Dependency Injection (Dependency Injection): In the process of creating this object in Spring, inject the properties that this object depends on. (The management of dependencies will be handed over to spring for maintenance in the future. Objects of other classes need to be used in the current class, which are provided by spring for us. We only need to explain them in the configuration file. The maintenance of dependencies is called dependency injection )
Data that can be injected by dependency injection:
- Primitive types and String
- Other bean types (beans configured in configuration files or annotations)
- complex type/collection type
Injection method:
- Provided using the constructor
- Use the set method to provide
- Use annotations to provide
Constructor:
<!--构造函数注入：使用的标签:constructor-arg
标签出现的位置：bean标签的内部
标签中的属性：
type：用于指定要注入的数据的数据类型，该数据类型也是构造函数中某个或某些参数的类型
index：用于指定要注入的数据给构造函数中指定索引位置的参数赋值。索引的位置是从0开始
name：用于指定给构造函数中指定名称的参数赋值
以上三个用于指定给构造函数中哪个参数赋值
value：用于提供基本类型和String类型的数据
ref：用于指定其他的bean类型数据。它指的就是在spring的Ioc核心容器中出现过的bean对象
优势：在获取bean对象时，注入数据是必须的操作，否则对象无法创建成功。
弊端：改变了bean对象的实例化方式，使我们在创建对象时，如果用不到这些数据，也必须提供。-->
<bean id="accountService" class="com.itheima.service.impl.AccountServiceImpl">
<constructor-arg name="name" value="泰斯特"></constructor-arg>
<constructor-arg name="age" value="18"></constructor-arg>
<constructor-arg name="birthday" ref="now"></constructor-arg>
</bean>
<!-- 配置一个日期对象 -->
<bean id="now" class="java.util.Date"></bean>public interface AccountService {
void saveAccount();
}
public class AccountServiceImpl implements AccountService {
private String name;
private Integer age;
private Date birthday;
public AccountServiceImpl(String name, Integer age, Date birthday) {
this.name = name;
this.age = age;
this.birthday = birthday;
}
public void saveAccount() {
System.out.println("service中的saveAccount方法执行了。。。"+name+","+age+","+birthday);
}
}
public class Client {
public static void main(String[] args) {
ApplicationContext ac = new ClassPathXmlApplicationContext("bean.xml");
AccountService as = (AccountService) ac.getBean("accountService");
as.saveAccount();
}
}Use the set method to provide:
<bean id="now" class="java.util.Date"></bean>
<!-- set方法注入
涉及的标签：property
出现的位置：bean标签的内部
标签的属性
name：用于指定注入时所调用的set方法名称
value：用于提供基本类型和String类型的数据
ref：用于指定其他的bean类型数据。它指的就是在spring的Ioc核心容器中出现过的bean对象
优势：
创建对象时没有明确的限制，可以直接使用默认构造函数
弊端：
如果有某个成员必须有值，则获取对象是有可能set方法没有执行。
-->
<bean id="accountService2" class="com.it.service.impl.AccountServiceImpl2">
<property name="name" value="Test"></property>
<property name="age" value="21"></property>
<property name="birthday" ref="now"></property>
</bean>public interface AccountService {
void saveAccount();
}
public class AccountServiceImpl implements AccountService {
private String name;
private Integer age;
private Date birthday;
public void setName(String name) {
this.name = name;
}
public void setAge(Integer age) {
this.age = age;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public void saveAccount() {
System.out.println("service中的saveAccount方法执行了。。。"+name+","+age+","+birthday);
}
}
public class Client {
public static void main(String[] args) {
ApplicationContext ac = new ClassPathXmlApplicationContext("bean.xml");
AccountService as = (AccountService) ac.getBean("accountService");
as.saveAccount();
}
}<!-- 复杂类型的注入/集合类型的注入
用于给List结构集合注入的标签：list array set
用于个Map结构集合注入的标签:map props
结构相同，标签可以互换
-->
<bean id="accountService3" class="com.it.service.impl.AccountServiceImpl3">
<property name="myStrs">
<set>
<value>AAA</value>
</set>
</property>
<property name="mySet">
<set>
<value>HELLO</value>
<value>WORLD</value>
</set>
</property>
<property name="myList">
<array>
<value>AAA</value>
<value>BBB</value>
<value>CCC</value>
</array>
</property>
<property name="myMap">
<props>
<prop key="testC"></prop>
<prop key="testD"></prop>
</props>
</property>
<property name="myProps">
<map>
<entry key="testA" value="aaa"></entry>
<entry key="testB">
<value>BBB</value>
</entry>
</map>
</property>
</bean>public interface AccountService {
void saveAccount();
}
public class AccountServiceImpl3 implements AccountService {
private String[] myStrs;
private List<String> myList;
private Set<String> mySet;
private Map<String,String> myMap;
private Properties myProps;
public void setMyStrs(String[] myStrs) {
this.myStrs = myStrs;
}
public void setMyList(List<String> myList) {
this.myList = myList;
}
public void setMySet(Set<String> mySet) {
this.mySet = mySet;
}
public void setMyMap(Map<String, String> myMap) {
this.myMap = myMap;
}
public void setMyProps(Properties myProps) {
this.myProps = myProps;
}
public void saveAccount() {
System.out.println(Arrays.toString(myStrs));
System.out.println(myList);
System.out.println(mySet);
System.out.println(myMap);
System.out.println(myProps);
}
}
public class Client {
public static void main(String[] args) {
ApplicationContext ac = new ClassPathXmlApplicationContext("bean.xml");
AccountService as = (AccountService) ac.getBean("accountService3");
as.saveAccount();
}
}