Nicksxs's Blog

What hurts more, the pain of hard work or the pain of regret?

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又到半年总结时，第一次写总结类型的文章感觉挺好写的，但是后面总觉得这过去的一段时间所做的事情，能力上的成长低于预期，但是是需要总结下，找找问题，顺便展望下未来。

这一年做的最让自己满意的应该就是看了一些书，由折腾群洋总发起的读书打卡活动，到目前为止已经读完了这几本书，《cUrl 必知必会》，《古董局中局 1》，《古董局中局 2》，《算法图解》，《每天 5 分钟玩转 Kubernetes》《幸福了吗？》《高可用可伸缩微服务架构：基于 Dubbo、Spring Cloud和 Service Mesh》《Rust 权威指南》后面可以写个专题说说看的这些书，虽然每天打卡如果时间安排不好，并且看的书像 rust 这样比较难的话还是会有点小焦虑，不过也是个调整过程，一方面可以在白天就抽空看一会，然后也不必要每次都看很大一章，注重吸收。

技术上的成长的话，有一些比较小的长进吧，对于一些之前忽视的 synchronized，ThreadLocal 和 AQS 等知识点做了下查漏补缺了，然后多了解了一些 Java 垃圾回收的内容，但是在实操上还是比较欠缺，成型的技术方案，架构上所谓的优化也比较少，一些想法也还有考虑不周全的地方，还需要多花时间和心思去学习加强，特别是在目前已经有的基础上如何做系统深层次的优化，既不要是鸡毛蒜皮的，也不能出现一些不可接受的问题和故障，这是个很重要的课题，需要好好学习，后面考虑定一些周期性目标，两个月左右能有一些成果和总结。

另外一部分是自己的服务，因为 ucloud 的机器太贵就没续费了，所以都迁移到腾讯云的小机器上了，顺便折腾了一点点 traefik，但是还很不熟练，不太习惯这一套，一方面是 docker 还不习惯，这也加重了对这套环境的不适应，还是习惯裸机部署，另一方面就是 k8s 了，家里的机器还没虚拟化，没有很好的条件可以做实验，这也是读书打卡的一个没做好的点，整体的学习效果受限于深度和实操，后面是看都是用 traefik，也找到了一篇文章可以 traefik 转发到裸机应用，因为主仓库用的是裸机的 gogs。

还有就是运动减肥上，唉，这又是很大的一个痛点，基本没效果，只是还算稳定，昨天看到一个视频说还需要力量训练来增肌，以此可以提升基础代谢，打算往这个方向尝试下，因为今天没有疫情限制了，在 6 月底完成了 200 公里的跑步小目标，只是有些膝盖跟大腿根外侧不适，抽空得去看下医生，后面打算每天也能做点卷腹跟俯卧撑。

下半年还希望能继续多看看书，比很多网上各种乱七八糟的文章会好很多，结合豆瓣评分，找一些评价高一些的文章，但也不是说分稍低点的就不行，有些也看人是不是适合，一般 6 分以上评价比较多的就可以试试。

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springboot 自动装配调用链

springboot 相比 spring能更方便开发人员上手，比较重要的一点就是自动装配，大致来看下这个逻辑

public static void main(String[] args) {
		SpringApplication.run(SpbDemoApplication.class, args);
	}

	/**
	 * Static helper that can be used to run a {@link SpringApplication} from the
	 * specified source using default settings.
	 * @param primarySource the primary source to load
	 * @param args the application arguments (usually passed from a Java main method)
	 * @return the running {@link ApplicationContext}
	 */

然后就是上面调用的 run 方法

public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
	return run(new Class<?>[] { primarySource }, args);
}

/**
 * Static helper that can be used to run a {@link SpringApplication} from the
 * specified sources using default settings and user supplied arguments.
 * @param primarySources the primary sources to load
 * @param args the application arguments (usually passed from a Java main method)
 * @return the running {@link ApplicationContext}
 */

