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--笔记

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Spring-Bean实例化方式

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常规方式

  • 通过构造方法实例化

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    <?xml version="1.0" encoding="UTF-8"?>
    <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
            https://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id="test" class="com.learn.Test" />
    <bean id="test1" class="com.learn.Test">
         <constructor-arg name="id" value="1"/>
    </bean>
    </beans>
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    import org.springframework.context.support.ClassPathXmlApplicationContext;

    public class DemoApplication {
        public static  void main(String[] args) {
            ClassPathXmlApplicationContext  ca=new ClassPathXmlApplicationContext("beans.xml");
            Test testA=(Test)ca.getBean("test");
        }
    }

  • 通过静态工厂实例化

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    <?xml version="1.0" encoding="UTF-8"?>
    <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
            https://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id="rFactory" class="com.test.TestFactory" factory-method="testFactory"/>
    <bean id="rFactory1" class="com.test.TestFactory" factory-method="testFactory">
        <constructor-arg name="id" value="111"/>
    </bean>
    </beans>
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    //TestFactory工厂类

    public class TestFactory {
      //静态方法
      public static Test testFactory(){
        return new Test();
      }
      public static Test testFactory(String id){
        return new Test(id);
      }
    }

    //DemoApplication.java
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    public class DemoApplication {
      public static  void main(String[] args) {
        ClassPathXmlApplicationContext  ca=new ClassPathXmlApplicationContext("beans.xml");
      }
    }

  • 通过实例工厂实例化

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    <?xml version="1.0" encoding="UTF-8"?>
    <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
                               https://www.springframework.org/schema/beans/spring-beans.xsd">
      <bean  id="rFactory" class="com.learn.TestFactory" />
      <bean id="test" factory-bean="rFactory" factory-method="testFactory"></bean>
      <bean id="test1" factory-bean="rFactory" factory-method="testFactory">
        <constructor-arg name="id" value="666"></constructor-arg>
      </bean>
    </beans>
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    //TestFactory.java
    public class TestFactory {
      //不能用静态方法
      public  Test testFactory(){
        return new Test();
      }
      public  Test testFactory(String id){
        return new Test(id);
      }
    }

    //DemoApplication.java
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    public class DemoApplication {
      public static  void main(String[] args) {
        ClassPathXmlApplicationContext  ca=new ClassPathXmlApplicationContext("beans.xml");
        //Test testA=(Test)ca.getBean("rFactory1");
      }
    }

  • 通过FactoryBean实例化

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    <?xml version="1.0" encoding="UTF-8"?>
    <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
                               https://www.springframework.org/schema/beans/spring-beans.xsd">
      <bean id="test-by-factoryBean"  class="com.learn.TestFactoryBean"/>
    </beans>
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    import org.springframework.beans.factory.FactoryBean;
    public class TestFactoryBean implements FactoryBean {
      @Override
      public Object getObject() throws Exception {
        return Test.createTest();
      }
      @Override
      public Class<?> getObjectType() {
        return Test.class;
      }
    }

    import org.springframework.context.support.ClassPathXmlApplicationContext;
    public class DemoApplication {
      public static  void main(String[] args) {
        ClassPathXmlApplicationContext  ca=new ClassPathXmlApplicationContext("beans.xml");
        Test testA=(Test)ca.getBean("test-by-factoryBean");
      }
    }

特殊方式

  • ServiceLoader 利用JDK里面的反向控制

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    public final class ServiceLoader<S>
        implements Iterable<S>
    {
        private static final String PREFIX = "META-INF/services/";
        //....
    }

    需要在classpath下创建META-INF/services/目录,在此目录下创建一个文件名为工厂接口的文件(注意不需要后缀),此文件里面放上此接口的全类路径

    └── resources
        ├── META-INF
        │   └── services
        │       └── com.learn.TestFactory
        ├── application.properties
        └── beans.xml
    注意:com.learn.TestFactory 是个文件
    里面的内容为工厂接口:
    com.learn.DefaultTestFactory
    调用DemoApplication.java
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    import org.springframework.context.support.ClassPathXmlApplicationContext;
    import java.util.Iterator;
    import java.util.ServiceLoader;
    public class DemoApplication {
        public static  void main(String[] args) {
            ClassPathXmlApplicationContext  ca=new ClassPathXmlApplicationContext("beans.xml");
            ServiceLoader<TestFactory> serviceLoader= ServiceLoader.load(TestFactory.class,Thread.currentThread().getContextClassLoader());
            Iterator<TestFactory> iterator = serviceLoader.iterator();
            while(iterator.hasNext()){
                TestFactory next = iterator.next();
                System.out.println(next.testFactory());
            }
        }
    }

  • ServiceLoaderFactoryBean 

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    beans.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"
           xsi:schemaLocation="http://www.springframework.org/schema/beans
            https://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id="instance-by-serviceLoaderFactoryBean" class="org.springframework.beans.factory.serviceloader.ServiceLoaderFactoryBean">
      <property name="serviceType" value="com.learn.TestFactory"></property>
    </bean>
    </beans>
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    //调用DemoApplication.java
    public class DemoApplication {
        public static  void main(String[] args) {
            ClassPathXmlApplicationContext  ca=new ClassPathXmlApplicationContext("beans.xml");
            ServiceLoader bean = ca.getBean("instance-by-serviceLoaderFactoryBean", ServiceLoader.class);
            Iterator iterator = bean.iterator();
            while (iterator.hasNext()){
                TestFactory next = (TestFactory) iterator.next();
                System.out.println(next.testFactory());
            }
        }
    }

  • AutowireCapableBeanFactory#createBean

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    package com.learn;
    public class DemoApplication {
      public static  void main(String[] args) {
        ApplicationContext ac=new ClassPathXmlApplicationContext("beans.xml");
        AutowireCapableBeanFactory abf = ac.getAutowireCapableBeanFactory();
        DefaultTestFactory bean = abf.createBean(DefaultTestFactory.class);
        System.out.println(bean.testFactory());
      }
    }

  • BeanDefinitionRegistry#registerBeanDefinition

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    public class DemoApplication {
      public static  void main(String[] args) {
        AnnotationConfigApplicationContext ac=new AnnotationConfigApplicationContext();
        ac.register(DemoApplication.class);
        registerBean(ac,"testa");
        ac.refresh();
        Test testa = (Test) ac.getBean("testa");
        System.out.println(testa);
        ac.close();
      }
      public static void registerBean(BeanDefinitionRegistry reg,String beanName){
        BeanDefinitionBuilder beanDefinitionBuilder = BeanDefinitionBuilder.genericBeanDefinition(Test.class);
        reg.registerBeanDefinition(beanName,beanDefinitionBuilder.getBeanDefinition());
      }
    }

来源：

https://rumenz.com/rumenbiji/Spring-Bean-common-instantiate.html

https://rumenz..com/rumenbiji/Spring-Bean-special-instantiate.html