淺談Spring中@Import注解的作用和使用

更新時間：2020年05月28日 11:41:50 作者：潘超博客

這篇文章主要介紹了淺談Spring中@Import注解的作用和使用，文中通過示例代碼介紹的非常詳細，對大家的學習或者工作具有一定的參考學習價值，需要的朋友們下面隨著小編來一起學習學習吧

@Import用來導入@Configuration注解的配置類、聲明@Bean注解的bean方法、導入ImportSelector的實現(xiàn)類或?qū)隝mportBeanDefinitionRegistrar的實現(xiàn)類。

@Import注解的作用

查看Import注解源碼

/**
 * Indicates one or more {@link Configuration @Configuration} classes to import.
 *
 * <p>Provides functionality equivalent to the {@code <import/>} element in Spring XML.
 * Only supported for classes annotated with {@code @Configuration} or declaring at least
 * one {@link Bean @Bean} method, as well as {@link ImportSelector} and
 * {@link ImportBeanDefinitionRegistrar} implementations.
 *
 * <p>{@code @Bean} definitions declared in imported {@code @Configuration} classes
 * should be accessed by using {@link org.springframework.beans.factory.annotation.Autowired @Autowired}
 * injection. Either the bean itself can be autowired, or the configuration class instance
 * declaring the bean can be autowired. The latter approach allows for explicit,
 * IDE-friendly navigation between {@code @Configuration} class methods.
 *
 * <p>May be declared at the class level or as a meta-annotation.
 *
 * <p>If XML or other non-{@code @Configuration} bean definition resources need to be
 * imported, use {@link ImportResource @ImportResource}
 *
 * @author Chris Beams
 * @since 3.0
 * @see Configuration
 * @see ImportSelector
 * @see ImportResource
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Import {

 /**
 * The @{@link Configuration}, {@link ImportSelector} and/or
 * {@link ImportBeanDefinitionRegistrar} classes to import.
 */
 Class<?>[] value();
}

分析類注釋得出結(jié)論：

聲明一個bean
導入@Configuration注解的配置類
導入ImportSelector的實現(xiàn)類
導入ImportBeanDefinitionRegistrar的實現(xiàn)類

@Import注解的使用

聲明一個bean

package com.example.demo.bean;

public class TestBean1 {
}

package com.example.demo;

import com.example.demo.bean.TestBean1;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

@Import({TestBean1.class})
@Configuration
public class AppConfig {
}

導入@Configuration注解的配置類

package com.example.demo.bean;

public class TestBean2 {
}

package com.example.demo.bean;

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

@Configuration
public class TestConfig {
  @Bean
  public TestBean2 getTestBean2(){
    return new TestBean2();
  }
}

package com.example.demo;

import com.example.demo.bean.TestBean1;
import com.example.demo.bean.TestConfig;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

@Import({TestBean1.class,TestConfig.class})
@Configuration
public class AppConfig {
}

導入ImportSelector的實現(xiàn)類

package com.example.demo.bean;

public class TestBean3 {
}

package com.example.demo.bean;

import org.springframework.context.annotation.ImportSelector;
import org.springframework.core.type.AnnotationMetadata;

public class TestImportSelector implements ImportSelector {
  @Override
  public String[] selectImports(AnnotationMetadata importingClassMetadata) {
    return new String[]{"com.example.demo.bean.TestBean3"};
  }
}

package com.example.demo;

import com.example.demo.bean.TestBean1;
import com.example.demo.bean.TestConfig;
import com.example.demo.bean.TestImportSelector;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

@Import({TestBean1.class,TestConfig.class,TestImportSelector.class})
@Configuration
public class AppConfig {
}

導入ImportBeanDefinitionRegistrar的實現(xiàn)類

package com.example.demo.bean;

public class TestBean4 {
}

package com.example.demo.bean;

import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.RootBeanDefinition;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.type.AnnotationMetadata;

public class TestImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {
  @Override
  public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    RootBeanDefinition rootBeanDefinition = new RootBeanDefinition(TestBean4.class);
    registry.registerBeanDefinition("TestBean4", rootBeanDefinition);
  }
}

package com.example.demo;

import com.example.demo.bean.TestBean1;
import com.example.demo.bean.TestConfig;
import com.example.demo.bean.TestImportBeanDefinitionRegistrar;
import com.example.demo.bean.TestImportSelector;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

@Import({TestBean1.class,TestConfig.class,TestImportSelector.class,TestImportBeanDefinitionRegistrar.class})
@Configuration
public class AppConfig {
}

最后，我們來看下導入結(jié)果：

package com.example.demo;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.Arrays;

@RunWith(SpringRunner.class)
@SpringBootTest
public class DemoApplicationTests {

  @Test
  public void test() {
    AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext(AppConfig.class);
    String[] beanDefinitionNames = annotationConfigApplicationContext.getBeanDefinitionNames();
    System.out.println("--------------------------------------------------------");
    for (String beanDefinitionName: beanDefinitionNames) {
      System.out.println(beanDefinitionName);
    }
    System.out.println("--------------------------------------------------------");
  }
}

打印結(jié)果如下：

--------------------------------------------------------
org.springframework.context.annotation.internalConfigurationAnnotationProcessor
org.springframework.context.annotation.internalAutowiredAnnotationProcessor
org.springframework.context.annotation.internalRequiredAnnotationProcessor
org.springframework.context.annotation.internalCommonAnnotationProcessor
org.springframework.context.event.internalEventListenerProcessor
org.springframework.context.event.internalEventListenerFactory
appConfig
com.example.demo.bean.TestBean1
com.example.demo.bean.TestConfig
getTestBean2
com.example.demo.bean.TestBean3
TestBean4
--------------------------------------------------------

可以看出TestBean1,TestBean2,TestBean3,TestBean4通過不同的4種導入方法被導入SpringIOC容器中。

到此這篇關于淺談Spring中@Import注解的作用和使用的文章就介紹到這了,更多相關Spring @Import注解內(nèi)容請搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關文章希望大家以后多多支持腳本之家！

您可能感興趣的文章: