SPRING IN ACTION 第4版笔记-第三章ADVANCING WIRING-006-给bean运行时注入值(Environment,Property文件)

一、

直观的给bean注入值如下：

@Bean
public CompactDisc sgtPeppers() {
    return new BlankDisc(
        "Sgt. Pepper‘s Lonely Hearts Club Band",
        "The Beatles");
}

< bean id = "sgtPeppers"
class = "soundsystem.BlankDisc"
c: _title = "Sgt. Pepper‘s Lonely Hearts Club Band"
c: _artist = "The Beatles" / >

都是以硬编码的形式，spring提供了提供了两种方式以运行进注入(1)Property placeholders  (2)The Spring Expression Language ( S p EL )

二、Property placeholders

1.app.properties

1 disc.title=Sgt. Peppers Lonely Hearts Club Band
2 disc.artist=The Beatles

2.

 1 package com.soundsystem;
 2
 3 import org.springframework.beans.factory.annotation.Autowired;
 4 import org.springframework.context.annotation.Bean;
 5 import org.springframework.context.annotation.Configuration;
 6 import org.springframework.context.annotation.PropertySource;
 7 import org.springframework.core.env.Environment;
 8
 9 @Configuration
10 @PropertySource("classpath:/com/soundsystem/app.properties")
11 public class EnvironmentConfig {
12
13   @Autowired
14   Environment env;
15
16   @Bean
17   public BlankDisc blankDisc() {
18     return new BlankDisc(
19         env.getProperty("disc.title"),
20         env.getProperty("disc.artist"));
21   }
22
23 }

3.

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <beans xmlns="http://www.springframework.org/schema/beans"
 3   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 4   xmlns:c="http://www.springframework.org/schema/c"
 5   xmlns:context="http://www.springframework.org/schema/context"
 6   xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
 7         http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">
 8
 9   <context:property-placeholder
10     location="com/soundsystem/app.properties" />
11
12   <bean class="com.soundsystem.BlankDisc"
13     c:_0 = "${disc.title}"
14     c:_1 = "${disc.artist}"/>
15
16 </beans>

三、进一步讨论SPRING ’ S E NVIRONMENT

getProperty() is overloaded into four variations:
? String getProperty(String key)
? String getProperty(String key, String defaultValue)
? T getProperty(String key, Class<T> type)
? T getProperty(String key, Class<T> type, T defaultValue)

给定默认值

@Bean
public BlankDisc disc() {
    return new BlankDisc(
        env.getProperty("disc.title", "Rattle and Hum"),
        env.getProperty("disc.artist", "U2"));
}

自动转型

int connectionCount =
env.getProperty("db.connection.count", Integer.class, 30);

@Bean
public BlankDisc disc() {
return new BlankDisc(
env.getRequiredProperty("disc.title"),
env.getRequiredProperty("disc.artist"));
}

Here, if either the disc.title property or the disc.artist property is undefined, an
IllegalStateException will be thrown.

检查是否存在

boolean titleExists = env.containsProperty("disc.title");