JAVA-设计模式-行为型模式

public class Request {
    private String name;
    private BigDecimal amount;

    public Request(String name, BigDecimal amount) {
        this.name = name;
        this.amount = amount;
    }

    public String getName() {
        return name;
    }

    public BigDecimal getAmount() {
        return amount;
    }
}

public interface Handler {
    // 返回Boolean.TRUE = 成功
    // 返回Boolean.FALSE = 拒绝
    // 返回null = 交下一个处理
	Boolean process(Request request);
}

public class ManagerHandler implements Handler {
    public Boolean process(Request request) {
        // 如果超过1000元，处理不了，交下一个处理:
        if (request.getAmount().compareTo(BigDecimal.valueOf(1000)) > 0) {
            return null;
        }
        // 对Bob有偏见:
        return !request.getName().equalsIgnoreCase("bob");
    }
}

public class HandlerChain {
    // 持有所有Handler:
    private List<Handler> handlers = new ArrayList<>();

    public void addHandler(Handler handler) {
        this.handlers.add(handler);
    }

    public boolean process(Request request) {
        // 依次调用每个Handler:
        for (Handler handler : handlers) {
            Boolean r = handler.process(request);
            if (r != null) {
                // 如果返回TRUE或FALSE，处理结束:
                System.out.println(request + " " + (r ? "Approved by " : "Denied by ") + handler.getClass().getSimpleName());
                return r;
            }
        }
        throw new RuntimeException("Could not handle request: " + request);
    }
}

// 构造责任链:
HandlerChain chain = new HandlerChain();
chain.addHandler(new ManagerHandler());
chain.addHandler(new DirectorHandler());
chain.addHandler(new CEOHandler());
// 处理请求:
chain.process(new Request("Bob", new BigDecimal("123.45")));
chain.process(new Request("Alice", new BigDecimal("1234.56")));
chain.process(new Request("Bill", new BigDecimal("12345.67")));
chain.process(new Request("John", new BigDecimal("123456.78")));

public class AHandler implements Handler {
    private Handler next;
    public void process(Request request) {
        if (!canProcess(request)) {
            // 手动交给下一个Handler处理:
            next.process(request);
        } else {
            ...
        }
    }
}

public class AuditFilter implements Filter {
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
        log(req);
        if (check(req)) {
            // 放行:
            chain.doFilter(req, resp);
        } else {
            // 拒绝:
            sendError(resp);
        }
    }
}

public class TextEditor {
    private StringBuilder buffer = new StringBuilder();

    public void copy() {
        ...
    }

    public void paste() {
        String text = getFromClipBoard();
        add(text);
    }

    public void add(String s) {
        buffer.append(s);
    }

    public void delete() {
        if (buffer.length() > 0) {
            buffer.deleteCharAt(buffer.length() - 1);
        }
    }

    public String getState() {
        return buffer.toString();
    }
}

TextEditor editor = new TextEditor();
editor.add("Command pattern in text editor.\n");
editor.copy();
editor.paste();
System.out.println(editor.getState());

public interface Command {
    void execute();
}

public class CopyCommand implements Command {
    // 持有执行者对象:
    private TextEditor receiver;

    public CopyCommand(TextEditor receiver) {
        this.receiver = receiver;
    }

    public void execute() {
        receiver.copy();
    }
}

public class PasteCommand implements Command {
    private TextEditor receiver;

    public PasteCommand(TextEditor receiver) {
        this.receiver = receiver;
    }

    public void execute() {
        receiver.paste();
    }
}

TextEditor editor = new TextEditor();
editor.add("Command pattern in text editor.\n");
// 执行一个CopyCommand:
Command copy = new CopyCommand(editor);
copy.execute();
editor.add("----\n");
// 执行一个PasteCommand:
Command paste = new PasteCommand(editor);
paste.execute();
System.out.println(editor.getState());

TextEditor editor = new TextEditor();
editor.add("Command pattern in text editor.\n");
editor.copy();
editor.paste();

public interface Command {
    void execute();
    void undo();
}

String s = "+861012345678";
System.out.println(s.matches("^\\+\\d+$"));

log("[{}] start {} at {}...", LocalTime.now().withNano(0), "engine", LocalDate.now());
// [11:02:18] start engine at 2020-02-21...

