百度工程师教你玩转设计模式（装饰器模式）

package com.baidu.demo;public class Decorator {    // 抽象组件    static abstract class TaskProcessor {        abstract void process();    }    // 具体组件    static class TaskProcessorA extends TaskProcessor {        @Override        void process() {            System.out.println("TaskProcessorA处理完成");        }    }    // 具体组件    static class TaskProcessorB extends TaskProcessor {        @Override        void process() {            System.out.println("TaskProcessorB处理完成");        }    }    // 抽象装饰器    static abstract class TaskProcessDecorator extends TaskProcessor {        protected TaskProcessor processor;        public TaskProcessDecorator(TaskProcessor processor) {            this.processor = processor;        }        abstract void process();    }    // 具体装饰器    static class AfterTaskProcessDecorator extends TaskProcessDecorator {        public AfterTaskProcessDecorator(TaskProcessor processor) {            super(processor);        }
        @Override        void process() {            processor.process();            afterProcess();        }
        void afterProcess() {            System.out.println("任务处理完毕，发送消息...");        }    }
    public static void main(String[] args) {        // 扩展之前        System.out.println("==========before==========");        TaskProcessor processorA = new TaskProcessorA();        processorA.process();        TaskProcessor processorB = new TaskProcessorB();        processorB.process();
        // 装饰器扩展之后：TaskProcessorA TaskProcessorB并未做任何修改，即可实现功能的扩展        System.out.println("==========after==========");        TaskProcessor decoratorA = new AfterTaskProcessDecorator(processorA);        decoratorA.process();        TaskProcessor decoratorB = new AfterTaskProcessDecorator(processorB);        decoratorB.process();    }}
// 输出结果如下==========before==========TaskProcessorA处理完成TaskProcessorB处理完成==========after==========TaskProcessorA处理完成任务处理完毕，发送消息...TaskProcessorB处理完成任务处理完毕，发送消息...

//具体组件，实现读取字节流public abstract class InputStream {    public int read(byte b[], int off, int len) {}}
//具体装饰器，作为InputStream的子类，扩展文件操作public class FileInputStream extends InputStream {    protected InputStream in;        public FileInputStream(String name) {        InputStream in = ... //此处省略，通过文件名创建对象        this.in = in;    }        public int read(byte b[], int off, int len) {        return this.in.read(b, off, len);    }}
//具体装饰器，作为FileInputStream的子类，扩展缓存操作public class BufferedInputStream extends FileInputStream {    protected FileInputStream in;    protected byte[] buffer;        public BufferedInputStream(FileInputStream in) {        this.in = in;    }        public int read(byte b[], int off, int len) {        if (this.buffer == null || this.buffer.length == 0) {            this.in.read(this.buffer, 0, in.lenght());        }                System.arraycopy(this.buffer, off, b, 0, len);        ...    }}
public static void main(String[] args) {    FileInputStream fs = new FileInputStream('./test.log');    BufferedInputStream bs = new BufferedInputStream(fs);        byte[] b;    bs.read(b, 0, 1);}

/** * 日志接口 */public interface Log {    void debug(String message);    void info(String message);    void warn(String message);    void error(String message);}
/** * Slf4j 日志 */public class Slf4jLog implements Log {
    //日志记录对象    private final Logger log = LoggerFactory.getLogger("system_log");
    @Override    public void debug(String message) {        if (log.isDebugEnabled()) {             log.debug(message);        }    }
    @Override    public void info(String message) {        if (log.isInfoEnabled()) {              log.info(message);        }    }
    @Override    public void warn(String message) {        if (log.isWarnEnabled()) {            log.warn(message);        }    }
    @Override    public void error(String message) {        if (log.isErrorEnabled()) {            log.error(message);        }    }}
/** * 日志装饰器 */public class LogDecorator implements Log {    protected Log log;
    public LogDecorator(Log log) {        this.log = log;    }
    @Override    public void debug(String message) {        log.debug(message);    }
    @Override    public void info(String message) {        log.info(message);    }
    @Override    public void warn(String message) {        log.warn(message);    }
    @Override    public void error(String message) {        log.error(message);    }}
/** * 邮件日志装饰器 */public class MailLogDecorator extends LogDecorator {    public MailLogDecorator(Log log) {        super(log);    }
    @Override    public void warn(String message) {        log.warn(message);        mail(message);    }
    @Override    public void error(String message) {        log.error(message);        mail(message);    }        public void mail(String message) {        //模拟邮件发送        log.info("邮件已发送，信息：" + message);    }}
/** * 短信日志装饰器 */public class SMSLogDecorator extends LogDecorator {    public SMSLogDecorator(Log log) {        super(log);    }        @Override    public void error(String message) {        log.error(message);        send(message);    }
    public void send(String message) {        //模拟短信发送        log.info("短信已发送，信息：" + message);    }}
/** * 如流日志装饰器 */public class InfoflowLogDecorator extends LogDecorator {    public InfoflowLogDecorator(Log log) {        super(log);    }
    @Override    public void warn(String message) {        log.warn(message);        send(message);    }        @Override    public void error(String message) {        log.error(message);        send(message);    }
        public void send(String message) {        //模拟如流发送        log.info("如流消息已发送，信息：" + message);    }}
/** * 日志测试类 */public class LogTest {
    /**     * 测试日志装饰器     */    @Test    public void testLogDecorator() {        Log log = new SMSLogDecorator(new InfoFlowLogDecorator(new MailLogDecorator(new Slf4jLog())));        log.debug("系统调试开启");        log.info("系统正常运行");        log.warn("数据为空警告");        log.error("db 连接错误");    }}===========output=========15:16:56.564 [main] DEBUG system_log - 系统调试开启15:16:56.566 [main] INFO  system_log - 系统正常运行15:16:56.566 [main] WARN  system_log - 数据为空警告15:16:56.566 [main] INFO  system_log - 邮件已发送，信息：数据为空警告15:16:56.566 [main] INFO  system_log - 如流消息已发送，信息：数据为空警告15:16:56.566 [main] ERROR system_log - db 连接错误15:16:56.566 [main] INFO  system_log - 邮件已发送，信息：db 连接错误15:16:56.566 [main] INFO  system_log - 如流消息已发送，信息：db 连接错误15:16:56.566 [main] INFO  system_log - 短信已发送，信息：db 连接错误
Process finished with exit code 0