在Spring配置文件中,不但可以将String、int等字面值注入bean中,还可以将集合、map等类型的数据注入Bean中, 此外还可以注入配置文件中其他定义的Bean.
所谓字面值一般指的是可以用字符串表示的值,这些值可以通过元素标签进行注入。
在默认情况下,基本数据类型及其封装类、String等类型都可以采用字面值注入的方式。
比如前几篇博文中经常使用的案例:
<bean id="plane" class="com.xgj.ioc.inject.set.Plane">
<property name="brand">
<value>value>
property>
<property name="color">
<value>redvalue>
property>
<property name="speed">
<value>700value>
property>
bean>
XML共有5个特殊符号 & < > " '
特殊符号 | 转移序列 |
---|---|
< | < |
> | > |
& | & |
“ | " |
‘ | ' |
一般情况下,xml解析器会忽略元素标签内部字符串的前后空格,但是Spring不会忽略空格。
举个例子:
<property name="brand">
<value> Airbus&A380 value>
property>
运行结果如下:
Spring IoC容器中定义的Bean可以相互引用,IoC容器充当“红娘”的角色。
警察类中有枪类型的属性
POJO类
package com.xgj.ioc.inject.construct.ref;
public class Police {
private Gun gun;
public void setGun(Gun gun) {
this.gun = gun;
}
public void userGun() {
gun.fire();
}
}
POJO类
package com.xgj.ioc.inject.construct.ref;
public class Gun {
public void fire() {
System.out.println("Gun Fires");
}
}
配置文件
<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="police" class="com.xgj.ioc.inject.construct.ref.Police">
<property name="gun">
<ref bean="gun" />
property>
bean>
<bean id="gun" class="com.xgj.ioc.inject.construct.ref.Gun" />
beans>
测试类
package com.xgj.ioc.inject.construct.ref;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class RefTest {
public static void main(String[] args) {
ApplicationContext ctx = new ClassPathXmlApplicationContext("classpath:com/xgj/ioc/inject/construct/ref/police-gun.xml");
Police police = ctx.getBean("police", Police.class);
police.userGun();
}
}
运行结果
演示子容器对父容器Bean的引用。 其中 beans_father.xml被父容器加载,beans_son.xml被子容器加载。
POJO类
package com.xgj.ioc.inject.construct.refParentBean;
public class Gun {
private String brand;
private int bulletNum;
private double price;
public void setBrand(String brand) {
this.brand = brand;
}
public void setBulletNum(int bulletNum) {
this.bulletNum = bulletNum;
}
public void setPrice(double price) {
this.price = price;
}
public void gunInfo() {
System.out.println("Gun Information brand:" + brand + ",bulletNum:"
+ bulletNum + ",price:" + price);
}
}
POJO类
package com.xgj.ioc.inject.construct.refParentBean;
public class Police {
private Gun gun;
public void setGun(Gun gun) {
this.gun = gun;
}
public void introduceGun() {
gun.gunInfo();
}
}
beans_father.xml
<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="gun" class="com.xgj.ioc.inject.construct.refParentBean.Gun">
<property name="brand" value="父容器--伯莱塔92F" />
<property name="bulletNum" value="11" />
<property name="price" value="2888" />
bean>
beans>
beans_son.xml
<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="gun" class="com.xgj.ioc.inject.construct.refParentBean.Gun">
<property name="brand" value="柯尔特M2000" />
<property name="bulletNum" value="7" />
<property name="price" value="999" />
bean>
<bean id="police" class="com.xgj.ioc.inject.construct.refParentBean.Police">
<property name="gun">
<ref parent="gun"/>
property>
bean>
beans>
测试类
package com.xgj.ioc.inject.construct.refParentBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class RefParentBeanTest {
public static void main(String[] args) {
// 父容器
ApplicationContext pFather = new ClassPathXmlApplicationContext(
"classpath:com/xgj/ioc/inject/construct/refParentBean/beans_father.xml");
// 指定pFather为该容器的父容器
ApplicationContext ctx = new ClassPathXmlApplicationContext(
new String[] { "com/xgj/ioc/inject/construct/refParentBean/beans_son.xml" },
pFather);
Police police = ctx.getBean("police", Police.class);
// 观察是否输出为父容器设置的属性
