问groovy -为什么使用这个代码块关闭连接？

EN

    DbService dbService = new DbService(DB_NAME);
    GroovyRowResult row = null;
    try {
        MyClass myObj  = new MyClass(dbService.singleRow(query));
        return myObj;
    } finally {
        dbService.cleanup();
    }

import groovy.sql.Sql;
public class DbService {
private Sql sql;
public void cleanup() {
    if (null != sql) {
        sql.close();
    }
}

9月28日，下午9:19:15 oracle.jdbc.driver.PhysicalConnection.createStatement(PhysicalConnection.java:3908) groovy.sql.Sql$AbstractQueryCommand执行警告:失败执行: select *来自mytable，id=9和rownum <=1，因为:关闭连接java.sql.SQLRecoverableException:关闭连接在groovy.sql.Sql.createStatement(Sql.java:4288) at groovy.sql.Sql.access$800(Sql.java:228) at groovy.sql.Sql.access$800 at groovy.sqlgroovy.sql.Sql$QueryCommand.runQuery(Sql.java:4637) at groovy.sql.Sql$AbstractQueryCommand.execute(Sql.java:4553) at groovy.sql.Sql.rows(Sql.java:1699) at groovy.sql.Sql.rows(Sql.java:1617) atcom.mycompany.qa.database.DbService.singleRow(DbService.java:146)