What's the difference between the dao layer and the service layer in java?

Dao layer: Dao layer is called data access layer and data access object. It is a relatively low-level and basic operation, specifically, adding, deleting, modifying and querying tables or entities.

Service layer: service layer is called service layer, and service layer is called service. It must be a higher-level structure, which is equivalent to encapsulating several operations.

As for why the service layer should be defined by interfaces, there are several advantages:

In java, interfaces are multi-inherited while classes are single-inherited. If you need a class to implement multiple services, you can use interfaces, but defining services with classes is not so flexible.

To provide services for different databases, you only need to implement interfaces with different classes, and you don't need to define classes repeatedly.

For the problem of programming specification, the purpose of interface programming is to encapsulate the implementation, but the caller only cares about the interface and does not care about the implementation, that is, the idea of "high cohesion and low coupling"

Extended data:

Java Web is the sum total of technologies that use Java technology to solve related Web Internet fields. Web includes two parts: web server and Web client. The client has java applets, but they are rarely used. Java is widely used in server, such as Servlet, JSP, third-party framework and so on. Java technology has injected a strong impetus into the development of Web field.

References:

Web service Baidu encyclopedia? Data Access Layer Baidu Encyclopedia