无法使用Java访问Windows中的环境变量

import java.util.Map;

public class EnvironmentVariableExample {
    public static void main(String[] args) {
        Map<String, String> env = System.getenv();
        String value = env.get("ENV_VAR_NAME");
        System.out.println(value);
    }
}

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

public class EnvironmentVariableExample {
    public static void main(String[] args) {
        try {
            Process process = new ProcessBuilder("cmd", "/c", "echo %ENV_VAR_NAME%").start();
            BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
            String value = reader.readLine();
            System.out.println(value);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}