2020 New Java Interview Questions-Spring Boot/Spring Cloud (2)

1. What is the difference between jpa and hibernate?

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• JPA Java Persistence API is the standard ORM interface of Java EE 5 and also Part of the ejb3 specification.

• Hibernate, a very popular ORM framework today, is an implementation of JPA, but its functionality is a superset of JPA.

• The relationship between JPA and Hibernate can be simply understood as JPA is the standard interface and Hibernate is the implementation. So how does Hibernate achieve this relationship with JPA? Hibernate is mainly implemented through three components, hibernate-annotation, hibernate-entitymanager and hibernate-core.

• hibernate-annotation is the basis for Hibernate to support annotation configuration. It includes standard JPA annotation and annotation for Hibernate's own special functions.

• hibernate-core is the core implementation of Hibernate and provides all core functions of Hibernate.

• hibernate-entitymanager implements standard JPA. It can be regarded as an adapter between hibernate-core and JPA. It does not directly provide ORM functions, but supports hibernate- The core is encapsulated to make Hibernate comply with JPA specifications.

2. What is spring cloud?

Literally understood, Spring Cloud is a framework dedicated to distributed systems and cloud services.

Spring Cloud is a new member of the entire Spring family and is an inevitable product of the recent popularity of cloud services.

Spring Cloud provides developers with tools to quickly build some common patterns in distributed systems, such as:

• Configuration Management

• Service registration and discovery

• Circuit breaker

• Intelligent routing

• Inter-service calls

• Load balancing

• Micro agent

• Control bus

• One-time token

• Global lock

• Leadership election

• Distributed Session

• Cluster status

• Distributed message

• ......

Using Spring Cloud developers can implement services and applications in these patterns out of the box. These services can run in any environment, including distributed environments, including developers' own laptops and various hosting platforms.

3. What is the function of spring cloud circuit breaker?

Hystrix is ​​used in Spring Cloud to implement the function of a circuit breaker. A circuit breaker can prevent an application from trying to perform an operation multiple times, that is, it is likely to fail, allowing it to continue without waiting for failure recovery. Or wasting CPU cycles, it determines that the fault is persistent.

Circuit breaker mode also enables applications to detect whether a fault has been resolved and the application can attempt to invoke an action if the problem appears to have been corrected.

Circuit breakers add stability and flexibility to a system, providing stability while the system recovers from failures and minimizing the impact of this failure on performance. It can help preserve system response times by quickly rejecting requests for an operation that is likely to fail, rather than waiting for the operation to time out (or not return).

If a circuit breaker raises an event each time it changes state, this information can be used to monitor the health of the components of the system protected by the circuit breaker, or to alert an administrator when a circuit breaker trips to turn on state.

4. What are the core components of spring cloud?

1. Service discovery - Netflix Eureka

A RESTful service used to locate middle-tier services running in AWS Regions. It consists of two components: Eureka server and Eureka client. Eureka server is used as a service registration server.

The Eureka client is a java client used to simplify interaction with the server, act as a polling load balancer, and provide failover support for services. Netflix uses a separate client in its production environment that provides weighted load balancing based on traffic, resource utilization, and error status.

2. Client-side load balancing - Netflix Ribbon

Ribbon mainly provides client-side software load balancing algorithms. The Ribbon client component provides a series of complete configuration options, such as connection timeout, retry, retry algorithm, etc. Ribbon has built-in pluggable and customizable load balancing components.

3. Circuit Breaker - Netflix Hystrix

A circuit breaker prevents an application from trying to perform an operation multiple times, which is likely to fail, allowing it to continue without waiting for failure recovery or wasting CPU cycles while it determines that the fault is persistent. Circuit breaker mode also enables applications to detect whether the fault has been resolved. If the problem appears to have been corrected, the application can try to invoke the operation.

4. Service Gateway - Netflix Zuul

Similar to nginx, reverse proxy function, but Netflix itself has added some features to cooperate with other components.

5. Distributed configuration——Spring Cloud Config

This is still static and needs to be coordinated with Spring Cloud Bus to achieve dynamic configuration updates.

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