Java Properties file examples

Normally, Java properties file is used to store project configuration data or settings. In this tutorial, we will show you how to read and write to/from a properties file.

1. Write to properties file

Set the property value, and write it into a properties file named config.properties.

App.java

package com.mkyong.properties;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Properties;

public class App {
  public static void main(String[] args) {

 Properties prop = new Properties();
 OutputStream output = null;

 try {

  output = new FileOutputStream("config.properties");

  // set the properties value
  prop.setProperty("database", "localhost");
  prop.setProperty("dbuser", "mkyong");
  prop.setProperty("dbpassword", "password");

  // save properties to project root folder
  prop.store(output, null);

 } catch (IOException io) {
  io.printStackTrace();
 } finally {
  if (output != null) {
   try {
    output.close();
   } catch (IOException e) {
    e.printStackTrace();
   }
  }

 }
  }
}

Output

config.properties

#Fri Jan 17 22:37:45 MYT 2014
dbpassword=password
database=localhost
dbuser=mkyong

P.S If file path is not specified, then this properties file will be stored in your project root folder.

2. Load a properties file

Load a properties file from the file system and retrieved the property value.

App.java

package com.mkyong.properties;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class App {
  public static void main(String[] args) {

 Properties prop = new Properties();
 InputStream input = null;

 try {

  input = new FileInputStream("config.properties");

  // load a properties file
  prop.load(input);

  // get the property value and print it out
  System.out.println(prop.getProperty("database"));
  System.out.println(prop.getProperty("dbuser"));
  System.out.println(prop.getProperty("dbpassword"));

 } catch (IOException ex) {
  ex.printStackTrace();
 } finally {
  if (input != null) {
   try {
    input.close();
   } catch (IOException e) {
    e.printStackTrace();
   }
  }
 }

  }
}

Output

localhost
mkyong
password

3. Load a properties file from classpath

Load a properties file config.properties from project classpath, and retrieved the property value.

P.S Assume properties file “config.properties” is in your project classpath root folder.

App.java

package com.mkyong.properties;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class App {

  public static void main( String[] args ){

     Properties prop = new Properties();
     InputStream input = null;

     try {

      String filename = "config.properties";
      input = App3.class.getClassLoader().getResourceAsStream(filename);
      if(input==null){
                 System.out.println("Sorry, unable to find " + filename);
          return;
      }

      //load a properties file from class path, inside static method
      prop.load(input);

                //get the property value and print it out
                System.out.println(prop.getProperty("database"));
             System.out.println(prop.getProperty("dbuser"));
             System.out.println(prop.getProperty("dbpassword"));

     } catch (IOException ex) {
      ex.printStackTrace();
        } finally{
         if(input!=null){
          try {
    input.close();
   } catch (IOException e) {
    e.printStackTrace();
   }
         }
        }

    }
}

Output

localhost
mkyong
password

For non-static method, use this :

prop.load(getClass().getClassLoader().getResourceAsStream("config.properties"));

4. Prints everything from a properties file

Load a properties file config.properties from project classpath, and get the keys and values.

App.java

package com.mkyong.properties;

import java.io.IOException;
import java.io.InputStream;
import java.util.Enumeration;
import java.util.Properties;

public class App {

  public static void main(String[] args) {
 App app = new App();
 app.printThemAll();
  }

  private void printThemAll() {

 Properties prop = new Properties();
 InputStream input = null;

 try {

  String filename = "config.properties";
  input = getClass().getClassLoader().getResourceAsStream(filename);
  if (input == null) {
   System.out.println("Sorry, unable to find " + filename);
   return;
  }

  prop.load(input);

  Enumeration<?> e = prop.propertyNames();
  while (e.hasMoreElements()) {
   String key = (String) e.nextElement();
   String value = prop.getProperty(key);
   System.out.println("Key : " + key + ", Value : " + value);
  }

 } catch (IOException ex) {
  ex.printStackTrace();
 } finally {
  if (input != null) {
   try {
    input.close();
   } catch (IOException e) {
    e.printStackTrace();
   }
  }
 }

  }

}

Output

Key : dbpassword, Value : password
Key : database, Value : localhost
Key : dbuser, Value : mkyong