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+# Spring PropertySources
+
+- Author: [HuiFer](https://github.com/huifer)
+- 源码阅读仓库: [SourceHot-spring](https://github.com/SourceHot/spring-framework-read)
+
+
+
+
+## MutablePropertySources
+
+- 全路径:  `org.springframework.core.env.MutablePropertySources`
+
+- `MutablePropertySources`类内部存储了`List<PropertySource<?>>`对象,主要是针对`List<PropertySource<?>>` 进行的操作.换句话说就是对 list 操作的实现
+
+- 类注解如下
+
+
+
+```java
+public class MutablePropertySources implements PropertySources {
+
+   private final List<PropertySource<?>> propertySourceList = new CopyOnWriteArrayList<>();
+
+
+   /**
+    * Create a new {@link MutablePropertySources} object.
+    *
+    * 构造方法
+    */
+   public MutablePropertySources() {
+   }
+
+   /**
+    * Create a new {@code MutablePropertySources} from the given propertySources
+    * object, preserving the original order of contained {@code PropertySource} objects.
+    * 构造方法, 传递一个集合, 将集合中的数据放入 {@code propertySourceList}.
+    */
+   public MutablePropertySources(PropertySources propertySources) {
+      this();
+      // PropertySources 是一个迭代器接口的实现,通过循环取出信息放入到 propertySourceList 中
+      for (PropertySource<?> propertySource : propertySources) {
+         // 放入方法
+         addLast(propertySource);
+      }
+   }
+
+
+   /**
+    * 获取迭代器对象
+    */
+   @Override
+   public Iterator<PropertySource<?>> iterator() {
+      return this.propertySourceList.iterator();
+   }
+
+   /**
+    * 获取 Spliterator 对象
+    */
+   @Override
+   public Spliterator<PropertySource<?>> spliterator() {
+      return Spliterators.spliterator(this.propertySourceList, 0);
+   }
+
+   /**
+    * 获取流
+    */
+   @Override
+   public Stream<PropertySource<?>> stream() {
+      return this.propertySourceList.stream();
+   }
+
+   /**
+    * 判断是否存在 name
+    * @param name the {@linkplain PropertySource#getName() name of the property source} to find
+    */
+   @Override
+   public boolean contains(String name) {
+      return this.propertySourceList.contains(PropertySource.named(name));
+   }
+
+   /**
+    * 获取 PropertySource 信息
+    * @param name the {@linkplain PropertySource#getName() name of the property source} to find
+    * @return
+    */
+   @Override
+   @Nullable
+   public PropertySource<?> get(String name) {
+      // 获取 name 所在的索引位置
+      int index = this.propertySourceList.indexOf(PropertySource.named(name));
+      // get方法获取结果
+      return (index != -1 ? this.propertySourceList.get(index) : null);
+   }
+
+
+   /**
+    * Add the given property source object with highest precedence.
+    *
+    * 头插数据
+    */
+   public void addFirst(PropertySource<?> propertySource) {
+      removeIfPresent(propertySource);
+      this.propertySourceList.add(0, propertySource);
+   }
+
+   /**
+    * Add the given property source object with lowest precedence.
+    *
+    * 尾插数据
+    */
+   public void addLast(PropertySource<?> propertySource) {
+      removeIfPresent(propertySource);
+      this.propertySourceList.add(propertySource);
+   }
+
+   /**
+    * Add the given property source object with precedence immediately higher
+    * than the named relative property source.
+    *
+    * 在relativePropertySourceName的索引位置前添加数据
+    */
+   public void addBefore(String relativePropertySourceName, PropertySource<?> propertySource) {
+      assertLegalRelativeAddition(relativePropertySourceName, propertySource);
+      removeIfPresent(propertySource);
+      int index = assertPresentAndGetIndex(relativePropertySourceName);
+      addAtIndex(index, propertySource);
+   }
+
+   /**
+    * Add the given property source object with precedence immediately lower
+    * than the named relative property source.
+    * 在relativePropertySourceName的索引位置后添加数据
+    */
+   public void addAfter(String relativePropertySourceName, PropertySource<?> propertySource) {
+      assertLegalRelativeAddition(relativePropertySourceName, propertySource);
+      // 删除存在的数据
+      removeIfPresent(propertySource);
+      // 获取所有
+      int index = assertPresentAndGetIndex(relativePropertySourceName);
+      // 在索引+1出添加数据
+      addAtIndex(index + 1, propertySource);
+   }
+
+   /**
+    * Return the precedence of the given property source, {@code -1} if not found.
+    * 获取索引位置
+    */
+   public int precedenceOf(PropertySource<?> propertySource) {
+      return this.propertySourceList.indexOf(propertySource);
+   }
+
+   /**
+    * Remove and return the property source with the given name, {@code null} if not found.
+    * 删除索引位置
+    * @param name the name of the property source to find and remove
+    */
+   @Nullable
+   public PropertySource<?> remove(String name) {
+      // 获取索引
+      int index = this.propertySourceList.indexOf(PropertySource.named(name));
+      // 删除索引上的数据
+      return (index != -1 ? this.propertySourceList.remove(index) : null);
+   }
+
+   /**
+    * Replace the property source with the given name with the given property source object.
+    * 替换 name 的信息
+    * @param name the name of the property source to find and replace
+    * @param propertySource the replacement property source
+    * @throws IllegalArgumentException if no property source with the given name is present
+    * @see #contains
+    */
+   public void replace(String name, PropertySource<?> propertySource) {
+      // 获取索引位置
+      int index = assertPresentAndGetIndex(name);
+      // 设置具体所应位置的值
+      this.propertySourceList.set(index, propertySource);
+   }
+
+   /**
+    * Return the number of {@link PropertySource} objects contained.
+    * 数量
+    */
+   public int size() {
+      return this.propertySourceList.size();
+   }
+
+   @Override
+   public String toString() {
+      return this.propertySourceList.toString();
+   }
+
+   /**
+    * Ensure that the given property source is not being added relative to itself.
+    * 确保两个 PropertySource 的 name不相同
+    */
+   protected void assertLegalRelativeAddition(String relativePropertySourceName, PropertySource<?> propertySource) {
+      // 获取 PropertySource 的名字
+      String newPropertySourceName = propertySource.getName();
+      // 历史名字和新的名字是否相同
+      if (relativePropertySourceName.equals(newPropertySourceName)) {
+         throw new IllegalArgumentException(
+               "PropertySource named '" + newPropertySourceName + "' cannot be added relative to itself");
+      }
+   }
+
+   /**
+    * Remove the given property source if it is present.
+    * 删除已存在的数据
+    */
+   protected void removeIfPresent(PropertySource<?> propertySource) {
+      this.propertySourceList.remove(propertySource);
+   }
+
+   /**
+    * Add the given property source at a particular index in the list.
+    * 指定索引位置插入数据
+    */
+   private void addAtIndex(int index, PropertySource<?> propertySource) {
+      removeIfPresent(propertySource);
+      this.propertySourceList.add(index, propertySource);
+   }
+
+   /**
+    * Assert that the named property source is present and return its index.
+    * 获取 name 所在的索引位置
+    * @param name {@linkplain PropertySource#getName() name of the property source} to find
+    * @throws IllegalArgumentException if the named property source is not present
+    */
+   private int assertPresentAndGetIndex(String name) {
+      int index = this.propertySourceList.indexOf(PropertySource.named(name));
+      if (index == -1) {
+         throw new IllegalArgumentException("PropertySource named '" + name + "' does not exist");
+      }
+      return index;
+   }
+
+}
+```
+
+
+
+
+
+## PropertySources
+
+- 类路径: `org.springframework.core.env.PropertySources`
+
+- 详细说明如下
+
+```java
+public interface PropertySources extends Iterable<PropertySource<?>> {
+
+   /**
+    * Return a sequential {@link Stream} containing the property sources.
