浅谈Java中注解Annotation的定义、使用、解析

package cc.rulian.ann;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/** 
 * 类注释
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface MyTable
{
  public String name() default "";
  public String version() default "1";
}

package cc.rulian.ann;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;


/** 
 * 字段注释
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)

public @interface MyField {
  public String name() default "";   //名称
  public String type() default "";  //类型
  
}

package cc.rulian.ann;

import java.util.Date;

/**
 * 基础日志
 * 
 */
@MyTable(name="T_BaseLog",version="2")
public class BaseLog{
  
  @MyField(name="addTime",type="Date")
  private Date log_time; // 时间

  @MyField(name="log_level",type="String")
  private String log_level; // 级别

  @MyField(name="message",type="String")
  private String message; // 日志内容

  public Date getLog_time()
  {
    return log_time;
  }

  public void setLog_time(Date log_time)
  {
    this.log_time = log_time;
  }

  public String getLog_level()
  {
    return log_level;
  }

  public void setLog_level(String log_level)
  {
    this.log_level = log_level;
  }

  public String getMessage()
  {
    return message;
  }

  public void setMessage(String message)
  {
    this.message = message;
  }

}

package cc.rulian.ann;

import java.lang.reflect.Field;

/**
 * 读取注释
 */
public class ReadAnn
{
  public static void main(String[] args)
  {
    // 读取类的注释
    BaseLog obj = new BaseLog();
    // Annotation[] arr = obj.getClass().getAnnotations(); //得到所有注释
    MyTable table = obj.getClass().getAnnotation(MyTable.class); // 取得指定注释

    System.out.println("类注释（name）: " + table.name());
    System.out.println("类注释（version）: " + table.version());

    // 读取属性的注释
    Field[] fields = obj.getClass().getDeclaredFields();
    for (Field f : fields)
    {
      // Annotation[] arr2 = f.getAnnotations(); //得到所有注释
      MyField ff = f.getAnnotation(MyField.class);// 取得指定注释
      if(ff != null)
      {
        System.out.println("属性（" + f.getName() + "）: " + ff.name() + " -- " + ff.type());
      }
    }
  }

}