환경변수 사용하기

참조사이트

: https://docs.spring.io/spring/docs/3.0.x/spring-framework-reference/html/expressions.html

: https://stackoverflow.com/questions/6285978/is-there-any-syntax-like-systempropertiesenvironment-variable-name-to-g

6.4 Expression support for defining bean definitions

SpEL expressions can be used with XML or annotation based configuration metadata for defining BeanDefinitions. In both cases the syntax to define the expression is of the form #{ <expression string> }.

6.4.1 XML based configuration

A property or constructor-arg value can be set using expressions as shown below

<bean id="numberGuess" class="org.spring.samples.NumberGuess">
    <property name="randomNumber" value="#{ T(java.lang.Math).random() * 100.0 }"/>

    <!-- other properties -->
</bean>

The variable 'systemProperties' is predefined, so you can use it in your expressions as shown below. Note that you do not have to prefix the predefined variable with the '#' symbol in this context.

<bean id="taxCalculator" class="org.spring.samples.TaxCalculator">
    <property name="defaultLocale" value="#{ systemProperties['user.region'] }"/>

    <!-- other properties -->
</bean>

You can also refer to other bean properties by name, for example.

<bean id="numberGuess" class="org.spring.samples.NumberGuess">
    <property name="randomNumber" value="#{ T(java.lang.Math).random() * 100.0 }"/>

    <!-- other properties -->
</bean>


<bean id="shapeGuess" class="org.spring.samples.ShapeGuess">
    <property name="initialShapeSeed" value="#{ numberGuess.randomNumber }"/>

    <!-- other properties -->
</bean>

6.4.2 Annotation-based configuration

The @Value annotation can be placed on fields, methods and method/constructor parameters to specify a default value.

Here is an example to set the default value of a field variable.

public static class FieldValueTestBean

  @Value("#{ systemProperties['user.region'] }")
  private String defaultLocale;

  public void setDefaultLocale(String defaultLocale)
  {
    this.defaultLocale = defaultLocale;
  }

  public String getDefaultLocale() 
  {
    return this.defaultLocale;
  }

}

The equivalent but on a property setter method is shown below.

public static class PropertyValueTestBean

  private String defaultLocale;

  @Value("#{ systemProperties['user.region'] }")
  public void setDefaultLocale(String defaultLocale)
  {
    this.defaultLocale = defaultLocale;
  }

  public String getDefaultLocale() 
  {
    return this.defaultLocale;
  }

}

Autowired methods and constructors can also use the @Value annotation.

public class SimpleMovieLister {

  private MovieFinder movieFinder;
  private String defaultLocale;

  @Autowired
  public void configure(MovieFinder movieFinder, 
                        @Value("#{ systemProperties['user.region'] }"} String defaultLocale) {
      this.movieFinder = movieFinder;
      this.defaultLocale = defaultLocale;
  }

  // ...
}

public class MovieRecommender {

  private String defaultLocale;

  private CustomerPreferenceDao customerPreferenceDao;

  @Autowired
  public MovieRecommender(CustomerPreferenceDao customerPreferenceDao,
                          @Value("#{systemProperties['user.country']}"} String defaultLocale) {
      this.customerPreferenceDao = customerPreferenceDao;
      this.defaultLocale = defaultLocale;
  }

  // ...
}

• #{systemProperties['databaseName']}
• #{systemProperties.databaseName}
• ${databaseName} //$ instead of # !!

#{configProperties[]} propertise 환경변수 접근

#{systemProperties[]} system 환경변수 접근

${} properties환경변수 접근 후 system 환경변수 접근!

SpEL 

: systemProperties, systemEnvironment 빈이 존재한다.

: JVM 에서 생성해준다.

: @Resource systemPeroperties를 통해서 가져와서 프로퍼티를 읽을 수 있다.

: 하지만 이런 번거로움을 SpEL을 통해서 프로퍼티 값을 가져올 수 있다.