Spring依赖注入的方式

Spring通过property(<property/>)和构造函数(<constructor-arg/>)对bean的依赖注入进行配置.

对String以及基本类型的注入:通过name/value的形式,如果是数字类型,boolean类型,value指定的值会被自动转换成期望的类型.

<constructor-arg/>与之类似,只是没有name指定参数名称,可以用index指定序号(从0开始).

<property name="XXX" value="YYY"/>

<constructor-arg index="0" value="1"/>

对对象类类型的注入:通过ref或者内部bean的形式.

<property name="refBean" ref="RefBean" />
<property name="target">
<bean class="com.example.Person"> <!-- this is the inner bean -->
<property name="name" value="Fiona Apple"/>
<property name="age" value="25"/>
</bean>
</property>

还可以用"P:"简写方式设置注入:注意必须放在<bean>内作为属性定义.

<bean name="TestBean" class="com.test.spring.di.cfg.TestBean" p:strVal="string value">

 <property name="refBean" ref="RefBean" /> == p:refBean-ref="RefBean">

对集合类型的注入:对应JAVA的List, Set, Map, and Properties.

<property name="listVal">
<list>
<value>a list element followed by a
reference</value>
<ref bean="RefBean" />
</list>
</property>

<property name="setVal">
<set>
<value>just some string</value>
<ref bean="RefBean" />
</set>
</property>

<property name="mapVal">
<map>
<entry key="an entry" value="just some string" />
<entry key="a ref" value-ref="RefBean" />
</map>
</property>

<property name="propVal">
<props>
<prop key="administrator">administrator@example.org</prop>
<prop key="support">support@example.org</prop>
<prop key="development">development@example.org</prop>
</props>
</property>

设置空字符串和null值:

<property name="email" value=""/> equals to XXX.setEmail("");

<property name="email"><null/></property> equals to XXX.setEmail(null);

一个完整的例子:

package com.test.spring.di.cfg;

import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;

public class TestBean {
private String strVal;
private int intVal;
private RefBean refBean;
private List listVal;
private Set setVal;
private Map mapVal;
private Properties propVal;

public TestBean(List listVal) {
this.listVal = listVal;
}
public TestBean(String strVal) {
this.strVal = strVal;
}

public String getStrVal() {
return strVal;
}
public void setStrVal(String strVal) {
this.strVal = strVal;
}

public int getIntVal() {
return intVal;
}
public void setIntVal(int intVal) {
this.intVal = intVal;
}
public RefBean getRefBean() {
return refBean;
}
public void setRefBean(RefBean refBean) {
this.refBean = refBean;
}
public List getListVal() {
return listVal;
}
public void setListVal(List listVal) {
this.listVal = listVal;
}
public Set getSetVal() {
return setVal;
}
public void setSetVal(Set setVal) {
this.setVal = setVal;
}
public Map getMapVal() {
return mapVal;
}
public void setMapVal(Map mapVal) {
this.mapVal = mapVal;
}
public Properties getPropVal() {
return propVal;
}
public void setPropVal(Properties propVal) {
this.propVal = propVal;
}
}

public class RefBean {
public String testFunc(){
return "Test Function";
}
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> 
<bean id="RefBean" class="com.test.spring.di.cfg.RefBean" />

<bean name="TestBean" class="com.test.spring.di.cfg.TestBean"p:strVal="string value">
<constructor-arg index="0">
<list>
<value>a list element followed by a reference</value>
<ref bean="RefBean" />
</list>
</constructor-arg>

<property name="intVal" value="100" />
<property name="refBean" ref="RefBean" />
<property name="setVal">
<set>
<value>just some string</value>
<ref bean="RefBean" />
</set>
</property>

<property name="mapVal">
<map>
<entry key="an entry" value="just some string" />
<entry key="a ref" value-ref="RefBean" />
</map>
</property>

<property name="propVal">
<props>
<prop key="administrator">administrator@example.org
</prop>
<prop key="support">support@example.org</prop>
<prop key="development">development@example.org</prop>
</props>
</property>
</bean>

</beans>

Spring支持自动注入(autowiring),减少XML配置.

通过指定<beans>的default-autowire="xxx">其适用范围为该配置文件内的所有bean,注意不是整个context.

也可以对单个bean设定:<bean .... autowire="byName" />,如果是byName方式,property的名称和需要reference的bean的ID必须相同,

并且该property必须要有set方法.

使用@Autowired注解的默认是byType,注意一般来将整个context中必须有一个也只能有一个符合这种type的bean,如果context中有多个符合该类型的bean,Spring会看有没有bean的名称和该属性的名称相同,如果能匹配上,则用这个有着相同名称的bean赋值给该属性,否则抛异常.@Autowired注解的成员变量不需要set方法.

@Autowired注解还可以用在方法上,根据方法里面的参数进行匹配.常用的做法是在beans设定default-autowire="byName",把一些常要用的bean按默认名配置,如<bean id="dataSource",<bean id="transactionManager"等.对不经常变化的配置通过注解配置,@Component,@Transactional配合<context:component-scan base-package="com.test.spring.tx.annotation"
/>和<tx:annotation-driven/>来简化XML配置.

被依赖的bean将在依赖bean之前被适当的初始化。