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doc: Spring-PropertySources.md

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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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