1. Person类

public class Person {
    String name;

    int age;

    public Person() {

    }

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Person{" + "name='" + name + '\'' + ", age=" + age + '}';
    }
}

2. String2PersonConvert类

import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.convert.converter.Converter;
import org.springframework.util.StringUtils;

public class String2PersonConvert implements Converter<String, Person> {
    @Override
    public Person convert(String source) {
        String[] sources = StringUtils.tokenizeToStringArray(source,
            ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
        Person person = new Person();
        person.setName(sources[0]);
        person.setAge(Integer.valueOf(sources[1]));
        return person;
    }
}

3. Main主函数

import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.core.env.MapPropertySource;

import java.util.HashMap;

public class Main {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext();
        MapPropertySource mps = new MapPropertySource("homeMap", new HashMap<>());
        mps.getSource().put("name", "Triagen");
        //mps.getSource().put("age", "25");
        mps.getSource().put("person", "${name},${age:999}");
        ctx.getEnvironment().getPropertySources().addLast(mps);
        ctx.getEnvironment().getConversionService().addConverter(new String2PersonConvert());

        System.out.println(ctx.getEnvironment().getRequiredProperty("person", Person.class));
        System.out.println(ctx.getEnvironment().resolvePlaceholders("${name},${age}"));

    }
}

4. 结果输出

Person{name='Triagen', age=999}
Triagen,${age}

5. 代码简析

ctx.getEnvironment().getPropertySources().addLast(mps);

向Environment中添加mps数据源，addLast添加一个继承自PropertySource的对象，此对象通过getProperty(String name)方法获取给定name的value。

ctx.getEnvironment().getConversionService().addConverter(new String2PersonConvert());

添加转换器，将String字符串转化为具体对象，需要实现Converter接口。

ctx.getEnvironment().getRequiredProperty("person", Person.class)

方法首先从mps数据源中取得name为person的字符串"{age:999}"，再进一步解析${}中name和age的值，取得name值为"Triagen"，age没有取到值，取默认值999，最后在返回时发现需要返回Person类型，但是输入是String类型，通过输入输出匹配到String2PersonConvert 转换器，最终返回Person对象。

ctx.getEnvironment().resolvePlaceholders("${name},${age}")

resolvePlaceholders，顾名思义，对占位符进行解析，这里取值同样从mps中取得，name为"Triagen"，age没有设置默认值，所以没有解析，返回原始占位符。