How to read write data in properties file using Java

For reading and writing data into properties file I am using Properties class in this post.
Create a file name with extension .properties like I have created “File.properties” below file:

Reading Data: Below code read data from above file using key and file name as an arguments.

package com.test;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.util.Properties;

public class FileReader {

   

    public String readData(String key, String fileName) {

           String value = "";

           try {

                         Properties properties = new Properties();

                         File file  = new File("File.properties");

                         if (file.exists()) {

                                             properties.load(new FileInputStream(file));

                                             value = properties.getProperty(key);

                        }

            } catch (Exception e) {

                        System.out.println(e);

            }

           return value;

    }

   

    public static void main(String []str){

                        

             FileReader fileReader = new FileReader();                           

                        

                         String name = fileReader.readData("Name", "fileName");

                         System.out.println("Name :"+name);

                         String url = fileReader.readData("URL", "fileName");

                         System.out.println("URL :"+url);

        }

}

If you run above file you will get Name and Url values and print on console

Writing Data: below code write data into mentioned file if key is already exist then it update value and if key not exist it add new key value.

package com.test;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.util.Properties;

public class FileReader {

   

    public void addData(String key, String val, String fileName) {

           try {

                         File file = new File("File.properties");                                               

                         Properties properties = new Properties();

                         properties.load(new FileInputStream(file));

                         FileOutputStream obj = new FileOutputStream(file);

                         properties.setProperty(key, val);

                         properties.store(obj, "Update data into file ");

   

           } catch (IOException ex) {

                         ex.printStackTrace();

           }

    }

   

    public static void main(String []str){

              FileReader fileReader = new FileReader();

                        

              fileReader.addData("Name", "Automatn", "fileName");

              fileReader.addData("FName", "Testing", "fileName");  

    } 

When you run you will see that values are updated and new key values added for the “NewName” key