如何用java运行外部java程序？

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

public class RunExternalJavaProgram {
    public static void main(String[] args) {
        try {
            // 创建ProcessBuilder对象，并指定要运行的外部Java程序的命令
            ProcessBuilder pb = new ProcessBuilder("java", "-jar", "externalProgram.jar");
            
            // 设置工作目录（可选）
            pb.directory(new File("path/to/externalProgram"));
            
            // 启动外部Java程序
            Process process = pb.start();
            
            // 获取外部程序的输出流
            InputStream inputStream = process.getInputStream();
            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
            
            // 读取输出内容
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
            
            // 等待外部程序执行完毕
            int exitCode = process.waitFor();
            
            // 输出外部程序的退出码
            System.out.println("External program exited with code: " + exitCode);
            
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        }
    }
}