【Spring】（3.5）依賴注入（擴展）

一、依賴注入擴展

該篇講依賴注入的擴展，用其他的方式注入。

使用：p-namespace、c-namespace 簡化代碼。

項目結構：

創建實體類Student和Address。

public class Address {
    private String address;

    @Override
    public String toString() {
        return "Address{" +
                "address='" + address + '\'' +
                '}';
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }
}

public class Student {
    private String name;
    /** 現住址 */
    private Address address;
    /** 籍貫 */
    private Address nativePlace;

    public Student() {
    }

    public Student(String name, Address address, Address nativePlace) {
        this.name = name;
        this.address = address;
        this.nativePlace = nativePlace;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", address=" + address +
                ", nativePlace=" + nativePlace +
                '}';
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    public Address getNativePlace() {
        return nativePlace;
    }

    public void setNativePlace(Address nativePlace) {
        this.nativePlace = nativePlace;
    }
}

設置配置文件

<?xml version="1.0" encoding="UTF-8"?>
<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"
       xmlns:c="http://www.springframework.org/schema/c"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <!-- 地址bean -->
    <bean id="address" class="com.shengjava.pojo.Address">
        <property name="address" value="中國浙江"></property>
    </bean>

    <!-- p-namespace使用（p-namespace中的p相當於property標籤，簡化代碼用的） -->
    <!-- 不使用p-namespace時，使用無參構造器創建bean對象 -->
    <bean id="student01Before" class="com.shengjava.pojo.Student">
        <property name="name" value="張三"></property>
        <property name="address">
            <ref bean="address"></ref>
        </property>
        <property name="nativePlace">
            <ref bean="address"></ref>
        </property>
    </bean>
    <!-- 使用p-namespace時，使用無參構造器創建bean對象 -->
    <bean id="student01After" class="com.shengjava.pojo.Student" p:name="張三" p:address-ref="address" p:nativePlace-ref="address"></bean>

    <!-- c-namespace使用（c-namespace中的c相當於constructor-arg標籤，簡化代碼用的） -->
    <!-- 不使用c-namespace時，使用有參構造器創建bean對象 -->
    <bean id="student02Before" class="com.shengjava.pojo.Student">
        <constructor-arg name="name" value="張三"/>
        <constructor-arg name="address" ref="address"/>
        <constructor-arg name="nativePlace" ref="address"/>
    </bean>
    <!-- 不使用c-namespace時，使用有參構造器創建bean對象 -->
    <bean id="student02After" class="com.shengjava.pojo.Student" c:name="張三" c:address-ref="address" c:nativePlace-ref="address"></bean>
</beans>

注意點:配置文件中，需要引入xml命名空間。

xmlns:p=“http://www.springframework.org/schema/p”，代表引入p-namespace

xmlns:c=“http://www.springframework.org/schema/c”，代表引入c-namespace

編寫測試類

public class StudentTest {
    public static void main(String[] args) {
        // 獲取context
        ApplicationContext context = new ClassPathXmlApplicationContext("studentBeans.xml");
        // 獲取對象
        Student student01Before = context.getBean("student01Before", Student.class);
        Student student01After = context.getBean("student01After", Student.class);
        Student student02Before = context.getBean("student02Before", Student.class);
        Student student02After = context.getBean("student02After", Student.class);
        System.out.println(student01Before);
        System.out.println(student01After);
        System.out.println(student02Before);
        System.out.println(student02After);
    }
}

輸出:

Student{name='張三', address=Address{address='中國浙江'}, nativePlace=Address{address='中國浙江'}}
Student{name='張三', address=Address{address='中國浙江'}, nativePlace=Address{address='中國浙江'}}
Student{name='張三', address=Address{address='中國浙江'}, nativePlace=Address{address='中國浙江'}}
Student{name='張三', address=Address{address='中國浙江'}, nativePlace=Address{address='中國浙江'}}

以上就是依賴注入的擴展，p-namespace、c-namespace 主要是減少一點代碼量。

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