Spring Framework Bean 实例化

Spring Framework：4.3.14.RELEASE

本文主要是论述 Spring Framework IOC 容器中 Bean 的实例化。

Bean 的实例化主要是两种方式：

• 通过构造函数实例化
• 通过静态方法实例化

通过构造函数实例化

通过构造函数实例化，前提条件是 Bean 含有一个无参构造器，可以是隐式无参构造器，也可以是显式无参构造器。

public class ExampleBeanOne {

	private String name;

	public void setName(String name) {
		this.name = name;
	}

	public String hello() {
		return "Hello " + name;
	}

}

public class ExampleBeanTwo {

	private String name;
	
	public ExampleBeanTwo() {
	}
	
	public ExampleBeanTwo(String name) {
		this.name = name;
	}
	
	public String hello() {
		return "Hello " + name;
	}

}

<bean id="exampleBeanOne" class="com.example.spring.ExampleBeanOne">
    <property name="name" value="ExampleBeanOne"></property>
</bean>

<bean id="exampleBeanTwo" class="com.example.spring.ExampleBeanTwo">
    <constructor-arg value="ExampleBeanTwo"></constructor-arg>
</bean>

通过静态方法实例化

通过静态方法实例化，前提条件是有一个静态方法可以实例化 Bean，可以是自身提供的静态方法，也可以是其他类提供的静态方法。

public class ExampleBeanThree {

	private static ExampleBeanThree exampleBeanThree = new ExampleBeanThree("ExampleBeanThree");
	
	private String name;
	
	public static ExampleBeanThree createInstance() {
		return exampleBeanThree;
	}
	
	private ExampleBeanThree(String name) {
		this.name = name;
	}
	
	public String hello() {
		return "Hello " + name;
	}

}

public class ExampleBeanFive {
	private String name;
	
	public ExampleBeanFive() {
	}
	
	public ExampleBeanFive(String name) {
		this.name = name;
	}
	
	public String hello() {
		return "Hello " + name;
	}
}

public class ExampleBeanSix {
	
	private static ExampleBeanFive exampleBeanFive = new ExampleBeanFive("ExampleBeanFive");
	
	public ExampleBeanFive createClientInstance() {
		return exampleBeanFive;
	}
	
}

<bean id="exampleBeanThree" class="com.example.spring.ExampleBeanThree" factory-method="createInstance">
</bean>

<bean id="exampleBeanSix" class="com.example.spring.ExampleBeanSix">
</bean>

<bean id="exampleBeanFive" factory-bean="exampleBeanSix" factory-method="createClientInstance">
</bean>

通过静态方法实例化不常见，推荐使用构造函数实例化

代码请参考example-03:
lxmuse-spring-example-03

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