SPRING IN ACTION 第4版笔记-第三章ADVANCING WIRING-003-@Conditional根据条件生成bean及处理profile

一、用@Conditional根据条件决定是否要注入bean

1.

package com.habuma.restfun;

public class MagicBean {

}

2.

package com.habuma.restfun;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MagicConfig {

  @Bean
  @Conditional(MagicExistsCondition.class)
  public MagicBean magicBean() {
    return new MagicBean();
  }
  
}

3.

package com.habuma.restfun;

import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.core.env.Environment;
import org.springframework.core.type.AnnotatedTypeMetadata;

public class MagicExistsCondition implements Condition {

  @Override
  public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
    Environment env = context.getEnvironment();
    return env.containsProperty("magic");
  }
  
}

4.

package com.habuma.restfun;

import static org.junit.Assert.*;

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

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes=MagicConfig.class)
public class MagicExistsTest {

  @Autowired
  private ApplicationContext context;
  
  /*
   * This test will fail until you set a "magic" property.
   * You can set this property as an environment variable, a JVM system property, by adding a @BeforeClass
   * method and calling System.setProperty() or one of several other options.
   */
  @Test
  public void shouldNotBeNull() {
    assertTrue(context.containsBean("magicBean"));
  }
  
}

二、用@Conditional处理profile

1.

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD})
@Documented
@Conditional(ProfileCondition.class)
public @interface Profile {
    String[] value();
}

2.

class ProfileCondition implements Condition {
    public boolean matches(
        ConditionContext context, AnnotatedTypeMetadata metadata) {
        if (context.getEnvironment() != null) {
            MultiValueMap < String, Object > attrs =
                metadata.getAllAnnotationAttributes(Profile.class.getName());
            if (attrs != null) {
                for (Object value: attrs.get("value")) {
                    if (context.getEnvironment()
                        .acceptsProfiles(((String[]) value))) {
                        return true;
                    }
                }
                return false;
            }
        }
        return true;
    }
}

As you can see, ProfileCondition fetches all the annotation attributes for the
@Profile annotation from AnnotatedTypeMetadata . With that, it checks explicitly for
the value attribute, which contains the name of the bean’s profile. It then consults
with the Environment retrieved from the ConditionContext to see whether the pro-
file is active (by calling the acceptsProfiles() method).