SpringBoot配置文件的加载原理和优先级
我们都知道:
- 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;
在跟踪源代码之前，先提一个问题：
当我们在通过启动参数传入的配置项时候优先使用呢,即会“顶掉”配置文件中的配置？
1.通过启动参数传入配置项
示例:
1.1 application.yml
server:
port: 8888
spring:
profiles:
active: dev
1.2 application-dev.yml
spring:
think: hello
1.3 在IDEA中使用命令行配置项
VM Options :
-Dserver.port=5555
如下图：
1.4 启动结果
Tomcat started on port(s): 5555 (http) with context path ‘’
结果: 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。
接下来开始从main函数启动处，跟入SpringBoot源码，看看SpringBoot是如何处理的。
2.系统说明
JDK：1.8
SpringBoot 版本： 2.2.2.RELEASE
IDE： IntelliJ IDEA 2018.1
3.启动参数传入配置项
跟踪源码：
可查看如下Spring Boot 2.2.2 版本的执行流程。
SpringBoot2原理—SpringApplication的执行流程
当看到3.6 创建 Environment 节如下代码时候：
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
configureIgnoreBeanInfo(environment);
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。说明prepareEnvironment方法做的事情就是将server.port 配置项才加载到 environment 环境配置中。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getOrCreateEnvironment()
ConfigurableEnvironment environment = getOrCreateEnvironment();
configureEnvironment(environment, applicationArguments.getSourceArgs());
listeners.environmentPrepared(environment);
bindToSpringApplication(environment);
if (!this.isCustomEnvironment) {
environment = new EnvironmentConverter(getClassLoader())
.convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());
}
ConfigurationPropertySources.attach(environment);
return environment;
}
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;
}
switch (this.webApplicationType) {
case SERVLET:
return new StandardServletEnvironment();
case REACTIVE:
return new StandardReactiveWebEnvironment();
default:
//跟入StandardEnvironment
return new StandardEnvironment();
}
}
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
//跟入AbstractEnvironment构造方法
public AbstractEnvironment() {
customizePropertySources(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getSystemProperties()方法
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。
protected void customizePropertySources(MutablePropertySources propertySources) {
//public static final String SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME = "systemProperties";
//跟入MapPropertySource
propertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));
propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));
}
MutablePropertySources是PropertySources的实现类。
#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
*/
4.加载指定目录下的配置文件
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？
让我们重新回到SpringApplication的prepareEnvironment方法。
##SpringApplication.java
private ConfigurableEnvironment prepareEnvironment(
SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
// Create and configure the environment
ConfigurableEnvironment environment = getOrCreateEnvironment();
configureEnvironment(environment, applicationArguments.getSourceArgs());
listeners.environmentPrepared(environment);
bindToSpringApplication(environment);
if (!this.isCustomEnvironment) {
environment = new EnvironmentConverter(getClassLoader())
.convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());
}
ConfigurationPropertySources.attach(environment);
return environment;
}
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);
}
}
}
这里解释一下监听器 ConfigFileApplicationListener为什么会有:
getApplicationListeners(event, type)方法执行完成之后,查看所有的监听器如下红框中显示的监听器–ConfigFileApplicationListener 。
#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);
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();
if (profile != null && !profile.isDefaultProfile()) {
addProfileToEnvironment(profile.getName());
}
load(profile, this::getPositiveProfileFilter,
addToLoaded(MutablePropertySources::addLast, false));
this.processedProfiles.add(profile);
}
resetEnvironmentProfiles(this.processedProfiles);
//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);
return;
}
}
}
Set<String> processed = new HashSet<>();
//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
if (processed.add(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, location + name, "." + 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();
if (profile != null && !profile.isDefaultProfile()) {
addProfileToEnvironment(profile.getName());
}
load(profile, this::getPositiveProfileFilter,
addToLoaded(MutablePropertySources::addLast, false));
this.processedProfiles.add(profile);
}
resetEnvironmentProfiles(this.processedProfiles);
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();
//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);
String lastAdded = null;
Set<String> added = new HashSet<>();
//先处理 application-dev.yml
for (MutablePropertySources sources : loaded) {
for (PropertySource<?> source : sources) {
if (added.add(source.getName())) {
//第一次进入: lastAdded:null
//跟入
addLoadedPropertySource(destination, lastAdded, source);
//第一次遍历结束: lastAdded: application-dev
lastAdded = source.getName();
}
}
}
}
private void addLoadedPropertySource(MutablePropertySources destination,
String lastAdded, PropertySource<?> source) {
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);
}
}
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 .
从图中也可以看出，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。
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