继续往下看

public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
	return new SpringApplication(primarySources).run(args);
}

调用SpringApplication的构造方法

/**
 * Create a new {@link SpringApplication} instance. The application context will load
 * beans from the specified primary sources (see {@link SpringApplication class-level}
 * documentation for details. The instance can be customized before calling
 * {@link #run(String...)}.
 * @param primarySources the primary bean sources
 * @see #run(Class, String[])
 * @see #SpringApplication(ResourceLoader, Class...)
 * @see #setSources(Set)
 */

public SpringApplication(Class<?>... primarySources) {
	this(null, primarySources);
}

/**
 * Create a new {@link SpringApplication} instance. The application context will load
 * beans from the specified primary sources (see {@link SpringApplication class-level}
 * documentation for details. The instance can be customized before calling
 * {@link #run(String...)}.
 * @param resourceLoader the resource loader to use
 * @param primarySources the primary bean sources
 * @see #run(Class, String[])
 * @see #setSources(Set)
 */
@SuppressWarnings({ "unchecked", "rawtypes" })
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
	this.resourceLoader = resourceLoader;
	Assert.notNull(primarySources, "PrimarySources must not be null");
	this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
	this.webApplicationType = WebApplicationType.deduceFromClasspath();
   // 注意看这里的，通过 SpringFactories 获取
	this.bootstrapRegistryInitializers = getBootstrapRegistryInitializersFromSpringFactories();
	setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
	setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
	this.mainApplicationClass = deduceMainApplicationClass();
}

这里就是重点了

private List<BootstrapRegistryInitializer> getBootstrapRegistryInitializersFromSpringFactories() {
	ArrayList<BootstrapRegistryInitializer> initializers = new ArrayList<>();
	getSpringFactoriesInstances(Bootstrapper.class).stream()
			.map((bootstrapper) -> ((BootstrapRegistryInitializer) bootstrapper::initialize))
			.forEach(initializers::add);
	initializers.addAll(getSpringFactoriesInstances(BootstrapRegistryInitializer.class));
	return initializers;
}
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
	return getSpringFactoriesInstances(type, new Class<?>[] {});
}

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
	ClassLoader classLoader = getClassLoader();
	// Use names and ensure unique to protect against duplicates
   // 去加载所有FACTORIES_RESOURCE_LOCATION路径下面，也就是 META-INF/spring.factories
	Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
	List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
	AnnotationAwareOrderComparator.sort(instances);
	return instances;
}

/**
 * Load the fully qualified class names of factory implementations of the
 * given type from {@value #FACTORIES_RESOURCE_LOCATION}, using the given
 * class loader.
 * <p>As of Spring Framework 5.3, if a particular implementation class name
 * is discovered more than once for the given factory type, duplicates will
 * be ignored.
 * @param factoryType the interface or abstract class representing the factory
 * @param classLoader the ClassLoader to use for loading resources; can be
 * {@code null} to use the default
 * @throws IllegalArgumentException if an error occurs while loading factory names
 * @see #loadFactories
 */
public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
	ClassLoader classLoaderToUse = classLoader;
	if (classLoaderToUse == null) {
		classLoaderToUse = SpringFactoriesLoader.class.getClassLoader();
	}
	String factoryTypeName = factoryType.getName();
	return loadSpringFactories(classLoaderToUse).getOrDefault(factoryTypeName, Collections.emptyList());
}
   private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) {
	Map<String, List<String>> result = cache.get(classLoader);
	if (result != null) {
		return result;
	}

	result = new HashMap<>();
	try {
           // 获取此 resources，作为 AutoConfiguration 的配置
		Enumeration<URL> urls = classLoader.getResources(FACTORIES_RESOURCE_LOCATION);
		while (urls.hasMoreElements()) {
			URL url = urls.nextElement();
			UrlResource resource = new UrlResource(url);
			Properties properties = PropertiesLoaderUtils.loadProperties(resource);
			for (Map.Entry<?, ?> entry : properties.entrySet()) {
				String factoryTypeName = ((String) entry.getKey()).trim();
				String[] factoryImplementationNames =
						StringUtils.commaDelimitedListToStringArray((String) entry.getValue());
				for (String factoryImplementationName : factoryImplementationNames) {
					result.computeIfAbsent(factoryTypeName, key -> new ArrayList<>())
							.add(factoryImplementationName.trim());
				}
			}
		}

