依赖注入
不同数据类型的注入方式
public class Student {
private String name;
private Address address;
private String[] stationeries;
private List<String> hobbies;
private Map<String, String> book;
private Set<String> games;
private String wife;
private Properties info;
...
<bean id="address" class="com.youzi.pojo.Address">
<property name="address" value="China"/>
</bean>
<bean id="student" class="com.youzi.pojo.Student">
<property name="name" value="张三"/>
<property name="address" ref="address"/>
<property name="stationeries">
<array>
<value>ruler</value>
<value>eraser</value>
<value>pencil</value>
</array>
</property>
<property name="wife">
<null/>
</property>
<property name="book">
<map>
<entry key="西游记" value="吴承恩"/>
<entry key="红楼梦" value="曹雪芹"/>
</map>
</property>
<property name="games">
<set>
<value>LOL</value>
<value>COD</value>
<value>CS</value>
</set>
</property>
<property name="hobbies">
<list>
<value>sing</value>
<value>dance</value>
<value>rap</value>
<value>basketball</value>
</list>
</property>
<property name="info">
<props>
<prop key="userName">zhangsan</prop>
<prop key="cardNo">12345678</prop>
</props>
</property>
</bean>
除了通过 setter 注入、构造器注入还可以通过类似的 p-namespace 和 c-namespace 进行注入，具体参看官方文档的例子，使用命名空间注入
Bean 作用域
| Scope | Description |
|---|---|
| singleton | (Default) Scopes a single bean definition to a single object instance for each Spring IoC container. |
| prototype | Scopes a single bean definition to any number of object instances. |
| request | Scopes a single bean definition to the lifecycle of a single HTTP request. That is, each HTTP request has its own instance of a bean created off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext. |
| session | Scopes a single bean definition to the lifecycle of an HTTP Session. Only valid in the context of a web-aware Spring ApplicationContext. |
| application | Scopes a single bean definition to the lifecycle of a ServletContext. Only valid in the context of a web-aware Spring ApplicationContext. |
| websocket | Scopes a single bean definition to the lifecycle of a WebSocket. Only valid in the context of a web-aware Spring ApplicationContext. |
Bean 的自动装配
- 自动装配是 Spring 满足 bean 依赖的一种方式
- Spring 会在上下文中自动寻找，并自动给 bean 装配属性
Spring 中有三种装配方式
- 再 xml 中显式地配置
- 再 Java 中显式地配置
- 隐式的自动装配 bean
xml 中显式的配置
public class People {
private String name;
private Animal cat;
private Animal Dog;
...
public class Cat implements Animal {
@Override
public void bark() {
System.out.println("miao~");
}
}
public class Dog implements Animal {
@Override
public void bark() {
System.out.println("wang~");
}
}
<bean id="cat" class="com.youzi.pojo.Cat"/>
<bean id="dog" class="com.youzi.pojo.Dog"/>
<bean id="people1" class="com.youzi.pojo.People">
<property name="name" value="zhangsan"/>
<property name="cat" ref="cat"/>
<property name="dog" ref="dog"/>
</bean>
隐式的自动装配 bean
- 通过名字自动装配，bean id 要和对应的 setter 方法名对应，且首字母小写，如
setAbc()对应的 bean id 就应该为abc
<bean id="cat" class="com.youzi.pojo.Cat"/>
<bean id="dog" class="com.youzi.pojo.Dog"/>
<bean id="people1" class="com.youzi.pojo.People" autowire="byName">
<property name="name" value="zhangsan"/>
</bean>
-
通过类型自动装配，需要参数为不同的类型才能使用，不然会报错
NoUniqueBeanDefinitionException也就是当前示例中的cat和dog不能再使用Animal声明，应改为private Cat cat;private Dog dog;
<bean id="cat" class="com.youzi.pojo.Cat"/>
<bean id="dog" class="com.youzi.pojo.Dog"/>
<bean id="people1" class="com.youzi.pojo.People" autowire="byType">
<property name="name" value="zhangsan"/>
</bean>
使用注解实现自动装配 Bean
修改配置支持注解的方式
<?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:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
https://www.springframework.org/schema/context/spring-context.xsd">
<context:annotation-config/>
<bean id="cat" class="com.youzi.pojo.Cat"/>
<bean id="dog" class="com.youzi.pojo.Dog"/>
<bean id="people1" class="com.youzi.pojo.People">
<property name="name" value="zhangsan"/>
</bean>
</beans>
代码中只需要加上 @Autowired 即可实现自动装配 bean
-
正确使用该方式的情况下可以不声明 setter 也能自动装配，与上面的 xml 不同
-
装配的方式为先按类型，再按名字
如果
cat声明为 Cat 类型，即cat和dog为不同类型的时候，那么 bean id 和属性不用同名（setter 可有可无所以也不用同名），类似于 xml 中的autowire="byType"如果
cat和dog为相同类型的时候，如代码中都声明为Animal类型，那么会通过名字去匹配，需要bean id 和属性名字相同，相当于 xml 中的autowire="byName"
public class People {
private String name;
@Autowired
private Animal cat;
@Autowired
private Animal dog;
...
如果存在多个 bean 想装配其中指定的某个的时候，可以使用 @Qualifier 注解实现
public class People {
private String name;
@Autowired
private Animal cat;
@Autowired
@Qualifier("dog2") //指定使用 dog2
private Animal dog;
...
<bean id="dog1" class="com.youzi.pojo.Dog" scope="prototype">
<property name="sound" value="wang~"/>
</bean>
<bean id="dog2" class="com.youzi.pojo.Dog" scope="prototype">
<property name="sound" value="wangwang~"/>
</bean>
也可以使用 @Resource 注解实现上述功能，功能和 @Autowired 相同，不过可以直接指定 bean id
import javax.annotation.Resource;
public class People {
private String name;
//@Autowired
@Resource
private Animal cat;
//@Autowired
//@Qualifier("dog2")
@Resource
private Animal dog;
...