springboot autoconfig 自动配置原理实现
转载: https://blog.****.net/a67474506/article/details/52013634
Spring Boot 运行原理,自动配置
启动流程
我们可以先看看这段代码发生了什么事情
SpringApplication.run(App.class, args);
在创建SpringApplication的时候初始化了一些ApplicationContext和ApplicationListener
主要通过getSpringFactoriesInstances方法来实现
上面的SpringFactoriesLoader.loadFactoryNames方法看这里
下面我们可以查看下spring.factories文件,spring-boot-autoconfigure和 spring-boot的jar包中都有
我们可以先看看Spring-boot里面的文件
当SpringApplication创建,初始化了上述的 Application Context和Application Listeners
通过spring.factories文件拿到一系列的Context和Listener之后 执行run方法
run方法会从spring.factories文件中获取到run listener,然后在spirng boot 执行到各个阶段时执行Listener事件和Context事件
所以,所谓的SpringApplicationRunListeners实际上就是在SpringApplication对象的run方法执行的不同阶段,去执行一些操作,并且这些操作是可配置的。
Spring boot总共有这些事件类型
Spring 事件体系
http://blog.****.net/caihaijiang/article/details/7460888
看下createAndRefreshContext方法
applyInitializers方法其中
DelegatingApplicationContextInitializer读取context.initializer.classes配置,这些类都是实现了ApplicationContextInitializer接口的类,读取之后执行initialize方法,所以我们在这里可以自己扩展一些东西
这里有一些listener和context的功能图
这里面代码看的晕乎乎的,都不知道理解的对不对,希望不会对你们产生误导
参考资料
http://blog.****.net/liaokailin/article/category/5765237
http://zhaox.github.io/java/2016/03/22/spring-boot-start-flow
http://blog.****.net/u011179993/article/details/51475732
自动配置
Spring Boot关于自动配置的源码在spring-boot-autoconfigure中.
上面的这些东西主要是靠condition包下面的注解来根据不同的条件自动创建Bean的
这些注解都是组合了@Conditional元注解,只是使用了不同的条件
我们可以查看下@ConditionalOnWebApplication这个注解
这个注解使用的条件是OnWebApplicationCondition这个类
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package org.springframework.boot.autoconfigure.condition;
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import org.springframework.context.annotation.Condition;
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import org.springframework.context.annotation.ConditionContext;
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import org.springframework.core.Ordered;
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import org.springframework.core.annotation.Order;
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import org.springframework.core.type.AnnotatedTypeMetadata;
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import org.springframework.util.ClassUtils;
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import org.springframework.util.ObjectUtils;
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import org.springframework.web.context.WebApplicationContext;
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import org.springframework.web.context.support.StandardServletEnvironment;
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/**
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* {@link Condition} that checks for the presence or absence of
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* {@link WebApplicationContext}.
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*
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* @author Dave Syer
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* @see ConditionalOnWebApplication
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* @see ConditionalOnNotWebApplication
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*/
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@Order(Ordered.HIGHEST_PRECEDENCE + 20)
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class OnWebApplicationCondition extends SpringBootCondition {
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private static final String WEB_CONTEXT_CLASS = "org.springframework.web.context."
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+ "support.GenericWebApplicationContext";
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@Override
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public ConditionOutcome getMatchOutcome(ConditionContext context,
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AnnotatedTypeMetadata metadata) {
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boolean webApplicationRequired = metadata
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.isAnnotated(ConditionalOnWebApplication.class.getName());
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//判断是否是web环境,并获取结果
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ConditionOutcome webApplication = isWebApplication(context, metadata);
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if (webApplicationRequired && !webApplication.isMatch()) {
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return ConditionOutcome.noMatch(webApplication.getMessage());
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}
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if (!webApplicationRequired && webApplication.isMatch()) {
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return ConditionOutcome.noMatch(webApplication.getMessage());
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}
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return ConditionOutcome.match(webApplication.getMessage());
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}
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private ConditionOutcome isWebApplication(ConditionContext context,
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AnnotatedTypeMetadata metadata) {
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//判断GenericWebApplicationContext是否在类路径中
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if (!ClassUtils.isPresent(WEB_CONTEXT_CLASS, context.getClassLoader())) {
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return ConditionOutcome.noMatch("web application classes not found");
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}
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//容器中是否有名为session的scope
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if (context.getBeanFactory() != null) {
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String[] scopes = context.getBeanFactory().getRegisteredScopeNames();
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if (ObjectUtils.containsElement(scopes, "session")) {
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return ConditionOutcome.match("found web application 'session' scope");
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}
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}
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//当前容器的enviroment是否为StandardServletEnviroment
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if (context.getEnvironment() instanceof StandardServletEnvironment) {
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return ConditionOutcome
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.match("found web application StandardServletEnvironment");
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}
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//当前容器的resourceLoader是否是WebApplicationContext
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if (context.getResourceLoader() instanceof WebApplicationContext) {
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return ConditionOutcome.match("found web application WebApplicationContext");
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}
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return ConditionOutcome.noMatch("not a web application");
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}
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}
最终通过ConditionOutcome返回是否web项目,还有判断结果
自定义starter pom
自己实现一个简单的例子,当某个类存在的时候,自动配置这个Bean,并且可以讲这个属性在application.properties中配置
新建一个maven项目
Pom.xml
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.ibigsea</groupId>
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<artifactId>spring-boot-starter-hello</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<packaging>jar</packaging>
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<name>spring-boot-starter-hello</name>
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<url>http://maven.apache.org</url>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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</properties>
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<dependencies>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-autoconfigure</artifactId>
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<version>1.3.3.RELEASE</version>
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</dependency>
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</dependencies>
