How to load Properties in Java? Properties class has methods to load properties from different sources – InputStream, Reader, and XML file. Here’s an example of Properties.load(InputStream).

java.util.Properties has three methods to load Properties from files:

• void load(InputStream inStream)
  Reads property list (key=value pairs) from given InputStream
• void load(Reader reader)
  Reads property list (key=value paris) from given Reader
• void loadFromXML(InputStream in)
  Loads all properties from XML document in format as produced by Properties.storeToXML() method.

In the following example we show how to use Properties.load(InputStream) to load a app-config.properties:

package com.farenda.java.util;

import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Properties;

public class PropertiesLoad {

    public static void main(String[] args) throws IOException {
        Properties config = loadFromFile("app-config.properties");

        printToSystemOutput(config);
    }

    private static void printToSystemOutput(Properties config) throws IOException {
        config.store(System.out, "Loaded properties:");
    }

    private static Properties loadFromFile(String filename) throws IOException {
        Path configLocation = Paths.get(filename);
        System.out.println("Config location: " + configLocation.toString());
        try (InputStream stream = Files.newInputStream(configLocation)) {
            Properties config = new Properties();
            config.load(stream);
            return config;
        }
    }
}

Put the following content in app-config.properties and place it in your projects directory (or src/main/resources if you are using Maven or Gradle):

database=localhost:2017
username=user
password=secretpassword

Running the code produces the following output:

Config location: app-config.properties
#Loaded properties:
#Sun Sep 06 17:53:59 CEST 2015
password=secretpassword
database=localhost\:2017
username=user

The code for Properties.load(Reader) is the same. You just need to create a Reader instead of InputStream.