前言：
当前各位老铁们对“让apache启动时可以动态加载文件吗为什么”都比较着重，咱们都想要学习一些“让apache启动时可以动态加载文件吗为什么”的相关知识。那么小编也在网摘上收集了一些对于“让apache启动时可以动态加载文件吗为什么””的相关内容，希望兄弟们能喜欢，兄弟们快快来了解一下吧！模块加载机制基本概述
Module 是 Skywalking 在 OAP 提供的一种管理功能特性的机制。通过 Module 机制，可以方便的定义模块，并且可以提供多种实现，在配置文件中任意选择实现。
模块相关配置文件可以参考：Backend setup、Configuration Vocabulary
类图
Skywalking 中模块管理相关功能都在 org.apache.skywalking.oap.server.library.module 包下。
通过类图可以了解 Skywalking 模块机制大致分成如下几个模块：
模块配置： ApplicationConfiguration 、 ModuleConfiguration 、 ProviderConfigurationPS：刚好对应 application.yml 三层结构：模块->模块实现->某个模块实现的配置。模块定义类： ModuleDefine模块提供类： ModuleProvider服务： Service管理类： ModuleManager一些辅助类ModuleDefineHolder ：模块管理类需要实现的接口，提供查找模块相关功能ModuleProviderHolder ：模块定义类需要实现的接口，提供获取模块的服务类功能ModuleServiceHolder ：模块提供类需要实现的接口，提供注册服务实现、获取服务对象的功能ModuleConfig ：模块配置类，模块定义类会将ProviderConfiguration 映射为 ModuleConfigApplicationConfigLoader：ApplicationConfiguration 的辅助类，将 application.yml 配置文件加载到内存， 设置 selector 对应的 Provider 的配置信息
类图源文件：Skywalking-Module.uml
源码解析ModuleDefine
package org.apache.skywalking.oap.server.library.module;import java.lang.reflect.Field;import java.util.Enumeration;import java.util.Properties;import java.util.ServiceLoader;import org.slf4j.Logger;import org.slf4j.LoggerFactory;// 模块定义public abstract class ModuleDefine implements ModuleProviderHolder { private static final Logger LOGGER = LoggerFactory.getLogger(ModuleDefine.class); // 模块实际的 private ModuleProvider loadedProvider = null; private final String name; public ModuleDefine(String name) { this.name = name; } // 模块名 public final String name() { return name; } // 实现类可以定义模块提供的服务类 public abstract Class[] services(); /** * Run the prepare stage for the module, including finding all potential providers, and asking them to prepare. * * @param moduleManager of this module * @param configuration of this module * @throws ProviderNotFoundException when even don't find a single one providers. */ // 准备阶段，找到configuration配置类对应的ModuleProvider对象，进行初始化操作 void prepare( // 模块管理对象 ModuleManager moduleManager, // 模块配置类 ApplicationConfiguration.ModuleConfiguration configuration, // 模块提供类的服务加载器 ServiceLoader<ModuleProvider> moduleProviderLoader ) throws ProviderNotFoundException, ServiceNotProvidedException, ModuleConfigException, ModuleStartException { // 找到configuration配置类对应的ModuleProvider对象 for (ModuleProvider provider : moduleProviderLoader) { if (!configuration.has(provider.name())) { continue; } if (provider.module().equals(getClass())) { if (loadedProvider == null) { loadedProvider = provider; loadedProvider.setManager(moduleManager); loadedProvider.setModuleDefine(this); } else { throw new DuplicateProviderException(this.name() + " module has one " + loadedProvider.name() + "[" + loadedProvider.getClass().getName() + "] provider already, " + provider.name() + "[" + provider.getClass().getName() + "] is defined as 2nd provider."); } } } if (loadedProvider == null) { throw new ProviderNotFoundException(this.name() + " module no provider found."); } // 复制提供类的配置文件至ModuleConfig对象 LOGGER.info("Prepare the {} provider in {} module.", loadedProvider.name(), this.name()); try { copyProperties( loadedProvider.createConfigBeanIfAbsent(), configuration.getProviderConfiguration(loadedProvider.name()), this.name(), loadedProvider.name() ); } catch (IllegalAccessException e) { throw new ModuleConfigException(this.name() + " module config transport to config bean failure.", e); } // 模块提供对象进入准备阶段 loadedProvider.prepare(); } // 使用反射复制属性 private void copyProperties(ModuleConfig dest, Properties src, String moduleName, String providerName) throws IllegalAccessException { if (dest == null) { return; } Enumeration<?> propertyNames = src.propertyNames(); while (propertyNames.hasMoreElements()) { String propertyName = (String) propertyNames.nextElement(); Class<? extends ModuleConfig> destClass = dest.getClass(); try { Field field = getDeclaredField(destClass, propertyName); field.setAccessible(true); field.set(dest, src.get(propertyName)); } catch (NoSuchFieldException e) { LOGGER.warn(propertyName + " setting is not supported in " + providerName + " provider of " + moduleName + " module"); } } } private Field getDeclaredField(Class<?> destClass, String fieldName) throws NoSuchFieldException { if (destClass != null) { Field[] fields = destClass.getDeclaredFields(); for (Field field : fields) { if (field.getName().equals(fieldName)) { return field; } } return getDeclaredField(destClass.getSuperclass(), fieldName); } throw new NoSuchFieldException(); } // 获取模块定义对应的Provider对象 @Override public final ModuleProvider provider() throws DuplicateProviderException, ProviderNotFoundException { if (loadedProvider == null) { throw new ProviderNotFoundException("There is no module provider in " + this.name() + " module!"); } return loadedProvider; }}ModuleProviderHolderpackage org.apache.skywalking.oap.server.library.module;// 模块提供持有接口，通过该接口，可以获取模块Provider对象对应的Service持有接口，从而拿到模块Provider对象对应的服务对象public interface ModuleProviderHolder { // 获取模块提供对象 ModuleServiceHolder provider() throws DuplicateProviderException, ProviderNotFoundException;}ModuleProviderpackage org.apache.skywalking.oap.server.library.module;import java.util.HashMap;import