		// Replace all lists with unmodifiable lists containing unique elements
		result.replaceAll((factoryType, implementations) -> implementations.stream().distinct()
				.collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList)));
		cache.put(classLoader, result);
	}
	catch (IOException ex) {
		throw new IllegalArgumentException("Unable to load factories from location [" +
				FACTORIES_RESOURCE_LOCATION + "]", ex);
	}
	return result;
}

我们可以看下 spring-boot-autoconfigure 的 META-INF/spring.factories

# Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener

# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.autoconfigure.BackgroundPreinitializer

# Environment Post Processors
org.springframework.boot.env.EnvironmentPostProcessor=\
org.springframework.boot.autoconfigure.integration.IntegrationPropertiesEnvironmentPostProcessor

# Auto Configuration Import Listeners
org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\
org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener

# Auto Configuration Import Filters
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
org.springframework.boot.autoconfigure.condition.OnClassCondition,\
org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition

# 注意这里，其实就是类似于 dubbo spi 的通过 org.springframework.boot.autoconfigure.EnableAutoConfiguration作为 key
# 获取下面所有的 AutoConfiguration 配置类
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.context.LifecycleAutoConfiguration,\
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\
org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.r2dbc.R2dbcDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.r2dbc.R2dbcRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.ElasticsearchRestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\
org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\
org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,\
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\
org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\
org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\
org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
org.springframework.boot.autoconfigure.availability.ApplicationAvailabilityAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\
org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
org.springframework.boot.autoconfigure.neo4j.Neo4jAutoConfiguration,\
org.springframework.boot.autoconfigure.netty.NettyAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\
org.springframework.boot.autoconfigure.r2dbc.R2dbcAutoConfiguration,\
org.springframework.boot.autoconfigure.r2dbc.R2dbcTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketRequesterAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketServerAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketStrategiesAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.rsocket.RSocketSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.saml2.Saml2RelyingPartyAutoConfiguration,\
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
org.springframework.boot.autoconfigure.sql.init.SqlInitializationAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.ClientHttpConnectorAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration

# Failure analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.autoconfigure.data.redis.RedisUrlSyntaxFailureAnalyzer,\
org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\
org.springframework.boot.autoconfigure.flyway.FlywayMigrationScriptMissingFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer,\
org.springframework.boot.autoconfigure.r2dbc.ConnectionFactoryBeanCreationFailureAnalyzer,\
org.springframework.boot.autoconfigure.session.NonUniqueSessionRepositoryFailureAnalyzer

# Template availability providers
org.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.mustache.MustacheTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.web.servlet.JspTemplateAvailabilityProvider

# DataSource initializer detectors
org.springframework.boot.sql.init.dependency.DatabaseInitializerDetector=\
org.springframework.boot.autoconfigure.flyway.FlywayMigrationInitializerDatabaseInitializerDetector

上面根据 org.springframework.boot.autoconfigure.EnableAutoConfiguration 获取的各个配置类，在通过反射加载就能得到一堆 JavaConfig配置类，然后再根据 ConditionalOnProperty等条件配置加载具体的 bean，大致就是这么个逻辑

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题目介绍

给定 n 个非负整数表示每个宽度为 1 的柱子的高度图，计算按此排列的柱子，下雨之后能接多少雨水。

示例


输入：height = [0,1,0,2,1,0,1,3,2,1,2,1]
输出：6
解释：上面是由数组 [0,1,0,2,1,0,1,3,2,1,2,1] 表示的高度图，在这种情况下，可以接 6 个单位的雨水（蓝色部分表示雨水）。

