一、源码时序图

本节，就以源码时序图的方式，直观的感受下@PropertySource注解在Spring源码层面的执行流程。@PropertySource注解在Spring源码层面的执行流程如图所示：

由图可以看出，@PropertySource注解在Spring源码层面的执行流程会涉及到PropertySourceTest类、AnnotationConfigApplicationContext类、AbstractApplicationContext类、PostProcessorRegistrationDelegate类、ConfigurationClassPostProcessor类、ConfigurationClassParser类、PropertySourceRegistry类、PropertySourceProcessor类和DefaultPropertySourceFactory类。具体的源码执行细节参见源码解析部分。

二、源码解析

@PropertySource注解在Spring源码层面的执行流程，结合源码执行的时序图，会理解的更加深刻。

1. 运行案例程序启动类

在PropertySourceTest类的main()方法中调用了AnnotationConfigApplicationContext类的构造方法，并传入了PropertySourceConfig类的Class对象来创建IOC容器。接下来，会进入AnnotationConfigApplicationContext类的构造方法。

注意：@PropertySource注解在Spring源码中的执行流程的（2）~（11）步与前面章节的@Import注解相同，这里不再赘述，直接跳到ConfigurationClassParser类的doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass, Predicatefilter)方法。

2. 解析ConfigurationClassParser类的doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass, Predicatefilter)方法

protected final SourceClass doProcessConfigurationClass(
    ConfigurationClass configClass, SourceClass sourceClass, Predicate<String> filter)
    throws IOException {
    //#############省略其他代码################
    for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
        sourceClass.getMetadata(), PropertySources.class,
        org.springframework.context.annotation.PropertySource.class)) {
        if (this.propertySourceRegistry != null) {
            this.propertySourceRegistry.processPropertySource(propertySource);
        }
    }
 //#############省略其他代码################
}

可以看到，在ConfigurationClassParser类的doProcessConfigurationClass()方法中，遍历获取到的@PropertySources注解和@PropertySource注解的属性，并且调用propertySourceRegistry对象的processPropertySource()方法解析注解属性的值。

3. 解析PropertySourceRegistry类的processPropertySource(AnnotationAttributes propertySource)方法

void processPropertySource(AnnotationAttributes propertySource) throws IOException {
    String name = propertySource.getString("name");
    if (!StringUtils.hasLength(name)) {
        name = null;
    }
    String encoding = propertySource.getString("encoding");
    if (!StringUtils.hasLength(encoding)) {
        encoding = null;
    }
    String[] locations = propertySource.getStringArray("value");
    Assert.isTrue(locations.length > 0, "At least one @PropertySource(value) location is required");
    boolean ignoreResourceNotFound = propertySource.getBoolean("ignoreResourceNotFound");
    Class<? extends PropertySourceFactory> factoryClass = propertySource.getClass("factory");
    Class<? extends PropertySourceFactory> factorClassToUse = (factoryClass != PropertySourceFactory.class ? factoryClass : null);
    PropertySourceDescriptor descriptor = new PropertySourceDescriptor(Arrays.asList(locations), ignoreResourceNotFound, name, factorClassToUse, encoding);
    this.propertySourceProcessor.processPropertySource(descriptor);
    this.descriptors.add(descriptor);
}

可以看到，在PropertySourceRegistry类的processPropertySource()方法中，解析@PropertySource注解中的属性后，将解析出的属性值封装到PropertySourceDescriptor对象中，调用propertySourceProcessor对象的processPropertySource()方法，并传入PropertySourceDescriptor对象进行进一步处理。

4. 解析PropertySourceProcessor类的processPropertySource(PropertySourceDescriptor descriptor)方法

public void processPropertySource(PropertySourceDescriptor descriptor) throws IOException {
    String name = descriptor.name();
    String encoding = descriptor.encoding();
    List<String> locations = descriptor.locations();
    Assert.isTrue(locations.size() > 0, "At least one @PropertySource(value) location is required");
    boolean ignoreResourceNotFound = descriptor.ignoreResourceNotFound();
    PropertySourceFactory factory = (descriptor.propertySourceFactory() != null ? instantiateClass(descriptor.propertySourceFactory()) : DEFAULT_PROPERTY_SOURCE_FACTORY);
    for (String location : locations) {
        try {
            String resolvedLocation = this.environment.resolveRequiredPlaceholders(location);
            Resource resource = this.resourceLoader.getResource(resolvedLocation);
            addPropertySource(factory.createPropertySource(name, new EncodedResource(resource, encoding)));
        }
        catch (IllegalArgumentException | FileNotFoundException | UnknownHostException | SocketException ex) {
   //#########省略其他代码################
        }
    }
}

可以看到，在processPropertySource()方法中，会通过@PropertySource注解的属性值解析出配置文件的内容，并且通过factory对象的createPropertySource()方法来创建PropertySource对象。

5. 解析DefaultPropertySourceFactory类的createPropertySource(String name, EncodedResource resource)方法

@Override
public PropertySource<?> createPropertySource(String name, EncodedResource resource) throws IOException {
    return (name != null ? new ResourcePropertySource(name, resource) : new ResourcePropertySource(resource));
}

6. 回到PropertySourceProcessor类的processPropertySource(PropertySourceDescriptor descriptor)方法

在PropertySourceProcessor类的processPropertySource()方法中，创建完PropertySource对象后，会调用addPropertySource()方法将获取到的属性值添加到Spring的环境变量中。

7. 解析PropertySourceProcessor类的addPropertySource(PropertySource<?> propertySource)方法

private void addPropertySource(org.springframework.core.env.PropertySource<?> propertySource) {
    String name = propertySource.getName();
    MutablePropertySources propertySources = this.environment.getPropertySources();
    if (this.propertySourceNames.contains(name)) {
        org.springframework.core.env.PropertySource<?> existing = propertySources.get(name);
        if (existing != null) {
            PropertySource<?> newSource = (propertySource instanceof ResourcePropertySource ?((ResourcePropertySource) propertySource).withResourceName() : propertySource);
            if (existing instanceof CompositePropertySource) {
                ((CompositePropertySource) existing).addFirstPropertySource(newSource);
            }
            else {
                if (existing instanceof ResourcePropertySource) {
                    existing = ((ResourcePropertySource) existing).withResourceName();
                }
                CompositePropertySource composite = new CompositePropertySource(name);
                composite.addPropertySource(newSource);
                composite.addPropertySource(existing);
                propertySources.replace(name, composite);
            }
            return;
        }
    }
    if (this.propertySourceNames.isEmpty()) {
        propertySources.addLast(propertySource);
    }
    else {
        String firstProcessed = this.propertySourceNames.get(this.propertySourceNames.size() - 1);
        propertySources.addBefore(firstProcessed, propertySource);
    }
    this.propertySourceNames.add(name);
}

可以看到，在PropertySourceProcessor类的addPropertySource()方法中，会将解析出的配置文件的内容添加到Spring的环境变量中。具体就是在PropertySourceProcessor类的addPropertySource()方法中，获取到ConfigurableEnvironment中的MutablePropertySources对象，用来存储解析出的配置文件中的配置项内容。如果有相同的配置项内容，将existing对象强转为CompositePropertySource类型，把新旧相同的配置项进行合并，再放到MutablePropertySources对象中。

后续就可以通过Spring的环境变量，来获取到配置文件中的配置项内容。

至此，@PropertySource注解在Spring源码中的执行流程分析完毕。