spring bean 的属性为 java.util.Properties 时如何初始化该属性

public class FooBean {

    private java.util.Properties attr;

    public java.util.Properties getAttr() {
        return attr;
    }

    public void setAttr(java.util.Properties attr) {
        this.attr = attr;
    }
    
}

    <bean id="fooBean" class="cn.zno.foo.FooBean">
        <property name="attr">
            <props>
                <prop key="a">some string</prop>
                <prop key="b">${user.home}\somedir</prop>
            </props>
        </property>
    </bean>

等价于：

        FooBean fooBean = new FooBean();
        fooBean.setAttr(new Properties());
        
        fooBean.getAttr().setProperty("a", "some string");
        fooBean.getAttr().setProperty("b", System.getProperty("user.home") + "\\somedir");
        
//      fooBean.getAttr().put(null,null);// 用put 添加对象

目前未发现有何种方法可以在 spring bean configuratoin 中实现 put 方法。java configuration 中可以

目前只发现a,b 两种用法。

Element : prop
The string value of the property. Note that whitespace is trimmed off to avoid unwanted
whitespace caused by typical XML formatting.

当${...} 指定的属性不存在时：

Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder 'user.home1' in string value "${user.home1}\somedir"
	at org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:174) ~[spring-core-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.util.PropertyPlaceholderHelper.replacePlaceholders(PropertyPlaceholderHelper.java:126) ~[spring-core-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.beans.factory.config.PropertyPlaceholderConfigurer$PlaceholderResolvingStringValueResolver.resolveStringValue(PropertyPlaceholderConfigurer.java:258) ~[spring-beans-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.beans.factory.config.BeanDefinitionVisitor.resolveStringValue(BeanDefinitionVisitor.java:282) ~[spring-beans-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.beans.factory.config.BeanDefinitionVisitor.resolveValue(BeanDefinitionVisitor.java:204) ~[spring-beans-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.beans.factory.config.BeanDefinitionVisitor.visitMap(BeanDefinitionVisitor.java:262) ~[spring-beans-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.beans.factory.config.BeanDefinitionVisitor.resolveValue(BeanDefinitionVisitor.java:198) ~[spring-beans-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.beans.factory.config.BeanDefinitionVisitor.visitPropertyValues(BeanDefinitionVisitor.java:141) ~[spring-beans-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.beans.factory.config.BeanDefinitionVisitor.visitBeanDefinition(BeanDefinitionVisitor.java:82) ~[spring-beans-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.beans.factory.config.PlaceholderConfigurerSupport.doProcessProperties(PlaceholderConfigurerSupport.java:208) ~[spring-beans-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.beans.factory.config.PropertyPlaceholderConfigurer.processProperties(PropertyPlaceholderConfigurer.java:222) ~[spring-beans-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.beans.factory.config.PropertyResourceConfigurer.postProcessBeanFactory(PropertyResourceConfigurer.java:86) ~[spring-beans-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:265) ~[spring-context-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:162) ~[spring-context-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:610) ~[spring-context-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:462) ~[spring-context-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:125) ~[spring-test-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:60) ~[spring-test-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.test.context.support.AbstractDelegatingSmartContextLoader.delegateLoading(AbstractDelegatingSmartContextLoader.java:109) ~[spring-test-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.test.context.support.AbstractDelegatingSmartContextLoader.loadContext(AbstractDelegatingSmartContextLoader.java:261) ~[spring-test-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.test.context.DefaultCacheAwareContextLoaderDelegate.loadContextInternal(DefaultCacheAwareContextLoaderDelegate.java:68) ~[spring-test-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	at org.springframework.test.context.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:86) ~[spring-test-4.1.9.RELEASE.jar:4.1.9.RELEASE]
	... 25 more