SpringBoot Profile是一个很常用的功能，我们可以通过为开发/测试/生产环境配置不同的profile来实现配置隔离，那么在SpringBoot项目中是如何实现profile功能的呢？
入口
相关逻辑的入口是listener类：ConfigFileApplicationListener，当容器广播器触发ApplicationEnvironmentPreparedEvent事件时，ConfigFileApplicationListener会收到广播器的通知，进而执行onApplicationEnvironmentPreparedEvent方法
入口处代码：
@Override
public void onApplicationEvent(ApplicationEvent event) {
if (event instanceof ApplicationEnvironmentPreparedEvent) {
onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event);
}
if (event instanceof ApplicationPreparedEvent) {
onApplicationPreparedEvent(event);
}
}接下来onApplicationEnvironmentPreparedEvent方法会加载容器中的EnvironmentPostProcessor并进行遍历，调用他们的postProcessEnvironment方法，我们可以看一下此时的PostProcessor有哪些：
我们发现ConfigFileApplicationListener本身也是其中一个PostProcessor 🙂
我们直接进入ConfigFileApplicationListener的postProcessEnvironment方法，它会调用一个addPropertySources方法
protected void addPropertySources(ConfigurableEnvironment environment, ResourceLoader resourceLoader) {
RandomValuePropertySource.addToEnvironment(environment);
new Loader(environment, resourceLoader).load();
}随机属性值部分暂且不表，我们看下loader.load方法
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));
addLoadedPropertySources();
}load方法的重点逻辑-initializeProfiles()
private void initializeProfiles() {
// The default profile for these purposes is represented as null. We add it
// first so that it is processed first and has lowest priority.
this.profiles.add(null);
Set<Profile> activatedViaProperty = getProfilesActivatedViaProperty();
this.profiles.addAll(getOtherActiveProfiles(activatedViaProperty));
// Any pre-existing active profiles set via property sources (e.g.
// System properties) take precedence over those added in config files.
addActiveProfiles(activatedViaProperty);
if (this.profiles.size() == 1) { // only has null profile
for (String defaultProfileName : this.environment.getDefaultProfiles()) {
Profile defaultProfile = new Profile(defaultProfileName, true);
this.profiles.add(defaultProfile);
}
}
}add(null) 可以处理application.properties/yml，接下来getProfilesActivatedViaProperty方法会从spring.profiles.active和spring.profiles.include配置中读取激活的profile~(这两者也是相对常用的配置)；再接下来会判断profiles大小是否为1，是的话会添加一个default profile，如图所示：
这也解释了为什么spring.profiles.default必须定义在其他属性源（命令行启动参数），因为这时候分散文件属性元还没有被解析到！
回到load方法，如果profiles不为空，就会进行while遍历，对其调用另外一个load方法：
（load-number2方法）：
private void load(Profile profile, DocumentFilterFactory filterFactory, DocumentConsumer consumer) {
getSearchLocations().forEach((location) -> {
boolean isFolder = location.endsWith("/");
Set<String> names = isFolder ? getSearchNames() : NO_SEARCH_NAMES;
names.forEach((name) -> load(location, name, profile, filterFactory, consumer));
});
}我们可以看到还会调用到另一个load方法
（load-number3方法）：
private void load(String location, String name, Profile profile, DocumentFilterFactory filterFactory,
DocumentConsumer consumer) {
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<>();
for (PropertySourceLoader loader : this.propertySourceLoaders) {
for (String fileExtension : loader.getFileExtensions()) {
if (processed.add(fileExtension)) {
loadForFileExtension(loader, location + name, "." + fileExtension, profile, filterFactory,
consumer);
}
}
}
}这里的propertySourceLoaders包括：
是不是很熟悉？这就是properties和yaml分别对应的PropertySourceLoader~
下面代码会调用loadForFileExtension方法，而这个方法又会调用新的load方法（😓）：
（load-number4方法）：
private void load(PropertySourceLoader loader, String location, Profile profile, DocumentFilter filter,
DocumentConsumer consumer) {
try {
Resource resource = this.resourceLoader.getResource(location);
if (resource == null || !resource.exists()) {
if (this.logger.isTraceEnabled()) {
StringBuilder description = getDescription("Skipped missing config ", location, resource,
profile);
this.logger.trace(description);
}
return;
}
if (!StringUtils.hasText(StringUtils.getFilenameExtension(resource.getFilename()))) {
if (this.logger.isTraceEnabled()) {
StringBuilder description = getDescription("Skipped empty config extension ", location,
resource, profile);
this.logger.trace(description);
}
return;
}
String name = "applicationConfig: [" + location + "]";
List<Document> documents = loadDocuments(loader, name, resource);
if (CollectionUtils.isEmpty(documents)) {
if (this.logger.isTraceEnabled()) {
StringBuilder description = getDescription("Skipped unloaded config ", location, resource,
profile);
this.logger.trace(description);
}
return;
}
List<Document> loaded = new ArrayList<>();
for (Document document : documents) {
if (filter.match(document)) {
addActiveProfiles(document.getActiveProfiles());
addIncludedProfiles(document.getIncludeProfiles());
loaded.add(document);
}
}
Collections.reverse(loaded);
if (!loaded.isEmpty()) {
loaded.forEach((document) -> consumer.accept(profile, document));
if (this.logger.isDebugEnabled()) {
StringBuilder description = getDescription("Loaded config file ", location, resource, profile);
this.logger.debug(description);
}
}
}
catch (Exception ex) {
throw new IllegalStateException("Failed to load property " + "source from location '" + location + "'",
ex);
}
}这个方法会读取application-profile.properties/yaml文件，并加载文件内激活的profile（如果有的话）
到这里已经读取到了所有的配置信息，主逻辑大概结束了，还差最后一个步骤：addLoadedPropertySources：
private void addLoadedPropertySources() {
MutablePropertySources destination = this.environment.getPropertySources();
List<MutablePropertySources> loaded = new ArrayList<>(this.loaded.values());
Collections.reverse(loaded);
String lastAdded = null;
Set<String> added = new HashSet<>();
for (MutablePropertySources sources : loaded) {
for (PropertySource<?> source : sources) {
if (added.add(source.getName())) {
addLoadedPropertySource(destination, lastAdded, source);
lastAdded = source.getName();
}
}
}
}这里会将所有属性加入到“destination”，即environment.getPropertySources()，到这里，加载配置属性的逻辑就完成了。