SSM and open source frameworks ------ interview guide

1.MyBatis：

1.1MyBatis important components:

Mapper Configuration: The entity class Student.java - Data Sheet student, XML or annotation
Mapper Interface: DAO layer interface. (Just write interfaces without writing a class that implements: the need to follow the conventions)
Mapper interfaces need to follow when writing conventions:

1. SQL method name and the id value profile (studentMapper.xml) must be the same

2. The method of input parameters, and must be of the type of SQL parameterType same profile;

3. The return value of the method, and must be of the type resultType same SQL profile

SQL Profiles

<select id="queryStudentByNo"  parameterType="int"  resultType="lanqiao.entity.Student" >
    select * from student where stuNo = #{stuNo}
</select>

interface

```
public interface StudentMapper
{
  Student queryStudentByNo(int stuNO)
   List<Student> queryStudentByNo()
}
```
special:

ParameterType 1. If not present, represents a non-parametric method is

2. If there is no resultType, it represents the return value is void

3. If the return value is a collection type, the actual resultType still the element type, rather than a collection type.

1.2MyBatis development of common objects

1.SqlSessionFactory: SqlSesssion factory. Generating SqlSesssion objects openSession SqlSesssion in (): by SqlSessionFactory.

2.SqlSesssion: SqlSesssion objects (similar to the JDBC Connection)

3.Executor: MyBatis all Mapper statement execution is carried out by Executor

1.3MyBatis four core subject

1.StatementHandler (responsible sql statement): processed database select ... from where id = # {} ..

2.PrameterHandler (responsible for parameters in sql): Process parameter object in SQL

3.Executor

4.ResultSetHandler: processing SQL returns result sets

1.5MyBatis four processor

StatementHandler、PrameterHandler、ResultSetHandler

A left: TypeHandler (type converter)

1.6 one to one, one to many, lazy loading

One to One

Use <resultMap> in <association>
One lazy loading:
Use <resultMap> in <association> select attribute specified delay loading sql statement
 <resultMap>    
        <Association select = "lazy loading sql statement">
        <<association>>
</resultMap>

Many:

　　　　The one in the association changed collection

2.Spring

IOC / DI: Inversion of Control / DI

　　Objective: decoupling

　　Student2 student = new Student2 () will result in the use of new highly coupled -> Mode Factory

　　Class -> new -> Object

　　Class -> Factory Mode -> Object, decoupling can be achieved, the question is: need to write your own factory

　　IOC: IoC to help us provide a factory. 1. Fill objects (Configuration [xml, comments]) to get the object from the plant 2 plants

　　Summary: Ioc allows us to create objects through the "configuration mode"

AOP: Aspect-Oriented Programming

　　Of OOP (object oriented) supplement, not replace

The benefits of using AOP

　　Use the actual scene of AOP:

　　Logs, security and unity check

Spring uses those design patterns

Factory pattern: create bean, bean acquisition

Singleton / prototype pattern: When creating bean, set the scope, singleton / prototype

Listening mode: Custom publishing time, listening mode. As ApplicationListener, when an action is triggered, it will automatically execute a notification.

Chain of Responsibility pattern: AOP

Strategy Mode: Create Agent

3.SpringMvc

SpringMvc implementation process

4.SpringBoot

The main functions: automatic assembly

Before (without spring boot), needs its own configuration framework configuration files.

Case spring, mybatis, SSM integration need to write a lot of configuration files.

If Spring Boot, the configuration may be omitted. Benefits: The development focus on business logic rather than on the configuration.

The principle of automatic assembly? Convention over configuration (core: some configuration features, front to achieve good underlying source code)

Two automatic assembly features:

1. Version Arbitration Center: Therefore, after the introduction of dependency, do not write the version number. Benefits: 1. do not mind 2. avoid conflict (preventing the introduction of more attracted, conflict due to incompatible versions of each depend caused)

2. Provide a lot of starter (Scene starter): Bulk jar.

Assuming that the development of web projects (json.jar tomcat.jar hibernate-validator.jar, spring-web.jar ...) => spring-boot-starter-web.

以后使用web项目，只需要引入spring-boot-starter-web

自动装配的应用时： @EnableAutoConfiguration 就是springboot提供自动装配的注解。

5.Spring Cloud

Spring Cloud：微服务治理框架

　　Eureka：服务注册中心，类似于dubbo中的zookeeper

需要注意：Eureka Client有两个角度：如果站在eureka来看，是一个客户端；如果站在系统角度来看，是一个服务端。

6.Ribbon

客户端负载均衡工具

7.Feign

声明式客户端负载均衡工具

Feign是建立在Ribbon之上。

Feign与Ribbon的区别： Ribbon面向URI地址的；Feign面向接口的

8.熔断器

熔断器：Hystrix

解决服务雪崩：熔断器

备用方法b2通常是错误提示或者日志记录

@HystrixCommand(fallbackMethod="b2")
public void a()
{
    
    b();//远程
}

puyblic void b2()
{
    ...
    
}