使用Spring创建对象的方式

小咪咪 2022-06-11 09:08 191阅读 0赞

使用Spring的IOC来创建对象一共有3中方式：

#    1）通过无参构造的方式来创建 #

Hello.java代码：

package com.myspring.bean;
    
    public class Hello {
    
    	private String name;
    	
    	public Hello() {
    		System.out.println("hello 被创建");
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    
    	public void show() {
    		System.out.println("hello," + name);
    	}
    
    }

beans.xml代码：

<?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 name="hello" class="com.myspring.bean.Hello">
    		<property name="name" value="张三" />
    	</bean>
    
    </beans>

测试类Test代码：

package com.myspring.test;
    
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    import com.myspring.bean.Hello;
    
    
    public class Test {
    
    	public static void main(String[] args) {
    		//解析beans.xml文件，生成管理相应的bean对象
    		ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml") ;
    		Hello hello = (Hello) context.getBean("hello") ;
    		hello.show();
    	}
    
    }

运行可以看到控制台打印信息如下：

![Center][]

#    2）有参构造 #

Hello.java代码：

package com.myspring.bean;
    
    
    public class Hello {
    
    	private String name;
    	
    	public Hello(String name) {
    		super();
    		System.out.println("有参构造name:"+name);
    		this.name = name;
    	}
    
    	public void show() {
    		System.out.println("hello," + name);
    	}
    
    }

beans.xml配置代码：

<?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 name="hello" class="com.myspring.bean.Hello">
    		<constructor-arg index="0" value="李四" />
    	</bean>
    
    </beans>

有参的也有三种：第一种是index

其中index指构造方法参数下标从0开始，当有多个时，配置如下：

<constructor-arg index="0" value="李四" />

<constructor-arg index="1" value="王五" />

第二种是根据参数名称，指定name，如图：

![Center 1][]

第三种：根据参数类型设置，

![Center 2][]

测试类代码Test不变，测试结果控制台打印如下：

![Center 3][]

#    3）通过工厂方法 #

分为两种：

第一种是静态工厂

HelloFactory代码：

package com.myspring.factory;
    
    import com.myspring.bean.Hello;
    
    /**
     * 静态工厂类
     */
    public class HelloFactory {
    
    	public static Hello newInstance(String name) {
    		return new Hello(name) ;
    	}
    	
    }

beans.xml代码：

<?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="hello" class="com.myspring.factory.HelloFactory"
    		factory-method="newInstance">
    		<constructor-arg index="0" value="李四" />
    	</bean>
    
    </beans>

第二种是动态工厂

动态工厂类代码：

package com.myspring.factory;
    
    import com.myspring.bean.Hello;
    
    /**
     * 动态工厂类
     */
    public class HelloDynamicFactory {
    
    	public Hello newInstance(String name) {
    		return new Hello(name) ;
    	}
    	
    }

注意这个代码的newInstance()方法，不是static的，否则运行程序会报错

beans.xml代码：

<?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="helloFactory" class="com.myspring.factory.HelloDynamicFactory" />
    	<bean id="hello" factory-bean="helloFactory" factory-method="newInstance">
    		<constructor-arg index="0" value="李四" />
    	</bean>
    
    </beans>

测试代码：

测试结果：

![Center 4][]

[Center]: /images/20220611/5d3aded76f0e44fca8e8e2a7767c7bb4.png
[Center 1]: /images/20220611/859b83559d25493ca5e314db35b78963.png
[Center 2]: /images/20220611/f435a6910f4e40bb878c409f411f87ac.png
[Center 3]: /images/20220611/88b50c4975de4e5f812bdf1e35ddcd8f.png
[Center 4]: /images/20220611/3082f8b25f194d7999df0b9d1718371f.png