上篇我们已经把SpringApplication.run过程中SpringApplicationRunListener的加载及starting流程讲解完了，本篇我们接着往下跟:
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
this.configureHeadlessProperty();
SpringApplicationRunListeners listeners = this.getRunListeners(args);
listeners.starting();
Collection exceptionReporters;
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
// 本篇的主角，prepareEnvironment方法
ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
...
}
}
具体看一下prepareEnvironment方法:
private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) {
// 根据应用类型，创建应用环境：如得到系统环境变量、JVM及Servlet等参数
ConfigurableEnvironment environment = this.getOrCreateEnvironment();
// 将 defaultProperties、commandLine及active-prifiles 属性加载到环境中
// commandLine 在 args 中配置
// 其它参数可在如下4个路径中配置：servletConfigInitParams、servletContextInitParams、systemProperties、systemEnvironment
this.configureEnvironment((ConfigurableEnvironment)environment, applicationArguments.getSourceArgs());
// listeners环境准备(就是广播ApplicationEnvironmentPreparedEvent事件)
listeners.environmentPrepared((ConfigurableEnvironment)environment);
// 将环境绑定到SpringApplication
this.bindToSpringApplication((ConfigurableEnvironment)environment);
// 如果是非web环境，将环境转换成StandardEnvironment
if (this.webApplicationType == WebApplicationType.NONE) {
environment = (new EnvironmentConverter(this.getClassLoader())).convertToStandardEnvironmentIfNecessary((ConfigurableEnvironment)environment);
}
// 配置PropertySources对它自己的递归依赖
ConfigurationPropertySources.attach((Environment)environment);
return (ConfigurableEnvironment)environment;
}
下面我们一行一行来看。
getOrCreateEnvironment
private ConfigurableEnvironment getOrCreateEnvironment() {
// 如果environment不为null，说明已初始化过，直接返回即可
if (this.environment != null) {
return this.environment;
} else {
// 若envirment为null，需要执行初始化
// 根据webApplicationType的类型来决定创建哪种environment
// 若是Web应用，则创建StandardServletEnvironment，否则创建StandardEnvironment
return (ConfigurableEnvironment)(this.webApplicationType == WebApplicationType.SERVLET ? new StandardServletEnvironment() : new StandardEnvironment());
}
}
我们以StandardServletEnvironment为例，看一下环境初始化过程中发生了什么。
public StandardServletEnvironment() {
}
额，好像就是个空构造函数，难道啥也没做？
哈哈哈，不要被迷惑了，我们知道，类执行构造函数时，会从顶层类往下依次执行，是不是StandardServletEnvironment的父类里有具体操作。
StandardServletEnvironment的父类为StandardEnvironment：
public StandardEnvironment() {
}
仍然为空构造，继续往上追踪父类，StandardEnvironment的父类为AbstractEnvironment：
哈哈哈，终于找到你了！！！
public AbstractEnvironment() {
this.propertySources = new MutablePropertySources(this.logger);
this.propertyResolver = new PropertySourcesPropertyResolver(this.propertySources);
// 关键是customizePropertySources方法
this.customizePropertySources(this.propertySources);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Initialized " + this.getClass().getSimpleName() + " with PropertySources " + this.propertySources);
}
}
整个的继承关系如下:
1.jpg
AbstractEnvironment的customizePropertySources方法为protected修饰的空方法:
protected void customizePropertySources(MutablePropertySources propertySources) {
}
很明显，customizePropertySources的具体实现在子类StandardEnvironment及StandardServletEnvironment中。
先看StandardEnvironment的customizePropertySources方法:
protected void customizePropertySources(MutablePropertySources propertySources) {
// 获取系统参数
propertySources.addLast(new MapPropertySource("systemProperties", this.getSystemProperties()));
// 获取系统环境变量
propertySources.addLast(new SystemEnvironmentPropertySource("systemEnvironment", this.getSystemEnvironment()));
}
本质上底层还是走的System.getSystemProperties()和System.getenv()。
public Map<String, Object> getSystemProperties() {
try {
return System.getProperties();
} catch (AccessControlException var2) {
return new ReadOnlySystemAttributesMap() {
@Nullable
protected String getSystemAttribute(String attributeName) {
try {
return System.getProperty(attributeName);
} catch (AccessControlException var3) {
if (AbstractEnvironment.this.logger.isInfoEnabled()) {
AbstractEnvironment.this.logger.info("Caught AccessControlException when accessing system property '" + attributeName + "'; its value will be returned [null]. Reason: " + var3.getMessage());
}
return null;
}
}
};
}
}
public Map<String, Object> getSystemEnvironment() {
if (this.suppressGetenvAccess()) {
return Collections.emptyMap();
} else {
try {
return System.getenv();
} catch (AccessControlException var2) {
return new ReadOnlySystemAttributesMap() {
@Nullable
protected String getSystemAttribute(String attributeName) {
try {
return System.getenv(attributeName);
} catch (AccessControlException var3) {
if (AbstractEnvironment.this.logger.isInfoEnabled()) {
AbstractEnvironment.this.logger.info("Caught AccessControlException when accessing system environment variable '" + attributeName + "'; its value will be returned [null]. Reason: " + var3.getMessage());
}
return null;
}
}
};
}
}
}
2.jpg
3.jpg
接着看StandardServletEnvironment的customizePropertySources方法:
protected void customizePropertySources(MutablePropertySources propertySources) {
// 增加servletConfig初始化参数，当前没有任何值
propertySources.addLast(new StubPropertySource("servletConfigInitParams"));
// 增加servletContext初始化参数，当前没有任何值
propertySources.addLast(new StubPropertySource("servletContextInitParams"));
if (JndiLocatorDelegate.isDefaultJndiEnvironmentAvailable()) {
propertySources.addLast(new JndiPropertySource("jndiProperties"));
}
// 紧接着调用StandardEnvironment的customizePropertySources方法
super.customizePropertySources(propertySources);
}
说白了，StandardServletEnvironment比StandardEnvironment增加了2项Servlet相关的配置。
4.jpg
总结一句，getOrCreateEnvironment方法就是根据应用类型，创建应用环境：如得到系统环境变量、JVM及Servlet等参数。
configureEnvironment
protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
this.configurePropertySources(environment, args);
this.configureProfiles(environment, args);
}
先看，configurePropertySources方法:
protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) {
// 从environment中获取PropertySources
MutablePropertySources sources = environment.getPropertySources();
// 如果defaultProperties不为null且不为空，将其加入sources
if (this.defaultProperties != null && !this.defaultProperties.isEmpty()) {
sources.addLast(new MapPropertySource("defaultProperties", this.defaultProperties));
}
// 否则，根据args重新构建SimpleCommandLinePropertySource，然后更新或添加进sources
if (this.addCommandLineProperties && args.length > 0) {
String name = "commandLineArgs";
if (sources.contains(name)) {
PropertySource<?> source = sources.get(name);
CompositePropertySource composite = new CompositePropertySource(name);
composite.addPropertySource(new SimpleCommandLinePropertySource("springApplicationCommandLineArgs", args));
composite.addPropertySource(source);
sources.replace(name, composite);
} else {
sources.addFirst(new SimpleCommandLinePropertySource(args));
}
}
}
SimpleCommandLinePropertySource构造过程中，主要完成解析args字符串，然后提取出相关配置，具体源码可以自行看一下。
总结一下，configurePropertySources方法的目的是将args里的相关配置添加进environment中。
接着看configureProfiles方法:
protected void configureProfiles(ConfigurableEnvironment environment, String[] args) {
environment.getActiveProfiles();
Set<String> profiles = new LinkedHashSet(this.additionalProfiles);
