注入正在被注入的类

Question

在我的应用程序中，我使用Google进行依赖注入。我有这样的班级结构，

示例取自这里

这是我的界面

package com.journaldev.di.services;

@ImplementedBy(EmailService.class)
public interface MessageService {

    boolean sendMessage(String msg, String receipient);
}

我将在这里实施

package com.journaldev.di.services;

import javax.inject.Singleton;

//import com.google.inject.Singleton;

@Singleton
public class EmailService implements MessageService {

    public boolean sendMessage(String msg, String receipient) {
        //some fancy code to send email
        System.out.println("Email Message sent to "+receipient+" with message="+msg);
        return true;
    }
}

如果我在这里注射EmailService。

package com.journaldev.di.consumer;

import javax.inject.Inject;

import com.journaldev.di.services.MessageService;

public class MyApplication {

    private MessageService service;

    @Inject
    public void setService(MessageService svc){
        this.service=svc;
    }

    public boolean sendMessage(String msg, String rec){
        //some business logic here
        return service.sendMessage(msg, rec);
    }
}

如果假设我的EmailService类是这样的，

package com.journaldev.di.services;

import javax.inject.Singleton;

//import com.google.inject.Singleton;

@Singleton
public class EmailService implements MessageService {
    public EmailService(int someValue) {
         FancyEmailService fancyEmailService = new FancyEmailService(someValue);
    }
    public boolean sendMessage(String msg, String receipient) {
        fancyEmailService.doSomething();
        System.out.println("Email Message sent to "+receipient+" with message="+msg);
        return true;
    }
}

为了测试上面的EmailService代码，我需要注入FancyEmailService而不是从构造函数中实例化。如何将FancyEmailService注入EmailService代码？仍能将EmailService注入MyApplication。

Answer 1

你需要看看这些- https://github.com/google/guice/wiki/InstanceBindings和https://github.com/google/guice/wiki/ProvidesMethods

public class GuiceTestModule extends AbstractModule {

    @Override
    protected void configure() {
        bind(Integer.class)
        .annotatedWith(Names.named("fancy"))
        .toInstance(10);
    }

    @Provides
    FancyEmailService fancyEmailServiceProvider(@Named("fancy") int i){
        return new FancyEmailService(i);
    }

}

我的FancyEmailService和EMailService如下所示。

public class FancyEmailService {

    private final int i;

    public FancyEmailService(int i){
        this.i = i;
    }

    public void doSomething(){
        System.out.println("i is injected with " + i);
    }

}

@Singleton
public class EmailService implements MessageService {

    private FancyEmailService fancyEmailService;

    @Inject
    public EmailService(@Named("fancy") int someValue){
       fancyEmailService = new FancyEmailService(someValue);
    }

    public boolean sendMessage(String msg, String receipient) {
        //some fancy code to send email
        System.out.println("Email Message sent to "+receipient+" with message="+msg);
        fancyEmailService.doSomething();
        return true;
    }
}

让我们来测试

public class GuiceTest {

    public static void main(String[] args) {


        Injector injector = Guice.createInjector(new GuiceTestModule());

        MyApplication appn = injector.getInstance(MyApplication.class);
        appn.sendMessage("msg", "guru");
    }

}

产出：

Email Message sent to guru with message=msg
i is injected with 10

EmailService也可以使用@Provides这样编写

@Singleton
public class EmailService implements MessageService {

    private FancyEmailService fancyEmailService;

    @Inject
    public EmailService(FancyEmailService fes){
       fancyEmailService = fes;
    }

    public boolean sendMessage(String msg, String receipient) {
        //some fancy code to send email
        System.out.println("Email Message sent to "+receipient+" with message="+msg);
        fancyEmailService.doSomething();
        return true;
    }
}