Question

所以我使用Spring注释@Autowire和@Qualifier进行依赖注入练习某些代码。代码完美地处理了输出中的一点异常。

Coach.java

package com.luv2code.springdemo;

public interface Coach {

public String getDailyWorkout();
public String getDailyFortune();

}

SwimCoach.java

package com.luv2code.springdemo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class SwimCoach implements Coach {

@Autowired
@Qualifier("randomFortuneService")
private FortuneService fortuneService;

@Value("${foo.email}")
private String email;

@Value("${foo.team}")
private String team;

public SwimCoach() {
System.out.println("Inside Swimcoach no-arg constructor");
} 

@Override
public String getDailyWorkout() {
    return "Swim 1000 meters as a warm up.";
}

@Override
public String getDailyFortune() {
    return fortuneService.getFortune();
}

public String getEmail() {
    return email;
}

public String getTeam() {
    return team;
}

}

FortuneService.java

package com.luv2code.springdemo;

public interface FortuneService {

public String getFortune();

}

RandomFortuneService.java

package com.luv2code.springdemo;

import java.util.Random;

import org.springframework.stereotype.Component;

//with @Component, the class is ready to be scanned by Spring.

@Component
public class RandomFortuneService implements FortuneService {

// create an array of strings
        private String[] data = { 
                "perseverance is the key to success.",
                "Diligence is the mother of good luck.",
                "Your Journey towards the success is itself a reward."
        };

        private Random myRandom = new Random();

@Override
public String getFortune() {

    int index = myRandom.nextInt(data.length);

    String theFortune = data[index];

    return theFortune;
}

}

PracticeHelloSpringApp.java

package com.luv2code.springdemo;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class PracticeHelloSpringApp {

public static void main(String[] args) {

    ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

    SwimCoach coach = context.getBean("swimCoach",SwimCoach.class);

    //In the above code,SwimCoach defines two extra methods getEmail and getTeam which are not a part of Coach interface. 
    //So we need to create coach variable of type SwimCoach class with which we can access interface methods as well as class methods.

    System.out.println(coach.getDailyWorkout());
    System.out.println(coach.getDailyFortune());
    System.out.println(coach.getEmail());
    System.out.println(coach.getTeam());

    context.close();


}

}

的applicationContext.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:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">

<context:component-scan base-package="com.luv2code.springdemo"/>
<context:property-placeholder location="classpath:sport.properties"/>

在SwimCoach.java中，我正在使用属性文件来注入值。还有另外三个fortuneService实现返回一些字符串。为了确保使用RandomFortuneService，我正在使用@Qualifier。现在输出有点奇怪。

    May 12, 2018 10:31:04 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@1a93a7ca: startup date [Sat May 12 10:31:04 IST 2018]; root of context hierarchy
May 12, 2018 10:31:05 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [applicationContext.xml]
inside constructor of PingPongCoach
Inside Swimcoach no-arg constructor
Swim 1000 meters as a warm up.
perseverance is the key to success.
myeasycoach@luv2code.com
Silly Java Coders
May 12, 2018 10:31:06 AM org.springframework.context.support.AbstractApplicationContext doClose
INFO: Closing org.springframework.context.support.ClassPathXmlApplicationContext@1a93a7ca: startup date [Sat May 12 10:31:04 IST 2018]; root of context hierarchy

如果你注意到，那里有 PingPongCoach的内部构造函数，它完全是Coach接口的不同实现。在这里我也使用 @Qualifier（“randomFortuneService”）作为构造函数注入。

PingPongCoach.java

package com.luv2code.springdemo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;

//Incase of default bean ID, It would be "pingPongCoach".
@Component("myPingPongCoach")
public class PingPongCoach implements Coach {

    private FortuneService fortuneService;


    //This is the case when we have multiple implementations of FortuneService and we are constructor injection for 
    //injecting dependency with the use of @Autowired and @Qualifier. Check the  @Qualifier annotation inside of the constructor arguments. 
    @Autowired
    public PingPongCoach(@Qualifier("randomFortuneService") FortuneService fortuneService) {
        super();
        System.out.println("inside constructor of PingPongCoach");
        this.fortuneService = fortuneService;
    }

    @Override
    public String getDailyWorkout() {

        return "Ping Pong is no sport...You don't need any practice!!";
    }

    @Override
    public String getDailyFortune() {

        return fortuneService.getFortune();
    }

}

有谁能告诉我为什么在这里调用PingPongCoach No-arg构造函数？

Answer 1

你用@Component

标记了你的课程

@Component("myPingPongCoach")
public class PingPongCoach implements Coach

因此，在组件扫描期间，spring创建并初始化它。

您为构造函数提供了一个参数来抑制默认构造函数，因此Spring会选择它。

Spring @Autowire和@Qualifier注释奇怪的行为

1 个答案: