从SpringBoot源码分析 配置文件的加载原理和优先级

本文从SpringBoot源码分析 配置文件的加载原理和配置文件的优先级

 

  跟入源码之前，先提一个问题：

  SpringBoot 既可以加载指定目录下的配置文件获取配置项，也可以通过启动参数（VM Options）传入配置项，为什么通过启动参数传入的配置项会“顶掉”配置文件中的配置？

 

示例：

 

application.yml 

server.port: 8888
spring.profiles.active: dev

 

application-dev.yml 

spring.think: hello

 

在IDEA中使用命令行配置项 

VM Options 

-Dserver.port=5555

如下图：

 

启动结果：

Tomcat started on port(s): 5555 (http) with context path ''

同时在application.yml 和 启动参数（VM options）中设置 server.port， 最终采用了 启动参数 中的值。

 

  下面开始从main函数启动处，跟入SpringBoot源码，看看SpringBoot是如何处理的。

 

 

系统说明

JDK：1.8

SpringBoot 版本： 2.0.2.RELEASE

IDE： IntelliJ IDEA 2017

 

 

跟入源码正文 

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

 

   从SpringApplication.run 函数开始，一个方法一个方法的跟入源码。需要跟入的方法给与注释或高亮。

 

IDEA 快捷键：

进入方法:  Ctrl + 鼠标左键

光标前进/后退： Ctrl + Shirt + 右方向键/左方向键

 

  依次跟入源码：

#SpringApplication.java
return run(new Class<?>[] { primarySource }, args)

#SpringApplication.java
return new SpringApplication(primarySources).run(args);

 #SpringApplication.java
    public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
        configureHeadlessProperty();
        SpringApplicationRunListeners listeners = getRunListeners(args);
        listeners.starting();
        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                    args);
            //跟入
            ConfigurableEnvironment environment = prepareEnvironment(listeners,
                    applicationArguments);
            configureIgnoreBeanInfo(environment);
            configureIgnoreBeanInfo(environment);

进入public ConfigurableApplicationContext run(String... args) 方法后，我们重点看 prepareEnvironment这个方法。

  这个方法之前的源码的从类名和源码注释上知道stopWatch用于计时，上下文context还未初始化，listeners监听器存储了EventPushlingRunListener。

 

  通过IDEA 一行行debug可以看到是在 prepareEnvironment方法执行后，server.port 配置项才被加载入 environment 环境配置中。

  如下图所示。注意：配置文件中的配置还未载入，请先接着往后看。

 

  因此，我们重新打断点跟入prepareEnvironment方法。

 

#SpringApplication.java
    private ConfigurableEnvironment prepareEnvironment(
            SpringApplicationRunListeners listeners,
            ApplicationArguments applicationArguments) {
        // Create and configure the environment
        //跟入
        ConfigurableEnvironment environment = getOrCreateEnvironment();
        configureEnvironment(environment, applicationArguments.getSourceArgs());

同样的套路，通过debug发现实在getOrCreateEnvironment方法执行后得到server.port的值 

 

#SpringApplication.java
    private ConfigurableEnvironment getOrCreateEnvironment() {
        if (this.environment != null) {
            return this.environment;
        }
        if (this.webApplicationType == WebApplicationType.SERVLET) {
            //跟入
            return new StandardServletEnvironment();
        }

虚拟机启动参数的加载 是在StandardServletEnvironment 的实例化过程中完成的。

  跟入StandardServletEnvironment的实例化过程之前，大家需要先了解 Java模板模式 。

  看一下StandardServletEnvironment的类继承关系图（通过IDEA 右键 类名 --> Diagrams --> Show Diagrams Popup 即可显示下图）

 

抽象父类AbstractEnvironment的实例化方法中，调用了可由子类继承的customizePropertySources方法。

 

#AbstractEnvironment.java
    public AbstractEnvironment() {
        //跟入
customizePropertySources(this.propertySources);
        if (logger.isDebugEnabled()) {
            logger.debug("Initialized " + getClass().getSimpleName() + " with PropertySources " + this.propertySources);
        }
    }

