使用JMX API实现Atomikos 5连接池监控，以下为示例代码：

1. 引入必要的依赖

    org.apache.tomcat
    tomcat-juli
    9.0.0.M26


    org.apache.tomcat.embed
    tomcat-embed-jmx
    9.0.0.M26


    com.atomikos
    transactions-jta
    5.0.13

2. 配置Tomcat JMX

-Dcom.sun.management.jmxremote.port=10086 \\
-Dcom.sun.management.jmxremote.authenticate=false \\
-Dcom.sun.management.jmxremote.ssl=false

3. 编写Atomikos连接池的代码

import javax.management.MBeanServerConnection;
import javax.management.MalformedObjectNameException;
import javax.management.ObjectName;
import javax.management.remote.JMXConnector;
import javax.management.remote.JMXConnectorFactory;
import javax.management.remote.JMXServiceURL;
import java.io.IOException;

public class AtomikosConnectionPoolMonitor {
    private static final String RMI_HOST = "localhost";
    private static final int RMI_PORT = 10086;

    public static void main(String[] args) throws IOException, MalformedObjectNameException {
        JMXServiceURL jmxUrl = new JMXServiceURL("service:jmx:rmi://" + RMI_HOST + ":" + RMI_PORT + "/jndi/rmi://" + RMI_HOST + ":" + RMI_PORT + "/jmxrmi");
        JMXConnector jmxConnector = JMXConnectorFactory.connect(jmxUrl);
        MBeanServerConnection connection = jmxConnector.getMBeanServerConnection();

        ObjectName objectName = new ObjectName("com.atomikos:type=ConnectionPool,*");
        connection.queryNames(objectName, null).forEach(name -> {
            try {
                System.out.println("name = " + name);
                System.out.println("activeCount = " + connection.getAttribute(name, "activeCount"));
                System.out.println("availableCount = " + connection.getAttribute(name, "availableCount"));
                System.out.println("maxPoolSize = " + connection.getAttribute(name, "maxPoolSize"));
                System.out.println("minPoolSize = " + connection.getAttribute(name, "minPoolSize"));
                System.out.println("poolSize = " + connection.getAttribute(name, "poolSize"));
            } catch (Exception e) {
                e.printStackTrace();
            }
        });
    }
}

以上代码中，使用JMXConnector连接到配置好的Tomcat JMX，并使用MBeanServerConnection查询所有带有“com.atomikos:type=ConnectionPool”的MBean，然后分别输出连接池的状态信息。

当需要监控Atomikos连接池时，可以通过运行上述代码获取连接池的状态信息。