Guice依赖注入(接口多实现)


本教程主要详细讲解Guice依赖注入中的特性接口多实现,一般使用到guice的框架的插件机制都是基于该方式实现。

基础环境


技术 版本
Java 1.8+
Guice 4.2.3

初始化项目


  • 初始化项目
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mvn archetype:generate -DgroupId=com.edurt.sli.guice -DartifactId=guice-binder-multiple -DarchetypeArtifactId=maven-archetype-quickstart -Dversion=1.0.0 -DinteractiveMode=false
  • 修改pom.xml增加Guice依赖
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<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

<parent>
<artifactId>learn-integration-guice</artifactId>
<groupId>com.edurt.sli.guice</groupId>
<version>1.0.0</version>
</parent>

<modelVersion>4.0.0</modelVersion>

<artifactId>guice-binder-multiple</artifactId>
<name>Guice依赖注入(接口多实现)</name>

<properties>
<system.java.version>1.8</system.java.version>
<guice.version>4.2.3</guice.version>
<lombok.version>1.18.2</lombok.version>
</properties>

<dependencies>
<dependency>
<groupId>com.google.inject</groupId>
<artifactId>guice</artifactId>
<version>${guice.version}</version>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>${lombok.version}</version>
</dependency>
</dependencies>

<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>${plugin.maven.compiler.version}</version>
<configuration>
<source>${system.java.version}</source>
<target>${system.java.version}</target>
</configuration>
</plugin>
</plugins>
</build>

</project>

guice: guice就是我们核心要使用的依赖

接口多实现注入


如果一个接口有多个实现,如果单单通过@InjectModule都难以直接实现,但多实现是经常会出现的,Guice提供了其它注入方式来解决此问题。

  • 创建com.edurt.sli.guice.multiple文件夹,并在该文件夹下创建Service接口文件,用于添加我们需要测试的函数
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package com.edurt.sli.guice.multiple;

public interface Service {

void print(String source);

}
  • 创建Service接口的实现类JavaServiceGuiceService,用于实现接口中的方法,代码如下
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package com.edurt.sli.guice.multiple;

public class JavaService implements Service {

@Override
public void print(String source) {
System.out.println("Java Service " + source);
}

}
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package com.edurt.sli.guice.multiple;

public class GuiceService implements Service {

@Override
public void print(String source) {
System.out.println("Guice Service " + source);
}

}
  • 创建GuiceJava注解类,用于提供guice框架标识
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package com.edurt.sli.guice.multiple;

import com.google.inject.BindingAnnotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.PARAMETER})
@BindingAnnotation
public @interface Guice {
}
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package com.edurt.sli.guice.multiple;

import com.google.inject.BindingAnnotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.PARAMETER})
@BindingAnnotation
public @interface Java {
}
  • 创建用于测试注入的应用类Application,代码如下
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package com.edurt.sli.guice.multiple;

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

public class Application {

@Inject
@Java
public Service java;

@Inject
@com.edurt.sli.guice.multiple.Guice
public Service guice;

public static void main(String[] args) {
Application application = Guice.createInjector(binder -> {
binder.bind(Service.class).annotatedWith(Java.class).to(JavaService.class);
binder.bind(Service.class).annotatedWith(com.edurt.sli.guice.multiple.Guice.class).to(GuiceService.class);
}).getInstance(Application.class);
application.guice.print("sss");
application.java.print("sss");
}

}

我们运行程序输出

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Guice Service sss
Java Service sss

我们注意看binder的配置中,我们将注解与实际的实现类绑定到了一起,这样就实现了绑定多接口实现的功能。

注意:在本次程序中我们使用的是lambda表达式进行的代码编程,需要jdk1.8及以上版本

静态代码注入


我们如果需要进行静态代码注入服务该怎么写呢?我们参照以前讲解的Guice依赖注入(构造函数注入)资源中,我们创建一个ApplicationStatic类进行static的注入,代码如下

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package com.edurt.sli.guice.multiple;

import com.google.inject.Inject;

public class ApplicationStatic {

@Inject
@Java
public static Service java;