实体化的过程中回过头来调用了子类StandardServletEnvironment的customizePropertySources方法

 

#StandardServletEnvironment.java
    protected void customizePropertySources(MutablePropertySources propertySources) {
        propertySources.addLast(new StubPropertySource(SERVLET_CONFIG_PROPERTY_SOURCE_NAME));
        propertySources.addLast(new StubPropertySource(SERVLET_CONTEXT_PROPERTY_SOURCE_NAME));
        if (JndiLocatorDelegate.isDefaultJndiEnvironmentAvailable()) {
            propertySources.addLast(new JndiPropertySource(JNDI_PROPERTY_SOURCE_NAME));
        }
        //跟入
        super.customizePropertySources(propertySources);
    }

又调用了父类StandardEnvironment的customizePropertySources方法

 

#StandardEnvironment.java
    protected void customizePropertySources(MutablePropertySources propertySources) {
        //跟入
        propertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));
        propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));
    }

 

  通过IDEA 的变量监听功能，可以看到正是StandardEnvironment类的getSystemProperties()方法获取到了之前设置的虚拟机启动参数server.port的值。

 

  继续跟进去

#AbstractEnvironment.java
    public Map<String, Object> getSystemProperties() {
        try {
            //跟入
            return (Map) System.getProperties();

#System.java
    public static Properties getProperties() {
        SecurityManager sm = getSecurityManager();
        if (sm != null) {
            sm.checkPropertiesAccess();
        }

        return props;

我们搜索一下有没有什么地方初始化 props

#System.java
    private static Properties props;
    private static native Properties initProperties(Properties props);

发现了静态方法 initProperties，从方法名上即可知道在类被加载的时候 就初始化了 props， 这是个本地方法，继续跟的话需要看对应的C++代码。

 

  回到StandardEnvironment类的customizePropertySources方法

 

#StandardEnvironment.java
    protected void customizePropertySources(MutablePropertySources propertySources) {
        //SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME: systemProperties
        //跟入
        propertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));
        propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));
    }

#MutablePropertySources.java
    /**
     * Add the given property source object with lowest precedence.
     * 添加属性源，并使其优先级最低
     */
    public void addLast(PropertySource<?> propertySource) {

 再看一下MutablePropertySources的类注释

 

 * <p>Where <em>precedence</em> is mentioned in methods such as {@link #addFirst}
 * and {@link #addLast}, this is with regard to the order in which property sources
 * will be searched when resolving a given property with a {@link PropertyResolver}.
 *
 * addFist 和 add Last 会设置属性源的优先级，
 * PropertyResolver解析配置时会根据优先级使用配置源
 *
 * @author Chris Beams
 * @author Juergen Hoeller
 * @since 3.1
 * @see PropertySourcesPropertyResolver
 */
public class MutablePropertySources implements PropertySources {

 

问题2：

 

  此时我们已经看到虚拟机的启动参数先添加到系统当中，那么后面添加进来的Property Source属性源的优先级是否比 SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME(systemProperties) 属性源的优先级高呢？

 

  回到SpringApplication的prepareEnvironment方法

  同样的debug套路发现listeners.environmentPrepared执行后，application.yml 和 application-dev.yml 两个配置文件的配置项都被加载完成，所以我们继续跟入environmentPrepared方法

 

  在跟入environmentPrepared方法之前，需要了解 Java事件监听机制

 

  跟入environmentPrepared中的源码

 

#SpringApplicationRunListeners.java
    public void environmentPrepared(ConfigurableEnvironment environment) {
        for (SpringApplicationRunListener listener : this.listeners) {
            //跟入
            listener.environmentPrepared(environment);
        }
    }

#EventPublishingRunListener.java
    public void environmentPrepared(ConfigurableEnvironment environment) {
        //广播ApplicationEnvrionmentPreparedEvnet事件
        //跟入
        this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent(
                this.application, this.args, environment));
    }

#SimpleApplicationEventMulticaster.java
    public void multicastEvent(ApplicationEvent event) {
        //跟入
        multicastEvent(event, resolveDefaultEventType(event));
    }

