DL
- 依賴注入:Dependency Injection。它是 spring 框架核心 ioc 的具體實現。
- 爲什麼需要DL?
我們的程序在編寫時,通過控制反轉,把對象的創建交給了 spring,但是代碼中不可能出現沒有依賴的情況。
ioc 解耦只是降低他們的依賴關係,但不會消除。例如:我們的業務層仍會調用持久層的方法。
那這種業務層和持久層的依賴關係,在使用 spring 之後,就讓 spring 來維護了。
簡單的說,就是坐等框架把持久層對象傳入業務層,而不用我們自己去獲取。
基於XML
構造函數注入:必須爲所有成員變量輔助
實現類:只使用構造函數
public class AccountServiceImpl implements IAccountService {
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;
}
@Override
public void saveAccount() {
System.out.println(name+","+age+","+birthday);
}
}
XML
<!-- 構造函數注入 -->
<bean id="UserService" class="com.itheima.service.impl.UserServiceImpl2">
<constructor-arg name="username" value="張三"></constructor-arg>
<constructor-arg name="id" value="1"></constructor-arg>
<constructor-arg name="birthday" ref="Date"></constructor-arg>
</bean>
set 方法注入:不需要爲所有成員變量賦值
實現類:只是用setter方法
public class UserServiceImpl3 implements UserService {
private int id;
private String username;
private Date birthday;
public void setId(int id) {
this.id = id;
}
public void setUsername(String username) {
this.username = username;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public void saveUser() {
System.out.println( "id:" + id +" " +
"username:"+ username +" "+
"birthday:" + birthday);
}
}
XML
<bean id="UserService" class="com.itheima.service.impl.UserServiceImpl3">
<property name="username" value="李四"></property>
</bean>
注入List 集合
實例化對象
public class UserServiceImpl4 implements UserService {
private List<String> list;
private Map<String,String> map;
public void setList(List<String> list) {
this.list = list;
}
public void setMap(Map<String, String> map) {
this.map = map;
}
public void saveUser() {
}
}
XML
<bean id="UserService" class="com.itheima.service.impl.UserServiceImpl4">
<property name="list">
<list>
<value>AAA</value>
<value>BBB</value>
<value>CCC</value>
</list>
</property>
<property name="map">
<map>
<entry key="1" value="AAA"></entry>
<entry key="2" value="BBB"></entry>
<entry key="3" value="CCC"></entry>
</map>
</property>
</bean>