Injecting external values

Injecting external values

运行时动态注入值，有三种方式：

• Spring Environment
• property placeholders
• The Spring Expression Language(SPEL)

前提条件

• 配置PropertyPlaceholderConfigurer，作为入口

    <bean id="propertyPlaceholderConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations">
            <list>
                <value>classpath*:*.properties</value>
            </list>
        </property>
        <property name="fileEncoding" value="UTF-8"/>
    </bean>

• 或者使用: <util:properties />

docs

• 流程：http://blog.csdn.net/nicewuranran/article/details/52518420
• systemProperties vs systemEnvironment: https://springframework.guru/introduction-spring-expression-language-spel/
• http://www.concretepage.com/spring/example_utilproperties_spring

1. Spring Environment

package com.soundsystem;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.core.env.Environment;

@Configuration
@PropertySource("classpath:/com/soundsystem/app.properties")
public class EnvironmentConfig {

  @Autowired
  Environment env;
  
  @Bean
  public BlankDisc blankDisc() {
    return new BlankDisc(
        env.getProperty("disc.title"),
        env.getProperty("disc.artist"));
  }
}

spring’s environment api

• String getProperty(String key): env.getProperty("disc.title")
• String getProperty(String key, String defaultValue): env.getProperty("disc.artist", "U2"));
• T getProperty(String key, Class<T> type): Class<CompactDisc> cdClass =
  env.getProperty("disc.title", String.class);
• T getProperty(String key, Class<T> type, T defaultValue): int connectionCount =
  env.getProperty("db.connection.count", Integer.class, 30);
• getRequiredProperty("disc.title"): 不存在抛 IllegalStateException
• env.containsProperty("disc.title");
• boolean titleExists = env.containsProperty("disc.title")： 判断是否存在
• Class<CompactDisc> cdClass =
  env.getPropertyAsClass("disc.class", CompactDisc.class): 解析a property 到一个类里

spring environment for profile

• String[] getActiveProfiles(): Returns an array of active profile names
• String[] getDefaultProfiles()—Returns an array of default profile names
• boolean acceptsProfiles(String... profiles)—Returns true if the envi-
  ronment supports the given profile(s)

2. property placeholders

component-scann 配置方式

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

xml 配置

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

3.SpEL

JavaConfig

public BlankDisc(
      @Value("#{systemProperties['disc.title']}") String title,
      @Value("#{systemProperties['disc.artist']}") String artist) {
  this.title = title;
  this.artist = artist;
}

xml

<bean id="sgtPeppers"
      class="soundsystem.BlankDisc"
      c:_title="#{systemProperties['disc.title']}"
      c:_artist="#{systemProperties['disc.artist']}" />