    @Override
    public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
        ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
        //注意此时 getApplicationListeners(event, type) 返回结果
        //包含 监听器 *ConfigFileApplicationListener*
                for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
            Executor executor = getTaskExecutor();
            if (executor != null) {
                executor.execute(() -> invokeListener(listener, event));
            }
            else {
                //跟入
                invokeListener(listener, event);
            }
        }
    }

#SimpleApplicationEventMulticaster.java
    /**
     * Invoke the given listener with the given event.
     * 调用对应事件的监听者
     * @param listener the ApplicationListener to invoke
     * @param event the current event to propagate
     * @since 4.1
     */
    protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) {
        ErrorHandler errorHandler = getErrorHandler();
        if (errorHandler != null) {
            try {
                doInvokeListener(listener, event);
            }
            catch (Throwable err) {
                errorHandler.handleError(err);
            }
        }
        else {
            //跟入
            doInvokeListener(listener, event);
        }
    }

    private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
        try {
            //跟入
            listener.onApplicationEvent(event);
        }

#ApplicationListener.java
    //实现接口的监听器当中，有并跟入ConfigFileApplicationListener的实现
    void onApplicationEvent(E event);

#ConfigFileApplicationListener.java
    public void onApplicationEvent(ApplicationEvent event) {
        if (event instanceof ApplicationEnvironmentPreparedEvent) {
            //跟入
            onApplicationEnvironmentPreparedEvent(
                    (ApplicationEnvironmentPreparedEvent) event);
        }
        if (event instanceof ApplicationPreparedEvent) {
            onApplicationPreparedEvent(event);
        }
    }

    private void onApplicationEnvironmentPreparedEvent(
            ApplicationEnvironmentPreparedEvent event) {
        List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
        postProcessors.add(this);
        AnnotationAwareOrderComparator.sort(postProcessors);
        for (EnvironmentPostProcessor postProcessor : postProcessors) {
            //跟入：当postProcessor 为 ConfigFileApplicationListener
            postProcessor.postProcessEnvironment(event.getEnvironment(),
                    event.getSpringApplication());
        }
    }

#ConfigFileApplicationListener.java
    public void postProcessEnvironment(ConfigurableEnvironment environment,
            SpringApplication application) {
        //跟入
        addPropertySources(environment, application.getResourceLoader());
    }

    protected void addPropertySources(ConfigurableEnvironment environment,
            ResourceLoader resourceLoader) {
        //environment的属性源中包含 systemProperties 属性源 即包含 server.port启动参数
        RandomValuePropertySource.addToEnvironment(environment);
        //跟入 load()方法
        new Loader(environment, resourceLoader).load();
    }

跟入load之前，需要了解  java lambda表达式

 

#ConfigFileApplicationListener.java
        public void load() {
            this.profiles = new LinkedList<>();
            this.processedProfiles = new LinkedList<>();
            this.activatedProfiles = false;
            this.loaded = new LinkedHashMap<>();
            initializeProfiles();
            while (!this.profiles.isEmpty()) {
                Profile profile = this.profiles.poll();
                load(profile, this::getPositiveProfileFilter,
                        addToLoaded(MutablePropertySources::addLast, false));
                this.processedProfiles.add(profile);
            }
            //跟入
load(null, this::getNegativeProfileFilter,
                    addToLoaded(MutablePropertySources::addFirst, true));
            addLoadedPropertySources();
        }

#ConfigFileApplicationListener.java
        private void load(Profile profile, DocumentFilterFactory filterFactory,
                DocumentConsumer consumer) {
            //getSearchLocations()默认返回：
            //[./config/, file:./, classpath:/config/, classpath:/]
            //即搜索这些路径下的文件
            getSearchLocations().forEach((location) -> {
                boolean isFolder = location.endsWith("/");
                //getSearchNames()返回：application
                Set<String> names = (isFolder ? getSearchNames() : NO_SEARCH_NAMES);
                //跟入load(.....)
                names.forEach(
                        (name) -> load(location, name, profile, filterFactory, consumer));
            });
        }

