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

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

2.

 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"));
   }

 }

3.给定默认值

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.core.env.Environment;

@Configuration
public class EnvironmentConfigWithDefaults {

  @Autowired
  Environment env;

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

}

4.properties必需有值，否则报错

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.core.env.Environment;

@Configuration
public class EnvironmentConfigWithRequiredProperties {

  @Autowired
  Environment env;

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

}

5.测试

 package com.soundsystem;

 import static org.junit.Assert.*;

 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.springframework.beans.factory.BeanCreationException;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

 public class EnvironmentInjectionTest {

   @RunWith(SpringJUnit4ClassRunner.class)
   @ContextConfiguration(classes=EnvironmentConfig.class)
   public static class InjectFromProperties {

     @Autowired
     private BlankDisc blankDisc;

     @Test
     public void assertBlankDiscProperties() {
       assertEquals("The Beatles", blankDisc.getArtist());
       assertEquals("Sgt. Peppers Lonely Hearts Club Band", blankDisc.getTitle());
     }

   }

   @RunWith(SpringJUnit4ClassRunner.class)
   @ContextConfiguration(classes=EnvironmentConfigWithDefaults.class)
   public static class InjectFromPropertiesWithDefaultValues {

     @Autowired
     private BlankDisc blankDisc;

     @Test
     public void assertBlankDiscProperties() {
       assertEquals("U2", blankDisc.getArtist());
       assertEquals("Rattle and Hum", blankDisc.getTitle());
     }

   }

   public static class InjectFromPropertiesWithRequiredProperties {

     @Test(expected=BeanCreationException.class)
     public void assertBlankDiscProperties() {
       new AnnotationConfigApplicationContext(EnvironmentConfigWithRequiredProperties.class);
     }

   }

   @RunWith(SpringJUnit4ClassRunner.class)
   @ContextConfiguration("classpath:placeholder-config.xml")
   public static class InjectFromProperties_XMLConfig {

     @Autowired
     private BlankDisc blankDisc;

     @Test
     public void assertBlankDiscProperties() {
       assertEquals("The Beatles", blankDisc.getArtist());
       assertEquals("Sgt. Peppers Lonely Hearts Club Band", blankDisc.getTitle());
     }

   }

 }

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");