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

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技术	版本
Java	1.8+
Guice	4.2.3

初始化项目

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• 初始化项目

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

<?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

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如果一个接口有多个实现，如果单单通过@Inject和Module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

package com.edurt.sli.guice.multiple;
public interface Service {
 void print(String source);
}

• 创建Service接口的实现类JavaService和GuiceService，用于实现接口中的方法，代码如下

package com.edurt.sli.guice.multiple;
public class JavaService implements Service {
     @Override
 public void print(String source) { System.out.println("Java Service " + source); }  }

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Guice和Java注解类，用于提供guice框架标识

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 {
}

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

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

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

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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

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

Guice Service sss
Java Service sss

属性绑定多接口

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先看一下多接口绑定的示例

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

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

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

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

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• 打包数据

mvn clean package -Dmaven.test.skip=true -X

运行打包后的文件即可

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

源码地址

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• GitHub
• Gitee