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：
- 服务启动调用:SpringApplication.run
- 创建默认的环境参数：ConfigurableEnvironment
- 触发事件：ApplicationEnvironmentPreparedEvent
- 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。
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：
public ConfigurableApplicationContext run(String... args) {
//无关的代码暂略
.......
ConfigurableApplicationContext context = null;
FailureAnalyzers analyzers = null;
configureHeadlessProperty();
//获取执行监听器实例
SpringApplicationRunListeners listeners = getRunListeners(args);
........
//创建全局系统参数实例
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
//创建 ConfigurableEnvironment 并触发ApplicationEnvironmentPreparedEvent事件
//加载配置的核心地方，spring启动首要做的事情
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
.........
}
prepareEnvironment方法
private ConfigurableEnvironment prepareEnvironment(
SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
// Create and configure the environment
//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
ConfigurableEnvironment environment = getOrCreateEnvironment();
configureEnvironment(environment, applicationArguments.getSourceArgs());
//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
listeners.environmentPrepared(environment);
if (!this.webEnvironment) {
environment = new EnvironmentConverter(getClassLoader())
.convertToStandardEnvironmentIfNecessary(environment);
}
return environment;
}
- ConfigFileApplicationListener：
public void onApplicationEvent(ApplicationEvent event) {
//从此处可以看到当事件为ApplicationEnvironmentPreparedEvent时，执行onApplicationEnvironmentPreparedEvent方法
if (event instanceof ApplicationEnvironmentPreparedEvent) {
onApplicationEnvironmentPreparedEvent(
(ApplicationEnvironmentPreparedEvent) event);
}
if (event instanceof ApplicationPreparedEvent) {
onApplicationPreparedEvent(event);
}
}
onApplicationEnvironmentPreparedEvent
private void onApplicationEnvironmentPreparedEvent(
ApplicationEnvironmentPreparedEvent event) {
//此处通过SpringFactoriesLoader加载EnvironmentPostProcessor所有扩展
List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
//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
postProcessors.add(this);
AnnotationAwareOrderComparator.sort(postProcessors);
//遍历所有的EnvironmentPostProcessor扩展调用postProcessEnvironment
//当然我们跟踪是application.properties所以主要查看当前实例的postProcessEnvironment方法
for (EnvironmentPostProcessor postProcessor : postProcessors) {
postProcessor.postProcessEnvironment(event.getEnvironment(),
event.getSpringApplication());
}
}
postProcessEnvironment
@Override
public void postProcessEnvironment(ConfigurableEnvironment environment,
SpringApplication application) {
//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
addPropertySources(environment, application.getResourceLoader());
configureIgnoreBeanInfo(environment);
bindToSpringApplication(environment, application);
}
addPropertySources
protected void addPropertySources(ConfigurableEnvironment environment,
ResourceLoader resourceLoader) {
//这里先添加一个Random名称的资源到环境信息中
RandomValuePropertySource.addToEnvironment(environment);
//通过Loader加载application.properties并将信息存入环境信息中
new Loader(environment, resourceLoader).load();
}
load
public void load() {
//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
this.propertiesLoader = new PropertySourcesLoader();
this.activatedProfiles = false;
//加载配置profile信息，默认为default
..........此处省略
while (!this.profiles.isEmpty()) {
Profile profile = this.profiles.poll();
//遍历所有查询路径，默认路径有：classpath:/,classpath:/config/,file:./,file:./config/
for (String location : getSearchLocations()) {
//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
if (!location.endsWith("/")) {
// location is a filename already, so don't search for more
// filenames
load(location, null, profile);
}
else {
//遍历要加载的文件名集合，默认为application
for (String name : getSearchNames()) {
load(location, name, profile);
}
}
}
this.processedProfiles.add(profile);
}
//将加载完成的配置信息全部保存到环境信息中共享
addConfigurationProperties(this.propertiesLoader.getPropertySources());
}
load
private void load(String location, String name, Profile profile) {
//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
String group = "profile=" + (profile == null ? "" : profile);
if (!StringUtils.hasText(name)) {
// Try to load directly from the location
loadIntoGroup(group, location, profile);
}
else {
// Also try the profile-specific section (if any) of the normal file
loadIntoGroup(group, location + name + "." + ext, profile);
}
}
}
loadIntoGroup
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private PropertySource<?> doLoadIntoGroup(String identifier, String location,
Profile profile) throws IOException {
Resource resource = this.resourceLoader.getResource(location);
PropertySource<?> propertySource = null;
if (resource != null && resource.exists()) {
String name = "applicationConfig: [" + location + "]";
String group = "applicationConfig: [" + identifier + "]";
//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
//当后缀为yml或者yaml时，调用YamlPropertySourceLoader
propertySource = this.propertiesLoader.load(resource,
}
return propertySource;
}
- PropertiesPropertySourceLoader：
@Override
public PropertySource<?> load(String name, Resource resource, String profile)
throws IOException {
if (profile == null) {
//此处调用PropertiesLoaderUtils工具类加载本地文件
Properties properties = PropertiesLoaderUtils.loadProperties(resource);
if (!properties.isEmpty()) {
return new PropertiesPropertySource(name, properties);
}
}
return null;
}
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