简单分析

其实最开始的想法是从左到右扫区间，就是示例中的第一个水槽跟第二个水槽都可以用这个办法解决

前面这种是属于右侧比左侧高的情况，对于左侧高右侧低的就不行了，（写这篇的时候想起来可以再反着扫一遍可能可以）

所以这个方案不好，贴一下这个方案的代码

public int trap(int[] height) {
    int lastLeft = -1;
    int sum = 0;
    int tempSum = 0;
    boolean startFlag = true;
    for (int j : height) {
        if (startFlag && j <= 0) {
            startFlag = false;
            continue;
        }
        if (j >= lastLeft) {
            sum += tempSum;
            tempSum = 0;
            lastLeft = j;
        } else {
            tempSum += lastLeft - j;
        }
    }
    return sum;
}

后面结合网上的解法，其实可以反过来，对于每个格子找左右侧的最大值，取小的那个和当前格子的差值就是这一个的储水量了

理解了这种想法，代码其实就不难了

代码

int n = height.length;
if (n <= 2) {
    return 0;
}
// 思路转变下，其实可以对于每一格算储水量，算法就是找到这一格左边的最高点跟这一格右边的最高点，
// 比较两侧的最高点，取小的那个，然后再跟当前格子的高度对比，差值就是当前格的储水量
int maxL[] = new int[n];
int maxR[] = new int[n];
int max = height[0];
maxL[0] = 0;
// 计算左侧的最高点
for (int i = 1; i < n - 1; i++) {
    maxL[i] = max;
    if (max < height[i]) {
        max = height[i];
    }
}
max = height[n - 1];
maxR[n - 1] = 0;
int tempSum, sum = 0;
// 计算右侧的最高点，并且同步算出来储水量，节省一个循环
for (int i = n - 2; i > 0; i--) {
    maxR[i] = max;
    if (height[i] > max) {
        max = height[i];
    }
    tempSum = Math.min(maxL[i], maxR[i]) - height[i];
    if (tempSum > 0) {
        sum += tempSum;
    }
}
return sum;

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Java并发

synchronized 的一些学习记录

jdk1.6 以后对 synchronized 进行了一些优化，包括偏向锁，轻量级锁，重量级锁等

这些锁的加锁方式大多跟对象头有关，我们可以查看 jdk 代码

首先对象头的位置注释

// Bit-format of an object header (most significant first, big endian layout below):
//
//  32 bits:
//  --------
//             hash:25 ------------>| age:4    biased_lock:1 lock:2 (normal object)
//             JavaThread*:23 epoch:2 age:4    biased_lock:1 lock:2 (biased object)
//             size:32 ------------------------------------------>| (CMS free block)
//             PromotedObject*:29 ---------->| promo_bits:3 ----->| (CMS promoted object)
//
//  64 bits:
//  --------
//  unused:25 hash:31 -->| unused:1   age:4    biased_lock:1 lock:2 (normal object)
//  JavaThread*:54 epoch:2 unused:1   age:4    biased_lock:1 lock:2 (biased object)
//  PromotedObject*:61 --------------------->| promo_bits:3 ----->| (CMS promoted object)
//  size:64 ----------------------------------------------------->| (CMS free block)
//
//  unused:25 hash:31 -->| cms_free:1 age:4    biased_lock:1 lock:2 (COOPs && normal object)
//  JavaThread*:54 epoch:2 cms_free:1 age:4    biased_lock:1 lock:2 (COOPs && biased object)
//  narrowOop:32 unused:24 cms_free:1 unused:4 promo_bits:3 ----->| (COOPs && CMS promoted object)
//  unused:21 size:35 -->| cms_free:1 unused:7 ------------------>| (COOPs && CMS free block)
enum { locked_value             = 0,
         unlocked_value           = 1,
         monitor_value            = 2,
         marked_value             = 3,
         biased_lock_pattern      = 5
};

