如何使SpEL（spring-el）默认为null表达式在Spring xml中工作？

Question

如果未找到属性键，或者该值为空，则默认为null。
为了在钱包和直接登录环境中工作，我需要该属性可以为空或可以为空。

null

Spring版本:3.0.7.发布
Java版本：1.6（不要评判，不是我的选择）

2018-02-27 11:13:52,982  FATAL class BatchDriver 166 - Server(): Unexpected exception
org.springframework.beans.factory.BeanDefinitionStoreException: Invalid bean definition with name 'dataSource' defined in class path resource [databaseContext.xml]: Could not resolve placeholder 'jdbc.credu:#{null'
    at org.springframework.beans.factory.config.PropertyPlaceholderConfigurer.processProperties(PropertyPlaceholderConfigurer.java:268)
    at org.springframework.beans.factory.config.PropertyResourceConfigurer.postProcessBeanFactory(PropertyResourceConfigurer.java:75)
    at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:553)
    at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:527)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:362)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
    ...

<beans xmlns="http://www.springframework.org/schema/beans"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:aop="http://www.springframework.org/schema/aop"
        xmlns:tx="http://www.springframework.org/schema/tx"
        xmlns:context="http://www.springframework.org/schema/context"
        xsi:schemaLocation="
            http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
            http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
            http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
            http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd"
    default-lazy-init="true">

    <bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer" scope="singleton">
        <property name="locations">
            <list>
                <value>classpath:/jdbc.properties</value>
                <value>classpath:/javadriver.properties</value>
            </list>
        </property>
    </bean>

    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
        destroy-method="close">
        <property name="driverClassName"><value>${jdbc.driverClassName}</value></property>
        <property name="url"><value>${jdbc.url}</value></property>
        <property name="username" value="${jdbc.credu:#{null}}"/>
        <property name="password" value="${jdbc.credp:#{null}}"/>
        ~~~ Other Settings ~~~
    </bean>

jdbc.driverClassName=oracle.jdbc.driver.OracleDriver

jdbc.url=jdbc:oracle:oci:/@WALLET_ALIAS
#jdbc.url=jdbc:oracle:thin:@255.255.255.255:9999/db_name
#jdbc.credu=username
#jdbc.credp=password

Answer 1

SpEL在占位符之后解析；试试像这样的事

#{'${jdbc.credu:xxx}' == 'xxx' ? null : '${jdbc.credu:xxx}'}

编辑

3.0.7是非常旧版本；Spring版本直到4.3.x都可以使用Java6。

<bean id="foo" class="com.example.Foo">
    <property name="foo" value="#{'${foo:bar}' == 'bar' ? null : '${foo:bar}'}"/>
</bean>

public class So49013862Application {

    public static void main(String[] args) {
        ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("foo.xml");
        System.out.println(ctx.getBean("foo"));
        ctx.close();
    }

}

null
Foo [foo=null]

与

public class Foo {

    private String foo;

    public void setFoo(String foo) {
        System.out.println(foo);
        this.foo = foo;
    }

    @Override
    public String toString() {
        return "Foo [foo=" + this.foo + "]";
    }

}

我没有时间用3.0.x测试它。