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Spring Boot yes Spring Subprojects under the open source organization , yes Spring Component one-stop solution , Mainly simplify the use Spring The difficulty of , Simplified heavy configuration , Various starters are available , So that developers can get started quickly .

Why use SpringBoot

Rapid development of , Fast integration , Configuration simplification 、 Embedded service container

SpringBoot And SpringCloud difference

SpringBoot It's rapidly developed Spring frame ,SpringCloud It's a complete microservice framework ,SpringCloud Depend on SpringBoot.

Spring Boot What are the advantages ？

Spring Boot The main advantages are as follows ：
1. Easy to use , Improve development efficiency , by Spring Development provides a faster 、 A simpler development framework .
2. Open the box , Stay away from cumbersome configuration .
3. It provides a series of common non business functions for large projects , for example ： Embedded Server 、 security management 、 Operation data monitoring 、 Health check and external configuration etc .
4. SpringBoot The conclusion is to make coding easier 、 Simple configuration 、 Deployment becomes simple 、 Monitoring becomes simple and so on

Spring Boot Which is the core annotation of ？ Which annotations does it consist of ？

The note above the startup class is @SpringBootApplication, So is it Spring Boot Core notes for , The main combinations include the following 3 A note ：
- @SpringBootConfiguration： Combined @Configuration annotation , Realize the function of configuration file .
- @EnableAutoConfiguration： Turn on auto configuration , You can also turn off an auto configuration option , for example ：java For example, turn off the automatic configuration function of data source ： @SpringBootApplication(exclude = { DataSourceAutoConfiguration.class }).
- @ComponentScan：Spring Component scan .

Spring Boot What logging frameworks are supported ？ Which is the recommended and default logging framework ？

Spring Boot Support Java Util Logging, Log4j2, Lockback As a logging framework , If you use Starters starter ,Spring Boot Will use Logback As default logging framework , But no matter what kind of logging framework, it supports exporting configuration files to the console or files .

SpringBoot Starter How it works

I personally understand SpringBoot It's made up of all kinds of Starter Combined , We can develop it ourselves Starter
stay sprinBoot Start time by @SpringBootApplication The annotation will go automatically maven Read each starter Medium spring.factories file , This file is configured to be created spring In container bean, And automatically configure bean Inject SpringContext in //（SpringContext yes Spring Configuration file for ）

Spring Boot 2.X What's new ？ And 1.X What's the difference? ？

Configuration change
JDK Version update
Third party class library upgrade
Response type Spring Programming support
HTTP/2 Support
Configure property binding
More improvements and enhancements

SpringBoot What front-end templates are supported ,

thymeleaf,freemarker,jsp, The government does not recommend JSP There will be restrictions

SpringBoot The shortcomings of

I think it's embarrassing ,SpringBoot At present, I don't think there are any shortcomings , I have to find one. I think it's just
- Because you don't have to make your own configuration , It's hard to locate when you report an error .

function Spring Boot What are the ways ？

Package with command or run in container
use Maven/ Gradle Plug-in run
Direct execution main Method run

Spring Boot Do you need a separate container to run ？

No need , Built in Tomcat/ Jetty Equal container .

Turn on Spring Boot How do features work ？

Inherit spring-boot-starter-parent project
Import spring-boot-dependencies Project dependence

SpringBoot How to implement hot deployment ？

Hot deployment means you don't have to run it again SpringBoot The project can realize the operation, and the background code can be automatically updated to the project running
There are two main ways ：
- Spring Loaded
- Spring-boot-devtools

SpringBoot The use of things

SpringBoot It's very simple , First use annotations EnableTransactionManagement After opening things up , And then in Service Add a comment to the method Transactional Can then .

Async Call methods asynchronously

stay SpringBoot It's easy to use asynchronous calls in , Just use... On the method @Async Annotation can realize asynchronous call of method . Be careful ： You need to add @EnableAsync Make asynchronous calls @Async Annotations to take effect .