我们可以用 java jol库来查看对象头，通过一段简单的代码来看下

public class ObjectHeaderDemo {
    public static void main(String[] args) throws InterruptedException {
        L l = new L();
        System.out.println(ClassLayout.parseInstance(l).toPrintable());
		}
}

Untitled

然后可以看到打印输出，当然这里因为对齐方式，我们看到的其实顺序是反过来的，按最后三位去看，我们这是 001，好像偏向锁都没开，这里使用的是 jdk1.8，默认开始偏向锁的，其实这里有涉及到了一个配置，jdk1.8 中偏向锁会延迟 4 秒开启，可以通过添加启动参数 -XX:+PrintFlagsFinal，看到

偏向锁延迟

因为在初始化的时候防止线程竞争有大量的偏向锁撤销升级，所以会延迟 4s 开启

我们再来延迟 5s 看看

public class ObjectHeaderDemo {
    public static void main(String[] args) throws InterruptedException {
				TimeUnit.SECONDS.sleep(5);
        L l = new L();
        System.out.println(ClassLayout.parseInstance(l).toPrintable());
		}
}

https://gitee.com/nicksxs/images/raw/master/uPic/2LBKpX.jpg

可以看到偏向锁设置已经开启了，我们来是一下加个偏向锁

public class ObjectHeaderDemo {
    public static void main(String[] args) throws InterruptedException {
        TimeUnit.SECONDS.sleep(5);
        L l = new L();
        System.out.println(ClassLayout.parseInstance(l).toPrintable());
        synchronized (l) {
            System.out.println("1\n" + ClassLayout.parseInstance(l).toPrintable());
        }
        synchronized (l) {
            System.out.println("2\n" + ClassLayout.parseInstance(l).toPrintable());
        }
		}
}

看下运行结果

https://gitee.com/nicksxs/images/raw/master/uPic/V2l78m.png

可以看到是加上了 101 = 5 也就是偏向锁，后面是线程 id

当我再使用一个线程来竞争这个锁的时候

public class ObjectHeaderDemo {
    public static void main(String[] args) throws InterruptedException {
        TimeUnit.SECONDS.sleep(5);
        L l = new L();
        System.out.println(ClassLayout.parseInstance(l).toPrintable());
        synchronized (l) {
            System.out.println("1\n" + ClassLayout.parseInstance(l).toPrintable());
        }
				Thread thread1 = new Thread() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(5L);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (l) {
                    System.out.println("thread1 获取锁成功");
                    System.out.println(ClassLayout.parseInstance(l).toPrintable());
                    try {
                        TimeUnit.SECONDS.sleep(5L);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        };
				thread1.start();
		}
}

https://gitee.com/nicksxs/images/raw/master/uPic/bRMvlR.png

可以看到变成了轻量级锁，在线程没有争抢，只是进行了切换，就会使用轻量级锁，当两个线程在竞争了，就又会升级成重量级锁

public class ObjectHeaderDemo {
    public static void main(String[] args) throws InterruptedException {
        TimeUnit.SECONDS.sleep(5);
        L l = new L();
        System.out.println(ClassLayout.parseInstance(l).toPrintable());
        synchronized (l) {
            System.out.println("1\n" + ClassLayout.parseInstance(l).toPrintable());
        }
        Thread thread1 = new Thread() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(5L);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (l) {
                    System.out.println("thread1 获取锁成功");
                    System.out.println(ClassLayout.parseInstance(l).toPrintable());
                    try {
                        TimeUnit.SECONDS.sleep(5L);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        };
        Thread thread2 = new Thread() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(5L);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (l) {
                    System.out.println("thread2 获取锁成功");
                    System.out.println(ClassLayout.parseInstance(l).toPrintable());
                }
            }
        };
        thread1.start();
        thread2.start();
    }
}

