Spring 實戰-第三章-條件化的bean
阿新 • • 發佈:2017-09-01
reg itl tcl span init bsp 測試 art port
在使用的時候,某些bean需要在某些特定條件化才能實例化,spring中使用的@Condition註解實現這個功能。
1.接口
package main.java.soundsystem; public interface CompactDisc { void play(); }
2.實現
package main.java.soundsystem; import org.springframework.context.annotation.Conditional; import org.springframework.context.annotation.Profile;import org.springframework.stereotype.Component; @Component @Profile("dev") public class SgtPepper implements CompactDisc { private String title ="Sgt. Pepper‘s Lonely Hearts Club Band"; private String artist="The Beatles"; @Override public void play() { System.out.println("Playing "+ title +" by "+artist); } }
3.增加Condition實現類,需要實現Condition接口的matches方法,
方法返回true,表示使用這個條件的bean滿足條件可創建,返回false,表示條件不滿足,無法創建
package main.java.soundsystem; import org.springframework.context.annotation.Condition; import org.springframework.context.annotation.ConditionContext;import org.springframework.core.type.AnnotatedTypeMetadata; public class SgtPepperCondition implements Condition { @Override public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) { return true; } }
ConditionContext是一個接口,大致如下
public interface ConditionContext { BeanDefinitionRegistry getRegistry(); ConfigurableListableBeanFactory getBeanFactory(); Environment getEnvironment(); ResourceLoader getResourceLoader(); ClassLoader getClassLoader(); }
通過ConditionContext可以做到如下幾點:
- 借助getRegistry()返回的BeanDefinitionRegistry檢查bean定義;
- 借助getBeanFactroy()返回的ConfigurationListableBeanFactory檢查bean是否存在,甚至探查bean的屬性;
- 借助getEnvironment()返回的Environment檢查環境變量是否存在以及它的值是什麽;
- 讀取並探查getResourceLoader()返回的ResourceLoader所加載的資源;
- 借助getClassLoader()返回的ClassLoader加載並檢查類是否存在。
4.配置增加條件
package main.java.soundsystem; import org.springframework.context.annotation.*; @Configuration //@ComponentScan public class CDPlayerConfig { @Bean @Conditional(SgtPepperCondition.class) @Profile("dev") public CompactDisc sgtPeppers() { return new SgtPepper(); } }
5.測試
package main.java.soundsystem; import static org.junit.Assert.*; import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.test.context.ActiveProfiles; import org.springframework.test.context.ContextConfiguration; import org.springframework.test.context.junit4.SpringJUnit4ClassRunner; @RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration(classes = {CDPlayerConfig.class}) @ActiveProfiles("dev") public class CDPlayerTest { @Autowired private CompactDisc cd; @Test public void cdShouldNotBeNull() { assertNotNull(cd); cd.play(); } }
Spring 實戰-第三章-條件化的bean