按类型将引用bean自动装配到列表中

Question

我有一个类有一个Daemon类型的对象列表.

class Xyz {    
    List<Daemon> daemons;
}

我的弹簧配置看起来像这样.

<bean id="xyz" class="package1.Xyz">
   <property name="daemons" ref="daemonsList">
</bean>

<bean id="daemon1" class="package1.DaemonImpl1"/>
<bean id="daemon2" class="package1.DaemonImpl2"/>

<bean id="daemonsList" class="java.util.ArrayList">
        <constructor-arg>
            <list>
                <ref bean="daemon1" />      
                <ref bean="daemon2" />
            </list>
        </constructor-arg>
</bean>

现在,不是在列表中显式连接每个守护进程实现,而是可以Daemon在列表中自动自动装配所有类型的bean .我试图解决的问题是,如果有人创建了一个新的Daemon类实现的bean 并忘记将其连接到列表中.

我在stackoverflow上的某个地方看到过这个问题,但是无法再找到它.为此道歉.

Answer 1

它应该像这样工作(从XML中删除ArrayList bean):

public Class Xyz {    

    private List<Daemon> daemons;

    @Autowired
    public void setDaemons(List<Daemon> daemons){
        this.daemons = daemons;
    }

}

我认为在XML中没有办法做到这一点.

见: 3.9.2.@Autowired并且@Inject:

通过将注释添加到需要该类型数组的字段或方法,还可以从ApplicationContext提供特定类型的所有bean:

public class MovieRecommender {

  @Autowired
  private MovieCatalog[] movieCatalogs;

  // ...
}

这同样适用于类型集合:

public class MovieRecommender {

  private Set<MovieCatalog> movieCatalogs;

  @Autowired
  // or if you don't want a setter, annotate the field
  public void setMovieCatalogs(Set<MovieCatalog> movieCatalogs) {
      this.movieCatalogs = movieCatalogs;
  }

  // ...
}

顺便说一句,从Spring 4.x开始,可以使用该@Ordered机制自动订购这些列表.

Answer 2

嗯，这可以通过Spring 文档中所述的两种方式来实现。

以下是文档的摘录。

使用 byType 或构造函数自动装配模式，您可以连接数组和类型化集合。

1. autowire =“按类型”

如果 xml 中定义的 bean 类型与列表类型匹配，则可以使用“byType”实现自动装配。

例子：

电机.java

package com.chiranth;
public interface Motor 
{
   public void start();
}

ElectricMotor1.java

package com.chiranth;
public class ElectricMotor1 implements Motor
{
     public void start() 
     { 
         System.out.println("Motor 1 Started.");
     }
}

ElectricMotor2.java

package com.chiranth;
public class ElectricMotor2 implements Motor
{
    public void start() 
    {
        System.out.println("Motor 2 Started.");
    }
}

TeslaModelX.java

package com.chiranth;
import java.util.List;
public class TeslaModelX 
{
    private List<Motor> motor;

    public List<Motor> getMotor()
    {
        return motor;
    }

    public void setMotor(List<Motor> motor) 
    {
        this.motor = motor;
    }

    public void goForward()
    {
        for(Motor m :motor)
            m.start();
        System.out.println("Going Forward.");
    }
}

Spring.xml

<?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"
   xsi:schemaLocation = "http://www.springframework.org/schema/beans
   http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="electricMotor1" class="com.chiranth.ElectricMotor1"/>
    <bean id="electricMotor2" class="com.chiranth.ElectricMotor2"/>

    <bean id="modelX" class="com.chiranth.TeslaModelX" autowire="byType"/>
</beans>

测试.java

package com.chiranth;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Test 
{
    public static void main(String[] args) 
    {
        ApplicationContext context= new ClassPathXmlApplicationContext("Spring.xml");
        TeslaModelX modelx=(TeslaModelX)context.getBean("modelX");
        modelx.goForward();
    }
}

输出：

Motor 1 Started.
Motor 2 Started.
Going Forward.

2. autowire =“构造函数”

如果 xml 中定义的 bean 类型与构造函数中的参数类型匹配，则可以使用“构造函数”实现自动装配。

例子：

考虑上面的 Motor.java 、 ElectricMotor1.java 和 ElectricMotor2.java 。

TeslaModelX.java

package com.chiranth;
import java.util.List;
public class TeslaModelX 
{
    private List<Motor> motor;

    public TeslaModelX(List<Motor> motor)
    {
        this.motor=motor;
    }

    public void goForward()
    {
        for(Motor m:motor)
            m.start();
        System.out.println("Going Forward.");
    }
}

Spring.xml

<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">

    <bean id="electricMotor1" class="com.chiranth.ElectricMotor1"/>
    <bean id="electricMotor2" class="com.chiranth.ElectricMotor2"/>

    <bean id="modelX" class="com.chiranth.TeslaModelX" autowire="constructor"/>
</beans>

测试.java

package com.chiranth;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Test 
{
    public static void main(String[] args) 
    {
        ApplicationContext context= new ClassPathXmlApplicationContext("Spring.xml");
        TeslaModelX modelX=(TeslaModelX)context.getBean("modelX");
        modelX.goForward();
    }
}

输出：

Motor 1 Started.
Motor 2 Started.
Going Forward.