注入分类
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。根据注入方式的不同，常用的有两类：设值注入、构造注入。
设值注入
设值注入是指，通过setter方法传入被调用者的实例。这种注入方式简单、直观，因而在Spring的依赖注入中大量使用。
代码：
// 定义学生类
public class Student {
private int age;
private String name;
private School school; // 对象属性，域属性
public void setName(String name) {
System.out.println("执行setName");
this.name = name;
}
public void setAge(int age) {
System.out.println("执行setAge");
this.age = age;
}
public void setSchool(School school) {
this.school = school;
}
@Override
public String toString() {
return "Student [age=" + age + ", name=" + name + ", school=" + school + "]";
}
}
// 定义学校类
public class School {
private String name;
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "School [name=" + name + "]";
}
}
// 注册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 definitions here -->
<!-- 注册student -->
<bean id="myStudent" class="love.minmin.di01.Student">
<property name = "name" value="minmin"></property>
<property name = "age" value="18"></property>
<property name = "school" ref="mySchool"></property>
</bean>
<!-- 注册school -->
<bean id="mySchool" class="love.minmin.di01.School">
<property name = "name" value="NNU"></property>
</bean>
</beans>
// 测试
public class MyTest {
@Test
public void test01() {
String resource = "/love/minmin/di01/applicationContext.xml";
ApplicationContext ac = new ClassPathXmlApplicationContext(resource);
Student student = (Student) ac.getBean("myStudent");
System.out.println(student);
((ClassPathXmlApplicationContext) ac).close();
}
}
构造注入
构造注入是指，在构造调用者实例的同时，完成被调用者的实例化。即使用构造器设置依赖关系。
代码：
// 定义学生类
public class Student {
private int age;
private String name;
private School school; // 对象属性，域属性
public Student(int age, String name, School school) {
super();
this.age = age;
this.name = name;
this.school = school;
}
@Override
public String toString() {
return "Student [age=" + age + ", name=" + name + ", school=" + school + "]";
}
}
// 定义school类
public class School {
private String name;
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "School [name=" + name + "]";
}
}
// 定义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 definitions here -->
<!-- 注册student -->
<bean id="myStudent" class="love.minmin.di02.Student">
<constructor-arg name="name" value="minmin"></constructor-arg>
<constructor-arg name="age" value="18"></constructor-arg>
<constructor-arg name="school" ref="mySchool"></constructor-arg>
</bean>
<!-- 注册school -->
<bean id="mySchool" class="love.minmin.di02.School">
<property name = "name" value="NNU"></property>
</bean>
</beans>
注意在Student中可以不用定义无参构造器，因为构造注入底层直接调用了带参构造器，而且也不用setter方法。但在实际情况中这种方法很少用，因为一个类的成员变量会有很多个，这个时候带参构造器就很难写。