java.util.Map;import lombok.Setter;// 模块提供抽象类，所有的模块提供类都需要继承该抽象类// 一个模块定义可以配置多个模块提供类，通过在application.yml进行切换public abstract class ModuleProvider implements ModuleServiceHolder { // 模块管理器 @Setter private ModuleManager manager; // 模块定义对象 @Setter private ModuleDefine moduleDefine; // 模块提供对应的服务对象map private final Map<Class<? extends Service>, Service> services = new HashMap<>(); public ModuleProvider() { } protected final ModuleManager getManager() { return manager; } // 获取服务提供实现类的name，需要子类实现 public abstract String name(); // 定义模块提供者所实现的模块定义类 public abstract Class<? extends ModuleDefine> module(); // 创建模块定义配置对象 public abstract ModuleConfig createConfigBeanIfAbsent(); // 准备阶段（初始化与其他模块无关的事情） public abstract void prepare() throws ServiceNotProvidedException, ModuleStartException; // 启动阶段（该阶段模块间可以互相操作） public abstract void start() throws ServiceNotProvidedException, ModuleStartException; // 完成后通知阶段（在所有模块成功启动后执行） public abstract void notifyAfterCompleted() throws ServiceNotProvidedException, ModuleStartException; // 该模块需要依赖的其他模块名 public abstract String[] requiredModules(); // 注册服务实现类 @Override public final void registerServiceImplementation(Class<? extends Service> serviceType, Service service) throws ServiceNotProvidedException { if (serviceType.isInstance(service)) { this.services.put(serviceType, service); } else { throw new ServiceNotProvidedException(serviceType + " is not implemented by " + service); } } // 确保所有服务被实现 void requiredCheck(Class<? extends Service>[] requiredServices) throws ServiceNotProvidedException { if (requiredServices == null) return; for (Class<? extends Service> service : requiredServices) { if (!services.containsKey(service)) { throw new ServiceNotProvidedException("Service:" + service.getName() + " not provided"); } } if (requiredServices.length != services.size()) { throw new ServiceNotProvidedException("The " + this.name() + " provider in " + moduleDefine.name() + " moduleDefine provide more service implementations than ModuleDefine requirements."); } } // 获取服务实现对象 @Override public @SuppressWarnings("unchecked") <T extends Service> T getService(Class<T> serviceType) throws ServiceNotProvidedException { Service serviceImpl = services.get(serviceType); if (serviceImpl != null) { return (T) serviceImpl; } throw new ServiceNotProvidedException("Service " + serviceType.getName() + " should not be provided, based on moduleDefine define."); } ModuleDefine getModule() { return moduleDefine; } String getModuleName() { return moduleDefine.name(); }}ModuleConfigpackage org.apache.skywalking.oap.server.library.module;// 模块配置类public abstract class ModuleConfig {}ModuleServiceHolderpackage org.apache.skywalking.oap.server.library.module;// 模块服务持有接口public interface ModuleServiceHolder { // 注册服务实现对象 void registerServiceImplementation(Class<? extends Service> serviceType, Service service) throws ServiceNotProvidedException; // 获取服务实现对象 <T extends Service> T getService(Class<T> serviceType) throws ServiceNotProvidedException;}Servicepackage org.apache.skywalking.oap.server.library.module;// 服务接口public interface Service {}ModuleDefineHolderpackage org.apache.skywalking.oap.server.library.module;// 模块定义持有接口public interface ModuleDefineHolder { // 判断是否有该模块 boolean has(String moduleName); // 通过模块名获取模块定义对象 ModuleProviderHolder find(String moduleName) throws ModuleNotFoundRuntimeException;}ModuleManagerpackage org.apache.skywalking.oap.server.library.module;import java.util.Arrays;import java.util.HashMap;import java.util.LinkedList;import java.util.Map;import java.util.ServiceLoader;// 模块管理类，管理模块的生命周期public class ModuleManager implements ModuleDefineHolder { // 所有模块是否已经通过准备阶段 private boolean isInPrepareStage = true; // 所有被加载的模块定义对象map private final Map<String, ModuleDefine> loadedModules = new HashMap<>(); // 初始化所有配置的模块 public void init(ApplicationConfiguration applicationConfiguration) throws ModuleNotFoundException, ProviderNotFoundException, ServiceNotProvidedException, CycleDependencyException, ModuleConfigException, ModuleStartException { // 获取配置类中的模块名 String[] moduleNames = applicationConfiguration.moduleList(); // SPI加载所有模块定义对象 ServiceLoader<ModuleDefine> moduleServiceLoader = ServiceLoader.load(ModuleDefine.class); // SPI加载所有模块提供对象 ServiceLoader<ModuleProvider> moduleProviderLoader = ServiceLoader.load(ModuleProvider.class); // 所有配置类中定义的模块，进行准备阶段 LinkedList<String> moduleList = new LinkedList<>(Arrays.asList(moduleNames)); for (ModuleDefine module : moduleServiceLoader) { for (String moduleName : moduleNames) { if (moduleName.equals(module.name())) { module.prepare(this, applicationConfiguration.getModuleConfiguration(moduleName), moduleProviderLoader); loadedModules.put(moduleName, module); moduleList.remove(moduleName); } } } // 准备阶段结束 isInPrepareStage = false; if (moduleList.size() > 0) { throw new ModuleNotFoundException(moduleList.toString() + " missing."); } // 根据模块提供对象中的requiredModules方法，确定模块的初始化顺序（被依赖的模块先行加载） BootstrapFlow bootstrapFlow = new BootstrapFlow(loadedModules); // 所有模块进入启动阶段 bootstrapFlow.start(this); // 所有模块进入完成后通知阶段 bootstrapFlow.notifyAfterCompleted(); } // 判断是否有该模块 @Override public boolean has(String moduleName) { return loadedModules.get(moduleName) != null; } // 