從SpringBoot原始碼分析 配置檔案的載入原理和優先順序
阿新 • • 發佈：2018-11-08
從SpringBoot原始碼分析 配置檔案的載入原理和優先順序
本文從SpringBoot原始碼分析 配置檔案的載入原理和配置檔案的優先順序
跟入原始碼之前，先提一個問題：
SpringBoot 既可以載入指定目錄下的配置檔案獲取配置項，也可以通過啟動引數（VM Options）傳入配置項，為什麼通過啟動引數傳入的配置項會“頂掉”配置檔案中的配置？
示例：
application.yml
server.port: 8888 spring.profiles.active: dev
application-dev.yml
spring.think: hello
在IDEA中使用命令列配置項
VM Options
-Dserver.port=5555
如下圖：
啟動結果：
Tomcat started on port(s): 5555 (http) with context path ''
同時在application.yml 和 啟動引數（VM options）中設定 server.port
下面開始從main函式啟動處，跟入SpringBoot原始碼，看看SpringBoot是如何處理的。
系統說明
JDK：1.8
SpringBoot 版本： 2.0.2.RELEASE
IDE： IntelliJ IDEA 2017
跟入原始碼正文
#ApplicationConfigLoadFlow.java
public static void main(String[] args) {
SpringApplication.run
從SpringApplication.run 函式開始，一個方法一個方法的跟入原始碼。需要跟入的方法給與註釋或高亮。
IDEA 快捷鍵：
進入方法: Ctrl + 滑鼠左鍵
游標前進/後退： Ctrl + Shirt + 右方向鍵/左方向鍵
依次跟入原始碼：
#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);
進入public ConfigurableApplicationContext run(String... args) 方法後，我們重點看 prepareEnvironment這個方法。
這個方法之前的原始碼的從類名和原始碼註釋上知道stopWatch用於計時，上下文context還未初始化，listeners監聽器儲存了EventPushlingRunListener。
通過IDEA 一行行debug可以看到是在 prepareEnvironment方法執行後，server.port 配置項才被載入入 environment 環境配置中。
如下圖所示。注意：配置檔案中的配置還未載入，請先接著往後看。
因此，我們重新打斷點跟入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());
同樣的套路，通過debug發現實在getOrCreateEnvironment方法執行後得到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();
}
虛擬機器啟動引數的載入 是在StandardServletEnvironment 的例項化過程中完成的。
跟入StandardServletEnvironment的例項化過程之前，大家需要先了解 Java模板模式 。
看一下StandardServletEnvironment的類繼承關係圖（通過IDEA 右鍵 類名 --> Diagrams --> Show Diagrams Popup 即可顯示下圖）
抽象父類AbstractEnvironment的例項化方法中，呼叫了可由子類繼承的customizePropertySources方法。
#AbstractEnvironment.java
public AbstractEnvironment() {
//跟入
customizePropertySources(this.propertySources);
if (logger.isDebugEnabled()) {
logger.debug("Initialized " + getClass().getSimpleName() + " with PropertySources " + this.propertySources);
}
}
實體化的過程中回過頭來呼叫了子類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);
}
又呼叫了父類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()));
}
通過IDEA 的變數監聽功能，可以看到正是StandardEnvironment類的getSystemProperties()方法獲取到了之前設定的虛擬機器啟動引數server.port的值。
繼續跟進去
#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;
我們搜尋一下有沒有什麼地方初始化 props
#System.java
private static Properties props;
private static native Properties initProperties(Properties props);
發現了靜態方法 initProperties，從方法名上即可知道在類被載入的時候 就初始化了 props， 這是個本地方法，繼續跟的話需要看對應的C++程式碼。
回到StandardEnvironment類的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.
