最近看到责任链模式的时候每增加一个处理类，就必须在责任链的实现类中手动增加到责任链中，具体代码基本就是list.add(new FilterImpl()),可以看到每次增加一个处理类，就必须添加一行上面的代码，不符合开闭原则(面向修改关闭，面向扩展开放)。于是想到了Java的SPI机制，可以实现插拔式组件，而Java自带的SPI机制是寻找借口的所有实现类，虽然一直被诟病，但是在本次的插拔式中，它却成了一个优点，因为我们需要把所有的实现类都放入处理器链中。

类图如下：

上代码，嘻嘻！

1 packagecom.liekkas.spi.responsibility_chain_model;2

3 importlombok.Data;4

5 /**

6 * description 被处理的类7 *8 *@authorliekkas 2020/12/02 23:339 */

10 @Data11 public classReceipt {12 publicReceipt(String code,String message){13 this.code =code;14 this.message =message;15 }16 privateString code;17 privateString message;18 }

1 packagecom.liekkas.spi.responsibility_chain_model;2

3 /**

4 * description 处理器接口5 *6 *@authorliekkas 2020/12/02 23:307 */

8 public interfaceFilter {9

10 /**

11 * 处理方法12 *@paramreceipt receipt13 *@paramfilterChain filterChain14 */

15 voidhandle(Receipt receipt,FilterChain filterChain);16 }

1 packagecom.liekkas.spi.responsibility_chain_model;2

3 /**

4 * description 处理器链接口5 *6 *@authorliekkas 2020/12/02 23:317 */

8 public interfaceFilterChain {9

10 /**

11 * 处理方法12 *@paramreceipt receipt13 */

14 voidhandleReceipt(Receipt receipt);15 }

1 packagecom.liekkas.spi.responsibility_chain_model.impl;2

3 importcom.liekkas.spi.responsibility_chain_model.Filter;4 importcom.liekkas.spi.responsibility_chain_model.FilterChain;5 importcom.liekkas.spi.responsibility_chain_model.Receipt;6

7 /**

8 * description 具体的处理器19 *10 *@authorliekkas 2020/12/02 23:3511 */

12 public class FilterImpl1 implementsFilter {13

14 @Override15 public voidhandle(Receipt receipt, FilterChain filterChain) {16 if ("test001".equals(receipt.getCode())) {17 System.out.println("我是Filter1,我能处理test001,已经处理" +receipt.getMessage());18 }19 //自己处理不了该回执就往下传递

20 else{21 filterChain.handleReceipt(receipt);22 }23 }24 }

1 packagecom.liekkas.spi.responsibility_chain_model.impl;2

3 importcom.liekkas.spi.responsibility_chain_model.Filter;4 importcom.liekkas.spi.responsibility_chain_model.FilterChain;5 importcom.liekkas.spi.responsibility_chain_model.Receipt;6

7 /**

8 * description 具体的处理器29 *10 *@authorliekkas 2020/12/02 23:3511 */

12 public class FilterImpl2 implementsFilter {13

14 @Override15 public voidhandle(Receipt receipt, FilterChain filterChain) {16 if ("test002".equals(receipt.getCode())) {17 System.out.println("我是Filter2,我能处理test002,已经处理" +receipt.getMessage());18 }19 //自己处理不了该回执就往下传递

20 else{21 filterChain.handleReceipt(receipt);22 }23 }24 }

1 packagecom.liekkas.spi.responsibility_chain_model.impl;2

3 importcom.liekkas.spi.responsibility_chain_model.Filter;4 importcom.liekkas.spi.responsibility_chain_model.FilterChain;5 importcom.liekkas.spi.responsibility_chain_model.Receipt;6

7 /**

8 * description 具体的处理器39 *10 *@authorliekkas 2020/12/02 23:3511 */

12 public class FilterImpl3 implementsFilter {13

14 @Override15 public voidhandle(Receipt receipt, FilterChain filterChain) {16 if ("test003".equals(receipt.getCode())) {17 System.out.println("我是Filter3,我能处理test003,已经处理" +receipt.getMessage());18 }19 //自己处理不了该回执就往下传递

