spring ioc---基本的依赖注入的方式(DI)

DI即Dependency injection.

实现依赖注入有两种方式,一个是基于有参构造器的方式,一个是基于setter方法的方式.

另可使用p和c的命名空间的编写方式替代,在xml配置文件中.其namespace的链接地址分别为:

http://www.springframework.org/schema/p和http://www.springframework.org/schema/c

在配置文件中的beans标签内,添加格式为`xmlns:p=""`和xmlns:c=""`.

方式	说明	使用的标签
构造器的方式	必须有有参构造器	constructor-arg
setter的方式	必须有相关属性的setter方法	property

说明,依赖解析的过程,官方参考文档原文件(4.3.20版本)

The container performs bean dependency resolution as follows:

The ApplicationContext is created and initialized with configuration metadata that describes all
the beans. Configuration metadata can be specified via XML, Java code, or annotations
For each bean, its dependencies are expressed in the form of properties, constructor arguments, or
arguments to the static-factory method if you are using that instead of a normal constructor. These
dependencies are provided to the bean, when the bean is actually created.
Each property or constructor argument is an actual definition of the value to set, or a reference to
another bean in the container.
Each property or constructor argument which is a value is converted from its specified format to the
actual type of that property or constructor argument. By default Spring can convert a value supplied
in string format to all built-in types, such as int, long, String, boolean, etc.

依赖于String类的类对象

package siye;
public class Obj
{
	String str;
	public Obj()
	{
	}
	public Obj(String str)
	{// 有参构造器处理依赖
		this.str = str;
	}
	public void setStr(String str)
	{// setter方法处理依赖
		this.str = str;
	}
}

xml配置文件,文件名`config.xml`

<bean id="objOthers" class="java.lang.String">       
	<constructor-arg name="original" value="message" 
		type="java.lang.String" />                   
</bean>                                              
<!--DI的方式:有参构造器 -->                                  
<bean id="obj0" class="siye.Obj">                    
	<constructor-arg index="0" ref="objOthers" />    
</bean>                                              
<!--DI的方式:setter方法 -->                               
<bean id="obj1" class="siye.Obj">                    
	<property name="str">                            
		<ref bean="objOthers" />                     
	</property>                                      
</bean>

测试类

package siye;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class UnitTest
{
	public static void main(String[] args)
	{
		ClassPathXmlApplicationContext context =
				new ClassPathXmlApplicationContext("classpath:/siye/config.xml");
		Obj obj0 = context.getBean("obj0", Obj.class);
		System.out.println(obj0.str);
		Obj obj1 = context.getBean("obj1", Obj.class);
		System.out.println(obj1.str);
		context.close();
	}
}

spring ioc---基本的依赖注入的方式(DI)

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