如何正确关闭JDBC连接以便重用？

I am able to retrieve information from my database the first time I establish a connection but whenever I try to reconnect to the database and retrieve more information from the database in different classes it doesn't work. I am trying to put the information I am retrieving from the database into TextViews in Android Studio but they keep showing up as "null". I will show you the code from when I first connect to the database, my connection manager class, and the next time I try to connect to the database. I think it might be because the connection isn't properly being closed but I make sure to close the resultSet, statement, and connection.I am able to retrieve information from my datab