Spring学习（四） 注入依赖对象

依赖注入（Dependency Injection）
所谓的依赖注入就是指：在运行期间，由外部容器动态地将依赖对象注入到组件中。
一、注入方式
1、通过构造方法注入

package com.bill.impl;
import com.bill.PersonService;
import com.bill.dao.PersonDao;
/**
 * @author Bill
 */
public class PersonServiceBean implements PersonService {
	private PersonDao personDao;
	private String name;
	
	public PersonServiceBean(PersonDao personDao, String name) {
		this.personDao = personDao;
		this.name = name;
	}
	public void save(){
		personDao.add();
		System.out.println(name);
	}	
}

	<bean id="personDao" class=" com.bill.dao.impl.PersonDaoBean"/>
	<bean id="personService" class="com.bill.impl.PersonServiceBean">
		<constructor-arg index="0" type="com.bill.dao.PersonDao" ref="personDao"></constructor-arg>
		<constructor-arg index="1" value="good"></constructor-arg>
	</bean>

测试代码：

		AbstractApplicationContext act = new ClassPathXmlApplicationContext("beans.xml");
		PersonService personService = (PersonService)act.getBean("personService");
		personService.save();
	    act.close();

2、通过属性setter方法注入
如二.1

3、使用注解方式注入
在java代码中使用@Autowired或者@Resource注解方式进行装配。这两个注解的区别是：@Autowired默认按类型装配，@Resource默认按名称装配，当找不到与名称匹配的bean才会按类型装配。需配置xml文件如下：

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-2.5.xsd">
    <context:annotation-config/>
	<bean id="personDao" class=" com.bill.dao.impl.PersonDaoBean"></bean>
	<bean id="personService" class="com.bill.impl.PersonServiceBean"></bean>
</beans>

这种配置隐式注册了多个对注解解析处理的处理器AutowriedAnnotationBeanPostProcessor，CommonAnnotationBeanPostProcessor，PersistenceAnnotationBeanPostProcessor，RequiredAnnotationBeanPostProcessor

使用@Resource注解的业务代码如下：
1）标注在字段上的方式

package com.bill.impl;
import javax.annotation.Resource;

import com.bill.PersonService;
import com.bill.dao.PersonDao;
/**
 * @author Bill
 */
public class PersonServiceBean implements PersonService {
	@Resource private PersonDao personDao;
	//@Resource(name="personDao") private PersonDao personDao;//采用指定name属性的方式，寻找xml中指定的bean
	public void save(){
		personDao.add();
	}
}

2）标注在setter方法上的方式

package com.bill.impl;

import javax.annotation.Resource;
import com.bill.PersonService;
import com.bill.dao.PersonDao;
/**
 * @author Bill
 */
public class PersonServiceBean implements PersonService {
	private PersonDao personDao;

	@Resource
	public void setPersonDao(PersonDao personDao) {
		this.personDao = personDao;
	}


	public void save(){
		personDao.add();
	}
}

在@Resource中没有指定name属性时，Spring会根据该字段的名称personDao去xml中寻找匹配的bean，假如找不到，再去根据该字段的类型去寻找匹配的bean。

注意：@Resource注解在Spring安装目录的lib\j2ee\common-annotations.jar

使用@Autowired注解的业务代码如下：

package com.bill.impl;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;

import com.bill.PersonService;
import com.bill.dao.PersonDao;
/**
 * @author Bill
 */
public class PersonServiceBean implements PersonService {
	//默认按类型装配
	@Autowired private PersonDao personDao;
	//使用@Qualifier("personDao")将@Autowired装配方式改为按名称装配
	//@Autowired @Qualifier("personDao") private PersonDao personDao;
	public void save(){
		personDao.add();
	}
}

二、注入类型
1、基本类型以及集合类型对象注入

public class PersonServiceBean implements PersonService {
	private String name;
	private Integer id;
	private Set<String> sets = new HashSet<String>();
	private Map<String, String> maps = new HashMap<String, String>();
	private Properties properties = new Properties();
	
	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
	
	public Properties getProperties() {
		return properties;
	}

	public void setProperties(Properties properties) {
		this.properties = properties;
	}

	public Map<String, String> getMaps() {
		return maps;
	}

	public void setMaps(Map<String, String> maps) {
		this.maps = maps;
	}

	public Set<String> getSets() {
		return sets;
	}

	public void setSets(Set<String> sets) {
		this.sets = sets;
	}
}

	<bean id="personService" class="com.bill.impl.PersonServiceBean">
		<property name="name" value="bill"/>
		<property name="id" value="88"/>
		<property name="sets">
			<set>
				<value>set1</value>
				<value>set2</value>
				<value>set3</value>
			</set>
		</property>
		<property name="maps">
			<map>
				<entry key="key1" value="value1"></entry>
				<entry key="key2" value="value2"></entry>
				<entry key="key3" value="value3"></entry>
			</map>
		</property>
		
		<property name="properties">
			<props>
				<prop key="key-1">propValue1</prop>
				<prop key="key-2">propValue2</prop>
				<prop key="key-3">propValue3</prop>
			</props>
		</property>
	</bean>

测试代码：

		System.out.println("===========set============");
		for(String value : personService.getSets()){
			System.out.println(value);
		}
		System.out.println("===========map============");
		for(String key : personService.getMaps().keySet()){
			System.out.println(key + "=" + personService.getMaps().get(key));
		}
		System.out.println("===========properties========");
		for(Object propsKey : personService.getProperties().keySet()){
			System.out.println(propsKey + "=" + personService.getProperties().getProperty((String) propsKey));
		}

2、注入其他bean类型
1）方式一

	<bean id="personDao" class=" com.bill.dao.impl.PersonDaoBean"/>
	<bean id="personService" class="com.bill.impl.PersonServiceBean">
		<property name="personDao" ref="personDao"></property>
	</bean>

2）方式二（使用内部bean的方式进行注入，但该bean不能被其他bean使用）

	<bean id="personService" class="com.bill.impl.PersonServiceBean">
		<property name="personDao">
			<bean class=" com.bill.dao.impl.PersonDaoBean"/>
		</property>
	</bean>