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</project>
Hello.java
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package com.ibigsea.spring_boot_starter_hello;
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/**
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* 通过application.properties的hello.msg来配置,默认为world
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* @author bigsea
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*
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*/
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public class Hello {
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private String msg;
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public String sayHello() {
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return "hello " + msg;
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}
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public String getMsg() {
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return msg;
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}
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public void setMsg(String msg) {
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this.msg = msg;
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}
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}
HelloProperties.java
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package com.ibigsea.spring_boot_starter_hello;
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import org.springframework.boot.context.properties.ConfigurationProperties;
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/**
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* 属性配置,Spring boot 自身的自动配置
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* @author bigsea
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*
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*/
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@ConfigurationProperties(prefix="hello")
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public class HelloProperties {
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private static final String MSG = "world";
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private String msg = MSG ;
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public String getMsg() {
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return msg;
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}
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public void setMsg(String msg) {
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this.msg = msg;
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}
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}
HelloAutoConfiguration.java
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package com.ibigsea.spring_boot_starter_hello;
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import org.springframework.beans.factory.annotation.Autowired;
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import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
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import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
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import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
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import org.springframework.boot.context.properties.EnableConfigurationProperties;
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import org.springframework.context.annotation.Bean;
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import org.springframework.context.annotation.Configuration;
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@Configuration
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@EnableConfigurationProperties(HelloProperties.class)//开启属性注入,通过@autowired注入
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@ConditionalOnClass(Hello.class)//判断这个类是否在classpath中存在
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//当设置hello=enabled的情况下,如果没有设置则默认为true,即条件符合
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@ConditionalOnProperty(prefix="hello", value="enabled", matchIfMissing = true)
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public class HelloAutoConfiguration {
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@Autowired
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private HelloProperties helloProperties;
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@Bean//使用java配置方式配置这个类
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@ConditionalOnMissingBean(Hello.class)//容器中如果没有Hello这个类,那么自动配置这个Hello
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public Hello hello() {
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Hello hello = new Hello();
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hello.setMsg(helloProperties.getMsg());
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return hello;
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}
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}
并且要添加spring.factories
# Auto Configure org.springframework.boot.autoconfigure.EnableAutoConfiguration=\ com.ibigsea.spring_boot_starter_hello.HelloAutoConfiguration
整个项目结构
好了,到这里我们就完成了一个starter项目了,下面自己测试下
Pom.xml
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.ibigsea</groupId>
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<artifactId>test-starter</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<packaging>jar</packaging>
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<name>test-starter</name>
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<url>http://maven.apache.org</url>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<boot.version>1.3.3.RELEASE</boot.version>
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</properties>
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<dependencies>
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<dependency>
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<groupId>com.ibigsea</groupId>
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<artifactId>spring-boot-starter-hello</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-web</artifactId>
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<version>${boot.version}</version>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-test</artifactId>
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<version>${boot.version}</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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</project>
App.java
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package com.ibigsea.test_starter;
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import org.springframework.beans.factory.annotation.Autowired;
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import org.springframework.boot.SpringApplication;
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import org.springframework.boot.autoconfigure.SpringBootApplication;
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import org.springframework.web.bind.annotation.RequestMapping;
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import org.springframework.web.bind.annotation.RestController;
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import com.ibigsea.spring_boot_starter_hello.Hello;
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@SpringBootApplication
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@RestController
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public class App {
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@Autowired
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private Hello hello;
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@RequestMapping("/")
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public String index() {
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return hello.sayHello();
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}
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public static void main(String[] args) {
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SpringApplication.run(App.class, args);
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}
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}
application.properties
hello.msg=bigsea
运行结果
开启dubug模式 可以看到自动配置信息
})()