編譯時src/main/java中*.java檔案會被編譯成*.class檔案,在classpath中建立對應目錄及class檔案
           src/main/resources目錄中的檔案會被複制到classpath目錄中

import java.io.InputStream;
import java.net.URL;

import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

@Component
 
public class Test implements CommandLineRunner {

    public void run(String... args) throws Exception {
        //當前專案根目錄
        System.out.println(System.getProperty("user.dir"));
        
        //classpath目錄， 一般是根目錄下/target/classes目錄
        URL url = getClass().getClassLoader().getResource("");
        System.out.println(url.getPath());
        
        
 
//讀取根目錄下/target/classes/test/settings.properties檔案,即讀取src/main/resources/test/settings.properties檔案
        InputStream inputStream = getClass().getClassLoader().getResourceAsStream("test/settings.properties");
        System.out.println(inputStream);
    }
}