Properties File in Java: Configuration, Reading Data, and Methods Explained

📘 Properties File in Java

A Properties file is a configuration file used to store application settings—most commonly database credentials—in the form of key-value pairs.

It helps separate configuration data from application logic, making the application easier to maintain and modify.

🔑 Format of a Properties File

Properties

db.url=jdbc:mysql://localhost:3306/testdb

db.username=root

db.password=admin

📦 Reading a Properties File in Java

To read data from a properties file, Java provides the Properties class, which is available in the java.util package.

Required Packages:

• java.util
• java.io

🧩 Steps to Read a Properties File

• Create an object of the Properties class
• Open the file using FileReader
• Load the key-value pairs into the Properties object
• Retrieve values using keys

🔧 Important Methods of Properties Class

🔹 load() Method

Used to load key-value pairs from a file into the Properties object.

void load(FileReader fr) throws IOException

📌 This method belongs to the Properties class.

🔹 getProperty() Methods

Used to retrieve values from the Properties object.

1️⃣ Basic Method

String getProperty(String key)

• Returns the value if the key exists
• Returns null if the key does not exist

2️⃣ Overloaded Method

String getProperty(String key, String defaultValue)

• Returns the value if the key exists
• Returns the default message if the key is invalid

⚠️ Exceptions During File Reading

While reading a properties file, the following exceptions may occur:

• FileNotFoundException
• IOException

These must be handled using try-catch or throws.

🌍 Real-Life Example

Think of a properties file like a settings page of an app:

• Username → login ID
• Password → security key
• Server URL → backend address

You can change settings without modifying the app code.

⭐ Advantages of Using Properties File

• Centralized configuration
• Easy maintenance
• Better security
• Supports loose coupling