profiles.addAll(Arrays.asList(environment.getActiveProfiles()));
environment.setActiveProfiles(StringUtils.toStringArray(profiles));
}
很明显，该方法的目的就是把active-prifiles属性加载到environment中。
environmentPrepared
public void environmentPrepared(ConfigurableEnvironment environment) {
Iterator var2 = this.listeners.iterator();
while(var2.hasNext()) {
SpringApplicationRunListener listener = (SpringApplicationRunListener)var2.next();
listener.environmentPrepared(environment);
}
}
本质上调用的是SpringApplicationRunListener的environmentPrepared方法。
看一下EventPublishingRunListener的environmentPrepared方法实现:
public void environmentPrepared(ConfigurableEnvironment environment) {
this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent(this.application, this.args, environment));
}
具体过程其实跟SpringApplicationRunListener的starting类似，也是先根据event类型筛选出符合条件的ApplicationListener继承类实例集合，然后分别调用各个ApplicationListener继承类实例的onApplicationEvent(event)方法完成事件的回调，具体过程可参见上篇--Springboot源码跟读2--SpringApplicationRunListener的加载及starting。
我们以spring.profiles.active配置的加载来看一下上述过程，在application.yml里配置：
spring:
profiles:
active: dev
5.jpg
Debug到上图断点处，看一下此时的environment：
6.jpg
可以看到，此时的activeProfiles仍旧为空，然后接着调用SpringApplicationRunListener的environmentPrepared，此时:
7.jpg
EventPublishingRunListener的environmentPrepared方法实现中，本质上是先将application、args、environment包装成ApplicationEnvironmentPreparedEvent，即表明环境已准备完毕的event。
上篇我们讲过，multicastEvent方法主要根据传入的event，从初始化后的ApplicationListeners中筛选出符合条件的ApplicationListener。
public void multicastEvent(ApplicationEvent event, @Nullable ResolvableType eventType) {
ResolvableType type = eventType != null ? eventType : this.resolveDefaultEventType(event);
Iterator var4 = this.getApplicationListeners(event, type).iterator();
while(var4.hasNext()) {
ApplicationListener<?> listener = (ApplicationListener)var4.next();
Executor executor = this.getTaskExecutor();
if (executor != null) {
executor.execute(() -> {
this.invokeListener(listener, event);
});
} else {
this.invokeListener(listener, event);
}
}
}
最后调用的是ApplicationListener的onApplicationEvent，而onApplicationEvent方法具体实现由ApplicationListener的各个继承类完成。
查看一下SpringApplication创建时初始化的所有ApplicationListener:
8.jpg
很明显，与配置加载相关的为ConfigFileApplicationListener。
查看一下ConfigFileApplicationListener的onApplicationEvent方法:
public void onApplicationEvent(ApplicationEvent event) {
if (event instanceof ApplicationEnvironmentPreparedEvent) {
this.onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent)event);
}
if (event instanceof ApplicationPreparedEvent) {
this.onApplicationPreparedEvent(event);
}
}
逻辑很简单，若传入的event是ApplicationEnvironmentPreparedEvent实例，则调用onApplicationEnvironmentPreparedEvent方法；若是ApplicationPreparedEvent实例，则调用onApplicationPreparedEvent方法。
跟一下onApplicationEnvironmentPreparedEvent方法：
private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {
List<EnvironmentPostProcessor> postProcessors = this.loadPostProcessors();
postProcessors.add(this);
// 此处打一个断点
AnnotationAwareOrderComparator.sort(postProcessors);
Iterator var3 = postProcessors.iterator();
while(var3.hasNext()) {
EnvironmentPostProcessor postProcessor = (EnvironmentPostProcessor)var3.next();
postProcessor.postProcessEnvironment(event.getEnvironment(), event.getSpringApplication());
}
}
9.jpg
然后调用所有被加载的postProcessor的postProcessEnvironment方法来对environment进行后置处理，而ConfigFileApplicationListener的postProcessEnvironment方法主要扫描"classpath:/,classpath:/config/,file:./,file:./config/"下的配置文件然后将相关配置更新到environment中，具体代码不细讲，自行查看。
至此，我们将prepareEnvironment方法中的重要点走读完毕。
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