如何让弹簧将值注入静态场 [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以前问过的问题，但我在这里面临不同的问题.

我有一个只有静态方法的实用程序类.我没有，我也不会拿它举例.

公共类Utils{私有静态属性 dataBaseAttr;公共静态无效方法A(){}公共静态无效方法B(){}}

现在我需要 Spring 用数据库属性 Properties.Spring 配置来填充 dataBaseAttr:

</豆类>

我已经在其他 bean 中完成了，但是这个类 (Utils) 中的问题不是 bean，如果我将它设为 bean，没有任何变化，我仍然无法使用该变量，因为该类不会被实例化并且变量总是等于空.

解决方案

你有两种可能:

1. 静态属性/字段的非静态设置器；
2. 使用 <代码>org.springframework.beans.factory.config.MethodInvokingFactoryBean 调用静态设置器.

在第一个选项中，您有一个带有常规 setter 的 bean，但您设置的是静态属性/字段，而不是设置实例属性.

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

但是为了做到这一点，您需要有一个 bean 实例来公开这个 setter(它更像是一种解决方法).

在第二种情况下，将按如下方式进行:

<块引用>

<property name="staticMethod" value="foo.bar.Class.setTheProperty"/><属性名称=参数"><列表><ref bean="theProperty"/></list></属性></bean>

在你的情况下，你将在 Utils 类上添加一个新的 setter:

public static setDataBaseAttr(Properties p)

并且在您的上下文中，您将使用上面举例说明的方法对其进行配置，或多或少类似于:

<块引用>

<property name="staticMethod" value="foo.bar.Utils.setDataBaseAttr"/><属性名称=参数"><列表><ref bean="dataBaseAttr"/></list></属性></bean>

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

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(){

    }
}

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>

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.

解决方案

You have two possibilities:

1. non-static setter for static property/field;
2. using org.springframework.beans.factory.config.MethodInvokingFactoryBean to invoke a static setter.

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;
}

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).

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>

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

public static setDataBaseAttr(Properties p)

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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