SpringBoot 2.0 系列006 --啟動實戰之注解使用

一些誤區說明

網上很多教程預設使用SpringBootApplcation注解，且隻用這個即可掃描啟動類包下所有的bean。而官方預設教程使用的是@EnableAutoConfiguration，這個注解和SpringBootApplication注解的差別是什麼？

參閱2.0.1官方文檔說明

If you don’t want to use @SpringBootApplication, the @EnableAutoConfiguration and @ComponentScan annotations that it imports defines that behaviour so you can also use that instead.

意思是如果你不想用@SpringBootApplication 可以使用@EnableAutoConfiguration and @ComponentScan 注解來代替它

@SpringBootApplication注解說明

很多開發者喜歡它們的app能auto-configuration, component scan 和在啟動類中做額外配置。那麼@SpringBootApplication可以滿足你的這三項要求

@EnableAutoConfiguration ：開啟自動配置
@ComponentScan ：開啟application所在包下的掃描
@Configuration ：允許你注冊額外的bean或者導入額外的配置classes

SpringBoot是如何掃描到我們的class的？

流程圖

原 SpringBoot 2.0 系列00SpringBoot 2.0 系列006 --啟動實戰之注解使用

從流程圖可知，在refreshContext時，會調用上層的refresh方法觸發invokeBeanFactoryPostProcessors，在到後邊會觸發到的ComponentScanAnnotationParser類中

ComponentScanAnnotationParser.java

在此方法中，我們可以判定出我們的basePackages目錄以友善我們掃描。

public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, final String declaringClass) {
		ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry,
				componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader);

		Class<? extends BeanNameGenerator> generatorClass = componentScan.getClass("nameGenerator");
		boolean useInheritedGenerator = (BeanNameGenerator.class == generatorClass);
		scanner.setBeanNameGenerator(useInheritedGenerator ? this.beanNameGenerator :
				BeanUtils.instantiateClass(generatorClass));

		ScopedProxyMode scopedProxyMode = componentScan.getEnum("scopedProxy");
		if (scopedProxyMode != ScopedProxyMode.DEFAULT) {
			scanner.setScopedProxyMode(scopedProxyMode);
		}
		else {
			Class<? extends ScopeMetadataResolver> resolverClass = componentScan.getClass("scopeResolver");
			scanner.setScopeMetadataResolver(BeanUtils.instantiateClass(resolverClass));
		}

		scanner.setResourcePattern(componentScan.getString("resourcePattern"));

		for (AnnotationAttributes filter : componentScan.getAnnotationArray("includeFilters")) {
			for (TypeFilter typeFilter : typeFiltersFor(filter)) {
				scanner.addIncludeFilter(typeFilter);
			}
		}
		for (AnnotationAttributes filter : componentScan.getAnnotationArray("excludeFilters")) {
			for (TypeFilter typeFilter : typeFiltersFor(filter)) {
				scanner.addExcludeFilter(typeFilter);
			}
		}

		boolean lazyInit = componentScan.getBoolean("lazyInit");
		if (lazyInit) {
			scanner.getBeanDefinitionDefaults().setLazyInit(true);
		}

		Set<String> basePackages = new LinkedHashSet<>();
		String[] basePackagesArray = componentScan.getStringArray("basePackages");
		for (String pkg : basePackagesArray) {
			String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg),
					ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
			Collections.addAll(basePackages, tokenized);
		}
		for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) {
			basePackages.add(ClassUtils.getPackageName(clazz));
		}
		// 預設使用@componentScan 不寫basePackages則使用此處做為基礎包路徑
		if (basePackages.isEmpty()) {
		    // declaringClass=com.ricky.SpringBootApplication05
		    // 即 com.ricky
			basePackages.add(ClassUtils.getPackageName(declaringClass));
		}

		scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) {
			@Override
			protected boolean matchClassName(String className) {
				return declaringClass.equals(className);
			}
		});
		return scanner.doScan(StringUtils.toStringArray(basePackages));
	}

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.ClassPathScanningCandidateComponentProvider