+    * 获取流
+    * @since 5.1
+    */
+   default Stream<PropertySource<?>> stream() {
+      return StreamSupport.stream(spliterator(), false);
+   }
+
+   /**
+    * Return whether a property source with the given name is contained.
+    * 判断是否存在 name
+    * @param name the {@linkplain PropertySource#getName() name of the property source} to find
+    */
+   boolean contains(String name);
+
+   /**
+    * Return the property source with the given name, {@code null} if not found.
+    * 获取 PropertySource 
+    * @param name the {@linkplain PropertySource#getName() name of the property source} to find
+    */
+   @Nullable
+   PropertySource<?> get(String name);
+
+}
+```
+
+
+
+
+
+
+
+## PropertySource
+
+- 类路径: `org.springframework.core.env.PropertySource`
+
+- 存有两个子类
+  1. StubPropertySource
+  2. ComparisonPropertySource
+     3. 调用`getSource`、`containsProperty`、`getProperty` 都会直接异常
+
+
+
+```java
+public abstract class PropertySource<T> {
+
+	protected final Log logger = LogFactory.getLog(getClass());
+
+	/**
+	 * 属性名称
+	 */
+	protected final String name;
+
+	/**
+	 * 值
+	 */
+	protected final T source;
+
+
+	/**
+	 * Create a new {@code PropertySource} with the given name and source object.
+	 */
+	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;
+	}
+
+	/**
+	 * Create a new {@code PropertySource} with the given name and with a new
+	 * {@code Object} instance as the underlying source.
+	 * <p>Often useful in testing scenarios when creating anonymous implementations
+	 * that never query an actual source but rather return hard-coded values.
+	 */
+	@SuppressWarnings("unchecked")
+	public PropertySource(String name) {
+		this(name, (T) new Object());
+	}
+
+	/**
+	 * Return a {@code PropertySource} implementation intended for collection comparison purposes only.
+	 * <p>Primarily for internal use, but given a collection of {@code PropertySource} objects, may be
+	 * used as follows:
+	 * <pre class="code">
+	 * {@code List<PropertySource<?>> sources = new ArrayList<PropertySource<?>>();
+	 * sources.add(new MapPropertySource("sourceA", mapA));
+	 * sources.add(new MapPropertySource("sourceB", mapB));
+	 * assert sources.contains(PropertySource.named("sourceA"));
+	 * assert sources.contains(PropertySource.named("sourceB"));
+	 * assert !sources.contains(PropertySource.named("sourceC"));
+	 * }</pre>
+	 * The returned {@code PropertySource} will throw {@code UnsupportedOperationException}
+	 * if any methods other than {@code equals(Object)}, {@code hashCode()}, and {@code toString()}
+	 * are called.
+	 * @param name the name of the comparison {@code PropertySource} to be created and returned.
+	 */
+	public static PropertySource<?> named(String name) {
+		return new ComparisonPropertySource(name);
+	}
+
+	/**
+	 * Return the name of this {@code PropertySource}.
+	 */
+	public String getName() {
+		return this.name;
+	}
+
+	/**
+	 * Return the underlying source object for this {@code PropertySource}.
+	 */
+	public T getSource() {
+		return this.source;
+	}
+
+	/**
+	 * Return whether this {@code PropertySource} contains the given name.
+	 * <p>This implementation simply checks for a {@code null} return value
+	 * from {@link #getProperty(String)}. Subclasses may wish to implement
+	 * a more efficient algorithm if possible.
+	 * @param name the property name to find
+	 */
+	public boolean containsProperty(String name) {
+		// getProperty 抽象方法子类实现
+		return (getProperty(name) != null);
+	}
+
+	/**
+	 * Return the value associated with the given name,
+	 * or {@code null} if not found.