通过模块名获取模块定义对象 @Override public ModuleProviderHolder find(String moduleName) throws ModuleNotFoundRuntimeException { assertPreparedStage(); ModuleDefine module = loadedModules.get(moduleName); if (module != null) return module; throw new ModuleNotFoundRuntimeException(moduleName + " missing."); } // 断言是否还在准备阶段，如果还在准备阶段，则抛出异常 private void assertPreparedStage() { if (isInPrepareStage) { throw new AssertionError("Still in preparing stage."); } }}BootstrapFlowpackage org.apache.skywalking.oap.server.library.module;import java.util.ArrayList;import java.util.LinkedList;import java.util.List;import java.util.Map;import org.apache.skywalking.oap.server.library.util.CollectionUtils;import org.slf4j.Logger;import org.slf4j.LoggerFactory;// 根据模块提供对象中的requiredModules方法，确定模块的初始化顺序（被依赖的模块先行加载）class BootstrapFlow { private static final Logger LOGGER = LoggerFactory.getLogger(BootstrapFlow.class); private Map<String, ModuleDefine> loadedModules; // 按依赖顺序排序的模块提供对象列表 private List<ModuleProvider> startupSequence; BootstrapFlow(Map<String, ModuleDefine> loadedModules) throws CycleDependencyException, ModuleNotFoundException { this.loadedModules = loadedModules; startupSequence = new LinkedList<>(); // 被依赖的模块先行加载 makeSequence(); } @SuppressWarnings("unchecked") void start( ModuleManager moduleManager) throws ModuleNotFoundException, ServiceNotProvidedException, ModuleStartException { for (ModuleProvider provider : startupSequence) { LOGGER.info("start the provider {} in {} module.", provider.name(), provider.getModuleName()); provider.requiredCheck(provider.getModule().services()); provider.start(); } } void notifyAfterCompleted() throws ServiceNotProvidedException, ModuleStartException { for (ModuleProvider provider : startupSequence) { provider.notifyAfterCompleted(); } } private void makeSequence() throws CycleDependencyException, ModuleNotFoundException { List<ModuleProvider> allProviders = new ArrayList<>(); // 判断所有被依赖的模块是否存在 for (final ModuleDefine module : loadedModules.values()) { String[] requiredModules = module.provider().requiredModules(); if (requiredModules != null) { for (String requiredModule : requiredModules) { if (!loadedModules.containsKey(requiredModule)) { throw new ModuleNotFoundException(requiredModule + " module is required by " + module.provider().getModuleName() + "." + module.provider().name() + ", but not found."); } } } allProviders.add(module.provider()); } do { int numOfToBeSequenced = allProviders.size(); for (int i = 0; i < allProviders.size(); i++) { ModuleProvider provider = allProviders.get(i); String[] requiredModules = provider.requiredModules(); if (CollectionUtils.isNotEmpty(requiredModules)) { // 是否所有依赖的模块都在startupSequence中 boolean isAllRequiredModuleStarted = true; for (String module : requiredModules) { boolean exist = false; for (ModuleProvider moduleProvider : startupSequence) { if (moduleProvider.getModuleName().equals(module)) { exist = true; break; } } if (!exist) { isAllRequiredModuleStarted = false; break; } } // 所有依赖的模块都在startupSequence，则将该模块提供对象加入startupSequence if (isAllRequiredModuleStarted) { startupSequence.add(provider); allProviders.remove(i); i--; } } else { // 如果该模块提供对象不依赖任何其他模块，则加入startupSequence startupSequence.add(provider); allProviders.remove(i); i--; } } // 如果一次循环后，没有任何一个对象加入到startupSequence，则证明有循环依赖 if (numOfToBeSequenced == allProviders.size()) { StringBuilder unSequencedProviders = new StringBuilder(); allProviders.forEach(provider -> unSequencedProviders.append(provider.getModuleName()).append("[provider=").append(provider.getClass().getName()).append("]\n")); throw new CycleDependencyException("Exist cycle module dependencies in \n" + unSequencedProviders.substring(0, unSequencedProviders.length() - 1)); } } while (allProviders.size() != 0); // 当提供对象列表不为空，则一直循环执行下去 }}ApplicationConfigurationpackage org.apache.skywalking.oap.server.library.module;import java.util.HashMap;import java.util.Properties;// OAP应用配置类public class ApplicationConfiguration { // 模块定义配置map private HashMap<String, ModuleConfiguration> modules = new HashMap<>(); // 模块配置名列表 public String[] moduleList() { return modules.keySet().toArray(new String[0]); } // 添加模块定义配置 public ModuleConfiguration addModule(String moduleName) { ModuleConfiguration newModule = new ModuleConfiguration(); modules.put(moduleName, newModule); return newModule; } // 判断指定模块名是否存在模块定义配置map中 public boolean has(String moduleName) { return modules.containsKey(moduleName); } // 获取模块定义配置 public ModuleConfiguration getModuleConfiguration(String name) { return modules.get(name); } // 模块定义配置类 public static class ModuleConfiguration { // 模块提供对象map private HashMap<String, ProviderConfiguration> providers = new HashMap<>(); private ModuleConfiguration() { } // 获取模块提供配置 public Properties getProviderConfiguration(String name) { return providers.get(name).getProperties(); } // 是否存在模块提供配置 public boolean has(String name) { return providers.containsKey(name); } // 添加模块提供配置 public ModuleConfiguration addProviderConfiguration(String name, Properties properties) { ProviderConfiguration newProvider = new ProviderConfiguration(properties); providers.put(name, newProvider); return