#ConfigFileApplicationListener.java
        private void load(String location, String name, Profile profile,
                DocumentFilterFactory filterFactory, DocumentConsumer consumer) {
            //name默认为：application，所以这个if分支略过
            if (!StringUtils.hasText(name)) {
                for (PropertySourceLoader loader : this.propertySourceLoaders) {
                    if (canLoadFileExtension(loader, location)) {
                        load(loader, location, profile,
                                filterFactory.getDocumentFilter(profile), consumer);
                    }
                }
            }
            //this.propertySourceLoaders: PropertiesPropertySourceLoader,YamlPropertySourceLoader
            for (PropertySourceLoader loader : this.propertySourceLoaders) {
                //PropertiesPropertySourceLoader.getFileExtensions(): properties, xml
                //YamlPropertySourceLoader.getFileExtensions(): yml, yaml
                for (String fileExtension : loader.getFileExtensions()) {
                    //location: [./config/, file:./, classpath:/config/, classpath:/]
                    //name: application
                    String prefix = location + name;
                    fileExtension = "." + fileExtension;
                    //profile: null, dev
                    //相当于对(location, fileExtension, profile)做笛卡尔积，
                    //遍历每一种可能，然后加载
                    //加载文件的细节在loadForFileExtension中完成
                    loadForFileExtension(loader, prefix, fileExtension, profile,
                            filterFactory, consumer);
                }
            }
        }

继续跟入 loadForFileExtension 方法，可以了解载入一个配置文件的更多细节。

 

  回到之前的load()方法

 

#ConfigFileApplicationListener.java
        public void load() {
            this.profiles = new LinkedList<>();
            this.processedProfiles = new LinkedList<>();
            this.activatedProfiles = false;
            this.loaded = new LinkedHashMap<>();
            initializeProfiles();
            while (!this.profiles.isEmpty()) {
                Profile profile = this.profiles.poll();
                load(profile, this::getPositiveProfileFilter,
                        addToLoaded(MutablePropertySources::addLast, false));
                this.processedProfiles.add(profile);
            }
            load(null, this::getNegativeProfileFilter,
                    addToLoaded(MutablePropertySources::addFirst, true));
            //跟入
addLoadedPropertySources();

#ConfigFileApplicationListener.java
        private void addLoadedPropertySources() {
            //destination: 进入ConfigFileApplicationListener监听器前已有的配置
            //即destination中包含 systemProperties 配置源
            MutablePropertySources destination = this.environment.getPropertySources();
            String lastAdded = null;
            //loaded: 此次监听通过扫描文件加载进来的配置源
            //loaded: application.yml, appcalition-dev.yml
            List<MutablePropertySources> loaded = new ArrayList<>(this.loaded.values());
            //倒序后 loaded: application-dev.yml, application.yml
            Collections.reverse(loaded);
            //先处理 application-dev.yml
            for (MutablePropertySources sources : loaded) {
                for (PropertySource<?> source : sources) {
                    //第一次进入: lastAdded:null
                    if (lastAdded == null) {
                        if (destination.contains(DEFAULT_PROPERTIES)) {
                            destination.addBefore(DEFAULT_PROPERTIES, source);
                        }
                        else {
                            //第一次进入: 把application-dev.yml至于最低优先级
                            destination.addLast(source);
                        }
                    }
                    else {
                        //第二次进入:
                        //让 application.yml 优先级比 application-dev.yml 低
                        destination.addAfter(lastAdded, source);
                    }
                    //第一次遍历结束: lastAdded: application-dev
                    lastAdded = source.getName();
                }
            }
        }

执行后得到各自的优先级，如下图：

 

   systemProperties优先级高，解析器会优先使用 systemProperties中的 server.port 配置项即 5555 所以最终Tomcat 启动端口是 5555

 

  从中也可以看出，如果application.yml 和 application-dev.yml中有相同的配置项，会优先采用application-dev.yml中的配置项。

  

参考：

1. SpringBoot源码分析之SpringBoot的启动过程

2. SpringBoot源码分析之配置环境的构造过程

3. springboot启动时是如何加载配置文件application.yml文件