+	 * // getProperty 抽象方法子类实现
+	 * @param name the property to find
+	 * @see PropertyResolver#getRequiredProperty(String)
+	 */
+	@Nullable
+	public abstract Object getProperty(String name);
+
+	/**
+	 * This {@code PropertySource} object is equal to the given object if:
+	 * <ul>
+	 * <li>they are the same instance
+	 * <li>the {@code name} properties for both objects are equal
+	 * </ul>
+	 * <p>No properties other than {@code name} are evaluated.
+	 */
+	@Override
+	public boolean equals(@Nullable Object other) {
+		return (this == other || (other instanceof PropertySource &&
+				ObjectUtils.nullSafeEquals(this.name, ((PropertySource<?>) other).name)));
+	}
+
+	/**
+	 * Return a hash code derived from the {@code name} property
+	 * of this {@code PropertySource} object.
+	 */
+	@Override
+	public int hashCode() {
+		return ObjectUtils.nullSafeHashCode(this.name);
+	}
+
+	/**
+	 * Produce concise output (type and name) if the current log level does not include
+	 * debug. If debug is enabled, produce verbose output including the hash code of the
+	 * PropertySource instance and every name/value property pair.
+	 * <p>This variable verbosity is useful as a property source such as system properties
+	 * or environment variables may contain an arbitrary number of property pairs,
+	 * potentially leading to difficult to read exception and log messages.
+	 * @see Log#isDebugEnabled()
+	 */
+	@Override
+	public String toString() {
+		if (logger.isDebugEnabled()) {
+			return getClass().getSimpleName() + "@" + System.identityHashCode(this) +
+					" {name='" + this.name + "', properties=" + this.source + "}";
+		}
+		else {
+			return getClass().getSimpleName() + " {name='" + this.name + "'}";
+		}
+	}
+
+	/**
+	 * {@code PropertySource} to be used as a placeholder in cases where an actual
+	 * property source cannot be eagerly initialized at application context
+	 * creation time.  For example, a {@code ServletContext}-based property source
+	 * must wait until the {@code ServletContext} object is available to its enclosing
+	 * {@code ApplicationContext}.  In such cases, a stub should be used to hold the
+	 * intended default position/order of the property source, then be replaced
+	 * during context refresh.
+	 * @see org.springframework.context.support.AbstractApplicationContext#initPropertySources()
+	 * @see org.springframework.web.context.support.StandardServletEnvironment
+	 * @see org.springframework.web.context.support.ServletContextPropertySource
+	 */
+	public static class StubPropertySource extends PropertySource<Object> {
+
+		public StubPropertySource(String name) {
+			super(name, new Object());
+		}
+
+		/**
+		 * Always returns {@code null}.
+		 */
+		@Override
+		@Nullable
+		public String getProperty(String name) {
+			return null;
+		}
+	}
+
+
+	/**
+	 * A {@code PropertySource} implementation intended for collection comparison
+	 * purposes.
+	 *
+	 * @see PropertySource#named(String)
+	 */
+	static class ComparisonPropertySource extends StubPropertySource {
+
+		// 异常信息
+		private static final String USAGE_ERROR =
+				"ComparisonPropertySource instances are for use with collection comparison only";
+
+		public ComparisonPropertySource(String name) {
+			super(name);
+		}
+
+		@Override
+		public Object getSource() {
+			// 抛异常
+			throw new UnsupportedOperationException(USAGE_ERROR);
+		}
+
+		@Override
+		public boolean containsProperty(String name) {
+			// 抛异常
+			throw new UnsupportedOperationException(USAGE_ERROR);
+		}
+
+		@Override
+		@Nullable
+		public String getProperty(String name) {
+			// 抛异常
+			throw new UnsupportedOperationException(USAGE_ERROR);
+		}
+	}
+
+}
+```
+
+
+
+
+
+类图
+
+![PropertySource.png](/images/spring/PropertySource.png)
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