How to be in Spring Boot Run some specific code at startup ？

Interface can be implemented ApplicationRunner perhaps CommandLineRunner, These two interfaces are implemented in the same way , They all offer only one run Method

Spring Boot What are the ways to read configuration ？

Spring Boot Can pass @PropertySource,@Value,@Environment, @ConfigurationPropertie Annotations to bind variables

What is? JavaConfig？

Spring JavaConfig yes Spring Community products ,Spring 3.0 Introduced him , It provides configuration Spring IOC The purity of the container Java Method . So it helps to avoid using XML To configure . Use JavaConfig The advantage is ：
- Object oriented configuration . Because the configuration is defined as JavaConfig Class in , So users can make full use of Java Object oriented functions in . One configuration class can inherit another , Rewrite its @Bean Such method .
- Reduce or eliminate XML To configure . The benefits of externalized configuration based on dependency injection principles have been proven . however , Many developers don't want to be in XML and Java Switch back and forth between .JavaConfig Provides a pure Java Method to configure and XML The concept of configuration is similar Spring Containers . Technically speaking , Use only JavaConfig Configuring classes to configure containers is possible , But in fact, many people think that they will JavaConfig And XML Mixed matching is ideal .
- Type safe and refactoring friendly .JavaConfig Provides a type safe way to configure Spring Containers . because Java 5.0 Support for generics , Now you can retrieve by type, not by name bean, No casts or string based lookups are required .
frequently-used Java config：
- @Configuration： Write this annotation on the class , Indicates that this class is a configuration class
- @ComponentScan： Add... To the configuration class @ComponentScan annotation . By default, this annotation will scan all configuration classes under the package where the class is located , Equivalent to the previous <context:component-scan >.
- @Bean：bean The injection of ： It's the same as before < bean id="objectMapper" class="org.codehaus.jackson.map.ObjectMapper" />
- @EnableWebMvc： amount to xml Of <mvc:annotation-driven >
- @ImportResource： amount to xml Of < import resource="applicationContext-cache.xml">

SpringBoot What is the auto configuration principle of

Mainly Spring Boot The core annotation on the startup class of SpringBootApplication Annotation main configuration class , With this main configuration class, it will be SpringBoot To start a @EnableAutoConfiguration Annotation auto configuration function .
With this EnableAutoConfiguration If you do, you'll ：
1. From the configuration file META_INF/Spring.factories Load auto configuration classes that may be used
2. duplicate removal , And will exclude and excludeName Property to carry the class exclusion
3. Filter , Will satisfy the condition （@Conditional） The automatic configuration class returns

How do you understand Spring Boot Configure load order ？

stay Spring Boot Inside , There are several ways to load a configuration .
- 1.properties file ;
- 2.YAML file ;
- 3. System environment variable ;
- 4. Command line arguments ;
- wait ……

What is? YAML？

YAML Is a human readable data serialization language . It is usually used for configuration files . Compared to property file , If we want to add complex properties to the configuration file ,YAML Files are more structured , And less confusion . It can be seen that YAML With hierarchical configuration data .

YAML What are the advantages of configuration ?

YAML Now it's a very popular configuration file format , Whether it's the front end or the back end , You can see it all YAML To configure . that YAML Configuration and traditional properties What are the advantages of configuration ？
- Orderly configuration , In some special situations , It's critical to have an orderly configuration
- Simple and clear , He also supports arrays , The elements in an array can be basic data types or objects
- comparison properties The configuration file ,YAML There is another drawback , It just doesn't support @PropertySource Annotation import custom YAML To configure .

Spring Boot Whether it can be used XML To configure ?

Spring Boot Recommended Java Configure not XML To configure , however Spring Boot Can also be used in XML To configure , adopt @ImportResource Annotations can introduce a XML To configure .

spring boot What are the core configuration files ？bootstrap.properties and application.properties What's the difference ?

Do it alone Spring Boot Development , It may not be easy to meet bootstrap.properties The configuration file , But in combination Spring Cloud when , This configuration will often encounter , Especially when you need to load some remote configuration files .
spring boot Two configuration files of the core ：
- bootstrap (. yml perhaps . properties)：boostrap By father ApplicationContext Loaded , Than applicaton Priority load , Configuration takes effect during the boot phase of the application context . Generally speaking, we are Spring Cloud Configuration will use this file . And boostrap The properties inside cannot be overridden ;
- application (. yml perhaps . properties)： from ApplicatonContext load , be used for spring boot Automatic configuration of project .

