Question

我是spring框架的新手。我根据教程在做下面的代码。但这给了我错误。显示我需要一个bean，但是找到了2个。但我正在使用@Qualifier，它应该可以工作。我用过@primary，效果很好。但仅适用于@Qualifier，按名称自动装配对我不起作用。

/pom.xml

<?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">
<modelVersion>4.0.0</modelVersion>
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.0.0.RELEASE</version>
    <relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.arman.spring.basics</groupId>
<artifactId>spring_project</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>spring_project</name>
<description>Demo project for Spring Boot</description>

<properties>
    <java.version>1.8</java.version>
</properties>

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
</dependencies>

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>
    </plugins>
</build>

<repositories>
    <repository>
        <id>spring-snapshots</id>
        <name>Spring Snapshots</name>
        <url>https://repo.spring.io/snapshot</url>
        <snapshots>
            <enabled>true</enabled>
        </snapshots>
    </repository>
    <repository>
        <id>spring-milestones</id>
        <name>Spring Milestones</name>
        <url>https://repo.spring.io/milestone</url>
    </repository>
</repositories>
<pluginRepositories>
    <pluginRepository>
        <id>spring-snapshots</id>
        <name>Spring Snapshots</name>
        <url>https://repo.spring.io/snapshot</url>
        <snapshots>
            <enabled>true</enabled>
        </snapshots>
    </pluginRepository>
    <pluginRepository>
        <id>spring-milestones</id>
        <name>Spring Milestones</name>
        <url>https://repo.spring.io/milestone</url>
    </pluginRepository>
</pluginRepositories>

BubbleSortAlgorithm.java类

package com.arman.spring.basics.spring_project;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;

@Component
@Qualifier("bubble")

public class BubbleSortAlgorithm implements SortAlgorithm {

public int[] sort(int[] numbers) {
    return numbers;
}
}

QuickSortAlgorithm.java

package com.arman.spring.basics.spring_project;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;
@Component
@Qualifier("quick")
public class QuickSortAlgorithm implements SortAlgorithm {
public int[] sort(int[] numbers) {
    return numbers;
}
}

SortAlgorithm.java接口

package com.arman.spring.basics.spring_project;
public interface SortAlgorithm {
public int[] sort(int[] numbers);

}

BinarySearchImpl.java类

package com.arman.spring.basics.spring_project;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;

@Component

public class BinarySearchImpl {
@Autowired
@Qualifier("quick")
private SortAlgorithm bubbleSortAlgorithm;

public BinarySearchImpl(SortAlgorithm sortAlgorithm) {
    this.bubbleSortAlgorithm = sortAlgorithm;
}

public SortAlgorithm getSortAlgorithm() {
    return bubbleSortAlgorithm;
}

public void setSortAlgorithm(SortAlgorithm sortAlgorithm) {
    this.bubbleSortAlgorithm = sortAlgorithm;
}

public int binarySearch(int[] numbers, int numberToSearchFor) {

    int[] sortedNumbers = bubbleSortAlgorithm.sort(numbers);
    System.out.println(bubbleSortAlgorithm);
    // search the array

    return 3;
}

}

包含主类的SpringProjectApplication.java类

package com.arman.spring.basics.spring_project;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;

@SpringBootApplication
public class SpringProjectApplication {

// what are the beans?
// what are the dependency of a bean?
// where to search for them?

public static void main(String[] args) {
    /*
     * BinarySearchImpl binarySearch= new BinarySearchImpl(new
     * QuickSortAlgorithm());
     */
    ApplicationContext applicationContext = SpringApplication.run(SpringProjectApplication.class);
    BinarySearchImpl binarySearchImpl = applicationContext.getBean(BinarySearchImpl.class);
    BinarySearchImpl binarySearchImpl2 = applicationContext.getBean(BinarySearchImpl.class);

    System.out.println(binarySearchImpl2);
    System.out.println(binarySearchImpl);

    int result = binarySearchImpl.binarySearch(new int[] { 12, 13, 10, 1, 3 }, 3);
    System.out.println(result);
}

}

该应用程序的日志。

2019-02-06 23:25:33.265  INFO 11068 --- [           main] c.a.s.b.s.SpringProjectApplication       : Starting SpringProjectApplication on DESKTOP-JDRMFHT with PID 11068 (C:\Users\Arman\git\spring-practice\spring_project\target\classes started by Arman in C:\Users\Arman\git\spring-practice\spring_project)
2019-02-06 23:25:33.275  INFO 11068 --- [           main] c.a.s.b.s.SpringProjectApplication       : No active profile set, falling back to default profiles: default
2019-02-06 23:25:33.382  INFO 11068 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@90c451: startup date [Wed Feb 06 23:25:33 BDT 2019]; root of context hierarchy
2019-02-06 23:25:34.687  WARN 11068 --- [           main] s.c.a.AnnotationConfigApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'binarySearchImpl' defined in file [C:\Users\Arman\git\spring-practice\spring_project\target\classes\com\arman\spring\basics\spring_project\BinarySearchImpl.class]: Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.arman.spring.basics.spring_project.SortAlgorithm' available: expected single matching bean but found 2: bubbleSortAlgorithm,quickSortAlgorithm
2019-02-06 23:25:34.705  INFO 11068 --- [           main] ConditionEvaluationReportLoggingListener : 

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2019-02-06 23:25:34.715 ERROR 11068 --- [           main] o.s.b.d.LoggingFailureAnalysisReporter   : 

***************************
APPLICATION FAILED TO START
***************************

Description:

Parameter 0 of constructor in com.arman.spring.basics.spring_project.BinarySearchImpl required a single bean, but 2 were found:
    - bubbleSortAlgorithm: defined in file [C:\Users\Arman\git\spring-practice\spring_project\target\classes\com\arman\spring\basics\spring_project\BubbleSortAlgorithm.class]
    - quickSortAlgorithm: defined in file [C:\Users\Arman\git\spring-practice\spring_project\target\classes\com\arman\spring\basics\spring_project\QuickSortAlgorithm.class]

操作：

考虑将其中一个bean标记为@Primary，更新使用者以接受多个bean，或使用@Qualifier标识应消耗的bean

Answer 1

您使用@Qualifier的方式错误。直接在@Component中设置bean名称：

@Component("bubble")
public class BubbleSortAlgorithm implements SortAlgorithm {
public int[] sort(int[] numbers) {
    return numbers;
}
}

@Component("quick")
public class QuickSortAlgorithm implements SortAlgorithm {
public int[] sort(int[] numbers) {
    return numbers;
}
}

是的，您是对的。构造函数的问题。春天还不清楚您要自动接线。使用构造函数自动布线具有优先权。

因此BinarySearchImpl应该如下所示：

private SortAlgorithm bubbleSortAlgorithm;

public Test(@Qualifier("quick") SortAlgorithm sortAlgorithm) {
    this.bubbleSortAlgorithm = sortAlgorithm;
}

或没有构造函数。

@Autowired
@Qualifier("quick")
private SortAlgorithm bubbleSortAlgorithm;

如何在Spring框架中修复UnsatisfiedDependencyException

1 个答案: