一个class对三个接口Guice的依赖

Question

我有以下应用程序 class，它使用服务器来运行它的逻辑应用class的实现如下：

    package edu.umd.fcmd.guice.application;

import com.google.inject.Guice;
import com.google.inject.Injector;


public class WebApplication {
    private WebServer server;

    public void run() {
        System.out.println("starting web application...");


        Injector injector = Guice.createInjector(new WebGuiceModule());
        server = injector.getInstance(WebServer.class);

        server.run();

        System.out.println("web application finished.");
    }

    public static void main(String[] args) {
        WebApplication app = new WebApplication();

        app.run();
    }
}

服务器class如下，依赖三个接口：

public class WebServer{

    private final Frontend frontend;
    private final Middleware middleware;
    private final Persistance persistance;

    @Inject
    public WebServer(@Named("front")Frontend frontend, @Named("middle")Middleware middleware, @Named("pers")Persistance persistance) {

        this.frontend = frontend;
        this.middleware = middleware;
        this.persistance = persistance;
    }

    public String getType() {

        return "WebServer";
    }

    public boolean run() {

        System.out.println("running " + this.getType());

        Injector injector = Guice.createInjector();
        Frontend frontend = injector.getInstance(Frontend.class);
        frontend.run();
        Middleware middleware = injector.getInstance(Middleware.class);
        middleware.run();
        Persistance persistance = injector.getInstance(Persistance.class);
        persistance.run();

        return true;
    }
}

我的webguice模块如下：

public class WebGuiceModule extends AbstractModule{
    @Override
    protected void configure(){
        bind(WebServer.class).annotatedWith(Names.named("front")).to(FrontEnd.class);  
        bind(WebServer.class).annotatedWith(Names.named("middle")).to(Middleware.class);
        bind(WebServer.class).annotatedWith(Names.named("pers")).to(Persistance.class);
    }

}

我不确定为什么我的模块不能正常工作。写bind语句的时候还是报错。不知道为什么我收到以下错误：

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
    The method to(Class<? extends WebServer>) in the type LinkedBindingBuilder<WebServer> is not applicable for the arguments (Class<FrontEnd>)
    FrontEnd cannot be resolved to a type
    The method to(Class<? extends WebServer>) in the type LinkedBindingBuilder<WebServer> is not applicable for the arguments (Class<Middleware>)
    Middleware cannot be resolved to a type
    The method to(Class<? extends WebServer>) in the type LinkedBindingBuilder<WebServer> is not applicable for the arguments (Class<Persistance>)
    Persistance cannot be resolved to a type

Answer 1

您没有正确使用 bind()。您已配置 WebGuiceModule，使得 FrontEnd、Middleware 和 Persistance 是 WebServer 的子类。但是，编译器错误表明情况并非如此。

你只需要说：

bind(FrontEnd.class);
bind(Middleware.class);
bind(Persistance.class);

然后当你向注入器请求 WebServer 的实例时，它会知道如何创建它需要传递给构造函数的对象。

WebServer server = injector.getInstance(WebServer.class);

在这种情况下，您不需要 @Named。这是针对这样的情况：

public class Foo {

    @Inject
    public Foo(@Named("bar") Jar bar, @Named("tar") Jar tar) {
    }
}

public interface Jar {}
public class Bar extends Jar {}
public class Tar extends Jar {}

然后在模块中...

bind(Jar.class).annotatedWith(Names.named("bar")).to(Bar.class);
bind(Jar.class).annotatedWith(Names.named("tar")).to(Tar.class);

"name" 消除了要创建和注入 Jar 的哪个实现的歧义。否则它不会知道，它会出错。

Answer 2

谢谢@JeremyHeiler。这个前端接口恰好在不同的包中。现在，前端依赖于一个称为身份验证的接口。当我尝试使用与网络服务器类似的代码来实现它时，出现了错误。我写的代码如下：

package edu.umd.fcmd.guice.interfaces;

import com.google.inject.Guice;
import com.google.inject.Inject;
import com.google.inject.Injector;

import edu.umd.fcmd.guice.application.WebServer;
import edu.umd.fcmd.guice.interfaces.Authentication;

public interface Frontend{
    private final Authentication authentication;

    @Inject
    public interface(Authentication authentication) {
        System.out.println("5");
        this.authentication = authentication;
    }
    public static String getType(){
        return "Frontend";
    }
    public default boolean run(){
        System.out.println("in frontend");
        authentication.run();
        return true;
    }
}

错误如下：

Multiple markers at this line
    - Duplicate field Frontend.authentication
    - Illegal modifier for the interface field Frontend.authentication; only public, static & final are 
     permitted

Syntax error on token "interface", Identifier expected

The static field Frontend.authentication should be accessed in a static way

我尝试在互联网上搜索了很多，但找不到答案。我想问题是文件在不同的包中。如果可以请告诉我。

一个class对三个接口Guice的依赖

Dependency of one class on three interfaces Guice

java

eclipse

dependency-injection

guice