this; } } // 模块提供配置类 public static class ProviderConfiguration { // 模块提供属性 private Properties properties; ProviderConfiguration(Properties properties) { this.properties = properties; } private Properties getProperties() { return properties; } }}ApplicationConfigLoaderpackage org.apache.skywalking.oap.server.starter.config;import java.io.FileNotFoundException;import java.io.Reader;import java.util.HashSet;import java.util.Map;import java.util.Properties;import java.util.Set;import lombok.extern.slf4j.Slf4j;import org.apache.skywalking.apm.util.PropertyPlaceholderHelper;import org.apache.skywalking.oap.server.library.module.ApplicationConfiguration;import org.apache.skywalking.oap.server.library.module.ProviderNotFoundException;import org.apache.skywalking.oap.server.library.util.CollectionUtils;import org.apache.skywalking.oap.server.library.util.ResourceUtils;import org.yaml.snakeyaml.Yaml;// application.yml加载类, 三层结构:模块定义名.模块提供名.属性key@Slf4jpublic class ApplicationConfigLoader implements ConfigLoader<ApplicationConfiguration> { // 当不配置模块提供者时，使用"-" private static final String DISABLE_SELECTOR = "-"; // 该字段选择模块提供者 private static final String SELECTOR = "selector"; private final Yaml yaml = new Yaml(); @Override public ApplicationConfiguration load() throws ConfigFileNotFoundException { ApplicationConfiguration configuration = new ApplicationConfiguration(); this.loadConfig(configuration); this.overrideConfigBySystemEnv(configuration); return configuration; } @SuppressWarnings("unchecked") private void loadConfig(ApplicationConfiguration configuration) throws ConfigFileNotFoundException { try { Reader applicationReader = ResourceUtils.read("application.yml"); Map<String, Map<String, Object>> moduleConfig = yaml.loadAs(applicationReader, Map.class); if (CollectionUtils.isNotEmpty(moduleConfig)) { selectConfig(moduleConfig); moduleConfig.forEach((moduleName, providerConfig) -> { if (providerConfig.size() > 0) { log.info("Get a module define from application.yml, module name: {}", moduleName); ApplicationConfiguration.ModuleConfiguration moduleConfiguration = configuration.addModule(moduleName); providerConfig.forEach((providerName, config) -> { log.info("Get a provider define belong to {} module, provider name: {}", moduleName, providerName); final Map<String, ?> propertiesConfig = (Map<String, ?>) config; final Properties properties = new Properties(); if (propertiesConfig != null) { propertiesConfig.forEach((propertyName, propertyValue) -> { if (propertyValue instanceof Map) { Properties subProperties = new Properties(); ((Map) propertyValue).forEach((key, value) -> { subProperties.put(key, value); replacePropertyAndLog(key, value, subProperties, providerName); }); properties.put(propertyName, subProperties); } else { properties.put(propertyName, propertyValue); replacePropertyAndLog(propertyName, propertyValue, properties, providerName); } }); } moduleConfiguration.addProviderConfiguration(providerName, properties); }); } else { log.warn("Get a module define from application.yml, but no provider define, use default, module name: {}", moduleName); } }); } } catch (FileNotFoundException e) { throw new ConfigFileNotFoundException(e.getMessage(), e); } } private void replacePropertyAndLog(final Object propertyName, final Object propertyValue, final Properties target, final Object providerName) { final String valueString = PropertyPlaceholderHelper.INSTANCE.replacePlaceholders(propertyValue + "", target); if (valueString != null) { if (valueString.trim().length() == 0) { target.replace(propertyName, valueString); log.info("Provider={} config={} has been set as an empty string", providerName, propertyName); } else { // Use YAML to do data type conversion. final Object replaceValue = yaml.load(valueString); if (replaceValue != null) { target.replace(propertyName, replaceValue); log.info("Provider={} config={} has been set as {}", providerName, propertyName, replaceValue.toString()); } } } } private void overrideConfigBySystemEnv(ApplicationConfiguration configuration) { for (Map.Entry<Object, Object> prop : System.getProperties().entrySet()) { overrideModuleSettings(configuration, prop.getKey().toString(), prop.getValue().toString()); } } private void selectConfig(final Map<String, Map<String, Object>> moduleConfiguration) { final Set<String> modulesWithoutProvider = new HashSet<>(); for (final Map.Entry<String, Map<String, Object>> entry : moduleConfiguration.entrySet()) { final String moduleName = entry.getKey(); final Map<String, Object> providerConfig = entry.getValue(); if (!providerConfig.containsKey(SELECTOR)) { continue; } final String selector = (String) providerConfig.get(SELECTOR); final String resolvedSelector = PropertyPlaceholderHelper.INSTANCE.replacePlaceholders( selector, System.getProperties() ); providerConfig.entrySet().removeIf(e -> !resolvedSelector.equals(e.getKey())); if (!providerConfig.isEmpty()) { continue; } if (!DISABLE_SELECTOR.equals(resolvedSelector)) { throw new ProviderNotFoundException("no provider found for module " + moduleName + ", " + "if you're sure it's not required module and want to remove it, " + "set the selector to -"); } // now the