* 新增屬性源，並使其優先順序最低
*/
public void addLast(PropertySource<?> propertySource) {
再看一下MutablePropertySources的類註釋
* <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 會設定屬性源的優先順序，
* PropertyResolver解析配置時會根據優先順序使用配置源
*
* @author Chris Beams
* @author Juergen Hoeller
* @since 3.1
* @see PropertySourcesPropertyResolver
*/
public class MutablePropertySources implements PropertySources {
問題2：
此時我們已經看到虛擬機器的啟動引數先新增到系統當中，那麼後面新增進來的Property Source屬性源的優先順序是否比 SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME(systemProperties) 屬性源的優先順序高呢？
回到SpringApplication的prepareEnvironment方法
同樣的debug套路發現listeners.environmentPrepared執行後，application.yml 和 application-dev.yml 兩個配置檔案的配置項都被載入完成，所以我們繼續跟入environmentPrepared方法
在跟入environmentPrepared方法之前，需要了解 Java事件監聽機制
跟入environmentPrepared中的原始碼
#SpringApplicationRunListeners.java
public void environmentPrepared(ConfigurableEnvironment environment) {
for (SpringApplicationRunListener listener : this.listeners) {
//跟入
listener.environmentPrepared(environment);
}
}
#EventPublishingRunListener.java
public void environmentPrepared(ConfigurableEnvironment environment) {
//廣播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));
//注意此時 getApplicationListeners(event, type) 返回結果
//包含 監聽器 *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.
* 呼叫對應事件的監聽者
* @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
//實現介面的監聽器當中，有並跟入ConfigFileApplicationListener的實現
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：當postProcessor 為 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的屬性源中包含 systemProperties 屬性源 即包含 server.port啟動引數
RandomValuePropertySource.addToEnvironment(environment);
//跟入 load()方法
new Loader(environment, resourceLoader).load();
}
跟入load之前，需要了解 java lambda表示式
#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()預設返回：
//[./config/, file:./, classpath:/config/, classpath:/]
//即搜尋這些路徑下的檔案
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預設為：application，所以這個if分支略過
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
//相當於對(location, fileExtension, profile)做笛卡爾積，
//遍歷每一種可能，然後載入
//載入檔案的細節在loadForFileExtension中完成
loadForFileExtension(loader, prefix, fileExtension, profile,
filterFactory, consumer);
}
}
}
繼續跟入 loadForFileExtension 方法，可以瞭解載入一個配置檔案的更多細節。
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: 進入ConfigFileApplicationListener監聽器前已有的配置
//即destination中包含 systemProperties 配置源
MutablePropertySources destination = this.environment.getPropertySources();
String lastAdded = null;
//loaded: 此次監聽通過掃描檔案載入進來的配置源
//loaded: application.yml, appcalition-dev.yml
List<MutablePropertySources> loaded = new ArrayList<>(this.loaded.values());
//倒序後 loaded: application-dev.yml, application.yml
Collections.reverse(loaded);
//先處理 application-dev.yml
for (MutablePropertySources sources : loaded) {
for (PropertySource<?> source : sources) {
//第一次進入: lastAdded:null
if (lastAdded == null) {
if (destination.contains(DEFAULT_PROPERTIES)) {
destination.addBefore(DEFAULT_PROPERTIES, source);
}
else {
//第一次進入: 把application-dev.yml至於最低優先順序
destination.addLast(source);
}
}
else {
//第二次進入:
//讓 application.yml 優先順序比 application-dev.yml 低
destination.addAfter(lastAdded, source);
}
//第一次遍歷結束: lastAdded: application-dev
lastAdded = source.getName();
}
}
}
執行後得到各自的優先順序，如下圖：
systemProperties優先順序高，解析器會優先使用 systemProperties中的 server.port 配置項即 5555 所以最終Tomcat 啟動埠是 5555
從中也可以看出，如果application.yml 和 application-dev.yml中有相同的配置項，會優先採用application-dev.yml中的配置項。
參考：
1. SpringBoot原始碼分析之SpringBoot的啟動過程
3. springboot啟動時是如何載入配置檔案application.yml檔案
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原文地址 :https://www.cnblogs.com/tanliwei/p/9304072.html