上來先來個例子

import org.junit.jupiter.api.Test;
import org.springframework.core.env.*;
import org.springframework.util.StringUtils;

import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/**
 * @author lwh
 * @date 2022/3/17
 */
public class PropertySourceTest {
    @Test
    public void test01(){
        class MyMapPropertySource extends EnumerablePropertySource<Map<String,Object>>{

            public MyMapPropertySource(String name, Map<String,Object> source) {
                super(name, source);
            }

            @Override
            public boolean containsProperty(String name) {
                return this.source.containsKey(name);
            }

            @Override
            public String[] getPropertyNames() {
                return StringUtils.toStringArray(this.source.keySet());
            }

            @Override
            public Object getProperty(String name) {
                return this.source.get(name);
            }
        }
        final HashMap<String, Object> lwhHashMap = new HashMap<>();
        lwhHashMap.put("lwh",123);
        lwhHashMap.put("ai","${USERNAME}");
        final MyMapPropertySource lwh = new MyMapPropertySource("lwh", lwhHashMap);
        final HashMap<String, Object> lsfHashMap = new HashMap<>();
        lsfHashMap.put("lsf",456);
        //只是一個迭代器而然
        final MyMapPropertySource lsf = new MyMapPropertySource("lsf", lsfHashMap);
        //可以自定義PropertySources，但是也沒必要
        MutablePropertySources propertySources = new MutablePropertySources();
        propertySources.addLast(lwh);
        propertySources.addLast(lsf);
    //需要解析器,自定義的解析器蛾坯，你可以選擇實現(xiàn)PropertySourcesPropertyResolver 或者AbstractPropertyResolver
        //PropertySourcesPropertyResolver propertySourcesPropertyResolver = new PropertySourcesPropertyResolver(propertySources);
        class MyPropertySourcesPropertyResolver extends PropertySourcesPropertyResolver{
            public MyPropertySourcesPropertyResolver(PropertySources propertySources) {
                super(propertySources);
            }

            //沒必要實現(xiàn)
            @Override
            protected String getPropertyAsRawString(String key) {
                return super.getPropertyAsRawString(key);
            }

            //沒必要實現(xiàn)
            @Override
            protected <T> T getProperty(String key, Class<T> targetValueType, boolean resolveNestedPlaceholders) {
                return super.getProperty(key, targetValueType, resolveNestedPlaceholders);
            }
        }

        //自定義加載系統(tǒng)的環(huán)境變量進來仲墨，也可以加載其他的環(huán)境變量
        class MyStandardEnvironment extends  AbstractEnvironment{
            public MyStandardEnvironment(MutablePropertySources propertySources) {
                super(propertySources);
            }
            @Override
            protected ConfigurablePropertyResolver createPropertyResolver(MutablePropertySources propertySources) {
                return new MyPropertySourcesPropertyResolver(propertySources);
            }
            //可以自定義的加入自己的MyMapPropertySource
            @Override
            protected void customizePropertySources(MutablePropertySources propertySources) {
                super.customizePropertySources(propertySources);
                propertySources.addLast(
                        new MapPropertySource("SystemProperties", getSystemProperties()));
                propertySources.addLast(
                        new SystemEnvironmentPropertySource("SystemEnvironment", getSystemEnvironment()));

            }
        }

        MyStandardEnvironment myStandardEnvironment = new MyStandardEnvironment(propertySources);
        final String ai = myStandardEnvironment.getProperty("ai");
        System.out.println(ai);
    }
}

在貼一張類圖

StandardEnvironment.jpg

說明一下勾缭，我希望你自己去看，畢竟目养，我能力有限俩由，寫上去的也不一定對

1.PropertySource

這個是一個抽象類，你可以繼承這個類癌蚁，定制自己的PropertySource 幻梯，已有的子類有
EnumerablePropertySource，MapPropertySource等努释，其實這個類就是一個name和source的屬性值得關(guān)注碘梢，
name可以說名是哪一個配置文件，source就是配置文件的內(nèi)容伐蒂，比如MapPropertySource的name是字符串
source就是Map<String,Object>煞躬，還有就是可以PropertySource.getProperty(“配置文件內(nèi)容中的key”)得到配置文件內(nèi)容中的value

PropertySources 其實就是一個PropertySource 迭代器

它有一個子類MutablePropertySources，你可以繼承MutablePropertySources自定義自己的PropertySources 逸邦，MutablePropertySources值得注意的是addFirst(PropertySource)和addLast(PropertySource）恩沛，這兩個方法會影響PropertyResolver的執(zhí)行，也就是說相同key的值昭雌，找到就不會在找了

PropertyResolver Property的解析器

它有個子類AbstractPropertyResolver复唤，可以解析${}占位符，當(dāng)然你也可以實現(xiàn)ConfigurablePropertyResolver自定義自己的占位符規(guī)則

Environment 表示的是當(dāng)前應(yīng)用的環(huán)境

它有個子類StandardEnvironment烛卧，集成了PropertySource 和PropertySources 和AbstractPropertyResolver佛纫，可以獲取得到系統(tǒng)的環(huán)境變量和jvm的環(huán)境變量妓局，當(dāng)然，你也可以繼承AbstractEnvironment自定義自己的Environment 呈宇，來獲取更多其他的環(huán)境變量