What is? Spring Profiles？

In the development of the project , Some configuration files are under development 、 It may be different in different environments such as testing or production , For example, database connections 、redis Configuration, etc . How can we automatically switch configurations in different environments ？Spring It provides us with profiles The mechanism provides us with the function of switching configuration files back and forth
Spring Profiles Allow users to （dev,test,prod etc. ） To register bean. therefore , When the application is running in development , There are only some bean Can be loaded , And in the PRODUCTION in , Some others bean Can be loaded . Suppose our request is Swagger The document only applies to QA Environmental Science , And disable all other documents . This can be done using a configuration file .Spring Boot Make using configuration files very simple .

SpringBoot The idea of splitting multiple data sources

First in properties Two data sources are configured in the configuration file , Create subcontract mapper, Use @ConfigurationProperties Read properties Configuration in , Use @MapperScan Register to the corresponding mapper In bag

SpringBoot How to manage multi data source transactions

The first way is in service Layer of @TransactionManager Use in transactionManager Appoint DataSourceConfig Transactions configured in
The second is to use jta-atomikos Realize distributed transaction management

Protect Spring Boot What are the methods of application ？

Used in production HTTPS
Use Snyk Check your dependencies
Upgrade to the latest version
Enable CSRF Protect
Use content security policies to prevent XSS attack

How to achieve Spring Boot Application security ？

In order to achieve Spring Boot The security of , We use spring-boot-starter-security Dependencies , And you have to add security configuration . It requires very little code . The configuration class will have to extend WebSecurityConfigurerAdapter And cover the method .

Compare the Spring Security and Shiro Advantages and disadvantages of each ?

because Spring Boot The official offers a lot of very convenient out of the box Starter , Include Spring Security Of Starter , Make in Spring Boot Use in Spring Security It's easier , Even just add a dependency to protect all interfaces , therefore , If it is Spring Boot project , General choice Spring Security . Of course, it's just a combination of suggestions , Technically speaking , Whatever combination , It's all right .Shiro and Spring Security comparison , It mainly has the following characteristics ：
- Spring Security It is a heavyweight security management framework ;Shiro It's a lightweight security management framework
- Spring Security The concept is complex , Complicated configuration ;Shiro Simple concept 、 Simple configuration
- Spring Security Powerful ;Shiro Simple function

Spring Boot How to solve cross domain problems in ?

Cross domain can pass through at the front end JSONP To solve , however JSONP You can only send GET request , Cannot send other types of requests , stay RESTful In the application of style , It's very chicken ribs , So we recommend to go through... In the back end （CORS,Cross-origin resource sharing） To solve cross domain problems . This solution is not Spring Boot Peculiar , In traditional SSM In the frame , You can go through CORS To solve cross domain problems , Just before we were XML Configuration in file CORS , Now it can be done by implementing WebMvcConfigurer The interface is then rewritten addCorsMappings Methods to solve cross domain problems .

  @Configuration
  public class CorsConfig implements WebMvcConfigurer {

      @Override
      public void addCorsMappings(CorsRegistry registry) {
          registry.addMapping("/**")
                  .allowedOrigins("*")
                  .allowCredentials(true)
                  .allowedMethods("GET", "POST", "PUT", "DELETE", "OPTIONS")
                  .maxAge(3600);
      }

  }
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Spring Boot What is the monitor in ？

Spring boot actuator yes spring One of the important functions in the startup framework .Spring boot Monitors help you access the current state of running applications in your production environment . There are several indicators that must be checked and monitored in the production environment . Even though some external applications may be using these services to trigger alert messages to interested people . The monitor module discloses a set of functions that can be directly used as HTTP URL Access to the REST Endpoint to check status .

How to use Spring Boot Implement global exception handling ？

Spring Provides a way to use ControllerAdvice A very useful way to handle exceptions . We can achieve a ControlerAdvice class , To handle all exceptions thrown by the controller class .

How do we monitor all Spring Boot Microservices ？

Spring Boot Provide monitor endpoints to monitor the measurement of individual microservices . These endpoints are for getting information about the application （ If they have been activated ） And their components （ Such as database, etc ） It's very helpful if it's working properly . however , One of the main disadvantages or difficulties of using a monitor is , We have to open the knowledge points of the application separately to understand its status or health . Imagine involving 50 Microservices for applications , The administrator will have to hit all 50 Application execution terminal . To help us deal with this situation , We will use the open source project located at . It is based on Spring Boot Actuator above , It provides a Web UI, Enables us to visualize metrics for multiple applications .

