writes the string to the file as a sequence of bytes.
• readLine(): Reads the next line of text from this file.
• getFilePointer(): Returns the current offset in this file.
• length(): Returns the length of this file and return type is long.
• close(): Closes this random access file stream and releases any system resources associated with the stream.
• setLength(long newLength): Sets the length of this file.
• seek(long pos): Sets the file-pointer offset, measured from the beginning of this file, at which the next read or write occurs.

File opening modes in Java: 

Value	Meaning
"r"	Open for reading only. Invoking any of the write methods of the resulting object will cause an IOException to be thrown.
"rw"	Open to reading and writing. If the file does not already exist then an attempt will be made to create it.
"rws"	Open for reading and writing, as with "rw", and also require that every update to the file's content or metadata be written synchronously to the underlying storage device.
"rwd"	Open for reading and writing, as with "rw", and also require that every update to the file's content be written synchronously to the underlying storage device.

Syntax of Opening File using RandomAccessFile:  

File file = new File( filename )
RandomAccessFile raf = new RandomAccessFile(file, mode)

CRUD operations using File Handling in Java

Example: Consider that you want to keep records of your friend's contact number in a file. To distinguish between your friend's name and contact number you need a separator. To do, so you need to select a separator such as '!' or '$' or some special symbol which does not appear in your friend's name. Then we will form a string consist of a name, special symbol and number to insert into the file.

Syntax of a Contact in the file friendsContact.txt:  

Name!Number

How to Create a File in Java? 

Output:

Compiling and Adding the contact in the newly created file:  

javac AddFriend.java 

java AddFriend abc 1111111111 
Friend added

java AddFriend pqr 1111111111
Input name or number already exist

File:

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How to Read a File in Java? 

Output:

Compiling and reading the contacts from the file:  

javac DisplayFriends.java 

java DisplayFriends
Friend Name: abc 
Contact Number: 1234567890

Friend Name: lmn
Contact Number: 3333333333

Friend Name: xyz 
Contact Number: 4444444444

File: 

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How to Update a File in Java?

Output:

Compiling and updating the contact in the file:  

javac UpdateFriend.java 

java UpdateFriend abc 1234567890
Friend updated.

java UpdateFriend tqr
Input name does not exists.

File:

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How to Delete a File in Java? 

Output:

Compiling and deleting the contact in the file:  

javac DeleteFriend.java 

java DeleteFriend pqr
Friend deleted.

java DeleteFriend tqr
Input name does not exists.

File: 

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