第四講 依賴注入（Dependency Injection，簡稱DI）

一、依賴注入-Dependency Injection

     依賴：指bean對象的創建依賴於容器；bean對象的依賴資源。

     注入：指bean對象依賴的資源由容器來設置和裝配。

二、Spring的注入

1. 構造器注入

   見“第二講 IoC創建對象的三種方式”。

2. setter注入（重點）

   要求被注入的屬性必須有setter方法。setter方法的方法名由：set+屬性名首字母大寫。如果屬性是boolean類型，返回沒有getter方法是

   is。

          常量注入：

public class Student {

     

     private String name;

     

     public void setName(String name) {

           this.name = name;

     }

     

     public void show() {

           System.out.println("name=" + name);

     }

     

}

     <bean id="student" class="com.liujie.model.Student">

           <property name="name" value="張三"></property>

     </bean>

          bean注入（對象注入）：

     public void setAddress(Address address) {

           this.address = address;

     }

     <bean id="address" class="com.liujie.model.Address">

           <property name="address" value="北京"></property>

     </bean>

     

     <bean id="student" class="com.liujie.model.Student">

           <property name="name" value="張三"></property>

           <property name="address" ref="address"></property>

     </bean>

          數組注入：

     public void setBooks(String[] books) {

           this.books = books;

     }

     <bean id="student" class="com.liujie.model.Student">

           <property name="name" value="張三"></property>

           <property name="address" ref="address"></property>

           <property name="books">

                <array>

                     <value>語文</value>

                     <value>英語</value>

                     <value>數學</value>

                </array>

           </property>

     </bean>

          List注入：

     public void setHobbies(List<String> hobbies) {

           this.hobbies = hobbies;

     }

           <property name="hobbies">

                <list>

                     <value>羽毛球</value>

                     <value>乒乓球</value>

                     <value>玻璃球</value>

                </list>

           </property>

          Map注入：

     public void setCards(Map<String, String> cards) {

           this.cards = cards;

     }

           <property name="cards">

                <map>

                     <entry key="中國銀行" value="15602822222222222"></entry>

                     <entry>

                           <key><value>建設銀行</value></key>

                           <value>6789990209833833</value>

                     </entry>

                </map>

           </property>

          Set注入：

     public void setGames(Set<String> games) {

           this.games = games;

     }

           <property name="games">

                <set>

                     <value>lol</value>

                     <value>dota</value>

                     <value>cs</value>

                </set>

           </property>

          Null注入：

     public void setWife(String wife) {

           this.wife = wife;

     }

           <property name="wife">

                <null></null>

           </property>

          Properties注入：

     public void setInfo(Properties info) {

           this.info = info;

     }

           <property name="info">

                <props>

                     <prop key="學號">2015052601</prop>

                     <prop key="sex">男</prop>

                     <prop key="name">小明</prop>

                </props>

           </property>

          p命名空間注入：

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 + "]";

     }

     

}

<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">

     <!-- p命名空間注入，屬性依然要設置setter方法 -->

     <bean id="user" class="com.liujie.model.User" p:name="李白" p:age="230"></bean>

          c命名空間注入：

public class User {

     

     private String name;

     private int age;

     

     public User() {

           super();

     }

     public User(String name, int age) {

           super();

           this.name = name;

           this.age = age;

     }

     

     @Override

     public String toString() {

           return "User [name=" + name + ", age=" + age + "]";

     }

     

}

<beans xmlns="http://www.springframework.org/schema/beans"

     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

     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">

     <!-- c命名空間注入要求有對應參數的構造方法 -->

     <bean id="user" class="com.liujie.model.User" c:name="杜甫" c:age="280"></bean>