PropertyPlaceholderConfigurer

spring提供的PropertyPlaceholderConfigurer實現類能夠使Bean在配置時引用外部屬性文件。
PropertyPlaceholderConfigurer實現了BeanFactoryPostProcessorBean接口，因而也是一個Bean工廠後處理器。

PropertyPlaceholderConfigurer的使用

xml配置及註解方式：

      <dependency>
        <groupId>org.springframework</groupId
 
>
        <artifactId>spring-core</artifactId>
        <version>4.3.16.RELEASE</version>
      </dependency>
      <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version
 
>4.3.16.RELEASE</version>
      </dependency>
      <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-beans</artifactId>
        <version>4.3.16.RELEASE</version>
      </dependency>

name=zhangsan
age=23
 

package test;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Driver {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("my.xml");
        User user = context.getBean("user", User.class);
        System.out.println(user.getName());
        System.out.println(user.getAge());
    }
}
class User {
    @Value("${name}")
    private String name;
    private int age;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
}

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:p="http://www.springframework.org/schema/p"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
      http://www.springframework.org/schema/beans
      http://www.springframework.org/schema/beans/spring-beans.xsd
      http://www.springframework.org/schema/context
      http://www.springframework.org/schema/context/spring-context.xsd">
    <!-- spring 引入屬性文件 -->
    <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"
        p:location="classpath:my.properties"
        p:fileEncoding="utf-8"/>
    <!-- 開啟包掃描，因為User類使用到了@Value註解；包掃描不支持裸體類上的註解 -->
    <context:component-scan base-package="test"/>
    <!-- 使用外部屬性文件值賦值 -->
    <bean id="user" class="test.User" p:age="${age}"/>
</beans>

PropertyPlaceholderConfigurer的其他屬性：
locations：可以引入多個屬性文件
fileEncoding：屬性文件的編碼格式
order：指定多個屬性的優先級
placeholderPrefix：默認值為“${”，可以修改
placeholderSuffix：默認為“}”

除了使用<bean>聲明PropertyPlaceholderConfigurer引入屬性文件這種方式外，還可以使用另一種簡潔的方式；但如果希望自定義一些額外的高級功能，如屬性加密、使用數據庫表來保存配置信息時，就必須使用<bean>聲明PropertyPlaceholderConfigurer的方式

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:p="http://www.springframework.org/schema/p"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
      http://www.springframework.org/schema/beans
      http://www.springframework.org/schema/beans/spring-beans.xsd
      http://www.springframework.org/schema/context
      http://www.springframework.org/schema/context/spring-context.xsd">
    <!-- spring 引入屬性文件 -->
    <context:property-placeholder location="my.properties"/>
    <!-- 開啟包掃描，因為User類使用到了@Value註解；包掃描不支持裸體類上的註解 -->
    <context:component-scan base-package="test"/>
    <!-- 使用外部屬性文件值賦值 -->
    <bean id="user" class="test.User" p:age="${age}"/>
</beans>

Java配置及註解方式：

      <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>4.3.16.RELEASE</version>
      </dependency>
      <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>4.3.16.RELEASE</version>
      </dependency>
      <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-beans</artifactId>
        <version>4.3.16.RELEASE</version>
      </dependency>

name=zhangsan
age=23

package test;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class Driver {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(MyConfig.class);
        User user = context.getBean("user", User.class);
        System.out.println(user.getName());
        System.out.println(user.getAge());
    }
}
class User {
    @Value("${name}")
    private String name;
    @Value("${age}")
    private int age;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
}

package test;

import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.io.ClassPathResource;

@Configuration
@ComponentScan
public class MyConfig {
    @Bean
    public User user() {
        return new User();
    }
    @Bean
    public PropertyPlaceholderConfigurer PropertyPlaceholderConfigurer() {
        PropertyPlaceholderConfigurer configurer = new PropertyPlaceholderConfigurer();
        configurer.setLocation(new ClassPathResource("my.properties"));
        return configurer;
    }

}

spring 使用外部屬性文件