Spring Extension （1） — BeanPostProcessor based Logger Injection

场景：
Log Wrapper：slf4j，编码中每个类都需要通过

[java]
private static final Logger LOGGER = LoggerFactory.getLogger(ErrorHandler.class);

private static final Logger LOGGER = LoggerFactory.getLogger(ErrorHandler.class);这种非智能的硬编码方式来生成logger实例.

优化：

在spring框架中,每个类实例化的是由spring ioc完成的.实现BeanPostProcessor接口能够在实例初始化完成后做一些自定义的逻辑。

spring基于Annotation的初始化类就是实现了BeanPostProcessor接口。例如：@Required && RequiredAnnotationBeanPostProcessor。

故使用如下方式自动化初始Logger实例-基于spring 2.5-3.x：

1、定义Annotation：
[java]
/**
* Log Annotation for Logger Injection
**/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
@Documented
public @inte易做图ce Log {
String value() default "";
}

/**
* Log Annotation for Logger Injection
**/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
@Documented
public @inte易做图ce Log {
String value() default "";
}

2、在目标类定义：

[java]
@Component
public class LoggerDemo{　　
     @Log　　
     private Logger logger;　　
     //some methods　　
     //some properties
}

@Component
public class LoggerDemo{　　
     @Log　　
     private Logger logger;　　
     //some methods　　
     //some properties
}

3、自定义BeanPostProcessor

[java]
/**
* init the slf4j logger in each spring bean
*/
@Component
public class LoggerBeanPostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
        ReflectionUtils.doWithFields(bean.getClass(),new FieldCallback() { // spring reflection utils
            @Override
            public void doWith(Field field) throws IllegalArgumentException, IllegalAccessException {
                ReflectionUtils.makeAccessible(field);

                if (field.getType().equals(Logger.class) && field.isAnnotationPresent(Log.class)) {//Log Annotation check
                    Log logAnnotation = field.getAnnotation(Log.class);
                    String loggerName = logAnnotation.value();
                    Logger logger = null;
                    if (loggerName != null && !loggerName.equals("")) {
                        logger = LoggerFactory.getLogger(loggerName);
                    }else {
                        logger = LoggerFactory.getLogger(bean.getClass());
                    }
                    field.set(bean, logger);// init value
                }
            }
        });
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

}

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补充：软件开发 , Java ,