module can be safely removed modulesWithoutProvider.add(moduleName); } moduleConfiguration.entrySet().removeIf(e -> { final String module = e.getKey(); final boolean shouldBeRemoved = modulesWithoutProvider.contains(module); if (shouldBeRemoved) { log.info("Remove module {} without any provider", module); } return shouldBeRemoved; }); } private void overrideModuleSettings(ApplicationConfiguration configuration, String key, String value) { int moduleAndConfigSeparator = key.indexOf('.'); if (moduleAndConfigSeparator <= 0) { return; } String moduleName = key.substring(0, moduleAndConfigSeparator); String providerSettingSubKey = key.substring(moduleAndConfigSeparator + 1); ApplicationConfiguration.ModuleConfiguration moduleConfiguration = configuration.getModuleConfiguration(moduleName); if (moduleConfiguration == null) { return; } int providerAndConfigSeparator = providerSettingSubKey.indexOf('.'); if (providerAndConfigSeparator <= 0) { return; } String providerName = providerSettingSubKey.substring(0, providerAndConfigSeparator); String settingKey = providerSettingSubKey.substring(providerAndConfigSeparator + 1); if (!moduleConfiguration.has(providerName)) { return; } Properties providerSettings = moduleConfiguration.getProviderConfiguration(providerName); if (!providerSettings.containsKey(settingKey)) { return; } Object originValue = providerSettings.get(settingKey); Class<?> type = originValue.getClass(); if (type.equals(int.class) || type.equals(Integer.class)) providerSettings.put(settingKey, Integer.valueOf(value)); else if (type.equals(String.class)) providerSettings.put(settingKey, value); else if (type.equals(long.class) || type.equals(Long.class)) providerSettings.put(settingKey, Long.valueOf(value)); else if (type.equals(boolean.class) || type.equals(Boolean.class)) { providerSettings.put(settingKey, Boolean.valueOf(value)); } else { return; } log.info("The setting has been override by key: {}, value: {}, in {} provider of {} module through {}", settingKey, value, providerName, moduleName, "System.properties"); }}ConfigLoaderpackage org.apache.skywalking.oap.server.starter.config;// 配置加载接口public interface ConfigLoader<T> { T load() throws ConfigFileNotFoundException;}OAPServerBootstrappackage org.apache.skywalking.oap.server.starter;import lombok.extern.slf4j.Slf4j;import org.apache.skywalking.oap.server.core.RunningMode;import org.apache.skywalking.oap.server.library.module.ApplicationConfiguration;import org.apache.skywalking.oap.server.library.module.ModuleManager;import org.apache.skywalking.oap.server.starter.config.ApplicationConfigLoader;import org.apache.skywalking.oap.server.starter.config.ConfigLoader;import org.apache.skywalking.oap.server.telemetry.TelemetryModule;import org.apache.skywalking.oap.server.telemetry.api.MetricsCreator;import org.apache.skywalking.oap.server.telemetry.api.MetricsTag;// OAP启动类，加载配置文件，初始化模块@Slf4jpublic class OAPServerBootstrap { public static void start() { String mode = System.getProperty("mode"); // 启动模式 RunningMode.setMode(mode); ApplicationConfigLoader configLoader = new ApplicationConfigLoader(); ModuleManager manager = new ModuleManager(); try { // 从配置文件中加载配置 ApplicationConfiguration applicationConfiguration = configLoader.load(); // 初始化模块 manager.init(applicationConfiguration); // 将启动时间发送给Telemetry manager.find(TelemetryModule.NAME) .provider() .getService(MetricsCreator.class) .createGauge("uptime", "oap server start up time", MetricsTag.EMPTY_KEY, MetricsTag.EMPTY_VALUE) // Set uptime to second .setValue(System.currentTimeMillis() / 1000d); if (RunningMode.isInitMode()) { log.info("OAP starts up in init mode successfully, exit now..."); System.exit(0); } } catch (Throwable t) { log.error(t.getMessage(), t); System.exit(1); } }}OAPServerStartUppackage org.apache.skywalking.oap.server.starter;// OAP启动类public class OAPServerStartUp { public static void main(String[] args) { OAPServerBootstrap.start(); }}以 Skywalking OAP 启动流程分析模块加载机制时序图源文件：OAPServerStartUp.sdt
案例：存储模块加载分析配置文件
从 application.yml 配置文件，可以看出。
模块是以三层结构来定义的：
第一层：模块定义名第二层：模块提供名/ selector第三层：模块提供配置信息/ selector 选择的模块提供配置
storage: selector: ${SW_STORAGE:h2} elasticsearch: nameSpace: ${SW_NAMESPACE:""} clusterNodes: ${SW_STORAGE_ES_CLUSTER_NODES:localhost:9200} # etc... elasticsearch7: nameSpace: ${SW_NAMESPACE:""} clusterNodes: ${SW_STORAGE_ES_CLUSTER_NODES:localhost:9200} # etc... h2: driver: ${SW_STORAGE_H2_DRIVER:org.h2.jdbcx.JdbcDataSource} url: ${SW_STORAGE_H2_URL:jdbc:h2:mem:skywalking-oap-db;DB_CLOSE_DELAY=-1} # etc... mysql: properties: jdbcUrl: ${SW_JDBC_URL:"jdbc:mysql://localhost:3306/swtest"} dataSource.user: ${SW_DATA_SOURCE_USER:root} dataSource.password: ${SW_DATA_SOURCE_PASSWORD:root@1234} # etc... tidb: properties: jdbcUrl: ${SW_JDBC_URL:"jdbc:mysql://localhost:4000/tidbswtest"} dataSource.user: ${SW_DATA_SOURCE_USER:root} dataSource.password: ${SW_DATA_SOURCE_PASSWORD:""} # etc... influxdb: url: ${SW_STORAGE_INFLUXDB_URL:} user: ${SW_STORAGE_INFLUXDB_USER:root} password: ${SW_STORAGE_INFLUXDB_PASSWORD:} # etc...加载配置经过 org.apache.skywalking.oap.server.starter.config.ApplicationConfigLoader#load 的调用， org.apache.skywalking.oap.server.starter.OAPServerBootstrap#start 获取到了所有需要加载的模块，其中包括存储模块。
