Spring基于XML的DI之设值注入
什么是注入
Bean实例在调用无参构造器创建了空值对象后,就要对Bean对象的属性进行初始化。初始化是由容器自动完成的,称为注入
注入分类
根据注入方式的不同,常用的有两类:设置注入、构造注入;还有一种是实现特定接口注入,由于这种注入方式采用了入侵编程,污染了代码,所以几乎不用。
设值注入
设值注入是指,通过setter方法传入被调用者的实例。这种注入方法简单、直观,因而在Spring的依赖注入中大量使用。
栗子
Student.java
package com.hk.spring.di01;
public class Student {
private String name;
private int age;
private School school;//域属性
public void setName(String name) {
this.name = name;
}
public void setAge(int age) {
this.age = age;
}
public void setSchool(School school) {
this.school = school;
}
@Override
public String toString() {
return "Student [name=" + name + ", age=" + age + ", school=" + school
+ "]";
}
}
School.java
package com.hk.spring.di01;
public class School {
private String schloolName;
public void setSchloolName(String schloolName) {
this.schloolName = schloolName;
}
@Override
public String toString() {
return "School [schloolName=" + schloolName + "]";
}
}
applicationContext.xml
<?xml version="1.0" encoding="UTF-8"?>
<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="mySchool" class="com.hk.spring.di01.School">
<property name="schloolName" value="红林小学"/>
</bean>
<bean id="myStudent" class="com.hk.spring.di01.Student">
<!-- 设值注入,为对象初始化 ,底层调用了bean的set方法-->
<property name="name" value="张三"/>
<property name="age" value="9"/>
<!-- 为域属性赋值,引用赋值-->
<property name="school" ref="mySchool"/>
</bean>
</beans>
测试类
package com.hk.spring.di01;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Mytest {
@Test
public void test1(){
String resource = "com/hk/spring/di01/applicationContext.xml";
ApplicationContext ac = new ClassPathXmlApplicationContext(resource);
Student stu = (Student) ac.getBean("myStudent");
System.out.println(stu);
}
}
结果
Student [name=张三, age=9, school=School [schloolName=红林小学]]