class ConnectionManager {
private Connection connect = null;

public Connection openConnection() {
if (connect == null) {
connect = DriverManager.getConnection();
}
return connect;
}

public void closeConnection() {
if (connect != null)
connect.close();
}
}

class Dao {
public void insert() {
ConnectionManager connectionManager = new ConnectionManager();
Connection connection = connectionManager.openConnection();

// 使用 connection 进行操作

connectionManager.closeConnection();
}
}
===========================================使用 ThreadLocal

public class ConnectionManager {

private static final ThreadLocal<Connection> dbConnectionLocal = new ThreadLocal<Connection>() {
@Override
protected Connection initialValue() {
try {
return DriverManager.getConnection("", "", "");
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
};

public Connection getConnection() {
return dbConnectionLocal.get();
}
}
===========================================不使用 ThreadLocal

这两者有什么区别呢