在 org.apache.skywalking.oap.server.starter.config.ApplicationConfigLoader#selectConfig 也通过 storage.selector=h2 ，存储模块只保留了 h2 的配置信息：
storage: h2: driver: ${SW_STORAGE_H2_DRIVER:org.h2.jdbcx.JdbcDataSource} url: ${SW_STORAGE_H2_URL:jdbc:h2:mem:skywalking-oap-db;DB_CLOSE_DELAY=-1} # etc...准备阶段在org.apache.skywalking.oap.server.library.module.ModuleManager#init 中，通过 SPI 加载了模块定义对象，存储模块对应的定义类如下：
PS：可以看到定义了大量 Service 接口
package org.apache.skywalking.oap.server.core.storage;import org.apache.skywalking.oap.server.core.storage.cache.INetworkAddressAliasDAO;import org.apache.skywalking.oap.server.core.storage.management.UITemplateManagementDAO;import org.apache.skywalking.oap.server.core.storage.profile.IProfileTaskLogQueryDAO;import org.apache.skywalking.oap.server.core.storage.profile.IProfileTaskQueryDAO;import org.apache.skywalking.oap.server.core.storage.profile.IProfileThreadSnapshotQueryDAO;import org.apache.skywalking.oap.server.core.storage.query.IAggregationQueryDAO;import org.apache.skywalking.oap.server.core.storage.query.IAlarmQueryDAO;import org.apache.skywalking.oap.server.core.storage.query.IBrowserLogQueryDAO;import org.apache.skywalking.oap.server.core.storage.query.ILogQueryDAO;import org.apache.skywalking.oap.server.core.storage.query.IMetadataQueryDAO;import org.apache.skywalking.oap.server.core.storage.query.IMetricsQueryDAO;import org.apache.skywalking.oap.server.core.storage.query.ITopNRecordsQueryDAO;import org.apache.skywalking.oap.server.core.storage.query.ITopologyQueryDAO;import org.apache.skywalking.oap.server.core.storage.query.ITraceQueryDAO;import org.apache.skywalking.oap.server.library.module.ModuleDefine;/** * StorageModule provides the capabilities(services) to interact with the database. With different databases, this * module could have different providers, such as currently, H2, MySQL, ES, TiDB. */public class StorageModule extends ModuleDefine { public static final String NAME = "storage"; public StorageModule() { super(NAME); } @Override public Class[] services() { return new Class[]{ IBatchDAO.class, StorageDAO.class, IHistoryDeleteDAO.class, INetworkAddressAliasDAO.class, ITopologyQueryDAO.class, IMetricsQueryDAO.class, ITraceQueryDAO.class, IMetadataQueryDAO.class, IAggregationQueryDAO.class, IAlarmQueryDAO.class, ITopNRecordsQueryDAO.class, ILogQueryDAO.class, IProfileTaskQueryDAO.class, IProfileTaskLogQueryDAO.class, IProfileThreadSnapshotQueryDAO.class, UITemplateManagementDAO.class, IBrowserLogQueryDAO.class }; }}同时也会调用 org.apache.skywalking.oap.server.library.module.ModuleDefine#prepare 进入准备阶段
String[] moduleNames = applicationConfiguration.moduleList(); ServiceLoader<ModuleDefine> moduleServiceLoader = ServiceLoader.load(ModuleDefine.class); ServiceLoader<ModuleProvider> moduleProviderLoader = ServiceLoader.load(ModuleProvider.class); LinkedList<String> moduleList = new LinkedList<>(Arrays.asList(moduleNames)); for (ModuleDefine module : moduleServiceLoader) { for (String moduleName : moduleNames) { if (moduleName.equals(module.name())) { module.prepare(this, applicationConfiguration.getModuleConfiguration(moduleName), moduleProviderLoader); loadedModules.put(moduleName, module); moduleList.remove(moduleName); } } }在 org.apache.skywalking.oap.server.library.module.ModuleDefine#prepare 会通过传入的配置，只匹配上配置文件选择的模块提供对象。
for (ModuleProvider provider : moduleProviderLoader) { if (!configuration.has(provider.name())) { continue; } if (provider.module().equals(getClass())) { if (loadedProvider == null) { loadedProvider = provider; loadedProvider.setManager(moduleManager); loadedProvider.setModuleDefine(this); } else { throw new DuplicateProviderException(this.name() + " module has one " + loadedProvider.name() + "[" + loadedProvider.getClass().getName() + "] provider already, " + provider.name() + "[" + provider.getClass().getName() + "] is defined as 2nd provider."); } } } if (loadedProvider == null) { throw new ProviderNotFoundException(this.name() + " module no provider found."); } LOGGER.info("Prepare the {} provider in {} module.", loadedProvider.name(), this.name()); try { copyProperties(loadedProvider.createConfigBeanIfAbsent(), configuration.getProviderConfiguration(loadedProvider.name()), this.name(), loadedProvider.name()); } catch (IllegalAccessException e) { throw new ModuleConfigException(this.name() + " module config transport to config bean failure.", e); } loadedProvider.prepare();例如“配置文件”一节选择的h2 ，则加载的提供类为 org.apache.skywalking.oap.server.storage.plugin.jdbc.h2.H2StorageProvider
它的 prepare 方法如下，可以看到：注册了所有 StorageModule 声明的 Service 接口
