通过装饰器模式，可以通过多个类包装在一起，组合多个功能，实现不同功能需求可拔插。

例：一个 redis 操作类，需要实现以下几个功能。

1. 执行 redis 命令
2. 统计耗时
3. 链路监控打点

public interface RedisClient {

    void exec(String cmd);

}

public class DefaultRedisClient implements RedisClient {

    @Override
    public void exec(final String cmd) {
        System.out.println("执行 redis 命令: " + cmd);
    }
}

public class TimeCostRedisClient implements RedisClient {

    // 被装饰对象
    private final RedisClient decorator;

    public TimeCostRedisClient(final RedisClient decorator) {
        this.decorator = decorator;
    }

    @Override
    public void exec(final String cmd) {
        final long start = System.currentTimeMillis();
        decorator.exec(cmd);
        final long end = System.currentTimeMillis();
        System.out.println("执行 redis 命令耗时: " + (end - start) + "ms");
    }
}


public class TraceRedisClient implements RedisClient {

    // 被装饰对象
    private final RedisClient decorator;

    public TraceRedisClient(final RedisClient decorator) {
        this.decorator = decorator;
    }

    @Override
    public void exec(final String cmd) {
        final String uuid = UUID.randomUUID().toString();
        System.out.println("链路监控开始: " + uuid);
        decorator.exec(cmd);
        System.out.println("链路监控结束: " + uuid);
    }
}

测试类

public class RedisApp {

    public static void main(String[] args) {
        final RedisClient client = new DefaultRedisClient();
        final TimeCostRedisClient timeCostRedisClient = new TimeCostRedisClient(client);
        final TraceRedisClient traceRedisClient = new TraceRedisClient(timeCostRedisClient);
        traceRedisClient.exec("set hello world");
    }
}