浅谈Spring中@Import注解的作用和使用
@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. * * <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(); }
分析类注释得出结论:
- 声明一个bean
- 导入@configuration注解的配置类
- 导入importselector的实现类
- 导入importbeandefinitionregistrar的实现类
@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。
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