【SpringBoot2.x】-自定义Spring boot Starter（原理、demo代码实现以及解决面试问题）

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
  String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
  Class<?>[] exclude() default {};
  String[] excludeName() default {};
}
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protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,
      AnnotationAttributes attributes) {
    List<String> configurations = SpringFactoriesLoader.loadFactoryNames(
        getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());
    Assert.notEmpty(configurations,
        "No auto configuration classes found in META-INF/spring.factories. If you "
            + "are using a custom packaging, make sure that file is correct.");
    return configurations;
}
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<dependencyManagement>
    <dependencies>
        <dependency>
            <!-- Import dependency management from Spring Boot -->
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-dependencies</artifactId>
            <version>2.1.5.RELEASE</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>
<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-autoconfigure</artifactId>
    </dependency>
</dependencies>
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public class PasswordService {
    //第三方系统获取密码所需的key
    private String objectKey;
    @Autowired
    //模拟的第三方系统service
    private ThirdPartySystemService thirdPartySystemService;
    public String getSystemPassword(String objectKey,String originalPassord){
            if(StringUtils.isEmpty(objectKey)){
                return  originalPassord;
            }
            //从第三方系统获取密码
            String password= thirdPartySystemService.getPassword(objectKey);
            //返回密码
            return password!=null?password:originalPassord;
    }
}
//模拟第三方系统service
public class ThirdPartySystemService {
    public String getPassword(String objectKey){
        //返回一个32位随机数
        return UUID.randomUUID().toString();
    }
}
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//通过@ConfigurationProperties注解获取属性值
@ConfigurationProperties(prefix = "project.starter")
public class BaseServiceProperties {
    private String serviceName;
    private String serviceVersion;
    public String getServiceName() {
        return serviceName;
    }
    public void setServiceName(String serviceName) {
        this.serviceName = serviceName;
    }
    public String getServiceVersion() {
        return serviceVersion;
    }
    public void setServiceVersion(String serviceVersion) {
        this.serviceVersion = serviceVersion;
    }
}
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public class BaseStarterService {
    public void addServiceName(BaseServiceProperties baseServiceProperties){
        System.out.println("serviceName:"+baseServiceProperties.getServiceName()+"----"+"serviceVersion"+baseServiceProperties.getServiceVersion());
    }
}
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//判断是否windows系统
public class WindowsCondition implements Condition {
    private final static String WINDOWS="Windows";
    /**
     * ConditionContext：判断条件能使用的上下文（环境）
     * AnnotatedTypeMetadata：注释信息
     */
    public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
        //获取当前环境变量
        Environment environment=conditionContext.getEnvironment();
        //获取bean注册器
        BeanDefinitionRegistry registry = conditionContext.getRegistry();
        //能获取到ioc使用的beanfactory
        ConfigurableListableBeanFactory beanFactory = conditionContext.getBeanFactory();
        //获取环境变量中操作系统
        String property = environment.getProperty("os.name");
        //判断操作系统是否为windows
        if(property.contains(WINDOWS)){
            //判断是否存在baseWindowsSevice类，不存在则进行bean注册
            boolean isWindowsSevice = registry.containsBeanDefinition("baseStarterService");
            if(!isWindowsSevice){
                //指定Bean定义信息；（Bean的类型，Bean的一系列信息）
                RootBeanDefinition beanDefinition = new RootBeanDefinition(BaseStarterService.class);
                //注册一个Bean，指定bean名
                registry.registerBeanDefinition("baseStarterService", beanDefinition);
                BaseStarterService windowsSevice = (BaseStarterService)beanFactory.getBean("baseStarterService");
            }
            return true;
        }
        return false;
    }
}
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@Configuration
//自动加载配置文件属性值
@EnableConfigurationProperties(BaseServiceProperties.class)
@Import(BeanConfiguration.class)
//判断当前环境是否为windows
@Conditional(WindowsCondition.class)：
//判断属性spring.project.ThirdPartySystemService.isPassword是否等于true
@ConditionalOnProperty(prefix = "spring.project.ThirdPartySystemService",value = "enablePassword", havingValue = "true",matchIfMissing = true)
public class AutoConfigurationPassoword {
    @Autowired
    private BaseServiceProperties baseServiceProperties;
    @Autowired
    private BaseStarterService baseWindowsService;
    //加载第三方系统service
    @Bean("thirdPartySystemService")
    public ThirdPartySystemService thirdPartySystemService(){
        baseWindowsService.addServiceName(baseServiceProperties);
        return new ThirdPartySystemService();
    }
    @Bean
    //判断IOC容器中是否存在ThirdPartySystemService类，存在则创建PasswordService bean
    @ConditionalOnClass(ThirdPartySystemService.class)
    public PasswordService passwordService(){
        baseWindowsService.addServiceName(baseServiceProperties);
        return new PasswordService();
    }
}
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org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  com.cn.ccww.configuration.AutoConfigurationPassoword
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<dependencies>
        <dependency>
            <artifactId>spring-boot-starter-base-service</artifactId>
            <groupId>com.cn.ccww</groupId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
</dependencies>
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//自定义Starter配置
//当该属性的值不为true时，才不会启动自定义starter
spring.project.ThirdPartySystemService.enablePassword=true
project.starter.serviceName=ccww
project.starter.serviceVersion=1.0
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