SpringBoot 2.0 系列006 --启动实战之注解使用

SpringBoot 2.0 系列006 --启动实战之注解使用

一些误区说明

网上不少教程默认使用SpringBootApplcation注解，且只用这个便可扫描启动类包下全部的bean。 而官方默认教程使用的是@EnableAutoConfiguration，这个注解和SpringBootApplication注解的区别是什么？

• 参阅2.0.1官方文档说明

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.

意思是若是你不想用@SpringBootApplication 可使用@EnableAutoConfiguration and @ComponentScan 注解来代替它

@SpringBootApplication注解说明

不少开发者喜欢它们的app能auto-configuration, component scan 和在启动类中作额外配置。那么@SpringBootApplication能够知足你的这三项要求

• @EnableAutoConfiguration ：开启自动配置
• @ComponentScan ：开启application所在包下的扫描
• @Configuration ：容许你注册额外的bean或者导入额外的配置classes

SpringBoot是如何扫描到咱们的class的？

• 流程图

从流程图可知，在refreshContext时，会调用上层的refresh方法触发invokeBeanFactoryPostProcessors，在到后边会触发到的ComponentScanAnnotationParser类中

ComponentScanAnnotationParser.java

在此方法中，咱们能够断定出咱们的basePackages目录以方便咱们扫描。

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));
		}
		// 默认使用@componentScan 不写basePackages则使用此处作为基础包路径
		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));
	}

.ClassPathScanningCandidateComponentProvider

会扫描咱们启动类packageSearchPath所在目录下的全部class,最终装载到Set candidates对象中。

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;
	}

• 相关图

项目目录结构

扫描到的目录

扫描到类

@SpringBootApplication 使用

• 注解源码

源码能够解释 为何官方说通常可使用@EnableAutoConfiguration和 @ComponentScan 进行替代。

@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 {};

}

• exclude 废弃指定class的EnableAutoConfiguration类型

只支持org.springframework.boot.autoconfigure包下的

@SpringBootApplication(exclude = HibernateJpaAutoConfiguration.class)

• excludeName 废弃指定全类名的EnableAutoConfiguration类型

只支持org.springframework.boot.autoconfigure包下的

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

• scanBasePackages 指定扫描的包

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

• scanBasePackageClasses 指定含有ComponentScan的类

能够自定义

@Configuration
@ComponentScan
public class Ricky03Config {
}

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

替代SpringBootApplication注解的方式

和实现上述功能同样的方式，须要EnableAutoConfiguration、ComponentScan或者配合Import

@Configuration
@ComponentScan
public class Ricky04Config {
}

@EnableAutoConfiguration
@ComponentScan(basePackages = {"com.ricky","com.ricky02","com.ricky03"},basePackageClasses = {Ricky04Config.class})
//@Import({Ricky04Config.class}) //ricky04目录的也扫描进来
public class SpringBootApplication06_3 {
    /**
     * 开启SpringBoot服务
     * @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();
    }
}

• Import

import通常能够引入咱们的@configuration相关的类。 咱们能够利用import和Configuration来实现开启 动态注入bean对象的场景。

• • 说明

这里是假定咱们redis实例都是经过公共模块来调用，相似单独的SB项目模块独立管理。在其余模块使用的时候须要引入该模块。

• • 定义一个开关注解

公共模块中

/**
 * 自定义开启redis
 *
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(RedisConfig.class)
public @interface EnableZDRedis {
}

• • redisConfig

公共模块中

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

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

• • 使用

调用模块中,开启咱们定义的注解便可。

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

演示项目地址,欢迎fork和star

码云：SpringBootLearn

最后

• SpringBoot 2.0 系列001 -- 入门介绍以及相关概念

• SpringBoot 2.0 系列002 --运行流程分析

• SpringBoot 2.0 系列003 -- 自定义Parent

• SpringBoot 2.0 系列004 -- 启动实战之配置文件

• SpringBoot 2.0 系列005 -- 启动实战之SpringApplication应用

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