阿里面试官：小伙子，你给我说一下Spring Bean初始化的几种常规方式吧
前言
通过构造方法实例化
通过静态工厂实例化
通过实例工厂实例化
通过FactoryBean实例化
RumenzA实体类
package com.rumenz;
public class RumenzA {
private String id;
private String name;
public static RumenzA createRumenzA(){
RumenzA rumenzA=new RumenzA();
rumenzA.setId("123");
rumenzA.setName("入门小站");
return rumenzA;
}
public RumenzA() {
System.out.println("RumenzA 无参构造方法");
}
public RumenzA(String id) {
this.id = id;
System.out.println("ID构造方法");
}
// set get省略
}
构造方法
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="rumenz" class="com.rumenz.RumenzA" />
<bean id="rumenz1" class="com.rumenz.RumenzA">
<constructor-arg name="id" value="1"/>
</bean>
</beans>
DemoApplication.java
package com.rumenz;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class DemoApplication {
public static void main(String[] args) {
ClassPathXmlApplicationContext ca=new ClassPathXmlApplicationContext("beans.xml");
RumenzA rumenzA=(RumenzA)ca.getBean("rumenz");
}
}
输出
xxx.DefaultListableBeanFactory - Creating shared instance of singleton bean 'rumenz' RumenzA 无参构造方法 xxx.DefaultListableBeanFactory - Creating shared instance of singleton bean 'rumenz1' ID构造方法
静态工厂
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="rFactory" class="com.rumenz.RumenzFactory" factory-method="rumenzFactory"/>
<bean id="rFactory1" class="com.rumenz.RumenzFactory" factory-method="rumenzFactory">
<constructor-arg name="id" value="111"/>
</bean>
</beans>
RumenzFactory工厂类
package com.rumenz;
public class RumenzFactory {
//静态方法
public static RumenzA rumenzFactory(){
return new RumenzA();
}
public static RumenzA rumenzFactory(String id){
return new RumenzA(id);
}
}
DemoApplication.java
package com.rumenz;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class DemoApplication {
public static void main(String[] args) {
ClassPathXmlApplicationContext ca=new ClassPathXmlApplicationContext("beans.xml");
}
}
输出
xxx.DefaultListableBeanFactory - Creating shared instance of singleton bean 'rFactory' RumenzA 无参构造方法 xxx.DefaultListableBeanFactory - Creating shared instance of singleton bean 'rFactory1' ID构造方法
实例工厂实例化
<?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.rumenz.RumenzFactory" />
<bean id="rumenz" factory-bean="rFactory" factory-method="rumenzFactory"></bean>
<bean id="rumenz1" factory-bean="rFactory" factory-method="rumenzFactory">
<constructor-arg name="id" value="666"></constructor-arg>
</bean>
</beans>
RumenzFactory.java
package com.rumenz;
public class RumenzFactory {
//不能用静态方法
public RumenzA rumenzFactory(){
return new RumenzA();
}
public RumenzA rumenzFactory(String id){
return new RumenzA(id);
}
}
DemoApplication.java
package com.rumenz;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class DemoApplication {
public static void main(String[] args) {
ClassPathXmlApplicationContext ca=new ClassPathXmlApplicationContext("beans.xml");
//RumenzA rumenzA=(RumenzA)ca.getBean("rFactory1");
}
}
输出
xxx.DefaultListableBeanFactory - Creating shared instance of singleton bean 'rumenz' RumenzA 无参构造方法 xxx.DefaultListableBeanFactory - Creating shared instance of singleton bean 'rumenz1' ID构造方法
通过FactoryBean实例化
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="rumenz-by-factoryBean" class="com.rumenz.RumenzAFactoryBean"/>
</beans>
RumenzAFactoryBean.java
package com.rumenz;
import org.springframework.beans.factory.FactoryBean;
public class RumenzAFactoryBean implements FactoryBean {
@Override
public Object getObject() throws Exception {
return RumenzA.createRumenzA();
}
@Override
public Class<?> getObjectType() {
return RumenzA.class;
}
}
DemoApplication.java
package com.rumenz;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class DemoApplication {
public static void main(String[] args) {
ClassPathXmlApplicationContext ca=new ClassPathXmlApplicationContext("beans.xml");
RumenzA rumenzA=(RumenzA)ca.getBean("rumenz-by-factoryBean");
}
}
输出/异步加载bean
xxx.DefaultListableBeanFactory - Creating shared instance of singleton bean 'rumenz-by-factoryBean' RumenzA 无参构造方法
最后
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