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DI exists in two major variants: Constructor-based dependency injection and Setter-based dependency injection.

bean的依赖注入

set方法注入

在类中写好属性名，为该属性提供set方法（必须）

<bean id="bookService" class="service.BookServiceImpl" scope="singleton" >
    <property name="bookDao1" ref="bookDao"/>
    <property name="connectionNum" value="10"/>
    <property name="databaseName" value="mysql"/>
</bean>

通过构造bean的方法进行注入

public BookServiceImpl(TestDao testDao, int i, String s){
}
<bean id="bookService" class="service.BookServiceImpl" scope="singleton"> 
	<constructor-arg index="0" ref="testDao"/>
    <constructor-arg index="1" value="2353"/>
    <constructor-arg index="2" value="南京"/>
</bean>

类中只有有参构造，在xml中就必须要提供

<constructor-arg/>

，用于实例化bean，Spring默认使用无参构造创建bean

有多个构造方法时，执行哪个方法，取决于

<constructor-arg>

数量，被执行的构造方法的参数个数和写的

<constructor-arg>

的个数相同

// 对于注解形式被@Component标注的bean
// 实例化bean时
// 构造器的权限修饰符无效,因为使用的反射
// 只有一个构造器时,就用那个构造器实例化对象,且可通过传递参数的方式进行DI
// 有多个构造器时,且没有使用@Autowired指定,就去找无参的,如果没有就会报错

// As of Spring Framework 4.3, an @Autowired annotation on such a constructor is no longer necessary 
// if the target bean defines only one constructor to begin with.
// However, if several constructors are available and there is no primary/default constructor, at least one 
// of the constructors must be annotated with @Autowired in order to instruct the container which one to use.
public class MovieRecommender {
    private final CustomerPreferenceDao customerPreferenceDao;
    @Autowired
    public MovieRecommender(CustomerPreferenceDao customerPreferenceDao) {
        this.customerPreferenceDao = customerPreferenceDao;
    }
    // ...
}

注入集合数据类型

public class BookDaoImpl implements BookDao {
    private int[] array1;
    private List<String> list1;
    private Set<String> set1;
    private Map<String,String> map1;
    private Properties properties1;
// set方法
    public void save(){
        System.out.println("数组:" + Arrays.toString(array1));
        System.out.println("List:" + list1);
        System.out.println("Set:" + set1);
        System.out.println("Map:" + map1);
        System.out.println("Properties:" + properties1);
    }
}

<bean id="bookDao" class="dao.BookDaoImpl">
    <property name="array1">// 数组:[10, 11, 12]
        <array>
            <value>10</value>
            <value>11</value>
            <value>12</value>
        </array>
    </property>
    <property name="list1">// List:["fjk", fjkl, "fjk"]
        <list>
            <value>"fjk"</value>
            <value>fjkl</value>
            <value>"fjk"</value>
        </list>
    </property>
    <property name="set1">// Set:[jdjks, "vd", jds]
        <set>
            <value>jdjks</value>
            <value>"vd"</value>
            <value>jds</value>
        </set>
    </property>
    <property name="map1">// Map:{country=china, province=henan, city=12}
        <map>
            <entry key="country" value="china"/>
            <entry key="province" value="henan"/>
            <entry key="city" value="12"/>
        </map>
    </property>
    <property name="properties1">// Properties:{country="china", province=12, city=kaifeng}
        <props>
            <prop key="country">"china"</prop>
            <prop key="province">12</prop>
            <prop key="city">kaifeng</prop>
        </props>
    </property>
</bean>

spring依赖注入的三种方式



三种注入方式



Spring的三种注入方式