吴裕雄天生自然SPRINGSpring Bean

Spring框架实例化Bean有三种方式：构造方法实例化、静态工厂实例化和实例工厂实例化（其中，最常用的实例方法是构造方法实例化）

演示Bean的实例化过程，具体步骤如下。

1．使用Eclipse创建Web应用并导入JAR包

2．创建实例化Bean的类

3．创建配置类

4．创建测试类

5．运行测试类

package instance;

public class BeanClass {
    public String message;

    public BeanClass() {
        message = "构造方法实例化Bean";
    }

    public BeanClass(String s) {
        message = s;
    }

}

package instance;

public class BeanInstanceFactory {
    public BeanClass createBeanClassInstance() {
        return new BeanClass("调用实例工厂方法实例化Bean");
    }

}

package instance;

public class BeanStaticFactory {
    private static BeanClass beanInstance = new BeanClass("调用静态工厂方法实例化Bean");

    public static BeanClass createInstance() {
        return beanInstance;
    }

}

package config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import instance.BeanClass;
import instance.BeanInstanceFactory;
import instance.BeanStaticFactory;

@Configuration
public class JavaConfig {
    /**
     * 构造方法实例化
     */
    @Bean(value = "beanClass") // value可以省略
    public BeanClass getBeanClass() {
        return new BeanClass();
    }

    /**
     * 静态工厂实例化
     */
    @Bean(value = "beanStaticFactory")
    public BeanClass getBeanStaticFactory() {
        return BeanStaticFactory.createInstance();
    }

    /**
     * 实例工厂实例化
     */
    @Bean(value = "beanInstanceFactory")
    public BeanClass getBeanInstanceFactory() {
        BeanInstanceFactory bi = new BeanInstanceFactory();
        return bi.createBeanClassInstance();
    }

}

package config;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import instance.BeanClass;

public class TestBean {
    public static void main(String[] args) {
        // 初始化Spring容器ApplicationContext
        AnnotationConfigApplicationContext appCon = new AnnotationConfigApplicationContext(JavaConfig.class);
        BeanClass b1 = (BeanClass) appCon.getBean("beanClass");
        System.out.println(b1 + b1.message);
        BeanClass b2 = (BeanClass) appCon.getBean("beanStaticFactory");
        System.out.println(b2 + b2.message);
        BeanClass b3 = (BeanClass) appCon.getBean("beanInstanceFactory");
        System.out.println(b3 + b3.message);
        appCon.close();
    }

}