JPAによるpg_stat_activity統計情報の取得方法です。

PgStatRepository.java


import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import org.springframework.stereotype.Repository;

@Repository
public class PgStatRepository {
	
	@PersistenceContext
	EntityManager entityManager;
	
	/**
	 * 接続数の取得
	 * @return 接続数
	 */
	public  int countClient() {
		String query = "SELECT count(application_name) FROM  pg_stat_activity WHERE datname = 'spring-sample';";
		return ((Number)entityManager.createNativeQuery(query).getSingleResult()).intValue();
	}
}