How to read properties file in java

Properties files are used in java projects to externalise configuration, for example, database settings.

Java uses Properties class to store the above key-values pair. Properties.load() method is very convenient to load properties file in form of key-values pairs.

Properties file looks something like this.

There are two ways you can do it.
[toc]

java code:

package org.arpit.java2blog;

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

/*
 * @author Arpit Mandliya
 */
public class ReadPropertiesFileJavaMain {

    public static void main(String args[]) throws IOException {
        System.out.println("Reading from properties file");
        System.out.println("-----------------------------");
        Properties prop = readPropertiesFile("config.properties");

        System.out.println("host : " + prop.getProperty("host"));
        System.out.println("username : " + prop.getProperty("username"));
        System.out.println("password : " + prop.getProperty("password"));
        System.out.println("-----------------------------");
    }

    public static Properties readPropertiesFile(String fileName) throws IOException {
        FileInputStream fis = null;
        Properties prop = null;
        try {
            fis = new FileInputStream(fileName);
            // create Properties class object
            prop = new Properties();
            // load properties file into it
            prop.load(fis);

        } catch (FileNotFoundException e) {

            e.printStackTrace();
        } catch (IOException e) {

            e.printStackTrace();
        } finally {
            fis.close();
        }

        return prop;
    }

}

When you run above program, you will get following output:

Read properties file from classpath

You can read properties file to classpath too. You have $project/src as default classpath as this src folder will be copied to classes. You can put it in $project/src folder and read it from there.

you need to use this.getClass().getResourceAsStream("/config.properties"); to read it from classpath.

package org.arpit.java2blog;

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

/*
 * @author Arpit Mandliya
 */
public class ReadPropertiesFileJavaMain {

    public static void main(String args[]) throws IOException {
        ReadPropertiesFileJavaMain rp = new ReadPropertiesFileJavaMain();
        System.out.println("Reading from properties file");
        System.out.println("-----------------------------");

        Properties prop = rp.readPropertiesFile("/config.properties");

        System.out.println("host : " + prop.getProperty("host"));
        System.out.println("username : " + prop.getProperty("username"));
        System.out.println("password : " + prop.getProperty("password"));
        System.out.println("-----------------------------");
    }

    public Properties readPropertiesFile(String fileName) throws IOException {
        InputStream fis = null;
        Properties prop = null;
        try {
            prop = new Properties();
            fis = this.getClass().getResourceAsStream(fileName);

            // create Properties class object
            if (fis != null) {
                // load properties file into it
                prop.load(fis);
            } else {
                throw new FileNotFoundException("property file '" + fileName + "' not found in the classpath");
            }

        } catch (FileNotFoundException e) {

            e.printStackTrace();
        } catch (IOException e) {

            e.printStackTrace();
        } finally {
            fis.close();
        }

        return prop;
    }

}

When you run above program, you will get following output:

That’s all about how to read properties file in java