Java设计模式应用——过滤器模式

storm引擎计算出一批中间告警结果，会发送一条kafka消息给告警入库服务，告警入库服务接收到kafka消息后读取中间告警文件，经过一系列处理后把最终告警存入mysql中。

实际上，中间告警结果可能有重复告警、错误告警、无用告警，告警入库服务会过滤，压缩中间告警，把用户关心的告警存入数据库。过滤的步骤较多，并且客户关心的告警可能会随时变化，写死的告警过滤很快就无法满足应用场景，这种场景下使用过滤器模式则很好满足业务上的不确定性欲扩展性。

告警入库服务涉及消息过滤和告警过滤，下面我们以消息过滤器来讲一下过滤器模式。

1、消息过滤器接口

package com.coshaho.learn.filter;

/**
 * 
 * IMessageFilter.java Create on 2017年5月13日 上午12:43:56    
 *    
 * 类功能说明:   告警消息过滤器
 *
 * Copyright: Copyright(c) 2013 
 * Company: COSHAHO
 * @Version 1.0
 * @Author coshaho
 */
public abstract class IMessageFilter implements Comparable<IMessageFilter>
{
    public int priority()
    {
        return 0;
    }
    
    public abstract boolean doFilter(Message msg);
    
    public int compareTo(IMessageFilter arg0)
    {
        return priority() - arg0.priority();
    }


}

2、时间过滤器

package com.coshaho.learn.filter;

import org.springframework.stereotype.Component;

/**
 * 
 * TimeFilter.java Create on 2017年5月13日 上午12:44:25    
 *    
 * 类功能说明:   时间过滤
 *
 * Copyright: Copyright(c) 2013 
 * Company: COSHAHO
 * @Version 1.0
 * @Author coshaho
 */
@Component
public class TimeFilter extends IMessageFilter
{
    
    public int priority() 
    {
        return 1;
    }

    public boolean doFilter(Message msg) 
    {
        if(msg.getHour() < 8 || msg.getHour() > 17)
        {
            System.out.println("Time filter false, message is " + msg);
            return false;
        }
        System.out.println("Time filter true, message is " + msg);
        return true;
    }

}

3、级别过滤器

package com.coshaho.learn.filter;

import org.springframework.stereotype.Component;

/**
 * 
 * ServerityFilter.java Create on 2017年5月13日 上午12:44:13    
 *    
 * 类功能说明:   级别过滤
 *
 * Copyright: Copyright(c) 2013 
 * Company: COSHAHO
 * @Version 1.0
 * @Author coshaho
 */
@Component
public class ServerityFilter extends IMessageFilter
{

    public int priority() {
        return 2;
    }

    public boolean doFilter(Message msg) {
        if(msg.getSeverity() == 0)
        {
            System.out.println("Severity filter false, message is " + msg);
            return false;
        }
        System.out.println("Severity filter true, message is " + msg);
        return true;
    }

}

4、类型过滤器

package com.coshaho.learn.filter;

import org.springframework.stereotype.Component;

/**
 * 
 * TypeFilter.java Create on 2017年5月13日 上午12:44:36    
 *    
 * 类功能说明:   类型过滤
 *
 * Copyright: Copyright(c) 2013 
 * Company: COSHAHO
 * @Version 1.0
 * @Author coshaho
 */
@Component
public class TypeFilter extends IMessageFilter{

    public int priority() 
    {
        return 3;
    }

    public boolean doFilter(Message msg) {
        
        if(msg.getType() < 3)
        {
            System.out.println("Type filter false, message is " + msg);
            return false;
        }
        System.out.println("Type filter true, message is " + msg);
        return false;
    }
    
    

}

5、消息监听服务

package com.coshaho.learn.filter;

import java.util.Collections;
import java.util.List;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.stereotype.Component;

/**
 * 
 * MessageListener.java Create on 2017年5月13日 上午12:44:49    
 *    
 * 类功能说明:   告警消息监听
 *
 * Copyright: Copyright(c) 2013 
 * Company: COSHAHO
 * @Version 1.0
 * @Author coshaho
 */
@Component
public class MessageListener 
{
    public static void main(String[] args)
    {
        @SuppressWarnings("resource")
        ApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring.xml"); 
        MessageListener listener = (MessageListener)context.getBean("messageListener");
        Message msg = new Message();
        msg.setHour(12);
        msg.setName("coshaho");
        msg.setType(5);
        msg.setSeverity(3);
        listener.listen(msg);
    }
    
    public void listen(Message msg)
    {
        excute(msg);
    }
    
    private boolean excute(Message msg)
    {
        @SuppressWarnings("unchecked")
        List<IMessageFilter> filters = (List<IMessageFilter>)SpringUtils.getBeansOfType(IMessageFilter.class);
        Collections.sort(filters);
        for(IMessageFilter filter : filters)
        {
            if(!filter.doFilter(msg))
            {
                return false;
            }
        }
        return true;
    }
}

6、Spring工具类

package com.coshaho.learn.filter;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Service;

@Service
public class SpringUtils implements ApplicationContextAware
{
    private static ApplicationContext context;

    public void setApplicationContext(ApplicationContext context)
            throws BeansException 
    {
        SpringUtils.context = context;
    }
    
    @SuppressWarnings({ "rawtypes", "unchecked" })
    public static List getBeansOfType(Class clazz)
    {
        Map map = context.getBeansOfType(clazz);
        return new ArrayList(map.values());
    }
}

7、消息类

package com.coshaho.learn.filter;

/**
 * 
 * Message.java Create on 2017年5月13日 上午12:43:37    
 *    
 * 类功能说明:   告警消息
 *
 * Copyright: Copyright(c) 2013 
 * Company: COSHAHO
 * @Version 1.0
 * @Author coshaho
 */
public class Message 
{
    private String name;
    
    private int hour;
    
    private int type;
    
    private int severity;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getHour() {
        return hour;
    }

    public void setHour(int hour) {
        this.hour = hour;
    }

    public int getType() {
        return type;
    }

    public void setType(int type) {
        this.type = type;
    }

    public int getSeverity() {
        return severity;
    }

    public void setSeverity(int severity) {
        this.severity = severity;
    }

    @Override
    public String toString() {
        return "Message [name=" + name + ", hour=" + hour + ", type=" + type
                + ", severity=" + severity + "]";
    }
}

可以看到，过滤器模式可以很方便的扩展过滤业务。