创建名为“应用程序”的 bean 时出错，未找到默认构造函数；嵌套异常是 java.lang.NoSuchMethodException

Question

我不太明白为什么这段代码给了我“没有找到默认构造函数”错误。构造函数是@Autowired。一切似乎都被正确注入。有人可以帮忙吗？谢谢

@SpringBootApplication
public class Application {

    private ApplicationContext applicationContext;
    private MessagingService messagingService;
    private Parser parser;

    private static final Logger log = LoggerFactory.getLogger(Application.class);

    @Autowired
    public Application(ApplicationContext applicationContext,
                       MessagingService messagingService,
                       Parser parser)
    {
        this.applicationContext = applicationContext;
        Assert.notNull(messagingService, "MessagingService must not be null");
        this.messagingService = messagingService;
        Assert.notNull(parser, "Parser must not be null");
        this.parser = parser;
    }

    public static void main (String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public CommandLineRunner app() {
        return args -> {
            Locale defaultLocale = Locale.getDefault();
            Locale.setDefault(defaultLocale);
            log.info("Using MessagingService: " + messagingService.getMyMessageCode());

            parser.parse();
        };
    }
}

编辑：更新了Application.class

@SpringBootApplication
public class Application {

    @Autowired
    private MessagingService messagingService;
    @Autowired
    private Parser parser;

    private static final Logger log = LoggerFactory.getLogger(Application.class);

    public Application() {}

    public static void main (String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public CommandLineRunner app() {
        return args -> {
            Locale defaultLocale = Locale.getDefault();
            Locale.setDefault(defaultLocale);
            log.info("Using MessagingService: " + messagingService.getMyMessageCode());

            parser.parse();
        };
    }
}

Answer 1

luboskrnac 的回答是正确的。

但是如果你真的想使用Constructor Injection你可以升级你的SpringBoot版本到1.4.0.RELEASE 将使用 Spring 4.3.2.RELEASE

从 Spring 4.3 构造函数注入 支持 @Configuration 类

New Features and Enhancements in Spring Framework 4.3

Answer 2

您不能自动装配到主 Spring Boot 类。您可以注入 CommandLineRunner 所需的依赖项作为使用 @Bean 注释的方法的参数，当然还可以删除主类的构造函数注入：

@SpringBootApplication
public class Application {
    private static final Logger log = LoggerFactory.getLogger(Application.class);

    public static void main (String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public CommandLineRunner app(ApplicationContext applicationContext,
                       MessagingService messagingService,
                       Parser parser) {
        return args -> {
            Locale defaultLocale = Locale.getDefault();
            Locale.setDefault(defaultLocale);
            log.info("Using MessagingService: " + messagingService.getMyMessageCode());

            parser.parse();
        };
    }
}

编辑： 编辑后正确的上下文配置：

@SpringBootApplication
public class Application {

    private static final Logger log = LoggerFactory.getLogger(Application.class);

    public Application() {}

    public static void main (String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public CommandLineRunner app(MessagingService messagingService, Parser parser) {
        return args -> {
            Locale defaultLocale = Locale.getDefault();
            Locale.setDefault(defaultLocale);
            log.info("Using MessagingService: " + messagingService.getMyMessageCode());

            parser.parse();
        };
    }
}