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Spring IoC依赖注入之构造器注入
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所谓构造器注入就是利用被Spring管理的对象的构造器完成对其属性的赋值。

1 简单类型、字符串和类类型的属性注入

为Student类添加两个构造器：

- 无参构造器，兼容Set方法注入
- 针对所有非集合类型属性的构造器

public class Student {
    ...

    public Student() {
    }

    public Student(String number, String name, String gender, int age,
                   Date enrollment, Subject subject) {
        this.number = number;
        this.name = name;
        this.gender = gender;
        this.age = age;
        this.enrollment = enrollment;
        this.subject = subject;
    }

    ...
}

配置对象：

<bean id="enrollment" class="java.util.Date" />

<bean id="sd" class="cn.tedu.springioc.beans.Student">
    <constructor-arg value="1001" />
    <constructor-arg value="张飞" />
    <constructor-arg value="男" />
    <constructor-arg value="20" />
    <constructor-arg ref="enrollment" />
    <constructor-arg>
        <bean class="cn.tedu.springioc.beans.Subject">
            <property name="name" value="Java" />
        </bean>
    </constructor-arg>
</bean>

- 类类型属性注入，或通过ref引用有名对象，或通过bean子标签定义匿名对象
- 书写顺序必须和构造器参数表的顺序严格一致，或通过index指定参数的位置

<bean id="sd" class="cn.tedu.springioc.beans.Student">
    <constructor-arg index="5" >
        <bean class="cn.tedu.springioc.beans.Subject">
            <property name="name" value="Java" />
        </bean>
    </constructor-arg>
    <constructor-arg index="3" value="20" />
    <constructor-arg index="1" value="张飞" />
    <constructor-arg index="0" value="1001" />
    <constructor-arg index="2" value="男" />
    <constructor-arg index="4" ref="enrollment" />
</bean>

测试：

public class SpringTest {
    public static void main(String[] args) {
        ...
        // 构造器注入
        Student sd = context.getBean("sd", Student.class);
        System.out.println(sd);
        ...
    }
}

例程：SpringIoC

2 集合类型的属性注入

为Student类再增加一个构造器，针对包括集合类型属性在内的所有属性。

public class Student {
    ...

    public Student(String number, String name, String gender, int age,
                   Date enrollment, Subject subject,
                   List<String> hobbies,
                   List<Course> courses,
                   Map<String, String> planA,
                   Map<String, Course> planB,
                   Map<Date, Course> planC,
                   Properties planD) {
        this.number = number;
        this.name = name;
        this.gender = gender;
        this.age = age;
        this.enrollment = enrollment;
        this.subject = subject;
        this.hobbies = hobbies;
        this.courses = courses;
        this.planA = planA;
        this.planB = planB;
        this.planC = planC;
        this.planD = planD;
    }

    ...
}

配置对象：

<bean id="enrollment" class="java.util.Date" />

<bean id="se" class="cn.tedu.springioc.beans.Student">
    <constructor-arg index="5" >
        <bean class="cn.tedu.springioc.beans.Subject">
            <property name="name" value="Java" />
        </bean>
    </constructor-arg>
    <constructor-arg index="3" value="20" />
    <constructor-arg index="1" value="张飞" />
    <constructor-arg index="0" value="1001" />
    <constructor-arg index="2" value="男" />
    <constructor-arg index="4" ref="enrollment" />
    <constructor-arg>
        <list>
            <value>旅游</value>
            <value>电影</value>
            <value>足球</value>
        </list>
    </constructor-arg>
    <constructor-arg>
        <list>
            <ref bean="course1" />
            <ref bean="course2" />
            <ref bean="course3" />
        </list>
    </constructor-arg>
    <constructor-arg>
        <map>
            <entry key="第一阶段">
                <value>Java语言</value>
            </entry>
            <entry key="第二阶段">
                <value>Java Web</value>
            </entry>
            <entry key="第三阶段">
                <value>SSM</value>
            </entry>
        </map>
    </constructor-arg>
    <constructor-arg>
        <map>
            <entry key="第一阶段" value-ref="course1" />
            <entry key="第二阶段" value-ref="course2" />
            <entry key="第三阶段" value-ref="course3" />
        </map>
    </constructor-arg>
    <constructor-arg>
        <map>
            <entry key-ref="date1" value-ref="course1" />
            <entry key-ref="date2" value-ref="course2" />
            <entry key-ref="date3" value-ref="course3" />
        </map>
    </constructor-arg>
    <constructor-arg>
        <props>
            <prop key="第一阶段">Java语言</prop>
            <prop key="第二阶段">Java Web</prop>
            <prop key="第三阶段">SSM</prop>
        </props>
    </constructor-arg>
</bean>

针对集合类型属性的构造器注入，在形式上与Set方法注入类似。

测试：

public class SpringTest {
    public static void main(String[] args) {
        ...
        // 构造器注入
        Student se = context.getBean("se", Student.class);
        System.out.println(se);
        ...
    }
}

例程：SpringIoC