SPRING IN ACTION 第4版笔记-第三章ADVANCING WIRING-007-给BEAN运行时注入值placeholder、@Value

一、用placeholder给bean运行时注入值的步骤

Spring取得placeholder的值是用${...}

1.声明placeholder bean

(1)java方式

In order to use placeholder values, you must configure either a PropertyPlaceholder-
Configurer bean or a PropertySourcesPlaceholderConfigurer bean. Starting with
Spring 3.1, PropertySourcesPlaceholderConfigurer is preferred because it resolves
placeholders against the Spring Environment and its set of property sources.
The following @Bean method configures PropertySourcesPlaceholderConfigurer
in Java configuration:

@Bean
public
static PropertySourcesPlaceholderConfigurer placeholderConfigurer() {
return new PropertySourcesPlaceholderConfigurer();
}

(2)xml方式

 <?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:c="http://www.springframework.org/schema/c"
   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-4.0.xsd">

   <context:property-placeholder
     location="com/soundsystem/app.properties" />

   <bean class="com.soundsystem.BlankDisc"
     c:_0 = "${disc.title}"
     c:_1 = "${disc.artist}"/>

 </beans>

2.注入

1.在java文件中用 @Value

如构造函数

public BlankDisc(
@Value("${disc.title}") String title,
@Value("${disc.artist}") String artist) {
    this.title = title;
    this.artist = artist;
}

2.xml

<bean id="sgtPeppers"
class="soundsystem.BlankDisc"
c:_title="${disc.title}"
c:_artist="${disc.artist}" />