设计模式-装饰者模式

深藏阁楼爱情的钟 2022-05-24 12:55 225阅读 0赞

#### 定义 ####

**装饰者模式**通过委托的方式，将对象的功能叠加，从而增强原有对象功能。

#### 角色 ####

<table> 
 <thead> 
  <tr> 
   <th>角色</th> 
   <th align="center">作用</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>组件接口</td> 
   <td align="center">是装饰者或者被装饰者的超类或者接口，定义了被装饰者的核心功能和修饰者需要加强的方法</td> 
  </tr> 
  <tr> 
   <td>具体组件</td> 
   <td align="center">实现了组件接口的核心方法，完成业务逻辑，是被装饰的对象</td> 
  </tr> 
  <tr> 
   <td>装饰者</td> 
   <td align="center">实现组件接口，并持有具体的被装饰者对象</td> 
  </tr> 
  <tr> 
   <td>具体装饰者</td> 
   <td align="center">具体实现装饰的业务逻辑，各个具体装饰者是可以叠加的</td> 
  </tr> 
 </tbody> 
</table>

#### 类图 ####

![这里写图片描述][70]

#### 应用 ####

假设要将某结果以HTML进行发布，那么首先需要将内容转化为HTML文本。同时，内容要通过HTTP传输，还需要为其添加HTTP头。

#### 代码 ####

/** * 装饰接口 * @author wzx * @time 2018/5/27 */
    public interface IPacketCreator { 
        String handlerContent();
    }

/** * 具体组件 * @author wzx * @time 2018/5/27 */
    public class PackeyBodyCreator implements IPacketCreator { 
        @Override
        public String handlerContent() {
            return "Content of Packet";
        }
    }

/** * 装饰者 * @author wzx * @time 2018/5/27 */
    public abstract class PacketDecorator implements IPacketCreator { 
    
        IPacketCreator packetCreator;
    
        public PacketDecorator(IPacketCreator packetCreator) {
            this.packetCreator = packetCreator;
        }
    
    }

/** * @author wzx * @time 2018/5/27 */
    public class PacketHTMLHeaderCreator extends PacketDecorator { 
    
        public PacketHTMLHeaderCreator(IPacketCreator packetCreator) {
            super(packetCreator);
        }
    
        @Override
        public String handlerContent() {
            String sb = "<html>" +
                "<body>" +
                packetCreator.handlerContent() +
                "</body>" +
                "</html>";
            return sb;
        }
    }

/** * @author wzx * @time 2018/5/27 */
    public class PacketHTTPHeaderCreator extends PacketDecorator{ 
    
        public PacketHTTPHeaderCreator(IPacketCreator packetCreator) {
            super(packetCreator);
        }
    
        @Override
        public String handlerContent() {
            StringBuilder sb = new StringBuilder();
            sb.append("Cache-Control:no-cache");
            sb.append(packetCreator.handlerContent());
            return sb.toString();
        }
    }

public class Main {
        public static void main(String[] args) {
            PacketHTTPHeaderCreator creator = new PacketHTTPHeaderCreator(new PacketHTMLHeaderCreator(
                new PackeyBodyCreator()
            ));
            System.out.println(creator.handlerContent());
        }
    }

#### 输出结果 ####

Cache-Control:no-cache<html><body>Content of Packet</body></html>

[70]: /images/20220524/7eee618d9cde4dbeab819674671aa4ac.png