职责连模式

落日映苍穹つ 2021-09-17 04:16 316阅读 0赞

职责链模式：为请求创建了一个接收者对象的链。这种模式给予请求的类型，对请求的发送者和接收者进行解耦。这种类型的设计模式属于行为型模式。

**意图：**避免请求发送者与接收者耦合在一起，让多个对象都有可能接收请求，将这些对象连接成一条链，并且沿着这条链传递请求，直到有对象处理它为止。

**主要解决：**职责链上的处理者负责处理请求，客户只需要将请求发送到职责链上即可，无须关心请求的处理细节和请求的传递，所以职责链将请求的发送者和请求的处理者解耦了。

**何时使用：**在处理消息的时候以过滤很多道。

**使用场景：** 1、有多个对象可以处理同一个请求，具体哪个对象处理该请求由运行时刻自动确定。 2、在不明确指定接收者的情况下，向多个对象中的一个提交一个请求。 3、可动态指定一组对象处理请求。

**注意事项：**在 JAVA WEB 中遇到很多应用。

实例UML图：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dhbmdfc2h1eXU_size_16_color_FFFFFF_t_70][]

实例代码：

@Slf4j
    public abstract class AbstractLogger {
    
        public static int INFO = 1;
        public static int DEBUG = 2;
        public static int ERROR = 3;
    
        protected int level;
    
        protected AbstractLogger nextLogger;
    
        public void setNextLogger(AbstractLogger abstractLogger) {
            this.nextLogger = abstractLogger;
        }
    
        public void logMessage(int level, String message) {
            if (this.level <= level) {
                write(message);
            }
            if (nextLogger != null) {
                nextLogger.logMessage(level, message);
            }
        }
    
    
        abstract protected void write(String message);
    
    }

@Slf4j
    public class ConsoleLogger extends AbstractLogger {
    
        public ConsoleLogger(int level) {
            this.level = level;
        }
    
        @Override
        protected void write(String message) {
            log.info("Standard Console::Logger: " + message);
        }
    }

@Slf4j
    public class ErrorLogger extends AbstractLogger {
        public ErrorLogger(int level){
            this.level=level;
        }
        @Override
        protected void write(String message) {
            log.info("Error Console::Logger: " + message);
        }
    }

@Slf4j
    public class FileLogger extends AbstractLogger {
    
        public FileLogger(int level) {
            this.level = level;
        }
    
        @Override
        protected void write(String message) {
            log.info("File::Logger: " + message);
        }
    }

public class LogTest {
    
        public static AbstractLogger getChainOfLoggers() {
    
            AbstractLogger errorLogger = new ErrorLogger(AbstractLogger.ERROR);
            AbstractLogger fileLogger = new FileLogger(AbstractLogger.DEBUG);
            AbstractLogger consoleLogger = new ConsoleLogger(AbstractLogger.INFO);
    
            errorLogger.setNextLogger(fileLogger);
            fileLogger.setNextLogger(consoleLogger);
    
            return errorLogger;
        }
    }

测试代码：

@RunWith(SpringRunner.class)
    @SpringBootTest
    public class ChainresponsibilityApplicationTests {
    
    	@Test
    	public void contextLoads() {
    
    		AbstractLogger loggerChain =LogTest.getChainOfLoggers();
    
    		loggerChain.logMessage(AbstractLogger.INFO,
    				"This is an information.");
    
    		loggerChain.logMessage(AbstractLogger.DEBUG,
    				"This is an debug level information.");
    
    		loggerChain.logMessage(AbstractLogger.ERROR,
    				"This is an error information.");
    	}
    
    }

运行结果：

2018-12-04 23:54:25.998  INFO 21860 --- \[           main\] com.shuyu.test.ConsoleLogger             : Standard Console::Logger: This is an information.  
2018-12-04 23:54:25.998  INFO 21860 --- \[           main\] com.shuyu.test.FileLogger                : File::Logger: This is an debug level information.  
2018-12-04 23:54:25.999  INFO 21860 --- \[           main\] com.shuyu.test.ConsoleLogger             : Standard Console::Logger: This is an debug level information.  
2018-12-04 23:54:25.999  INFO 21860 --- \[           main\] com.shuyu.test.ErrorLogger               : Error Console::Logger: This is an error information.  
2018-12-04 23:54:25.999  INFO 21860 --- \[           main\] com.shuyu.test.FileLogger                : File::Logger: This is an error information.  
2018-12-04 23:54:25.999  INFO 21860 --- \[           main\] com.shuyu.test.ConsoleLogger             : Standard Console::Logger: This is an error information

代码github地址：[https://github.com/iot-wangshuyu/designpatterns/tree/master/chainresponsibility][https_github.com_iot-wangshuyu_designpatterns_tree_master_chainresponsibility]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dhbmdfc2h1eXU_size_16_color_FFFFFF_t_70]: /images/20210901/c33fee312c4b42a2931abbf37e9e1e77.png
[https_github.com_iot-wangshuyu_designpatterns_tree_master_chainresponsibility]: https://github.com/iot-wangshuyu/designpatterns/tree/master/chainresponsibility