About layer Three (Dao,serviece,servlet)

In the login check,

DAO: The ResultSet object is returned, that is ps.executequery (the specific process that needs to be hardened is JDBC)

Where the database is connected you can write it yourself

Can be obtained through factory class

Connection pools that can be passed through the database

Service: Returns a Boolean

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(Three steps to process the request, then the logic that invokes the processing of the service layer that processes the request, and returns the page and data)

The servlet invokes the service,

You need to instantiate two objects in a

One is the Bean object. Then is called by the request object, the Bean's set method, the parameter passed by the method is the parameter in the request

One is services, which is called the logic of its checksum, where the arguments passed are the object

About layer Three (Dao,serviece,servlet)