顾名思义,责任链模式为请求创建了一系列接收者对象.此模式根据请求类型将请求的发送方和接收方解耦.这种模式属于行为模式.
在这种模式中,通常每个接收者都包含对另一个接收者的引用.如果一个对象无法处理请求,则将其传递给下一个接收者,依此类推.
我们创建了一个抽象类 AbstractLogger 具有一定级别的日志记录.然后我们创建了三种类型的记录器,扩展了 AbstractLogger .每个记录器检查消息的级别并相应地打印,否则不打印并将消息传递给下一个记录器.
创建一个抽象记录器类.
AbstractLogger.java
public abstract class AbstractLogger { public static int INFO = 1; public static int DEBUG = 2; public static int ERROR = 3; protected int level; //next element in chain or responsibility protected AbstractLogger nextLogger; public void setNextLogger(AbstractLogger nextLogger){ this.nextLogger = nextLogger; } 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); }
创建扩展记录器的具体类.
ConsoleLogger.java
public class ConsoleLogger extends AbstractLogger { public ConsoleLogger(int level){ this.level = level; } @Override protected void write(String message) { System.out.println("Standard Console::Logger: " + message); } }
ErrorLogger.java
public class ErrorLogger extends AbstractLogger { public ErrorLogger(int level){ this.level = level; } @Override protected void write(String message) { System.out.println("Error Console::Logger: " + message); } }
FileLogger.java
public class FileLogger extends AbstractLogger { public FileLogger(int level){ this.level = level; } @Override protected void write(String message) { System.out.println("File::Logger: " + message); } }
创建不同类型的记录器.为每个记录器分配错误级别并设置下一个记录器.每个记录器中的下一个记录器代表链的一部分.
ChainPatternDemo.java
public class ChainPatternDemo { private 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; } public static void main(String[] args) { AbstractLogger loggerChain = 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."); } }
验证输出.
Standard Console::Logger: This is an information. File::Logger: This is an debug level information. Standard Console::Logger: This is an debug level information. Error Console::Logger: This is an error information. File::Logger: This is an error information. Standard Console::Logger: This is an error information.