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这篇文章主要讲解了Spring中@Import注解的作用和使用方法，内容清晰明了，对此有兴趣的小伙伴可以学习一下，相信大家阅读完之后会有帮助。
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@Import用来导入@Configuration注解的配置类、声明@Bean注解的bean方法、导入ImportSelector的实现类或导入ImportBeanDefinitionRegistrar的实现类。
@Import注解的作用
查看Import注解源码
/**
* Indicates one or more {@link Configuration @Configuration} classes to import.
*
* Provides functionality equivalent to the {@code
{@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.
*
*
May be declared at the class level or as a meta-annotation.
*
*
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();
}
分析类注释得出结论：
@Import注解的使用
声明一个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 {
}导入@Configuration注解的配置类
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 {
}导入ImportSelector的实现类
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 {
}导入ImportBeanDefinitionRegistrar的实现类
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，我们来看下导入结果：
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("--------------------------------------------------------");
}
}打印结果如下：
--------------------------------------------------------
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通过不同的4种导入方法被导入SpringIOC容器中。
看完上述内容，是不是对Spring中@Import注解的作用和使用方法有进一步的了解，如果还想学习更多内容，欢迎关注创新互联行业资讯频道。
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