Spring Boot Application

spring boot默认已经配置了很多环境变量，例如，tomcat的默认端口是8080，项目的contextpath是“/”等等，spring boot允许你自定义一个application.properties文件，然后放在以下的地方，来重写spring boot的环境变量

spring对配置application.properties的加载过程：

1. 服务启动调用:SpringApplication.run
2. 创建默认的环境参数：ConfigurableEnvironment
3. 触发事件：ApplicationEnvironmentPreparedEvent
4. 完成加载

整个过程主要使用spring boot 内置的ConfigFileApplicationListener监听器监听ApplicationEnvironmentPreparedEvent事件完成对application.properties加载以及设置。

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下面我们来跟踪源码，看下spring boot是怎样完成对application.properties文件的加载

• SpringApplication 入口 run：

1. public ConfigurableApplicationContext run(String... args) {
2. //无关的代码暂略
3. .......
4. ConfigurableApplicationContext context = null;
5. FailureAnalyzers analyzers = null;
6. configureHeadlessProperty();
7. //获取执行监听器实例
8. SpringApplicationRunListeners listeners = getRunListeners(args);
9. ........
10. //创建全局系统参数实例
11. ApplicationArguments applicationArguments = new DefaultApplicationArguments(
12. args);
13. //创建 ConfigurableEnvironment 并触发ApplicationEnvironmentPreparedEvent事件
14. //加载配置的核心地方，spring启动首要做的事情
15. ConfigurableEnvironment environment = prepareEnvironment(listeners,
16. applicationArguments);
17. .........
18. }

prepareEnvironment方法

1. private ConfigurableEnvironment prepareEnvironment(
2. SpringApplicationRunListeners listeners,
3. ApplicationArguments applicationArguments) {
4. // Create and configure the environment
5. //创建一个配置环境信息，当是web环境时创建StandardServletEnvironment实例，非web环境时创建StandardEnvironment实例
6. ConfigurableEnvironment environment = getOrCreateEnvironment();
7. configureEnvironment(environment, applicationArguments.getSourceArgs());
8. //核心事件触发方法，此方法执行后会执行所有监听ApplicationEnvironmentPreparedEvent事件的监听器，这里我们是跟踪application.properties文件的加载，就查看ConfigFileApplicationListener监听器都做了什么工作
9. listeners.environmentPrepared(environment);
10. if (!this.webEnvironment) {
11. environment = new EnvironmentConverter(getClassLoader())
12. .convertToStandardEnvironmentIfNecessary(environment);
13. }
14. return environment;
15. }

• ConfigFileApplicationListener：

1. public void onApplicationEvent(ApplicationEvent event) {
2. //从此处可以看到当事件为ApplicationEnvironmentPreparedEvent时，执行onApplicationEnvironmentPreparedEvent方法
3. if (event instanceof ApplicationEnvironmentPreparedEvent) {
4. onApplicationEnvironmentPreparedEvent(
5. (ApplicationEnvironmentPreparedEvent) event);
6. }
7. if (event instanceof ApplicationPreparedEvent) {
8. onApplicationPreparedEvent(event);
9. }
10. }

onApplicationEnvironmentPreparedEvent

1. private void onApplicationEnvironmentPreparedEvent(
2. ApplicationEnvironmentPreparedEvent event) {
3. //此处通过SpringFactoriesLoader加载EnvironmentPostProcessor所有扩展
4. List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
5. //因为此监听器同样是EnvironmentPostProcessor的扩展实例，所以在此处将自己加入集合
6. postProcessors.add(this);
7. AnnotationAwareOrderComparator.sort(postProcessors);
8. //遍历所有的EnvironmentPostProcessor扩展调用postProcessEnvironment
9. //当然我们跟踪是application.properties所以主要查看当前实例的postProcessEnvironment方法
10. for (EnvironmentPostProcessor postProcessor : postProcessors) {
11. postProcessor.postProcessEnvironment(event.getEnvironment(),
12. event.getSpringApplication());
13. }
14. }

