[스프링 코어] 4. SpEL (스프링 Expression Language)

스프링 EL?

• 객체 그래프 조작, 조작
• Unified EL과 비슷하지만 메소드 호출 기능 지원, 문자열 템플릿 기능 제공
• 자바에서 사용 가능한 EL이 있지만, SpEL은 모든 스프링 프로젝트에 걸쳐 사용할 EL
• (스프링 3.0부터 지원)

간단한 예제)

package me.jinmin;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.stereotype.Component;

@Component
public class AppRunner implements ApplicationRunner {

    @Value("#{1 + 1}")
    int value;

    @Value("#{'hello ' + 'world'}")
    String greeting;

    @Value("#{1 eq 1}")
    boolean trueOrFalse;

    @Value("hello")
    String hello;

    @Value("${my.value}")
    int myValue;

    @Value("#{${my.value} + 1}")
    int myValuePlus;

    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("===============");
        System.out.println(value);
        System.out.println(greeting);
        System.out.println(trueOrFalse);
        System.out.println(hello);
        System.out.println(myValue);
        System.out.println(myValuePlus);
    }
}

• 결과

  print:
  ===============
  2
  hello world
  true
  hello
  100
  101

• 표현식 : #{} // 프로퍼티 : ${}

• 표현식(#{})을 실행하고 결과값을 프로퍼티(int value;, String greeting;에 넣는다.

• 표현식은 프로퍼티를 가질 수 있지만, 반대는 안 된다.

  • ex) #{${my.value} + 1} 가능.

• 문법 참고

• 빈을 참고하는 것도 가능하다.

  • \main\java\me\jinmin\Sample

    package me.jinmin;
    
    import org.springframework.stereotype.Component;
    
    @Component
    public class Sample {
    
        private int value = 200;
    
    }

  • \main\java\me\jinmin\AppRunner

    package me.jinmin;
    
    import org.springframework.beans.factory.annotation.Value;
    import org.springframework.boot.ApplicationArguments;
    import org.springframework.boot.ApplicationRunner;
    import org.springframework.stereotype.Component;
    
    @Component
    public class AppRunner implements ApplicationRunner {
    
        @Value("#{sample.value}")
        int sampleValue;
        
        @Override
        public void run(ApplicationArguments args) throws Exception {
            System.out.println("===============");
            System.out.println(sampleValue);
        }
    }

    print:
    ===============
    200

실제 사용은 어디서 할까?

• @Value(위의 예제들)

• @ConditionalOnExpression

• Spring Security

  

  • 메소드 시큐리티, @PreAuthorize, @PostAuthorize, @PreFilter, @PostFilter

    • 간단 예)

      @PreAuthorize("hasRole('ROLE_USER')")
        public void create(Contact contact);
      
      @PreAuthorize("hasPermission(#contact, 'admin')")
        public void deletePermission(Contact contact, Sid recipient, Permission permission);
      
      @PreAuthorize("#contact.name == authentication.name")
        public void doSomething(Contact contact);

• Spring Data

  • @Query

    • 간단 예)

      @Query("select u from User u where u.age = ?#{[0]}")
      List<User> findUsersByAge(int age);
      
      @Query("select u from User u where u.firstname = :#{#customer.firstname}")
      List<User> findUsersByCustomersFirstname(@Param("customer") Customer customer);

• Thymeleaf 등

ExpressionParser의 예) (⇒ ConversionService를 사용)

package me.jinmin;

import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.stereotype.Component;

@Component
public class AppRunner implements ApplicationRunner {

    @Override
    public void run(ApplicationArguments args) throws Exception {
        ExpressionParser parser = new SpelExpressionParser();
        Expression expression = parser.parseExpression("2 + 100");
        int value = expression.getValue(Integer.class);
        System.out.println(value);
    }
}

print:
102