Spring重头再来之PropertySource解析

PropertySource解析

PropertySource用途

org.springframework.core.env.PropertySource顾名思义就是属性源的意思,再具体一点就是对获取键值对资源的抽象类.

aa.png

从类结构信息可以看出主要包含containesProperty(String),getProperty(String),getName(),getSource()这几个方法，其中通过getSource()获取的source可以是任何封装了属性集的类型(eg:Map,Properties,Redis客户端,Zookeeper客户端等)。相应的实现类有MapPropertySource、PropertiesPropertySource等，对于基于Redis、Zookeeper我们可以自己来进行实现

bb.png

但是一般情况下不会单独使用PropertySource，而是通过PropertySources来获取相关属性

PropertySources

PropertySources聚合了PropertySource,提供了property的多数据源访问。其中MutablePropertySources是PropertySources的默认实现,org.springframework.core.env.Environment的子接口ConfigurableEnvironment的属性源就是MutablePropertySources。

/**
     * Return the {@link PropertySources} for this {@code Environment} in mutable form,
     * allowing for manipulation of the set of {@link PropertySource} objects that should
     * be searched when resolving properties against this {@code Environment} object.
     * The various {@link MutablePropertySources} methods such as
     * {@link MutablePropertySources#addFirst addFirst},
     * {@link MutablePropertySources#addLast addLast},
     * {@link MutablePropertySources#addBefore addBefore} and
     * {@link MutablePropertySources#addAfter addAfter} allow for fine-grained control
     * over property source ordering. This is useful, for example, in ensuring that
     * certain user-defined property sources have search precedence over default property
     * sources such as the set of system properties or the set of system environment
     * variables.
     * @see AbstractEnvironment#customizePropertySources
     */
    MutablePropertySources getPropertySources();

MutablePropertySources

mutable本意是可变的，我们可以在运行时添加PropertySource来进行动态的扩展

image-20190725195851665.png

其中addFirst、addLast、addBefore、addAfter赋予了PropertySources控制属性源获取的权限，比如我们可以编写自定义的属性使之优先级高于默认的属性源.具体可查看示例代码

PropertySource使用示例

使用示例下载：https://github.com/stoneHah/spring-learn/blob/master/src/test/java/com/zq/learn/springlearn/env/PropertySourceTest.java

使用Map自定义属性源

Map<String,Object> customerSource;

@Before
public void before(){
    customerSource = new HashMap<>();
    customerSource.put("hello", "chenye");
    customerSource.put("name", "sxx");

}

/**
     * 使用map作为属性源
     */
@Test
public void testMapPropertySource(){
  PropertySource mapSource = new MapPropertySource("mapSource", customerSource);
  assertEquals("chenye",mapSource.getProperty("hello"));
}

使用MutablePropertySources测试如果优先获取自定义的属性而非系统属性

/**
     * 通过 addLast、addFist方法设置属性源的优先级
     */
    @Test
    public void testPropertySources(){
        MapPropertySource systemPropertySource = new MapPropertySource("systemProperties", (Map) System.getProperties());
        MutablePropertySources pss = new MutablePropertySources();

        pss.addLast(systemPropertySource);

        /**
         * 自定义系统属性变量，调用addFirst方法使之优先级高于系统属性源
         */
        customerSource.put("user.name", "sxx");
        pss.addFirst(new MapPropertySource("customerProperties",customerSource));

        assertEquals("sxx",fetchPropertyValue(pss,"user.name"));

//        printPropertySources(systemPropertySource);

    }