SpringBoot How to optimize performance

If the project is large , There are many classes , Don't use @SpringBootApplication, use @Compoment Specify the scan range
Set... At project startup JVM The initial memory is the same as the maximum memory
take springboot The built-in server is made up of tomcat Set to undertow

How to reload Spring Boot Changes on , Without restarting the server ？Spring Boot How to hot deploy the project ？

This can be used DEV Tools to implement . Through this dependency , You can save any changes , The embedded tomcat will restart .Spring Boot There is a development tool （DevTools） modular , It helps improve developer productivity .Java A major challenge for developers is to automatically deploy file changes to the server and restart the server automatically . Developers can reload Spring Boot Changes on , Without restarting the server . This eliminates the need for every manual deployment change .Spring Boot This feature was not available at the time of its first release . This is what developers need most .DevTools Modules fully meet the needs of developers . The module will be disabled in the production environment . It also provides H2 Database console for better application testing .

<dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-devtools</artifactId>
</dependency>
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SpringBoot How to implement session share ?

In microservices , A complete project is divided into several different independent services , Each service is independently deployed on a different server , Respective session Separated from physical space , But often , We need to share... Between different microservices session , The common solution is Spring Session + Redis To achieve session share . All microservices session The unity is preserved in Redis On , When each microservice pair session When there are related reading and writing operations , All operate Redis Upper session . That's it session share ,Spring Session be based on Spring Proxy filter implementation in , bring session Is transparent to developers , It's very simple .

What do you use starter maven Dependencies ？

Some of the following dependencies are used
- spring-boot-starter-web The embedded tomcat and web Development needs servlet And jsp Support
- spring-boot-starter-data-jpa Database support
- spring-boot-starter-data-redis redis Database support
- spring-boot-starter-data-solr solr Support
- mybatis-spring-boot-starter A third party mybatis Integrate starter
- Self defined starter( If you have developed it yourself, you can say it )

Spring Boot Medium starter What is it ?

First , This Starter It's not a new technology , Basically, it's based on Spring It has functions to realize . First, it provides an automatic configuration class , It is generally named XXXAutoConfiguration , In this configuration class, condition annotation is used to determine whether a configuration is effective （ The condition annotation is Spring There are some in the Central Plains ）, Then it will provide a series of default configurations , It also allows developers to customize the configuration according to the actual situation , And then through type safe properties (spring.factories) Injection injects these configuration properties , The newly injected property will replace the default property . Because of that , A lot of third-party frameworks , We just need to introduce dependency to use it directly . Of course , Developers can also customize Starter

Spring Boot How to achieve a scheduled task in ?

stay Spring Boot There are two main ways to use timed tasks in , One is to use Spring Medium @Scheduled annotation , The other - One is to use a third-party framework Quartz.
Use Spring Medium @Scheduled The way is mainly through @Scheduled Annotation to implement .

spring-boot-starter-parent What's the usage? ?

We all know , Create a new Spring Boot project , By default, there are parent Of , This parent Namely spring-boot-starter-parent ,spring-boot-starter-parent It has the following functions ：
1. Defined Java The compiled version is 1.8 .
2. Use UTF-8 Format encoding .
3. Inherited from spring-boot-dependencies, This defines the dependent version , It is precisely because of the inheritance of this dependence , So we don't need to write version number when writing dependency .
4. Configuration to perform packaging operations .
5. Automated resource filtering .
6. Automatic plug-in configuration .
7. in the light of application.properties and application.yml Resource filtering , Including passage profile Profiles for different environments defined , for example application-dev.properties and application-dev.yml.
Summary is for packaging

SpringBoot How to implement packaging

Enter the project directory and enter... On the console mvn clean package,clean Is to empty the existing project package ,package package
Or click... In the options bar on the left Mavne, First click clean Click on package

Spring Boot It's a fight jar And ordinary jar What's the difference? ?

Spring Boot The project is finally packaged into jar It's executable jar , such jar You can go directly through java -jar xxx.jar Command to run , such jar It can't be used as an ordinary jar Dependent on other projects , You can't use the classes even if you depend on them .
Spring Boot Of jar Can't be relied on by other projects , Mainly he and the ordinary jar The structure of is different . ordinary jar package , After decompression, it is the package name directly , There's our code in the bag , and Spring Boot Packaged as executable jar After decompressing , stay \BOOT-INF\classes Directory is our code , So it can't be quoted directly . If you have to quote , Can be in pom.xml Add configuration... To the file , take Spring Boot The project is packaged into two jar , An executable , One can quote .

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