20 else{21 filterChain.handleReceipt(receipt);22 }23 }24 }

1 packagecom.liekkas.spi.responsibility_chain_model.impl;2

3 importcom.liekkas.spi.responsibility_chain_model.Filter;4 importcom.liekkas.spi.responsibility_chain_model.FilterChain;5 importcom.liekkas.spi.responsibility_chain_model.Receipt;6 importcom.liekkas.spi.responsibility_chain_model.container.ReceiptHandlerContainer;7

8 importjava.util.List;9

10 /**

11 * description 处理器链默认的实现类12 *13 *@authorliekkas 2020/12/02 23:3814 */

15 public class DefaultFilterChainImpl implementsFilterChain {16

17 /**

18 * 记录当前处理者位置19 */

20 private int index = 0;21 /**

22 * 处理器集合23 */

24 private static final ListFILTER_LIST;25

26 static{27 //从容器中获取处理器对象

28 FILTER_LIST =ReceiptHandlerContainer.getReceiptHandlerList();29 }30

31 @Override32 public voidhandleReceipt(Receipt receipt) {33 if (FILTER_LIST != null && FILTER_LIST.size() > 0) {34 if (index

1 packagecom.liekkas.spi.responsibility_chain_model.container;2

3 importcom.liekkas.spi.responsibility_chain_model.Filter;4

5 importjava.util.ArrayList;6 importjava.util.List;7 importjava.util.ServiceLoader;8

9 /**

10 * description 装在过滤器的容器，采用SPI实现,当添加过滤器的时候只需按照SPI的格式要求，便可自动装载，11 * 无需其他操作，即实现了插拔式，即插即用。12 *13 *@authorliekkas 2020/12/02 23:4314 */

15 public classReceiptHandlerContainer {16 privateReceiptHandlerContainer() {17 }18

19 public static ListgetReceiptHandlerList() {20 //SPI机制，寻找所有的实现类

21 ServiceLoader filtersImplements = ServiceLoader.load(Filter.class);22 List receiptHandlerList = new ArrayList<>();23 //把找到的所有的Filter的实现类放入List中

24 for(Filter filtersImplement : filtersImplements) {25 receiptHandlerList.add(filtersImplement);26 }27 returnreceiptHandlerList;28 }29 }

最后在resources目录下建一个文件名为com.liekkas.spi.responsibility_chain_model.Filter的文件，文件名即是接口的全限定接口名，完整的目录如下：

src/main/resources/META-INF/services/com.liekkas.spi.responsibility_chain_model.Filter

文件内容为：

com.liekkas.spi.responsibility_chain_model.impl.FilterImpl1

com.liekkas.spi.responsibility_chain_model.impl.FilterImpl2

com.liekkas.spi.responsibility_chain_model.impl.FilterImpl3

下面我们就建一个客户端的测试类，来看一下效果，激动人心的时刻到了，嘿嘿嘿

packagecom.liekkas.spi.responsibility_chain_model;importcom.liekkas.spi.responsibility_chain_model.impl.DefaultFilterChainImpl;importjava.util.ArrayList;importjava.util.List;/*** description 测试客户端

*

*@authorliekkas 2020/12/02 23:52*/

public classClient {public static voidmain(String[] args) {//模拟回执

List receiptList =ReceiptBuilder.generateReceiptList();for(Receipt receipt : receiptList) {//回执处理链对象

FilterChain receiptHandleChain = newDefaultFilterChainImpl();

receiptHandleChain.handleReceipt(receipt);

}

}static classReceiptBuilder{public static ListgenerateReceiptList(){

List resultList = new ArrayList<>();

resultList.add(new Receipt("test001","测试消息one"));

resultList.add(new Receipt("test002","测试消息two"));

resultList.add(new Receipt("test003","测试消息three"));returnresultList;

}

}

}

执行的结果如下：

小结：通过本次的学习，不仅对责任链模式有了更深的理解也对SPI机制有了更深的理解，同时两者的结合实现了插拔式，也让我对软件的设计原则有了更深一步的认识！