如何使用构造函数来初始化下一个链来构建责任链

Question

如何使用构造函数初始化链来构建责任链。这是我的Runner.class，我正在使用setNext方法构建我的链。

public class Runner {
private static final String ENTER_PATH = "Enter path: ";
private static final String FILTER_BY_NAME = "Filter by name? (0/1)";
private static final String ENTER_NAME_PARAMETER = "Enter name parameter please: ";
private static final String FILTER_BY_EXTENSION = "Filter by extension? (0/1)";
private static final String ENTER_EXTENSION_PARAMETER = "Enter extension please (without '.'): ";
private static final String FILTER_BY_SIZE = "Filter by size? (0/1)";
private static final String ENTER_SIZE_TO = "Enter upper limit searching files in kb";
private static final String ENTER_SIZE_FROM = "Enter lower limit searching files in kb";
private static final String TRUE="1";
private Scanner scanner;
private List<File> fileList;

public Runner() {
    this.scanner = new Scanner(System.in);
    this.fileList = new ArrayList<>();
}
private String getDirName(){
    System.out.println(ENTER_PATH);
    return scanner.nextLine();
}

private Handler getChainOfResponsibility(){
    GeneralHandler generalHandler = new GeneralHandler();
    Handler lastHandler = generalHandler;

    System.out.println(FILTER_BY_NAME);
    if (scanner.nextLine().equals(TRUE)) {
        System.out.println(ENTER_NAME_PARAMETER);
        String name = scanner.nextLine();
        Handler nameHandler = new NameHandler(name);
        lastHandler.setHandler(nameHandler);
        lastHandler = nameHandler;
    }
    System.out.println(FILTER_BY_EXTENSION);
    if (scanner.nextLine().equals(TRUE)) {
        System.out.println(ENTER_EXTENSION_PARAMETER);
        Handler extensionHandler = new ExtensionHandler(scanner.nextLine());
        lastHandler.setHandler(extensionHandler);
        lastHandler = extensionHandler;
    }

    System.out.println(FILTER_BY_SIZE);
    if (scanner.nextLine().equals(TRUE)) {
        System.out.println(ENTER_SIZE_FROM);
        double fromSize = scanner.nextDouble();
        System.out.println(ENTER_SIZE_TO);
        double toSize = scanner.nextDouble();
        Handler sizeHandler = new SizeHandler(fromSize, toSize);
        lastHandler.setHandler(sizeHandler);
    }
    return generalHandler;
}

public void run() throws InterruptedException, IOException {
    findAllFiles(getDirName(), getChainOfResponsibility());
    showListOfFilteredFiles();
}

这是我的Handler抽象类

    public abstract class Handler {
    private Handler handler;
    public void setHandler(Handler handler) {
        this.handler = handler;
    }
    protected abstract boolean handleFilter(File file);
    public boolean doFilter(File file){
        if(handleFilter(file)){
            if(Objects.nonNull(handler)){
                return handler.doFilter(file);
            }
            return true;
        }
        return false;
    }
}

我也有它的实现。如何使它通过构造函数初始化!请帮助!

Answer 1

引言

你的实现是错误的;实现责任链模式的一般方法是，如果链中的每个链接无法处理请求，则将请求转发给下一个链接。传统上，如果当前类无法处理请求，则通过将其委托给抽象super类来完成。因此，简而言之，按照传统，我将重写您的Handler类如下:

public abstract class Handler {
  private Handler next;
  public void setHandler(Handler next) {
    this.next = next;
  }
  public boolean doFilter(File file) {
    return next.doFilter(file);
  }
}

我没有读过你的Handler或NameHandler类的合同，但我只是做一些假设，以便提供一个例子，NameHandler在重构其父类后可能看起来像:

public class NameHandler extends Handler {
  private final String name;
  public NameHandler(String name){
    this.name = name;
  }
  @Override
  public boolean doFilter(File file){
    final boolean result;
    if(file.getName().equals(name)){
      result = true;
    }else{
      result = super.doFilter(file);
    }
    return result;
  }
}

使用构造函数来配置链中的下一个链接，而不是像setHandler方法那样的"setter":

public abstract class Handler {
  private final Handler next;
  public Handler(Handler next){
    this.next = next;
  }
  public boolean doFilter(File file){
    return next.doFilter(file);
  }
}

现在你的子类需要处理非默认构造函数:

public class NameHandler extends Handler {
  private final String name;
  public NameHandler(String name, Handler next){
    super(next);
    this.name = name;
  }
  @Override
  public boolean doFilter(File file){
    final boolean result;
    if(file.getName().equals(name)){
      result = true;
    }else{
      result = super.doFilter(file);
    }
    return result;
  }
}