minte9
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Config 

 
/**
 * Loading a properties file (best practice)
 * 
 * Configuration files should be placed in:
 *      src/main/resources
 * 
 * Example:
 *      src/main/resources/config.properties
 * 
 * Maven/Gradle automatically puts everything in /resources
 * onto the application's CLASSPATH - even inside a JAR.
 * 
 * Classpath loading works everywhere, we can get it using:
 *      Config.class.getClassLoader().getResourceAsStream()
 */

package com.minte9.collections.properties;

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

public class Config {
    public static void main(String[] args) throws IOException {

        InputStream input = Config.class
            .getClassLoader()
            .getResourceAsStream("config.properties");

        if (input == null) {
            throw new RuntimeException("config.properties not found");
        }

        Properties props = new Properties();
        props.load(input);
        props.list(System.out);

            /**
             * db.user=myuser
             * db.pass=mypassword
             * db.port=9000
             * db.url=localhost
             */

        System.out.println(props.getProperty("db.user"));  // myuser
        System.out.println(props.getProperty("db.port"));  // 9000
    }
}

MultiConfig 

 
/**
 * Loading multiple configuration files.
 * 
 * Folder (classpath):
 *  src/main/resources/
 *      database-dev.properties
 *      database-prod.properties
 */

package com.minte9.collections.properties;

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

public class MultiConfig {
    public static void main(String[] args) throws IOException {
        
        // Determine environment (dev / prod)
        String env = System.getProperty("env", "dev");  // default 'dev'
        System.out.println("Environment: " + env);  // dev

        // Load properties
        Properties props = new Properties();
        loadProps(props, "database-" + env + ".properties");

        // Use properties
        System.out.println(props.getProperty("db.url"));  // localhost
        System.out.println(props.getProperty("db.user"));  // dev_user
    }    

    private static void loadProps(Properties props, String filename) throws IOException {
        InputStream input = MultiConfig.class
            .getClassLoader()
            .getResourceAsStream(filename);

        if (input == null) {
            throw new RuntimeException("Propertis file not found: " + filename);
        }
        props.load(input);
    }
}






Questions and answers:
Clink on Option to Answer




1. Where should configuration files be placed in a Java project?

  • a) src/main/resources
  • b) src/main/java

2. What does Maven/Gradle do with everything inside /resources?

  • a) Ignores it
  • b) Puts it on the application’s classpath

3. What does getResourceAsStream() do?

  • a) Loads a file from the classpath
  • b) Loads a file only from the file system

4. If a config file is missing, what should your program do?

  • a) Throw an error
  • b) Silently continue

5. In the multi-config example, how is the environment chosen (dev/prod)?

  • a) Using a system property (System.getProperty("env"))
  • b) Hard-coded inside the code

6. What happens if you call props.getProperty("db.url")?

  • a) It retrieves the value of the property
  • b) It deletes the property

7. Why use classpath loading instead of absolute file paths?

  • a) Works everywhere, including inside JAR files
  • b) Only works on Windows


References: