PropertyOverrideConfigurer 和 PropertyPlaceholderConfigurer 有什么区别？

Question

在Spring框架中使用PropertyOverrideConfigurer和PropertyPlaceholderConfigurer有什么区别？我找不到这两个类.

之间的任何实质性区别

Answer 1

PropertyOverrideConfigurer :

"Property resource configurer that overrides bean property values in an application context definition. It pushes values from a properties file into bean definitions."

它允许您覆盖 bean 的某些值，这意味着您可以从属性文件

中定义的属性覆盖 spring bean 的某些值

声明：

<bean class="org.springframework.beans.factory.config.PropertyOverrideConfigurer">
    <property name="location" value="classpath:myproperties.properties" />
</bean>

<bean id="person" class="com.sample.Employee" >
       <property name="name" value="Dugan"/>
       <property name="age" value="50"/>       
</bean>

myproperties.properties:

person.age=40
person.name=Stanis

所以当你加载 bean 时

Employee e  = (Employee)context.getBean(Employee.class);

e.getAge() => 40
e.getName() => "Stanis"

PropertyPlaceholderConfigurer :

resolves ${...} placeholders against local properties and/or system properties and environment variables.

它允许您解析 bean 定义中的 ${..} 占位符，它还检查系统属性的值。可以使用 systemPropertiesMode

控制此行为

never (0): 从不检查系统属性
fallback (1): 如果无法解析则检查系统属性指定的属性文件。这是默认设置。
覆盖（2）：首先检查系统属性，然后再尝试指定的属性文件。这允许系统属性覆盖任何其他属性来源。

配置

<bean id="dataSource"
        class="org.springframework.jdbc.datasource.DriverManagerDataSource">

        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/mydb" />
        <property name="username" value="root" />
        <property name="password" value="password" />
        <property name="systemPropertiesMode" value="0" />
    </bean>

将 'dataSource' 属性移动到属性个文件

database.properties

jdbc.driverClassName=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mydb
jdbc.username=root
jdbc.password=password

然后用占位符引用他们 =>

<bean
    class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">

    <property name="location">
        <value>database.properties</value>
    </property>
</bean>

<bean id="dataSource"
        class="org.springframework.jdbc.datasource.DriverManagerDataSource">

        <property name="driverClassName" value="${jdbc.driverClassName}" />
        <property name="url" value="${jdbc.url}" />
        <property name="username" value="${jdbc.username}" />
        <property name="password" value="${jdbc.password}" />
    </bean>

PropertyOverrideConfigurer 和 PropertyPlaceholderConfigurer 有什么区别？

What is difference between PropertyOverrideConfigurer and PropertyPlaceholderConfigurer?

java

xml

spring

javabeans