Spring中PropertySource属性源配置文件的优先级、顺序问题大解析（加载流程）【享学Spring】（上）

// @since 3.1 
public abstract class PropertySource<T> {
  protected final String name; // 该属性源的名字
  protected final T source;
  public PropertySource(String name, T source) {
    Assert.hasText(name, "Property source name must contain at least one character");
    Assert.notNull(source, "Property source must not be null");
    this.name = name;
    this.source = source;
  }
  // 若没有指定source 默认就是object  而不是null
  public PropertySource(String name) {
    this(name, (T) new Object());
  }
  // getProperty是个抽象方法  子类去实现~~~
  // 小细节：若对应的key存在但是值为null，此处也是返回false的  表示不包含~
  public boolean containsProperty(String name) {
    return (getProperty(name) != null);
  }
  @Nullable
  public abstract Object getProperty(String name);
  // 此处特别特别注意重写的这两个方法，我们发现它只和name有关，只要name相等  就代表着是同一个对象~~~~ 这点特别重要~
  @Override
  public boolean equals(Object other) {
    return (this == other || (other instanceof PropertySource &&
        ObjectUtils.nullSafeEquals(this.name, ((PropertySource<?>) other).name)));
  }
  @Override
  public int hashCode() {
    return ObjectUtils.nullSafeHashCode(this.name);
  }
  // 静态方法：根据name就创建一个属性源~  ComparisonPropertySource是StubPropertySource的子类~
  public static PropertySource<?> named(String name) {
    return new ComparisonPropertySource(name);
  }
}

// @since 3.1  它的source源是JndiLocatorDelegate
public class JndiPropertySource extends PropertySource<JndiLocatorDelegate> {
  public Object getProperty(String name) {
    ...
    Object value = this.source.lookup(name);
    ...
  }
}

public abstract class EnumerablePropertySource<T> extends PropertySource<T> {
  public EnumerablePropertySource(String name, T source) {
    super(name, source);
  }
  protected EnumerablePropertySource(String name) {
    super(name);
  }
  @Override
  public boolean containsProperty(String name) {
    return ObjectUtils.containsElement(getPropertyNames(), name);
  }
  // 返回所有Property的names（keys）
  public abstract String[] getPropertyNames();
}

public class ServletContextPropertySource extends EnumerablePropertySource<ServletContext> {
  public ServletContextPropertySource(String name, ServletContext servletContext) {
    super(name, servletContext);
  }
  @Override
  public String[] getPropertyNames() {
    return StringUtils.toStringArray(this.source.getInitParameterNames());
  }
  @Override
  @Nullable
  public String getProperty(String name) {
    return this.source.getInitParameter(name);
  }
}

public class MapPropertySource extends EnumerablePropertySource<Map<String, Object>> {
  public MapPropertySource(String name, Map<String, Object> source) {
    super(name, source);
  }
  @Override
  @Nullable
  public Object getProperty(String name) {
    return this.source.get(name);
  }
  @Override
  public boolean containsProperty(String name) {
    return this.source.containsKey(name);
  }
  // map里所有的key就行~
  @Override
  public String[] getPropertyNames() {
    return StringUtils.toStringArray(this.source.keySet());
  }
}

 // @since 3.1  若你的Properties资源使用的Resource装机进来的  直接使用它即可
 public class ResourcePropertySource extends PropertiesPropertySource {
  @Nullable
  private final String resourceName;
  public ResourcePropertySource(String name, EncodedResource resource) throws IOException {
    // 注意此处加载的最好是EncodedResource，因为Properties文件是需要处理乱码的~
    super(name, PropertiesLoaderUtils.loadProperties(resource));
    this.resourceName = getNameForResource(resource.getResource());
  }
  public ResourcePropertySource(EncodedResource resource) throws IOException {
    super(getNameForResource(resource.getResource()), PropertiesLoaderUtils.loadProperties(resource));
    this.resourceName = null;
  }
  public ResourcePropertySource(String name, Resource resource) throws IOException {
    super(name, PropertiesLoaderUtils.loadProperties(new EncodedResource(resource)));
    this.resourceName = getNameForResource(resource);
  }
  public ResourcePropertySource(String name, String location, ClassLoader classLoader) throws IOException {
    this(name, new DefaultResourceLoader(classLoader).getResource(location));
  }
  public ResourcePropertySource(String location, ClassLoader classLoader) throws IOException {
    this(new DefaultResourceLoader(classLoader).getResource(location));
  }
  public ResourcePropertySource(String name, String location) throws IOException {
    this(name, new DefaultResourceLoader().getResource(location));
  }
  ...
 }

    public static void main(String[] args) throws Exception {
        CommandLinePropertySource clps = new SimpleCommandLinePropertySource(args);
        // 启动容器
        AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
        ConfigurableEnvironment environment = ctx.getEnvironment();
        environment.getPropertySources().addFirst(clps);
        ctx.register(RootConfig.class);
        ctx.refresh();
        System.out.println(ArrayUtils.toString(args)); //{--server.port=8080}
        System.out.println(environment.getProperty("server.port")); //8080
    }

@Slf4j
public class Main {
    public static void main(String[] args) throws Exception {
        // vm参数里（其实就是java -Xmx512m -Dmyname=fsx）  的-D参数最终都会到System系统属性里面去
        System.out.println(System.getProperty("myname")); //fsx
        // --开头的命令行参数  是可以被spring应用识别的特定格式
        System.out.println(ArrayUtils.toString(args)); // {--server.port=8080,fsx}
    }
}