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This article focuses on "what are the two ways of hot deployment of springboot?". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn what are the two ways of hot deployment of springboot.

The difference between springboot and springmvc

Spring boot has built-in tomcat,Jetty and Undertow containers, which can be run directly without deployment.

Spring boot automatic configuration reduces a large number of configuration of xml files, and reduces the complexity of project construction.

Spring MVC is a MVC framework based on Servlet that mainly solves the problem of WEB development, because the configuration of Spring is very complex, and it is cumbersome to deal with all kinds of XML, JavaConfig and hin. So in order to simplify the use of developers, and thus creatively launched Spring boot, convention is better than configuration, simplifying the configuration process of spring.

Spring is an "engine"

Spring MVC is a MVC framework based on Spring

Spring Boot is a set of rapid development integration packages based on Spring4 conditional registration.

Two ways of Hot deployment of springboot

Hot deployment of SpringBoot devtools is not available until after SpringBoot 1.3.

①: spring-boot-devtools ②: Spring Loaded

Method 1:

Add dependencies to the project's pom file:

Org.springframework.boot spring-boot-devtools

Then: use shift+ctrl+alt+ "/" (shortcut key in IDEA) to select "Registry" and then check compiler.automake.allow.when.app.running

Method 2:

Add the following code to the project

Org.springframework.boot spring-boot-maven-plugin org.springframework springloaded 1.2.6.RELEASE

After adding, you need to use the mvn instruction to run:

First find the Edit configurations in IDEA, and then do the following: (click "+" in the upper left corner, then select maven and the right panel will appear. Enter the instruction shown in the red underlined area, and you can name the instruction (named MvnSpringBootRun here).

Click Save will appear in the IDEA project operation site, click the green arrow to run

Springboot profile

Spring boot uses a global profile: there are two main types

Application.properties: example: server.port=9998

Application.yml (YAML): example: server:

Port:8080

The main purpose of the configuration file is to modify the default configuration of spring boot at the bottom.

Core annotations of Spring Boot

The above annotation of the startup class is @ SpringBootApplication, which is also the core annotation of SpringBoot. The main combination includes the following three annotations:

@ SpringBootConfiguration: combines @ Configuration annotations to implement the function of configuration files.

EnableAutoConfiguration: turn on the auto-configuration feature, or turn off an auto-configuration option, such as turning off the data source auto-configuration feature: @ SpringBootApplication (exclude = {DataSourceAutoConfiguration.class}).

@ ComponentScan:Spring component scan.

The implementation principle of starter of spring boot

Using starter to realize automatic configuration only needs two conditions-maven dependency and configuration file. Here is a brief introduction to the process of realizing automatic configuration with starter.

To introduce maven is essentially to import the jar package. When spring-boot starts, it will find the resources/META-INF/spring.factories file in the starter jar package, and find the classes that need to be automatically configured according to the configuration in the spring.factories file.

The difference between Spring Boot and Spring MVC

Spring Boot is the integration of Spring and Spring MVC, while Spring MVC is just a module of Spring, a lightweight Web layer framework.

Spring Boot can achieve almost zero configuration, all functions are developed with annotations, and the idea of "convention is greater than configuration" is used to simplify project development.

Difficulty, while Spring MVC needs to rely on xml configuration for development

Spring Boot provides a built-in tomcat, which can be run directly as a jar package or with external tomcat.

Spring Boot also inherits many configurations of third-party libraries, such as JDBC, Mongo, Redis and so on. Using these third-party libraries, the configuration can be almost zero.

How does springcloud's service registration and discovery work?

Eureka contains two components: Eureka Server and Eureka Client

Eureka Server provides service registration service

After each node is started, it will be registered in EurekaServer, so that the information of all available service nodes will be stored in the service registry in EurekaServer, and the information of service nodes can be seen intuitively in the interface.

EurekaClient is a Java client that simplifies Eureka Server interaction and also has a built-in load balancer that uses the polling (round-robin) load algorithm. After the application starts, a heartbeat is sent to the Eureka Server (the default period is 30 seconds). If EurekaServer does not receive a heartbeat from a node in multiple heartbeat cycles, EurekaServer will remove the service node from the service registry (default is 90 seconds)

The three major roles of Eureka:

Eureka Server provides service registration and discovery

Service Provider service providers register their services with Eureka so that service consumers can find

Service Consumer service consumers get a list of registered services from Eureka, so they can consume services

As a service registry, the advantages of Eureka and Zookeeper are:

The famous CAP theory points out that a distributed system cannot satisfy C (consistency), A (availability) and P (partition fault tolerance) at the same time. Because partition fault tolerance P must be guaranteed in distributed systems, we can only make a tradeoff between An and C.

therefore

Zookeeper guarantees CP.

Eureka is AP.

The difference between # and $in mybatis

# is equivalent to putting double quotation marks on the data, and $is equivalent to displaying the data directly

# treat all the incoming data as a string and put a double quotation mark on the automatically passed data. For example: order by # user_id#, if the value passed in is 111, then the value parsed to sql is order by "111". If the value passed in is id, the parsed sql is order by" id ".

The incoming data is directly displayed and generated in sql. For example: order by $user_id$, if the value passed in is 111, then the value parsed to sql is order by user_id, and if the value passed in is id, the parsed sql is order by id.

Sql injection can be prevented to a great extent by the resume mode.

The $method cannot prevent Sql injection.

The $method is generally used to pass in database objects, such as table names.

Don't use $if you can use #.

Note that when using order by dynamic parameters when MyBatis sorting, use $instead of #

String substitution

By default, using syntax in the format # {} causes MyBatis to create a preprocessing statement property and set a safe value (such as?) against it. This is safe, quick, and preferred, and sometimes you just want to insert an immutable string directly into the SQL statement. For example, like ORDER BY, you can use it like this:

ORDER BY ${columnName}

Here MyBatis does not modify or escape strings.

How does Redis eliminate data

Volatile-lru: select the least recently used data elimination from the dataset with an expiration time set (server. DB [I]. Obsolete).

Volatile-ttl: select the expired data from the dataset (server. DB [I]. Expires) that will expire.

Volatile-random: randomly select data for elimination from datasets with an expiration time set (server.db [I] .expires)

Allkeys-lru: select the least recently used data elimination from the dataset (server. DB [I]. Dict).

Allkeys-random: randomly pick data from the dataset (server.db [I] .dict) and eliminate it.

No-envivtion (expulsion): prohibition of eviction data

LRU mechanism:

Redis saves the lru counter server.lrulock, which is updated at a fixed time (redis timer severCorn ()). Each redis object sets the corresponding LRU value, and redis updates redisObject.lru every time the object is accessed.

LRU elimination mechanism: several key-value pairs are randomly selected in the data set, and the largest key-value pair of lru is eliminated. Therefore, redis does not guarantee that the obsolete data is the least recently used, but rather the randomly selected key-value pairs.

TTL mechanism:

The expiration schedule of key-value pairs, namely redisDb.expires, is saved in the redis dataset structure.

TTL elimination mechanism: randomly select several key-value pairs in the data set, and take out the key-value pairs closest to the expiration time. Therefore, redis does not guarantee that the obsolete data is closest to the expiration time, but is in the randomly selected key-value pair.

When redis executes a command per service client, it detects whether the memory used is excessive.

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