class L {
    private boolean myboolean = true;
}

https://gitee.com/nicksxs/images/raw/master/uPic/LMzMtR.png

可以看到变成了重量级锁。

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Synchronized 关键字在 Java 的并发体系里也是非常重要的一个内容，首先比较常规的是知道它使用的方式，可以锁对象，可以锁代码块，也可以锁方法，看一个简单的 demo

public class SynchronizedDemo {

    public static void main(String[] args) {
        SynchronizedDemo synchronizedDemo = new SynchronizedDemo();
        synchronizedDemo.lockMethod();
    }

    public synchronized void lockMethod() {
        System.out.println("here i'm locked");
    }

    public void lockSynchronizedDemo() {
        synchronized (this) {
            System.out.println("here lock class");
        }
    }
}

然后来查看反编译结果，其实代码（日光）之下并无新事，即使是完全不懂的也可以通过一些词义看出一些意义

  Last modified 2021年6月20日; size 729 bytes
  MD5 checksum dd9c529863bd7ff839a95481db578ad9
  Compiled from "SynchronizedDemo.java"
public class SynchronizedDemo
  minor version: 0
  major version: 53
  flags: (0x0021) ACC_PUBLIC, ACC_SUPER
  this_class: #2                          // SynchronizedDemo
  super_class: #9                         // java/lang/Object
  interfaces: 0, fields: 0, methods: 4, attributes: 1
Constant pool:
   #1 = Methodref          #9.#22         // java/lang/Object."<init>":()V
   #2 = Class              #23            // SynchronizedDemo
   #3 = Methodref          #2.#22         // SynchronizedDemo."<init>":()V
   #4 = Methodref          #2.#24         // SynchronizedDemo.lockMethod:()V
   #5 = Fieldref           #25.#26        // java/lang/System.out:Ljava/io/PrintStream;
   #6 = String             #27            // here i\'m locked
   #7 = Methodref          #28.#29        // java/io/PrintStream.println:(Ljava/lang/String;)V
   #8 = String             #30            // here lock class
   #9 = Class              #31            // java/lang/Object
  #10 = Utf8               <init>
  #11 = Utf8               ()V
  #12 = Utf8               Code
  #13 = Utf8               LineNumberTable
  #14 = Utf8               main
  #15 = Utf8               ([Ljava/lang/String;)V
  #16 = Utf8               lockMethod
  #17 = Utf8               lockSynchronizedDemo
  #18 = Utf8               StackMapTable
  #19 = Class              #32            // java/lang/Throwable
  #20 = Utf8               SourceFile
  #21 = Utf8               SynchronizedDemo.java
  #22 = NameAndType        #10:#11        // "<init>":()V
  #23 = Utf8               SynchronizedDemo
  #24 = NameAndType        #16:#11        // lockMethod:()V
  #25 = Class              #33            // java/lang/System
  #26 = NameAndType        #34:#35        // out:Ljava/io/PrintStream;
  #27 = Utf8               here i\'m locked
  #28 = Class              #36            // java/io/PrintStream
  #29 = NameAndType        #37:#38        // println:(Ljava/lang/String;)V
  #30 = Utf8               here lock class
  #31 = Utf8               java/lang/Object
  #32 = Utf8               java/lang/Throwable
  #33 = Utf8               java/lang/System
  #34 = Utf8               out
  #35 = Utf8               Ljava/io/PrintStream;
  #36 = Utf8               java/io/PrintStream
  #37 = Utf8               println
  #38 = Utf8               (Ljava/lang/String;)V
{
  public SynchronizedDemo();
    descriptor: ()V
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #1                  // Method java/lang/Object."<init>":()V
         4: return
      LineNumberTable:
        line 5: 0