@Override public void prepare() throws ServiceNotProvidedException, ModuleStartException { Properties settings = new Properties(); settings.setProperty("dataSourceClassName", config.getDriver()); settings.setProperty("dataSource.url", config.getUrl()); settings.setProperty("dataSource.user", config.getUser()); settings.setProperty("dataSource.password", config.getPassword()); h2Client = new JDBCHikariCPClient(settings); this.registerServiceImplementation(IBatchDAO.class, new H2BatchDAO(h2Client)); this.registerServiceImplementation( StorageDAO.class, new H2StorageDAO( getManager(), h2Client, config.getMaxSizeOfArrayColumn(), config.getNumOfSearchableValuesPerTag()) ); this.registerServiceImplementation( INetworkAddressAliasDAO.class, new H2NetworkAddressAliasDAO(h2Client)); this.registerServiceImplementation(ITopologyQueryDAO.class, new H2TopologyQueryDAO(h2Client)); this.registerServiceImplementation(IMetricsQueryDAO.class, new H2MetricsQueryDAO(h2Client)); this.registerServiceImplementation( ITraceQueryDAO.class, new H2TraceQueryDAO( getManager(), h2Client, config.getMaxSizeOfArrayColumn(), config.getNumOfSearchableValuesPerTag() )); this.registerServiceImplementation(IBrowserLogQueryDAO.class, new H2BrowserLogQueryDAO(h2Client)); this.registerServiceImplementation( IMetadataQueryDAO.class, new H2MetadataQueryDAO(h2Client, config.getMetadataQueryMaxSize())); this.registerServiceImplementation(IAggregationQueryDAO.class, new H2AggregationQueryDAO(h2Client)); this.registerServiceImplementation(IAlarmQueryDAO.class, new H2AlarmQueryDAO(h2Client)); this.registerServiceImplementation( IHistoryDeleteDAO.class, new H2HistoryDeleteDAO(h2Client)); this.registerServiceImplementation(ITopNRecordsQueryDAO.class, new H2TopNRecordsQueryDAO(h2Client)); this.registerServiceImplementation( ILogQueryDAO.class, new H2LogQueryDAO( h2Client, getManager(), config.getMaxSizeOfArrayColumn(), config.getNumOfSearchableValuesPerTag() ) ); this.registerServiceImplementation(IProfileTaskQueryDAO.class, new H2ProfileTaskQueryDAO(h2Client)); this.registerServiceImplementation(IProfileTaskLogQueryDAO.class, new H2ProfileTaskLogQueryDAO(h2Client)); this.registerServiceImplementation( IProfileThreadSnapshotQueryDAO.class, new H2ProfileThreadSnapshotQueryDAO(h2Client)); this.registerServiceImplementation(UITemplateManagementDAO.class, new H2UITemplateManagementDAO(h2Client)); }启动阶段在org.apache.skywalking.oap.server.library.module.ModuleManager#init 通过调用 org.apache.skywalking.oap.server.library.module.BootstrapFlow#start 进入启动阶段
void start( ModuleManager moduleManager) throws ModuleNotFoundException, ServiceNotProvidedException, ModuleStartException { for (ModuleProvider provider : startupSequence) { LOGGER.info("start the provider {} in {} module.", provider.name(), provider.getModuleName()); provider.requiredCheck(provider.getModule().services()); provider.start(); } }例如“配置文件”一节选择的h2 ，则加载的提供类为 org.apache.skywalking.oap.server.storage.plugin.jdbc.h2.H2StorageProvider
它的 start 方法如下，可以看到：启动 h2client 并监听 ModelCreator
@Override public void start() throws ServiceNotProvidedException, ModuleStartException { final ConfigService configService = getManager().find(CoreModule.NAME) .provider() .getService(ConfigService.class); final int numOfSearchableTracesTags = configService.getSearchableTracesTags().split(Const.COMMA).length; if (numOfSearchableTracesTags * config.getNumOfSearchableValuesPerTag() > config.getMaxSizeOfArrayColumn()) { throw new ModuleStartException("Size of searchableTracesTags[" + numOfSearchableTracesTags + "] * numOfSearchableValuesPerTag[" + config.getNumOfSearchableValuesPerTag() + "] > maxSizeOfArrayColumn[" + config.getMaxSizeOfArrayColumn() + "]. Potential out of bound in the runtime."); } final int numOfSearchableLogsTags = configService.getSearchableLogsTags().split(Const.COMMA).length; if (numOfSearchableLogsTags * config.getNumOfSearchableValuesPerTag() > config.getMaxSizeOfArrayColumn()) { throw new ModuleStartException("Size of searchableLogsTags[" + numOfSearchableLogsTags + "] * numOfSearchableValuesPerTag[" + config.getNumOfSearchableValuesPerTag() + "] > maxSizeOfArrayColumn[" + config.getMaxSizeOfArrayColumn() + "]. Potential out of bound in the runtime."); } MetricsCreator metricCreator = getManager().find(TelemetryModule.NAME) .provider() .getService(MetricsCreator.class); HealthCheckMetrics healthChecker = metricCreator.createHealthCheckerGauge( "storage_h2", MetricsTag.EMPTY_KEY, MetricsTag.EMPTY_VALUE); h2Client.registerChecker(healthChecker); try { h2Client.connect(); H2TableInstaller installer = new H2TableInstaller( h2Client, getManager(), config.getMaxSizeOfArrayColumn(), config.getNumOfSearchableValuesPerTag()); getManager().find(CoreModule.NAME).provider().getService(ModelCreator.class).addModelListener(installer); } catch (StorageException e) { throw new ModuleStartException(e.getMessage(), e); } }完成后通知阶段在org.apache.skywalking.oap.server.library.module.ModuleManager#init 通过调用 org.apache.skywalking.oap.server.library.module.BootstrapFlow#notifyAfterCompleted 进入完成后通知阶段
void notifyAfterCompleted() throws ServiceNotProvidedException, ModuleStartException { for (ModuleProvider provider : startupSequence) { provider.notifyAfterCompleted(); } }例如“配置文件”一节选择的h2 ，则加载的提供类为 org.apache.skywalking.oap.server.storage.plugin.jdbc.h2.H2StorageProvider
它的 notifyAfterCompleted 方法如下，可以看到：不需要做什么