@Inject
@com.edurt.sli.guice.multiple.Guice
public static Service guice;

public static void main(String[] args) {
com.google.inject.Guice.createInjector(binder -> {
binder.bind(Service.class).annotatedWith(Java.class).to(JavaService.class);
binder.bind(Service.class).annotatedWith(com.edurt.sli.guice.multiple.Guice.class).to(GuiceService.class);
binder.requestStaticInjection(ApplicationStatic.class);
});
ApplicationStatic.guice.print("sss");
ApplicationStatic.java.print("sss");
}

}

我们只需要在binder阶段将我们的主类注入到guice容器中,也就是我们看到的binder.requestStaticInjection(ApplicationStatic.class);代码,运行程序输出以下内容

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Guice Service sss
Java Service sss

属性绑定多接口


先看一下多接口绑定的示例

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package com.edurt.sli.guice.multiple;

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

public class ApplicationMultipleProperty {

@Inject
public Service java;

@Inject
public Service guice;

public static void main(String[] args) {
ApplicationMultipleProperty application = Guice.createInjector(binder -> {
binder.bind(Service.class).annotatedWith(Java.class).to(JavaService.class);
binder.bind(Service.class).annotatedWith(com.edurt.sli.guice.multiple.Guice.class).to(GuiceService.class);
}).getInstance(ApplicationMultipleProperty.class);
application.guice.print("sss");
application.java.print("sss");
}

}

运行以上代码,就会出现以下错误

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Exception in thread "main" com.google.inject.ConfigurationException: Guice configuration errors:

1) No implementation for com.edurt.sli.guice.multiple.Service was bound.
Did you mean?
* com.edurt.sli.guice.multiple.Service annotated with interface com.edurt.sli.guice.multiple.Java
* com.edurt.sli.guice.multiple.Service annotated with interface com.edurt.sli.guice.multiple.Guice
while locating com.edurt.sli.guice.multiple.Service
for field at com.edurt.sli.guice.multiple.Application.guice(Application.java:6)
while locating com.edurt.sli.guice.multiple.Application

2) No implementation for com.edurt.sli.guice.multiple.Service was bound.
Did you mean?
* com.edurt.sli.guice.multiple.Service annotated with interface com.edurt.sli.guice.multiple.Java
* com.edurt.sli.guice.multiple.Service annotated with interface com.edurt.sli.guice.multiple.Guice
while locating com.edurt.sli.guice.multiple.Service
for field at com.edurt.sli.guice.multiple.Application.java(Application.java:6)
while locating com.edurt.sli.guice.multiple.Application

2 errors
at com.google.inject.internal.InjectorImpl.getProvider(InjectorImpl.java:1120)
at com.google.inject.internal.InjectorImpl.getProvider(InjectorImpl.java:1078)
at com.google.inject.internal.InjectorImpl.getInstance(InjectorImpl.java:1131)
at com.edurt.sli.guice.multiple.Application.main(Application.java:18)

这是因为我们使用了属性绑定了多接口实现,导致guice无法识别具体是哪个实现类,不过guice是强大的这种问题也被考虑到了,只需要使用@Named模板生成注解即可解决,我们姜代码修改为以下内容

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package com.edurt.sli.guice.multiple;

import com.google.inject.Guice;
import com.google.inject.Inject;
import com.google.inject.name.Named;
import com.google.inject.name.Names;

public class ApplicationMultipleProperty {

@Inject
@Named("Java")
public Service java;

@Inject
@Named("Guice")
public Service guice;

public static void main(String[] args) {
ApplicationMultipleProperty application = Guice.createInjector(binder -> {
binder.bind(Service.class).annotatedWith(Names.named("Java")).to(JavaService.class);
binder.bind(Service.class).annotatedWith(Names.named("Guice")).to(GuiceService.class);
}).getInstance(ApplicationMultipleProperty.class);
application.guice.print("sss");
application.java.print("sss");
}

}

运行程序后,输出以下结果

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Guice Service sss
Java Service sss

这个示例也很好理解,其实我们只是做了两步操作

  • 在绑定实现的时候使用annotatedWith(Names.named("Java"))进行对该服务实现做名称标志
  • 在需要使用服务实现的地方使用@Named("Java")进行服务的引用即可

打包文件部署


  • 打包数据
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mvn clean package -Dmaven.test.skip=true -X

运行打包后的文件即可

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java -jar target/guice-binder-multiple-1.0.0.jar

源码地址