police.introduceGun();
}
}
运行结果
如果某个bean只会被其中一个引用,而不会被容器中的其它Bean引用,可以以内部Bean的方式注入。
内部bean和Java匿名内部类相似,既没有名字,也不会被前台bean引用,只能在声明处为外部Bean提供实例注入。
内部Bean即使提供了id、name、scope等属性,也会被忽略,scope默认prototype类型
举例:
其他类同上,区别仅在于beans的配置文件。
<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="police" class="com.xgj.ioc.inject.construct.innerBean.Police">
<property name="gun">
<bean class="com.xgj.ioc.inject.construct.innerBean.Gun">
<property name="brand" value="柯尔特M2000"/>
<property name="bulletNum" value="7"/>
<property name="price" value="788"/>
bean>
property>
bean>
beans>
运行结果
如果希望往一个属性中注入一个null值? 使用专用的元素标签
POJO类
package com.xgj.ioc.inject.construct.nullValue;
public class Pilot {
private Plane plane;
public void setPlane(Plane plane) {
this.plane = plane;
}
public void drivePlane() {
System.out.println("Pilot is driving plane....");
plane.info();
}
}
POJO类
package com.xgj.ioc.inject.construct.nullValue;
public class Plane {
private String brand;
public void setBrand(String brand) {
this.brand = brand;
}
public void info() {
System.out.println("Plane brand:" + brand);
}
}
配置文件
<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="plane" class="com.xgj.ioc.inject.construct.nullValue.Plane">
<property name="brand" value="null" />
bean>
<bean id="pilot" class="com.xgj.ioc.inject.construct.nullValue.Pilot">
<property name="plane">
<ref bean="plane" />
property>
bean>
beans>
测试类
package com.xgj.ioc.inject.construct.nullValue;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class NullValueTest {
public static void main(String[] args) {
// TODO Auto-generated method stub
ApplicationContext ctx = new ClassPathXmlApplicationContext(
"classpath:com/xgj/ioc/inject/construct/nullValue/beans.xml");
Pilot pilot = ctx.getBean("pilot", Pilot.class);
pilot.drivePlane();
}
}
运行结果:
Spring支持级联属性的配置,假设我们希望在定义Pilot时,直接为Plane的属性提供注入值,可以采取如下方式:
<bean id="pilot" class="com.xgj.ioc.inject.construct.cascadeProperty.Pilot">
<property name="plane.brand" value="A380"/>
bean>
上述配置的含义:Spring将调用Pilot.getPlane().setBrand(“A380”)方法进行属性的注入操作。
此时,必须对Pilot的类进行改造,为Plane属性声明一个初始化对象。
实例:
POJO类
package com.xgj.ioc.inject.construct.cascadeProperty;
public class Pilot {
// 声明初始化对象
private Plane plane = new Plane();
// 获取实例
public Plane getPlane() {
return plane;
}
public void setPlane(Plane plane) {
this.plane = plane;
}
public void introduce() {
plane.info();
}
}
POJO类
package com.xgj.ioc.inject.construct.cascadeProperty;
public class Plane {
private String brand;
public void setBrand(String brand) {
this.brand = brand;
}
public void info() {
System.out.println("【Plane brand:】" + brand);
}
}
配置文件
<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="pilot" class="com.xgj.ioc.inject.construct.cascadeProperty.Pilot">
<property name="plane.brand" value="A380"/>
bean>
beans>
测试类
package com.xgj.ioc.inject.construct.cascadeProperty;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class CascadePropertyTest {
public static void main(String[] args) {
ApplicationContext ctx = new ClassPathXmlApplicationContext(
"classpath:com/xgj/ioc/inject/construct/cascadeProperty/beans.xml");
Pilot pilot = ctx.getBean("pilot", Pilot.class);
pilot.introduce();
}
}
运行结果
如果没有未Plane属性提供Plan对象,Spring在设置级联属性时将抛出NullValueInNestedPathException异常。
我们在Plane类中 ,不对Plane进行new实例化操作,仅仅声明,再次运行NullValueInNestedPathException异常。
Caused by: org.springframework.beans.NullValueInNestedPathException: Invalid property 'plane' of bean class [com.xgj.ioc.inject.construct.cascadeProperty.Pilot]: Value of nested property 'plane' is null
Spring对级联属性的层级没有限制。