Spring——@Autowire冲突问题

雨点打透心脏的1/2处 2022-06-16 05:57 286阅读 0赞

# Spring——@Autowire冲突问题 #

spring中使用@Autowire实现依赖注入。在使用的时候需要注意的是，满足注入条件的bean有多个的时候需要添加标识来区分目前需要注入的是哪个bean。

好，下面上货：

1、新建一个maven项目

mvn archetype:generate -DarchetypeCatalog=internal

2、修改pom文件

<properties>
            <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
            <springframework.version>4.3.7.RELEASE</springframework.version>
        </properties>
    
        <dependencies>
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>4.12</version>
                <scope>test</scope>
            </dependency>
            
            <dependency>
                <groupId>org.springframework</groupId>
                <artifactId>spring-context</artifactId>
                <version>${springframework.version}</version>
            </dependency>
            
            <dependency>
                <groupId>org.springframework</groupId>
                <artifactId>spring-test</artifactId>
                <version>${springframework.version}</version>
            </dependency>
    
        </dependencies>
        <build>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <configuration>
                        <source>1.8</source>
                        <target>1.8</target>
                        <encoding>utf-8</encoding>
                    </configuration>
                </plugin>
                <plugin>
                    <artifactId>maven-assembly-plugin</artifactId>
                    <version>3.0.0</version>
                    <configuration>
                        <archive>
                            <manifest>
                                <mainClass>com.xueyou.demo.App</mainClass>
                            </manifest>
                        </archive>
                        <descriptorRefs>
                            <descriptorRef>jar-with-dependencies</descriptorRef>
                        </descriptorRefs>
                    </configuration>
                    <executions>
                        <execution>
                            <id>make-assembly</id> 
                            <phase>package</phase> 
                            <goals>
                                <goal>single</goal>
                            </goals>
                        </execution>
                    </executions>
                </plugin>
            </plugins>
        </build>

3、先看一下类图：

![Center][]

4、Eat接口

package com.xueyou.demo2;
    
    public interface Eat {
        void eatMeal();
    }

EatImpl1

package com.xueyou.demo2;
    
    import org.springframework.stereotype.Component;
    
    @Component
    public class EatImpl1 implements Eat {
        @Override
        public void eatMeal() {
            System.out.println("this is eatImpl1");
        }
    }

EatImpl2

package com.xueyou.demo2;
    
    import org.springframework.stereotype.Component;
    
    @Component
    public class EatImpl2 implements Eat{
        @Override
        public void eatMeal() {
            System.out.println("this is eatImpl2");
        }
    }

EatImpl3

package com.xueyou.demo2;
    
    import org.springframework.stereotype.Component;
    
    
    @Component
    public class EatImpl3 implements Eat{
        @Override
        public void eatMeal() {
            System.out.println("this is eatImpl3");
        }
    }

Animal

package com.xueyou.demo2;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.beans.factory.annotation.Qualifier;
    import org.springframework.stereotype.Component;
    
    @Component
    public class Animal {
    
        @Autowired
        private Eat eat;
    
        public void eatDetail() {
            eat.eatMeal();
        }
    }

App

package com.xueyou.demo;
    
    import com.xueyou.demo2.Animal;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.annotation.AnnotationConfigApplicationContext;
    import org.springframework.context.annotation.ComponentScan;
    import org.springframework.context.annotation.Configuration;
    
    /**
     * Hello world!
     */
    @Configuration
    @ComponentScan(basePackages = {"org.xueyou.demo","com.xueyou.demo","com.xueyou.demo2"})
    public class App {
    
        public static void main(String[] args) {
            System.out.println("Hello World!");
            ApplicationContext applicationContext = new AnnotationConfigApplicationContext(com.xueyou.demo.App.class);
    //        Person p = applicationContext.getBean(Person.class);
    //        p.showMyBody();
            Animal animal = applicationContext.getBean(Animal.class);
            animal.eatDetail();
        }
    }

5、运行结果：

![Center 1][]

从运行结果上能够看出，现在出现的错误是NoUniqueBeanDefinitionException。

原因是这样的在@Autowired注解进行自动装配的时候，发现有三个类都满足要求，这个时候spring不能够从这三个bean中选择一个bean进行装配，从而出现异常。

解决方法：

1、使用@Primary注解

2、使用@Qualifier注解

3、自定义注解

前两种方法比较简单，就是类似这样

package com.xueyou.demo2;
    
    import org.springframework.beans.factory.annotation.Qualifier;
    import org.springframework.stereotype.Component;
    
    
    @Component
    @Qualifier("firstEat")
    public class EatImpl1 implements Eat {
        @Override
        public void eatMeal() {
            System.out.println("this is eatImpl1");
        }
    }

然后在Animal使用的时候制定标志

package com.xueyou.demo2;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.beans.factory.annotation.Qualifier;
    import org.springframework.stereotype.Component;
    
    
    @Component
    public class Animal {
    
        @Autowired
        @Qualifier("firstEat")
        private Eat eat;
    
        public void eatDetail() {
            eat.eatMeal();
        }
    }

再次运行会发现已经可以了。

这里主要介绍一下自定义注解的方式：

首先要新建注解。

package com.xueyou.demo2;
    
    import org.springframework.beans.factory.annotation.Qualifier;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    
    @Target({ElementType.CONSTRUCTOR, ElementType.FIELD, ElementType.METHOD, ElementType.TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    @Qualifier
    public @interface EatAnno {
        String value() default "";
    }

使用自定义注解。

package com.xueyou.demo2;
    
    import org.springframework.beans.factory.annotation.Qualifier;
    import org.springframework.stereotype.Component;
    
    @Component
    @EatAnno(value = "firstEat")
    public class EatImpl1 implements Eat {
        @Override
        public void eatMeal() {
            System.out.println("this is eatImpl1");
        }
    }

package com.xueyou.demo2;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.beans.factory.annotation.Qualifier;
    import org.springframework.stereotype.Component;
    
    
    @Component
    public class Animal {
    
        @Autowired
        @EatAnno(value = "firstEat")
        private Eat eat;
    
        public void eatDetail() {
            eat.eatMeal();
        }
    }

运行结果：

![Center 2][]

[Center]: /images/20220616/ea95ea921ee7497bab03d7c559869373.png
[Center 1]: /images/20220616/8c56ebdd41b3444bb44552330bfda899.png
[Center 2]: /images/20220616/e4600cec8a4c4a95b2fbdd90b27a794e.png