java - 我收到一个错误—— "No qualifying bean of type [hello.MessagePrinter] is defined"

Question

这是我从 spring 网站执行示例 spring 应用程序时遇到的错误。我试图找到解决方案但徒劳无功。请帮忙。我想它相当简单，但无法弄清楚。

文件应用程序.java

package hello;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.*;
import org.springframework.context.support.AbstractApplicationContext;

@Configuration
@ComponentScan
public class Application {

    @Bean
    MessageService mockMessageService(){
        return new MessageService() {
            public String getMessage() {
                return "Hello World!";
            }
        };
    }

    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext();
        ((AbstractApplicationContext) context).refresh();
        MessagePrinter printer = context.getBean(MessagePrinter.class);
        printer.printMessage();

    }

}

消息打印机.java

package hello;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class MessagePrinter {
    final private MessageService service;

    @Autowired
    public MessagePrinter(MessageService service){
        this.service = service;
    }

    public void printMessage(){
        System.out.println(this.service.getMessage());
    }

}

消息服务.java

package hello;

public interface MessageService {
    String getMessage();

}

pom.xml

<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>

  <groupId>org.springframework</groupId>
  <artifactId>gs-maven</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>gs-maven</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.1</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer
                                    implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>hello.Application</mainClass>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>4.1.5.RELEASE</version>
    </dependency>
    <!-- tag::joda[] -->
    <dependency>
            <groupId>joda-time</groupId>
            <artifactId>joda-time</artifactId>
            <version>2.2</version>
        </dependency>
      <!-- end::joda[] -->
  </dependencies>
</project>

错误:

Mar 2, 2015 10:50:01 AM org.springframework.context.annotation.AnnotationConfigApplicationContext prepareRefresh INFO: Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@c1b531: startup date [Mon Mar 02 10:50:01 IST 2015]; root of context hierarchy Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [hello.MessagePrinter] is defined at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:371) at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:331) at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:968) at hello.Application.main(Application.java:23)

请让我知道我错过了什么

Answer 1

看这个样本

http://www.tutorialspoint.com/spring/spring_java_based_configuration.htm

ApplicationContext context = new AnnotationConfigApplicationContext(); 行采用入口点 bean 的参数。

所以你的代码应该是

ApplicationContext context = 
               new AnnotationConfigApplicationContext(MessagePrinter.class);

如果你想注册一些 beans 那么你可以使用 register 或使用 scan 来扫描一个包