| 责任链模式 责任链模式顾名思义，对于一个请求会去创建一条接受者链。这种模式会解耦一种类型的请求中接受者和发送者，该模式模式属于行为模式的一种。
在该模式当中，一般情况下，每个接受者都会有另外一个接受者的引用，如果该接受者无法处理该请求，请求会通过引用传入下一个接受者。 实现 我们创建一个抽象类AbstaractLogger，该类中含有日志的记录等级。然后我们会创建三个logger实现AbstractLogger。每一个logger都会检查并且比较消息的等级与该logger等级，判断打印或者不打印，并且传递消息到下一个logger。 
第一步 创建一个抽象的Logger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);
-
- }
创建具体的类实现AtstractLogger 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logger。设置每个Logger的错误等级以及每个logger的Next logger，每一个logger的NextLogger都是当前链的一部分。 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.");
- }
- }
校验输出 - 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.
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