依赖注入
6. 依赖注入
6.1 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 .
6.2 构造器注入
我们在之前的案例已经讲过了(有参构造)
6.3 Set 注入 (重点)
要求被注入的属性 , 必须有set方法 , set方法的方法名由set + 属性首字母大写 , 如果属性是boolean类型 , 没有set方法 , 是 is Xxx
测试pojo类 :
Address.java
public class Address {
private String address;
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
}
Student.java
定义多个不同类型的属性 来实现不同的注入方式
package com.kuang.pojo;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
public class Student {
private String name;
private Address address;
private String[] books;
private List<String> hobbys;
private Map<String,String> card;
private Set<String> games;
private String wife;
private Properties info;
public void setName(String name) {
this.name = name;
}
public void setAddress(Address address) {
this.address = address;
}
public void setBooks(String[] books) {
this.books = books;
}
public void setHobbys(List<String> hobbys) {
this.hobbys = hobbys;
}
public void setCard(Map<String, String> card) {
this.card = card;
}
public void setGames(Set<String> games) {
this.games = games;
}
public void setWife(String wife) {
this.wife = wife;
}
public void setInfo(Properties info) {
this.info = info;
}
public void show(){
System.out.println("name="+ name
+ ",address="+ address.getAddress()
+ ",books="
);
for (String book:books){
System.out.print("<<"+book+">>\t");
}
System.out.println("\n爱好:"+hobbys);
System.out.println("card:"+card);
System.out.println("games:"+games);
System.out.println("wife:"+wife);
System.out.println("info:"+info);
}
}
1、常量注入
<bean id="student" class="com.yhn.domain.Student">
<property name="name" value="yhn"></property>
</bean>
测试:
@Test
public void test01(){
ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
Student student = (Student) context.getBean("student");
System.out.println(student.getName());
}
2、Bean注入
注意点:这里的值是一个引用,ref
<bean id="ads" class="com.yhn.domain.Address">
<property name="address" value="西宁"></property>
</bean>
<bean id="student" class="com.yhn.domain.Student">
<property name="name" value="yhn"></property>
<!--引用值-->
<property name="address" ref="ads"></property>
</bean>
3、数组注入
<!--数组-->
<property name="books">
<array>
<value>人性的弱点</value>
<value>小王子</value>
<value>傲慢与偏见</value>
</array>
</property>
4、List注入
<!--List-->
<property name="hobbys">
<list>
<value>篮球</value>
<value>足球</value>
<value>网球</value>
</list>
</property>
5、Map注入
<!--Map-->
<property name="card">
<map>
<entry key="身份证" value="123456"></entry>
<entry key="校园卡" value="666666"></entry>
</map>
</property>
6、set注入
<!--Set-->
<property name="games">
<set>
<value>CF</value>
<value>LOL</value>
<value>DNF</value>
</set>
</property>
7、Null注入
<!--null-->
<property name="wife">
<null/>
</property>
8、Properties注入
<!--properties-->
<property name="info">
<props>
<prop key="学号">20200707</prop>
<prop key="性别">男</prop>
</props>
</property>
测试结果:
Student(
* name=yhn,
* address=Address{address='西宁'},
* books=[人性的弱点, 小王子, 傲慢与偏见],
* hobbys=[篮球, 足球, 网球],
* card={身份证=123456, 校园卡=666666},
* games=[CF, LOL, DNF], wife=null,
* info={
* 学号=20200707,
* 性别=男
* }
* )
6.4 p命名和c命名注入
User.java :【注意:这里没有有参构造器!】
public class User {
private String name;
private int age;
public void setName(String name) {
this.name = name;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "User{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}
1、P命名空间注入 : 需要在头文件中加入约束文件
导入约束 : xmlns:p="http://www.springframework.org/schema/p"
<!--P(属性: properties)命名空间 , 属性依然要设置set方法-->
<bean id="user" class="com.kuang.pojo.User" p:name="狂神" p:age="18"/>
2、c 命名空间注入 : 需要在头文件中加入约束文件
导入约束 : xmlns:c="http://www.springframework.org/schema/c"
<!--C(构造: Constructor)命名空间 , 属性依然要设置set方法-->
<bean id="user" class="com.kuang.pojo.User" c:name="狂神" c:age="18"/>
发现问题:爆红了,刚才我们没有写有参构造!
解决:把有参构造器加上,这里也能知道,c 就是所谓的构造器注入!
测试代码:
@Test
public void test(){
ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
User user = (User) context.getBean("user");
System.out.println(user);
}