Spring之bean的实例化方式

1.使用构造方法实例化bean（利用反射）

import lombok.Data;@Data
public class People {private String name;private Integer age;private String eat;
}

<?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 http://www.springframework.org/schema/beans/spring-beans.xsd"><bean id="people" class="People"><property name="name" value="张三"/><property name="age" value="18"/><property name="eat" value="吃饭"/></bean>
</beans>

注：无参构造方法如果不存在，将抛出异常BeanCreationException

2.静态工厂实例化对象

package domain;import lombok.Data;@Data
public class People {private String name;private Integer age;private String eat;
}package factory;import domain.People;public class PeopleFactory {public static People getPeople() {return new People();}
}

<?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 http://www.springframework.org/schema/beans/spring-beans.xsd"><bean id="people" class="factory.PeopleFactory" factory-method="getPeople"><property name="name" value="张三"/><property name="age" value="18"/><property name="eat" value="吃饭"/></bean>
</beans>

3.实例工厂初始化bean

package domain;import lombok.Data;@Data
public class People {private String name;private Integer age;private String eat;
}package factory;import domain.People;public class PeopleFactory {public People getPeople() {return new People();}
}

<?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 http://www.springframework.org/schema/beans/spring-beans.xsd"><bean id="PeopleFactory" class="factory.PeopleFactory"/><bean id="people" factory-bean="PeopleFactory" factory-method="getPeople"><property name="name" value="张三"/><property name="age" value="18"/><property name="eat" value="吃饭"/></bean>
</beans>

4.对实例工厂初始化bean的方式进行优化

package domain;import lombok.Data;@Data
public class People {private String name;private Integer age;private String eat;
}package factory;import domain.People;
import org.springframework.beans.factory.FactoryBean;public class PeopleFactoryBean implements FactoryBean<People> {@Overridepublic People getObject() throws Exception {return new People();}@Overridepublic Class<?> getObjectType() {return People.class;}@Overridepublic boolean isSingleton() {return true;}
}

<?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 http://www.springframework.org/schema/beans/spring-beans.xsd"><bean id="people" class="factory.PeopleFactoryBean" />
</beans>