  public static void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=2, locals=2, args_size=1
         0: new           #2                  // class SynchronizedDemo
         3: dup
         4: invokespecial #3                  // Method "<init>":()V
         7: astore_1
         8: aload_1
         9: invokevirtual #4                  // Method lockMethod:()V
        12: return
      LineNumberTable:
        line 8: 0
        line 9: 8
        line 10: 12

  public synchronized void lockMethod();
    descriptor: ()V
    flags: (0x0021) ACC_PUBLIC, ACC_SYNCHRONIZED
    Code:
      stack=2, locals=1, args_size=1
         0: getstatic     #5                  // Field java/lang/System.out:Ljava/io/PrintStream;
         3: ldc           #6                  // String here i\'m locked
         5: invokevirtual #7                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
         8: return
      LineNumberTable:
        line 13: 0
        line 14: 8

  public void lockSynchronizedDemo();
    descriptor: ()V
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=3, args_size=1
         0: aload_0
         1: dup
         2: astore_1
         3: monitorenter
         4: getstatic     #5                  // Field java/lang/System.out:Ljava/io/PrintStream;
         7: ldc           #8                  // String here lock class
         9: invokevirtual #7                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
        12: aload_1
        13: monitorexit
        14: goto          22
        17: astore_2
        18: aload_1
        19: monitorexit
        20: aload_2
        21: athrow
        22: return
      Exception table:
         from    to  target type
             4    14    17   any
            17    20    17   any
      LineNumberTable:
        line 17: 0
        line 18: 4
        line 19: 12
        line 20: 22
      StackMapTable: number_of_entries = 2
        frame_type = 255 /* full_frame */
          offset_delta = 17
          locals = [ class SynchronizedDemo, class java/lang/Object ]
          stack = [ class java/lang/Throwable ]
        frame_type = 250 /* chop */
          offset_delta = 4
}
SourceFile: "SynchronizedDemo.java"

其中lockMethod中可以看到是通过 ACC_SYNCHRONIZED flag 来标记是被 synchronized 修饰，前面的 ACC 应该是 access 的意思，并且通过 ACC_PUBLIC 也可以看出来他们是同一类访问权限关键字来控制的，而修饰类则是通过3: monitorenter和13: monitorexit来控制并发，这个是原来就知道，后来看了下才知道修饰方法是不一样的，但是在前期都比较诟病是 synchronized 的性能，像 monitor 也是通过操作系统的mutex lock互斥锁来实现的，相对是比较重的锁，于是在 JDK 1.6 之后对 synchronized 做了一系列优化，包括偏向锁，轻量级锁，并且包括像 ConcurrentHashMap 这类并发集合都有在使用 synchronized 关键字配合 cas 来做并发保护，

jdk 对于 synchronized 的优化主要在于多重状态锁的升级，最初会使用偏向锁，当一个线程访问同步块并获取锁时，会在对象头和栈帧中的锁记录里存储锁偏向的线程ID，以后该线程在进入和退出同步块时不需要进行CAS操作来加锁和解锁，只需简单地测试一下对象头的Mark Word里是否存储着指向当前线程的偏向锁。引入偏向锁是为了在无多线程竞争的情况下尽量减少不必要的轻量级锁执行路径，因为轻量级锁的获取及释放依赖多次CAS原子指令，而偏向锁只需要在置换ThreadID的时候依赖一次CAS原子指令（由于一旦出现多线程竞争的情况就必须撤销偏向锁，所以偏向锁的撤销操作的性能损耗必须小于节省下来的CAS原子指令的性能消耗）。
而当出现线程尝试进入同步块时发现已有偏向锁，并且是其他线程时，会将锁升级成轻量级锁，并且自旋尝试获取锁，如果自旋成功则表示获取轻量级锁成功，否则将会升级成重量级锁进行阻塞，当然这里具体的还很复杂，说的比较浅薄主体还是想将原先的阻塞互斥锁进行轻量化，区分特殊情况进行加锁。