如何使弹簧注入值进入静态字段 [英] How to make spring inject value into a static field

问题描述

我知道这可能看起来像一个以前提出的问题，但我面临着一个不同的问题。

I know this may looks like a previously asked question but I'm facing a different problem here.

我有一个只有静态方法的实用程序类。我不会，我不会从它的实例。

I have a utility class that has only static methods. I don't and I won't take an instance from it.

public class Utils{
    private static Properties dataBaseAttr;
    public static void methodA(){

    }

    public static void methodB(){

    }
}

现在我需要Spring用dataBaseAttr来填充数据库属性Properties.Spring config是：

Now I need Spring to fill dataBaseAttr with database attributes Properties.Spring config is:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
    http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.0.xsd">

<util:properties id="dataBaseAttr"
        location="file:#{classPathVariable.path}/dataBaseAttr.properties" />
</beans>

我已经在其他bean中做了，但是这个类（Utils）中的问题不是bean，如果我把它变成一个bean没有什么变化，我仍然不能使用该变量，因为类不会被实例化，变量总是等于null。

I already done it in other beans but the problem here in this class (Utils) isn't a bean, And if I make it a bean nothing changes I still can't use the variable since the class will not be instantiated and variable always equals null.

推荐答案

您有两种可能性：

1. 静态属性/字段的非静态设置器;


2. 使用 org.springframework.beans.factory.config.MethodInvokingFactoryBean 以调用静态设置器。

在第一个选项中，你有一个具有常规安装程序的bean，而是设置一个实例属性，你设置静态属性/字段。

In the first option you have a bean with a regular setter but instead setting an instance property you set the static property/field.

public void setTheProperty(Object value) {
    foo.bar.Class.STATIC_VALUE = value;
}

但是为了做到这一点你需要一个bean的实例

but in order to do this you need to have an instance of a bean that will expose this setter (its more like an workaround).

在第二种情况下，将执行以下操作：

In the second case it would be done as follows:

<bean class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
    <property name="staticMethod" value="foo.bar.Class.setTheProperty"/>
    <property name="arguments">
        <list>
            <ref bean="theProperty"/>
        </list>
   </property>
</bean>

在这种情况下，您将在 Utils class：

On you case you will add a new setter on the Utils class:

public static setDataBaseAttr(Properties p)

在上下文中，您将使用上面列举的方法配置它，或多或少像：

and in your context you will configure it with the approach exemplified above, more or less like:

<bean class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
    <property name="staticMethod" value="foo.bar.Utils.setDataBaseAttr"/>
    <property name="arguments">
        <list>
            <ref bean="dataBaseAttr"/>
        </list>
   </property>
</bean>

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