Set System Property With Spring Configuration File

You can achieve that with the combination of two MethodInvokingFactoryBeans

Create an inner bean that accesses System.getProperties and an outer bean that invokes putAll on the properties acquired by the inner bean:

<bean
    class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
    <property
        name="targetObject">
        <!-- System.getProperties() -->
        <bean
            class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
            <property name="targetClass" value="java.lang.System" />
            <property name="targetMethod" value="getProperties" />
        </bean>
    </property>
    <property
        name="targetMethod"
        value="putAll" />
    <property
        name="arguments">
        <!-- The new Properties -->
        <util:properties>
            <prop
                key="my.key">myvalue</prop>
            <prop
                key="my.key2">myvalue2</prop>
            <prop
                key="my.key3">myvalue3</prop>

        </util:properties>
    </property>
</bean>

(You could of course use just one bean and target System.setProperties(), but then you'd be replacing existing properties which is not a good idea.

Anyway, here's my little test method:

public static void main(final String[] args) {

    new ClassPathXmlApplicationContext("classpath:beans.xml");

    System.out.println("my.key: "+System.getProperty("my.key"));
    System.out.println("my.key2: "+System.getProperty("my.key2"));
    System.out.println("my.key3: "+System.getProperty("my.key3"));

    // to test that we're not overwriting existing properties
    System.out.println("java.io.tmpdir: "+System.getProperty("java.io.tmpdir"));
}

And here's the output:

my.key: myvalue
my.key2: myvalue2
my.key3: myvalue3
java.io.tmpdir: C:\DOKUME~1\SEANFL~1\LOKALE~1\Temp\

There was a request in the comments for a Spring 3 example on how to do this.

<bean id="systemPrereqs"
    class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
    <property name="targetObject" value="#{@systemProperties}" />
    <property name="targetMethod" value="putAll" />
    <property name="arguments">
        <!-- The new Properties -->
        <util:properties>
            <prop key="java.security.auth.login.config">/super/secret/jaas.conf</prop>
        </util:properties>
    </property>
</bean>