Spring Boot运行原理

查看当前项目已启用和未启用的自动配置的报告

1.运行jar时增加--debug参数

java -jar xx.jar --debug

2.在application.properties中设置属性

debug=true

本质还是基于条件来配置Bean

当某个类存在时，自动配置这个类的Bean,并将Bean属性在application.properties中配置。

写一个starter.pom和自动配置

新建starter的Maven项目

pom.xml修改

<projectxmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

<modelVersion>4.0.0</modelVersion>

<groupId>com.hand</groupId>

<artifactId>spring-boot-starter-hello</artifactId>

<version>1.0-SNAPSHOT</version>

<packaging>jar</packaging>

<name>spring-boot-starter-hello</name>

<url>http://maven.apache.org</url>

<properties>

<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

</properties>

<dependencies>

<dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-autoconfigure</artifactId>

<version>1.3.8.RELEASE</version>

</dependency>

<dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-configuration-processor</artifactId>

<version>1.5.8.RELEASE</version>

<optional>true</optional>

</dependency>

<dependency>

<groupId>junit</groupId>

<artifactId>junit</artifactId>

<version>3.8.1</version>

<scope>test</scope>

</dependency>

</dependencies>

<repositories>

<repository>

<id>spring-snapshots</id>

<name>Spring Snapshots</name>

<url>https://repo.spring.io/snapshot</url>

<snapshots>

<enabled>true</enabled>

</snapshots>

</repository>

<repository>

<id>spring-milestones</id>

<name>Spring Milestones</name>

<url>https://repo.spring.io/milestone</url>

<snapshots>

<enabled>false</enabled>

</snapshots>

</repository>

</repositories>

<pluginRepositories>

<pluginRepository>

<id>spring-snapshots</id>

<name>Spring Snapshots</name>

<url>https://repo.spring.io/snapshot</url>

<snapshots>

<enabled>true</enabled>

</snapshots>

</pluginRepository>

<pluginRepository>

<id>spring-milestones</id>

<name>Spring Milestones</name>

<url>https://repo.spring.io/milestone</url>

<snapshots>

<enabled>false</enabled>

</snapshots>

</pluginRepository>

</pluginRepositories>

</project>

属性配置的类

packagecom.hand;

importorg.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties(prefix ="hello")

public classhelloServiceProperties {

private static finalStringMSG="world";

privateStringmsg=MSG;

publicString getMsg(){

returnmsg;

}

public voidsetMsg(String msg){

this.msg=msg;

}

}

判断依据类

packagecom.hand;

public classhelloService {

privateStringmsg;

publicString sayHello(){

return"hello"+msg;

}

publicString getMsg(){

returnmsg;

}

public voidsetMsg(String msg){

this.msg=msg;

}

}

自动配置类

packagecom.hand;

importorg.springframework.beans.factory.annotation.Autowired;

importorg.springframework.boot.autoconfigure.condition.ConditionalOnClass;

importorg.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;

importorg.springframework.boot.autoconfigure.condition.ConditionalOnProperty;

importorg.springframework.boot.context.properties.EnableConfigurationProperties;

importorg.springframework.context.annotation.Bean;

importorg.springframework.context.annotation.Configuration;

@Configuration

@EnableConfigurationProperties(helloServiceProperties.class)//开启属性注入

@ConditionalOnClass(helloService.class)

@ConditionalOnProperty(prefix ="hello",value ="enabled",matchIfMissing =true)//设置hello为enabled，没设置默认true,即条件符合

public classhelloServiceAutoConfiguration {

//根据helloServiceProperties提供参数，通过ConditionalOnClass判断helloService类在类路径是否存在，容器中无此Bean的情况下

// 则自动配置Bean

@Autowired

privatehelloServicePropertieshelloServiceProperties;

@Bean

@ConditionalOnMissingBean(helloService.class)

publichelloService helloService(){

helloService helloService=newhelloService();

helloService.setMsg(helloServiceProperties.getMsg());

returnhelloService;

}

}

注册配置

若想自动配置生效，需要注册自动配置类

在src/main/resources下新建META-INF/spring.factories

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\

xxxx(配置类)

若多个自动配置，则“,”隔开，此处\是为了换行后仍能读到属性

将上面构建的starter安装到本地

mvn clean install

新建Spring Boot项目，将starter作为依赖

pom.xml加入

<dependency>

<groupId>com.hand</groupId>

<artifactId>spring-boot-start</artifactId>

<version>0.0.1-SNAPSHOT</version>

</dependency>

运行类代码：

packagecom.hand;

importorg.springframework.beans.factory.annotation.Autowired;

importorg.springframework.boot.SpringApplication;

importorg.springframework.boot.autoconfigure.SpringBootApplication;

importorg.springframework.web.bind.annotation.RequestMapping;

importorg.springframework.web.bind.annotation.RestController;

importcom.hand.spring_boot_starter.helloService;

@RestController

@SpringBootApplication

public classSpringBootTestApplication {

@Autowired

privatehelloServicehelloService;

@RequestMapping("/")

publicString index(){

returnhelloService.sayHello();

}

public static voidmain(String[] args) {

SpringApplication.run(SpringBootTestApplication.class, args);

}

}

访问结果

在application.properties新增debug=true，查看自动配置报告