没有 XML 的 Spring Bean 注解

Question

我正在尽我最大的努力在这里几乎不使用 XML。我做了一个非常简单的程序，但它不工作。希望有人能帮帮我。

public class App {

    public static void main(String[] args) {

        AnnotationConfigApplicationContext ctx = new    
AnnotationConfigApplicationContext(Logger.class);

        Logger logger = ctx.getBean(Logger.class);

        logger.writeConsole("Hello there");
        logger.writeFile("Hi again");

        ctx.close();
    }

}

界面

public interface LogWriter {
    public void write(String text);
}

文件编写器

public class FileWriter implements LogWriter {

    public void write(String text) {

    System.out.println("FileWriter: " + text);

   }

}

控制台编写器

 public class ConsoleWriter implements LogWriter{

      public void write(String text) {
      System.out.println("Console Writer: "+text);

   }

}

记录器

public class Logger {

@Autowired
private ConsoleWriter consoleWriter;
@Autowired
private FileWriter fileWriter;

public void setConsoleWriter(ConsoleWriter consoleWriter) {
    this.consoleWriter = consoleWriter;
}

public void setFileWriter(FileWriter fileWriter) {
    this.fileWriter = fileWriter;
}


public void writeFile(String text) {
    fileWriter.write(text);
}

public void writeConsole(String text) {
    consoleWriter.write(text);
}

@Bean
public Logger getLogger(){
    return new Logger();
    }

}

错误

Jul 02, 2015 2:52:49 PM org.springframework.context.annotation.AnnotationConfigApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@246b179d: startup date [Thu Jul 02 14:52:49 CEST 2015]; root of context hierarchy
Exception in thread "main" java.lang.NoSuchMethodError: org.springframework.core.GenericTypeResolver.resolveReturnTypeForGenericMethod(Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Class;
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.getTypeForFactoryMethod(AbstractAutowireCapableBeanFactory.java:650)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.predictBeanType(AbstractAutowireCapableBeanFactory.java:575)
    at org.springframework.beans.factory.support.AbstractBeanFactory.isFactoryBean(AbstractBeanFactory.java:1344)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doGetBeanNamesForType(DefaultListableBeanFactory.java:356)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanNamesForType(DefaultListableBeanFactory.java:327)
    at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:644)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:461)
    at org.springframework.context.annotation.AnnotationConfigApplicationContext.<init>(AnnotationConfigApplicationContext.java:73)
    at com.main.application.App.main(App.java:10)

这是我的 XML 文件，但我试图摆脱使用 XML 而只使用注释，所以我将这个简单的程序作为实践来理解。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans 
http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context 
http://www.springframework.org/schema/context/spring-context-3.2.xsd">


    <context:annotation-config></context:annotation-config>

</beans>

Answer 1

这不需要任何 xml 配置

public class App {

 public static void main(String[] args) {

  ApplicationContext ctx = new AnnotationConfigApplicationContext(Config.class);

  Logger logger = ctx.getBean(Logger.class);
  logger.writeConsole("Hello there");
  logger.writeFile("Hi again");
 }
}

配置类

@Configuration
@ComponentScan
public class Config {
}

控制台编写器

@Component
public class ConsoleWriter implements LogWriter{

  public void write(String text) {
      System.out.println("Console Writer: "+text);

  }
}

文件编写器

@Component
public class FileWriter implements LogWriter {
   public void write(String text) {
      System.out.println("FileWriter: " + text);
   }
}

Loger

@Component
public class Logger {

@Autowired
private ConsoleWriter consoleWriter;
@Autowired
private FileWriter fileWriter;

public void setConsoleWriter(ConsoleWriter consoleWriter) {
    this.consoleWriter = consoleWriter;
}

public void setFileWriter(FileWriter fileWriter) {
    this.fileWriter = fileWriter;
}


public void writeFile(String text) {
    fileWriter.write(text);
}

public void writeConsole(String text) {
    consoleWriter.write(text);
}

}

接口 LogWriter

public interface LogWriter {

  public void write(String text);

}

Answer 2

假设您使用的是 Spring 3.2。您的 App.java 应如下所示：

@Configuration
@ComponentScan
public class App {

  public static void main(String[] args) {
    AnnotationConfigApplicationContext ctx = new    
            AnnotationConfigApplicationContext(App.class);

    Logger logger = ctx.getBean(Logger.class);

    logger.writeConsole("Hello there");
    logger.writeFile("Hi again");

    ctx.close();
  }

}

@Configuration：告诉Spring这个类是一个配置类

@ComponentScan：告诉 Spring 扫描该包中的所有类。

从此起点不再需要 xml。

FileWriter、ConsoleWriter 和 Logger 是组件。当您定义组件时，您可以在这些类上使用 @Autowired 注释。您需要在这些类上添加@Component 注解。

请注意，@Bean getLogger() 方法会在运行时产生异常，因为 Spring 会找到两个名为“logger”的定义。因此，要使您的应用程序正确运行，您需要删除该方法。