Spring框架中的@Import、@ImportResource注解
spring@Import
- @Import注解在4.2之前只支持导入配置类
- 在4.2,@Import注解支持导入普通的java类,并将其声明成一个bean
使用场景：
import注解主要用在基于java代码显式创建bean的过程中，用于将多个分散的java config配置类融合成一个更大的config类。其实除了 import注解外，还有 importResource注解，其作用都类似。配置类的组合主要发生在跨模块或跨包的配置类引用过程中。
示例1：
一般来说, 需要按模块或类别 分割Spring XML bean文件 成多个小文件, 使事情更容易维护和模块化。 例如，
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"> <import resource="config/customer.xml"/> <import resource="config/scheduler.xml"/> </beans>
Spring3 JavaConfig它等效于 @Import 功能
package com.yiibai.config; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Import; @Configuration @Import({ CustomerConfig.class, SchedulerConfig.class }) public class AppConfig { }
在列表中，@Import 是被用来整合所有在@Configuration注解中定义的bean配置。这其实很像我们将多个XML配置文件导入到单个文件的情形。@Import注解实现了相同的功能。本文会介绍使用@Import注解来导入spring工程中的JavaConfig文件.
在下面的例子中，我创建了两个配置文件，然后导入到主配置文件中。最后使用主配置文件来创建context.
示例2：spring4.2之前导入配置类
//Car.java package javabeat.net.basic; public interface Car { public void print(); } //Toyota.java package javabeat.net.basic; import org.springframework.stereotype.Component; @Component public class Toyota implements Car{ public void print(){ System.out.println("I am Toyota"); } } //Volkswagen.java package javabeat.net.basic; import org.springframework.stereotype.Component; @Component public class Volkswagen implements Car{ public void print(){ System.out.println("I am Volkswagen"); } } //JavaConfigA.java package javabeat.net.basic; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class JavaConfigA { @Bean(name="volkswagen") public Car getVolkswagen(){ return new Volkswagen(); } } //JavaConfigB.java package javabeat.net.basic; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class JavaConfigB { @Bean(name="toyota") public Car getToyota(){ return new Toyota(); } } //ParentConfig.java package javabeat.net.basic; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Import; @Configuration @Import({JavaConfigA.class,JavaConfigB.class}) public class ParentConfig { //Any other bean definitions } //ContextLoader.java package javabeat.net.basic; import org.springframework.context.annotation.AnnotationConfigApplicationContext; public class ContextLoader { public static void main (String args[]){ AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(ParentConfig.class); Car car = (Toyota)context.getBean("toyota"); car.print(); car = (Volkswagen)context.getBean("volkswagen"); car.print(); context.close(); } }
程序执行输出
I am Toyata
I am Volkswagen
示例3：spring4.2之后导入普通java bean
package com.dxz.imports; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Import; @Configuration @Import(DemoService.class) // 在spring 4.2之前是不不支持的 public class DemoConfig { } package com.dxz.imports; public class DemoService { public void doSomething() { System.out.println("everything is all fine"); } } package com.dxz.imports; import org.springframework.context.annotation.AnnotationConfigApplicationContext; public class Test { public static void main(String[] args) { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext("com.dxz.imports"); DemoService ds = context.getBean(DemoService.class); ds.doSomething(); } }
结果：
everything is all fine
总结
本文作者介绍了@Import注解的使用。这个注解帮助我们将多个配置文件（可能是按功能分，或是按业务分）导入到单个主配置中，以避免将所有配置写在一个配置中。
二、@ImportResource
相当于：
<import resource="applicationContext-democonfig2.xml" />
示例4：
学习如何使用@ImportResource 和 @Value 注解进行资源文件读取
例子：
先创建一个MyDriverManager类（模拟读取数据库配置信息）
package com.dxz.imports4; public class MyDriverManager { public MyDriverManager(String url, String username, String password) { System.out.println("url : " + url); System.out.println("username : " + username); System.out.println("password : " + password); } }
创建StoreConfig
package com.dxz.imports4; import org.springframework.beans.factory.annotation.Value; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.ImportResource; @Configuration @ImportResource("classpath:applicationContext-democonfig2.xml") public class StoreConfig { @Value("${url}") private String url; @Value("${username}") private String username; @Value("${password}") private String password; @Bean public MyDriverManager myDriverManager() { return new MyDriverManager(url, username, password); } }
XML配置（context:property-placeholder 指定资源文件的位置）applicationContext-democonfig2.xml
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.1.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.1.xsd"> <context:property-placeholder location="classpath:config4.properties" /> <context:component-scan base-package="com.dxz.imports4"> </context:component-scan> </beans>
创建资源文件config4.properties
url=127.0.0.1
username=root
password=123456
单元测试：
package com.dxz.imports4; import org.junit.Test; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class UnitTest { @Test public void test() { ApplicationContext context = new ClassPathXmlApplicationContext("classpath:applicationContext-democonfig2.xml"); MyDriverManager service = (MyDriverManager) context.getBean("myDriverManager"); System.out.println(service.getClass().getName()); } }
结果：