會掃描我們啟動類packageSearchPath所在目錄下的所有class,最終裝載到Set candidates對象中。

private Set<BeanDefinition> scanCandidateComponents(String basePackage) {
		Set<BeanDefinition> candidates = new LinkedHashSet<>();
		try {
			String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
					resolveBasePackage(basePackage) + '/' + this.resourcePattern;
			Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
			boolean traceEnabled = logger.isTraceEnabled();
			boolean debugEnabled = logger.isDebugEnabled();
			for (Resource resource : resources) {
				if (traceEnabled) {
					logger.trace("Scanning " + resource);
				}
				if (resource.isReadable()) {
					try {
						MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);
						if (isCandidateComponent(metadataReader)) {
							ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
							sbd.setResource(resource);
							sbd.setSource(resource);
							if (isCandidateComponent(sbd)) {
								if (debugEnabled) {
									logger.debug("Identified candidate component class: " + resource);
								}
								candidates.add(sbd);
							}
							else {
								if (debugEnabled) {
									logger.debug("Ignored because not a concrete top-level class: " + resource);
								}
							}
						}
						else {
							if (traceEnabled) {
								logger.trace("Ignored because not matching any filter: " + resource);
							}
						}
					}
					catch (Throwable ex) {
						throw new BeanDefinitionStoreException(
								"Failed to read candidate component class: " + resource, ex);
					}
				}
				else {
					if (traceEnabled) {
						logger.trace("Ignored because not readable: " + resource);
					}
				}
			}
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
		}
		return candidates;
	}

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相關圖

項目目錄結構

掃描到的目錄

掃描到類

@SpringBootApplication 使用

注解源碼

源碼可以解釋為什麼官方說一般可以使用@EnableAutoConfiguration和 @ComponentScan 進行替代。

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
		@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {

	@AliasFor(annotation = EnableAutoConfiguration.class)
	Class<?>[] exclude() default {};

	@AliasFor(annotation = EnableAutoConfiguration.class)
	String[] excludeName() default {};

	@AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
	String[] scanBasePackages() default {};

	@AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
	Class<?>[] scanBasePackageClasses() default {};

}

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exclude 廢棄指定class的EnableAutoConfiguration類型

隻支援org.springframework.boot.autoconfigure包下的

@SpringBootApplication(exclude = HibernateJpaAutoConfiguration.class)

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excludeName 廢棄指定全類名的EnableAutoConfiguration類型

隻支援org.springframework.boot.autoconfigure包下的

@SpringBootApplication(excludeName = "org.springframework.boot.autoconfigure.orm.jpaHibernateJpaAutoConfiguration.class")

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scanBasePackages 指定掃描的包

@SpringBootApplication(scanBasePackages = {"com.ricky","com.ricky02"})

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scanBasePackageClasses 指定含有ComponentScan的類

可以自定義

@Configuration
@ComponentScan
public class Ricky03Config {
}

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@SpringBootApplication(scanBasePackages = {"com.ricky","com.ricky02"},scanBasePackageClasses = Ricky03Config.class)

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替代SpringBootApplication注解的方式

和實作上述功能一樣的方式，需要EnableAutoConfiguration、ComponentScan或者配合Import

@Configuration
@ComponentScan
public class Ricky04Config {
}

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@EnableAutoConfiguration
@ComponentScan(basePackages = {"com.ricky","com.ricky02","com.ricky03"},basePackageClasses = {Ricky04Config.class})
//@Import({Ricky04Config.class}) //ricky04目錄的也掃描進來
public class SpringBootApplication06_3 {
    /**
     * 開啟SpringBoot服務
     * @param args
     */
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(SpringBootApplication06_3.class, args);

        String[] names = context.getBeanDefinitionNames();
        for (String name:names){
            System.out.println(name);
        }

        context.close();
    }
}

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Import

import一般可以引入我們的@configuration相關的類。我們可以利用import和Configuration來實作開啟動态注入bean對象的場景。

- 說明

這裡是假定我們redis執行個體都是通過公共子產品來調用，類似單獨的SB項目子產品獨立管理。在其他子產品使用的時候需要引入該子產品。

- 定義一個開關注解

公共子產品中

/**
 * 自定義開啟redis
 *
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(RedisConfig.class)
public @interface EnableZDRedis {
}

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- redisConfig

公共子產品中

@Configuration
@ConditionalOnClass(Jedis.class)
public class RedisConfig {

    @Bean
    @ConditionalOnMissingBean
    public Jedis jedis(){
        return new Jedis("127.0.0.1",6379);
    }
}

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- 使用

調用子產品中,開啟我們定義的注解即可。

@SpringBootApplication
@EnableZDRedis
public class SpringBootApplication06_2 {
    @AutoWired
    private Jedis jedis;
}

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示範項目位址,歡迎fork和star

碼雲：SpringBootLearn

原 SpringBoot 2.0 系列00SpringBoot 2.0 系列006 --啟動實戰之注解使用

SpringBoot 2.0 系列006 --啟動實戰之注解使用

一些誤區說明

@SpringBootApplication注解說明

SpringBoot是如何掃描到我們的class的？

ComponentScanAnnotationParser.java

.ClassPathScanningCandidateComponentProvider

@SpringBootApplication 使用

替代SpringBootApplication注解的方式

示範項目位址,歡迎fork和star