postProcessEnvironment

1. @Override
2. public void postProcessEnvironment(ConfigurableEnvironment environment,
3. SpringApplication application) {
4. //此处添加配置信息到environment实例中，此方法完成后就将application.properties加载到环境信息中
5. addPropertySources(environment, application.getResourceLoader());
6. configureIgnoreBeanInfo(environment);
7. bindToSpringApplication(environment, application);
8. }

addPropertySources

1. protected void addPropertySources(ConfigurableEnvironment environment,
2. ResourceLoader resourceLoader) {
3. //这里先添加一个Random名称的资源到环境信息中
4. RandomValuePropertySource.addToEnvironment(environment);
5. //通过Loader加载application.properties并将信息存入环境信息中
6. new Loader(environment, resourceLoader).load();
7. }

load

1. public void load() {
2. //创建一个资源加载器，spring boot默认支持PropertiesPropertySourceLoader，YamlPropertySourceLoader两种配置文件的加载
3. this.propertiesLoader = new PropertySourcesLoader();
4. this.activatedProfiles = false;
5. //加载配置profile信息，默认为default
6. ..........此处省略
7. while (!this.profiles.isEmpty()) {
8. Profile profile = this.profiles.poll();
9. //遍历所有查询路径，默认路径有：classpath:/,classpath:/config/,file:./,file:./config/
10. for (String location : getSearchLocations()) {
11. //这里不仅仅是加载application.properties，当搜索路径不是以/结束，默认认为是文件名已存在的路径
12. if (!location.endsWith("/")) {
13. // location is a filename already, so don't search for more
14. // filenames
15. load(location, null, profile);
16. }
17. else {
18. //遍历要加载的文件名集合，默认为application
19. for (String name : getSearchNames()) {
20. load(location, name, profile);
21. }
22. }
23. }
24. this.processedProfiles.add(profile);
25. }
27. //将加载完成的配置信息全部保存到环境信息*享
28. addConfigurationProperties(this.propertiesLoader.getPropertySources());
29. }

load

1. private void load(String location, String name, Profile profile) {
2. //此处根据profile组装加载的文件名称以及资源所放置的组信息
3. String group = "profile=" + (profile == null ? "" : profile);
4. if (!StringUtils.hasText(name)) {
5. // Try to load directly from the location
6. loadIntoGroup(group, location, profile);
7. }
8. else {
10. // Also try the profile-specific section (if any) of the normal file
11. loadIntoGroup(group, location + name + "." + ext, profile);
12. }
13. }
14. }

loadIntoGroup

1. private PropertySource<?> doLoadIntoGroup(String identifier, String location,
2. Profile profile) throws IOException {
3. Resource resource = this.resourceLoader.getResource(location);
4. PropertySource<?> propertySource = null;
5. if (resource != null && resource.exists()) {
6. String name = "applicationConfig: [" + location + "]";
7. String group = "applicationConfig: [" + identifier + "]";
8. //资源加载核心方法，此处有两个实现，当后缀为，xml或者properties调用PropertiesPropertySourceLoader
9. //当后缀为yml或者yaml时，调用YamlPropertySourceLoader
11. propertySource = this.propertiesLoader.load(resource,
12. }
14. return propertySource;
15. }

• PropertiesPropertySourceLoader：

1. @Override
2. public PropertySource<?> load(String name, Resource resource, String profile)
3. throws IOException {
4. if (profile == null) {
5. //此处调用PropertiesLoaderUtils工具类加载本地文件
6. Properties properties = PropertiesLoaderUtils.loadProperties(resource);
7. if (!properties.isEmpty()) {
8. return new PropertiesPropertySource(name, properties);
9. }
10. }
11. return null;
12. }

到此application.properties就真正的加载并共享到环境信息中，供系统其它地方调用