Summary

In Java, properties files are used to store data and configuration. This tutorial will show you how to store and read properties files in Java 8.

Using InputStream and OutputStream

Write to properties file​

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

public class PropertiesFileSample {
 
 final private static String PROPERTIES_FILE_PATH="config.properties";

 public static void main(String[] args) {
  
  Properties properties = new Properties();
  
  // using java 8 try-with-resources structure,
  // so the output stream will be closed automatically
  try(OutputStream outputStream = new FileOutputStream(PROPERTIES_FILE_PATH)){
   
   // set some values
   properties.setProperty("username", "sampleusername");
   properties.setProperty("url", "tutoref.com");
   
   // store the values
   properties.store(outputStream, null);
   
  } catch (IOException e) {
   e.printStackTrace();
  } 
 }

}

The result will look like this :

#Sat Jul 08 23:55:53 EDT 2017
url=tutoref.com
username=sampleusername

Read from a properties file​

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

public class PropertiesFileSample {
 
 final private static String PROPERTIES_FILE_PATH="config.properties";

 public static void main(String[] args) {
 
  Properties properties = new Properties();
 
  // using java 8 try-with-resources structure
  // so the input stream will be closed automatically
  try(InputStream inputStream = new FileInputStream(PROPERTIES_FILE_PATH)){
 
  // read a value
  String url = properties.getProperty("url");
 
  // display the value
  System.out.println(url);
 
 } catch (IOException e) {
  e.printStackTrace();
 } 
 }
}

Load properties from classpath

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

public class PropertiesFileSample {
 
 final private static String PROPERTIES_FILE_PATH="config.properties";

 public static void main(String[] args) {
  
  Properties properties = new Properties();
  
  // using java 8 try-with-resources structure
  // so the input stream will be closed automatically
  try(
    InputStream inputStream=
    PropertiesFileSample.class.getResourceAsStream(PROPERTIES_FILE_PATH)
    ){
   
   // load the properties
   properties.load(inputStream);
   
   // read a value
   String url = properties.getProperty("url");
   
   // display the value
   System.out.println(url);
   
  } catch (IOException e) {
   e.printStackTrace();
  } 
 }
}

If you want to load the properties file from a non-static method, you should use the following:

InputStream is = getClass().getClassLoader().getResourceAsStream(PROPERTIES_FILE_PATH);