@Override public void notifyAfterCompleted() throws ServiceNotProvidedException, ModuleStartException { }H2StorageProvider 完整源码package org.apache.skywalking.oap.server.storage.plugin.jdbc.h2;// etc.../** * H2 Storage provider is for demonstration and preview only. I will find that haven't implemented several interfaces, * because not necessary, and don't consider about performance very much. * <p> * If someone wants to implement SQL-style database as storage, please just refer the logic. */@Slf4jpublic class H2StorageProvider extends ModuleProvider { private H2StorageConfig config; private JDBCHikariCPClient h2Client; public H2StorageProvider() { config = new H2StorageConfig(); } @Override public String name() { return "h2"; } @Override public Class<? extends ModuleDefine> module() { return StorageModule.class; } @Override public ModuleConfig createConfigBeanIfAbsent() { return config; } @Override public void prepare() throws ServiceNotProvidedException, ModuleStartException { Properties settings = new Properties(); settings.setProperty("dataSourceClassName", config.getDriver()); settings.setProperty("dataSource.url", config.getUrl()); settings.setProperty("dataSource.user", config.getUser()); settings.setProperty("dataSource.password", config.getPassword()); h2Client = new JDBCHikariCPClient(settings); this.registerServiceImplementation(IBatchDAO.class, new H2BatchDAO(h2Client)); this.registerServiceImplementation( StorageDAO.class, new H2StorageDAO( getManager(), h2Client, config.getMaxSizeOfArrayColumn(), config.getNumOfSearchableValuesPerTag()) ); this.registerServiceImplementation( INetworkAddressAliasDAO.class, new H2NetworkAddressAliasDAO(h2Client)); this.registerServiceImplementation(ITopologyQueryDAO.class, new H2TopologyQueryDAO(h2Client)); this.registerServiceImplementation(IMetricsQueryDAO.class, new H2MetricsQueryDAO(h2Client)); this.registerServiceImplementation( ITraceQueryDAO.class, new H2TraceQueryDAO( getManager(), h2Client, config.getMaxSizeOfArrayColumn(), config.getNumOfSearchableValuesPerTag() )); this.registerServiceImplementation(IBrowserLogQueryDAO.class, new H2BrowserLogQueryDAO(h2Client)); this.registerServiceImplementation( IMetadataQueryDAO.class, new H2MetadataQueryDAO(h2Client, config.getMetadataQueryMaxSize())); this.registerServiceImplementation(IAggregationQueryDAO.class, new H2AggregationQueryDAO(h2Client)); this.registerServiceImplementation(IAlarmQueryDAO.class, new H2AlarmQueryDAO(h2Client)); this.registerServiceImplementation( IHistoryDeleteDAO.class, new H2HistoryDeleteDAO(h2Client)); this.registerServiceImplementation(ITopNRecordsQueryDAO.class, new H2TopNRecordsQueryDAO(h2Client)); this.registerServiceImplementation( ILogQueryDAO.class, new H2LogQueryDAO( h2Client, getManager(), config.getMaxSizeOfArrayColumn(), config.getNumOfSearchableValuesPerTag() ) ); this.registerServiceImplementation(IProfileTaskQueryDAO.class, new H2ProfileTaskQueryDAO(h2Client)); this.registerServiceImplementation(IProfileTaskLogQueryDAO.class, new H2ProfileTaskLogQueryDAO(h2Client)); this.registerServiceImplementation( IProfileThreadSnapshotQueryDAO.class, new H2ProfileThreadSnapshotQueryDAO(h2Client)); this.registerServiceImplementation(UITemplateManagementDAO.class, new H2UITemplateManagementDAO(h2Client)); } @Override public void start() throws ServiceNotProvidedException, ModuleStartException { final ConfigService configService = getManager().find(CoreModule.NAME) .provider() .getService(ConfigService.class); final int numOfSearchableTracesTags = configService.getSearchableTracesTags().split(Const.COMMA).length; if (numOfSearchableTracesTags * config.getNumOfSearchableValuesPerTag() > config.getMaxSizeOfArrayColumn()) { throw new ModuleStartException("Size of searchableTracesTags[" + numOfSearchableTracesTags + "] * numOfSearchableValuesPerTag[" + config.getNumOfSearchableValuesPerTag() + "] > maxSizeOfArrayColumn[" + config.getMaxSizeOfArrayColumn() + "]. Potential out of bound in the runtime."); } final int numOfSearchableLogsTags = configService.getSearchableLogsTags().split(Const.COMMA).length; if (numOfSearchableLogsTags * config.getNumOfSearchableValuesPerTag() > config.getMaxSizeOfArrayColumn()) { throw new ModuleStartException("Size of searchableLogsTags[" + numOfSearchableLogsTags + "] * numOfSearchableValuesPerTag[" + config.getNumOfSearchableValuesPerTag() + "] > maxSizeOfArrayColumn[" + config.getMaxSizeOfArrayColumn() + "]. Potential out of bound in the runtime."); } MetricsCreator metricCreator = getManager().find(TelemetryModule.NAME) .provider() .getService(MetricsCreator.class); HealthCheckMetrics healthChecker = metricCreator.createHealthCheckerGauge( "storage_h2", MetricsTag.EMPTY_KEY, MetricsTag.EMPTY_VALUE); h2Client.registerChecker(healthChecker); try { h2Client.connect(); H2TableInstaller installer = new H2TableInstaller( h2Client, getManager(), config.getMaxSizeOfArrayColumn(), config.getNumOfSearchableValuesPerTag()); getManager().find(CoreModule.NAME).provider().getService(ModelCreator.class).addModelListener(installer); } catch (StorageException e) { throw new ModuleStartException(e.getMessage(), e); } } @Override public void notifyAfterCompleted() throws ServiceNotProvidedException, ModuleStartException { } @Override public String[] requiredModules() { return new String[] {CoreModule.NAME}; }}总结Skywalking 提供的模块机制是非常优良的设计，在工作中，如果有多个 N 选 1 的场景，是可以借鉴它的设计的。
参考文档Backend setupConfiguration Vocabulary
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