DI(依赖注入)
概念
依赖注入（Dependency Injection,DI）。
依赖 : 指Bean对象的创建依赖于容器 . Bean对象的依赖资源 .
注入 : 指Bean对象所依赖的资源 , 由容器来设置和装配 .
构造器注入
创建对象时已经讲过，这里列举最常用的一种方式。
<!-- 第二种根据参数名字设置 -->
<bean id="userT" class="com.kuang.pojo.UserT">
<!-- name指参数名 -->
<constructor-arg name="name" value="kuangshen2"/>
</bean>set注入（重点）
环境搭建
1.复杂类型 Address
public class Address {
private String address;
public Address(String address) {
this.address = address;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@Override
public String toString() {
return "Address{" +
"address='" + address + '\'' +
'}';
}
}2.真实测试对象 Student
public class Student {
private String name;
private Address address;
private String[] books;
private List<String> hobbies;
private Map<String,String> card;
private Set<String> games;
private String wife;
private Properties info;
//get set toString方法
}3.beans.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="student" class="com.allen.pojo.Student">
<!-- 第一种，普通值注入，value-->
<property name="name" value="allen"/>
</bean>
</beans>4.测试
@Test
public void test(){
ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
Student student = (Student) context.getBean("student");
System.out.println(student.getName());
}全部注入
<?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="address" class="com.allen.pojo.Address">
<!-- 构造器注入-->
<constructor-arg name="address" value="CHINA"/>
<!-- 对同一属性赋值时，property 优先级高于 constructor-arg-->
<property name="address" value="china"/>
</bean>
<bean id="student" class="com.allen.pojo.Student">
<!-- 普通值注入，value-->
<property name="name" value="allen"/>
<!-- bean注入，ref-->
<property name="address" ref="address"/>
<!-- Array -->
<property name="books">
<array>
<value>西游记</value>
<value>红楼梦</value>
<value>水浒传</value>
</array>
</property>
<!-- List-->
<property name="hobbies">
<list>
<value>听歌</value>
<value>看电影</value>
<value>游戏</value>
</list>
</property>
<!-- Map-->
<property name="card">
<map>
<entry key="身份证" value="111111222222223333"/>
<entry key="校园卡" value="0000000000"/>
</map>
</property>
<!-- Set-->
<property name="games">
<set>
<value>LOL</value>
<value>COC</value>
</set>
</property>
<!-- null-->
<property name="wife">
<null/>
</property>
<!-- properties-->
<property name="info">
<props>
<prop key="学号">20211126</prop>
<prop key="性别">男</prop>
<prop key="username">111111</prop>
<prop key="pwd">222222</prop>
</props>
</property>
</bean>
</beans>输出结果
Student{name='allen', address=Address{address='china'}, books=[西游记, 红楼梦, 水浒传], hobbies=[听歌, 看电影, 游戏], card={身份证=111111222222223333, 校园卡=0000000000}, games=[LOL, COC], wife='null', info={学号=20211126, pwd=222222, username=111111, 性别=男}}其中，address值为小写的 china， 说明对同一属性赋值时，property 优先级高于 constructor-arg.
扩展方式
环境搭建
新建实体类 User
public class User {
private String name;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "User{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}新建 userBeans.xml.
p命名空间依赖注入(properties)
编写 userBeans.xml，注意导入
xmlns:p="http://www.springframework.org/schema/p"然后使用 p:age 和 p:name 进行赋值。
<?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.xsd">
<bean name="user" class="com.allen.pojo.User" p:age="18" p:name="allen"/>
</beans>测试
@Test
public void test2(){
ApplicationContext context = new ClassPathXmlApplicationContext("userBeans.xml");
User user = (User) context.getBean("user");
System.out.println(user.toString());
}输出
User{name='allen', age=18}c命名空间依赖注入(constructor-arg)
编写 userBeans.xml，注意导入
xmlxmlns:c="http://www.springframework.org/schema/c"然后使用 c:age 和 c:name 进行赋值。
注意：此时需要对 User 类加入有参和无参构造器。有参构造器为了c依赖注入，无参构造器为了p依赖注入。默认是无参构造，但加上有参构造将会覆盖无参构造，因此需要重载无参构造。
User 类
public class User {
private String name;
private int age;
//无参
public User() {
}
//有参
public User(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "User{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}userBeans.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"
xmlns:p="http://www.springframework.org/schema/p"
xmlns:c="http://www.springframework.org/schema/c"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<!-- <bean name="user" class="com.allen.pojo.User" p:age="18" p:name="allen"/>-->
<bean name="user2" class="com.allen.pojo.User" c:age="20" c:name="china"/>
</beans>测试
@Test
public void test3(){
ApplicationContext context = new ClassPathXmlApplicationContext("userBeans.xml");
User user = (User) context.getBean("user2");
System.out.println(user.toString());
}输出
User{name='china', age=20}注意点：p 命名空间和 c 命名空间不能直接使用，需要导入 xml 约束。
xmlns:p="http://www.springframework.org/schema/p"
xmlns:c="http://www.springframework.org/schema/c"
