定义：使多个对象都有机会处理请求，从而避免请求的发送者和接收者之间的耦合关系。将这个对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它为止
使用场景：一连串对象处理一个请求的场景
实现：定义一个请求处理抽象类，包括一个自己的对象，作为后继处理者，定义处理方法包括处理逻辑和交给下一个处理者处理的调用代码
优点：减少请求者与处理者的耦合
代码示例：日志系统，当前级别大于等于日志处理者则记录
public abstract class Logger { public static int INFO = 1; public static int DEBUG = 2; public static int ERROR = 3;
protected Logger logger; protected int level;
public Logger(int level) { this.level = level; }
public Logger getLogger() { return logger; }
public void setLogger(Logger logger) { this.logger = logger; }
public abstract void log(int level, String message); }
public class InfoLogger extends Logger {
public InfoLogger(int level) { super(level); }
@Override public void log(int level, String message) { if (this.level <= level) { System.out.println("info："+message); } if (this.logger != null) { this.logger.log(level, message); } }
}
public class DebugLogger extends Logger {
public DebugLogger(int level) { super(level); }
@Override public void log(int level, String message) { if (this.level <= level) { System.out.println("debug："+message); } if (this.logger != null) { this.logger.log(level, message); }
}
}
public class ErrorLogger extends Logger {
public ErrorLogger(int level) { super(level); }
@Override public void log(int level, String message) { if (this.level <= level) { System.out.println("error："+message); } if (this.logger != null) { this.logger.log(level, message); }
}
}
public class Main {
public static void main(String[] args) { InfoLogger info = new InfoLogger(Logger.INFO); DebugLogger debug = new DebugLogger(Logger.DEBUG); ErrorLogger error = new ErrorLogger(Logger.ERROR); info.setLogger(debug); debug.setLogger(error); System.out.println("debug"); info.log(Logger.DEBUG, "debug级别日志消息"); System.out.println("error"); info.log(Logger.ERROR, "error级别日志消息"); }
} 结果：