List<String> list = ...
for (Iterator<String> it = list.iterator(); it.hasNext(); ) {
    String s = it.next();
}

List<String> list = ...
for (String s : list) {

}

public class ReverseArrayCollection<T> implements Iterable<T> {
    // 以数组形式持有集合:
    private T[] array;

    public ReverseArrayCollection(T... objs) {
        this.array = Arrays.copyOfRange(objs, 0, objs.length);
    }

    public Iterator<T> iterator() {
        return ???;
    }
}

public class ReverseArrayCollection<T> implements Iterable<T> {
    private T[] array;

    public ReverseArrayCollection(T... objs) {
        this.array = Arrays.copyOfRange(objs, 0, objs.length);
    }

    public Iterator<T> iterator() {
        return new ReverseIterator();
    }

    class ReverseIterator implements Iterator<T> {
        // 索引位置:
        int index;

        public ReverseIterator() {
            // 创建Iterator时,索引在数组末尾:
            this.index = ReverseArrayCollection.this.array.length;
        }

        public boolean hasNext() {
            // 如果索引大于0,那么可以移动到下一个元素(倒序往前移动):
            return index > 0;
        }

        public T next() {
            // 将索引移动到下一个元素并返回(倒序往前移动):
            index--;
            return array[index];
        }
    }
}

public class Main {
    public static void main(String[] args) {
        new OrderFrame("Hanburger", "Nugget", "Chip", "Coffee");
    }
}

class OrderFrame extends JFrame {
    public OrderFrame(String... names) {
        setTitle("Order");
        setSize(460, 200);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Container c = getContentPane();
        c.setLayout(new FlowLayout(FlowLayout.LEADING, 20, 20));
        c.add(new JLabel("Use Mediator Pattern"));
        List<JCheckBox> checkboxList = addCheckBox(names);
        JButton selectAll = addButton("Select All");
        JButton selectNone = addButton("Select None");
        selectNone.setEnabled(false);
        JButton selectInverse = addButton("Inverse Select");
        new Mediator(checkBoxList, selectAll, selectNone, selectInverse);
        setVisible(true);
    }

    private List<JCheckBox> addCheckBox(String... names) {
        JPanel panel = new JPanel();
        panel.add(new JLabel("Menu:"));
        List<JCheckBox> list = new ArrayList<>();
        for (String name : names) {
            JCheckBox checkbox = new JCheckBox(name);
            list.add(checkbox);
            panel.add(checkbox);
        }
        getContentPane().add(panel);
        return list;
    }

    private JButton addButton(String label) {
        JButton button = new JButton(label);
        getContentPane().add(button);
        return button;
    }
}

public class Mediator {
    // 引用UI组件:
    private List<JCheckBox> checkBoxList;
    private JButton selectAll;
    private JButton selectNone;
    private JButton selectInverse;

    public Mediator(List<JCheckBox> checkBoxList, JButton selectAll, JButton selectNone, JButton selectInverse) {
        this.checkBoxList = checkBoxList;
        this.selectAll = selectAll;
        this.selectNone = selectNone;
        this.selectInverse = selectInverse;
        // 绑定事件:
        this.checkBoxList.forEach(checkBox -> {
            checkBox.addChangeListener(this::onCheckBoxChanged);
        });
        this.selectAll.addActionListener(this::onSelectAllClicked);
        this.selectNone.addActionListener(this::onSelectNoneClicked);
        this.selectInverse.addActionListener(this::onSelectInverseClicked);
    }

    // 当checkbox有变化时:
    public void onCheckBoxChanged(ChangeEvent event) {
        boolean allChecked = true;
        boolean allUnchecked = true;
        for (var checkBox : checkBoxList) {
            if (checkBox.isSelected()) {
                allUnchecked = false;
            } else {
                allChecked = false;
            }
        }
        selectAll.setEnabled(!allChecked);
        selectNone.setEnabled(!allUnchecked);
    }

    // 当点击select all:
    public void onSelectAllClicked(ActionEvent event) {
        checkBoxList.forEach(checkBox -> checkBox.setSelected(true));
        selectAll.setEnabled(false);
        selectNone.setEnabled(true);
    }

    // 当点击select none:
    public void onSelectNoneClicked(ActionEvent event) {
        checkBoxList.forEach(checkBox -> checkBox.setSelected(false));
        selectAll.setEnabled(true);
        selectNone.setEnabled(false);
    }

    // 当点击select inverse:
    public void onSelectInverseClicked(ActionEvent event) {
        checkBoxList.forEach(checkBox -> checkBox.setSelected(!checkBox.isSelected()));
        onCheckBoxChanged(null);
    }
}

public class TextEditor {
    private StringBuilder buffer = new StringBuilder();

    public void add(char ch) {
        buffer.append(ch);
    }

    public void add(String s) {
        buffer.append(s);
    }

    public void delete() {
        if (buffer.length() > 0) {
            buffer.deleteCharAt(buffer.length() - 1);
        }
    }
}

public class TextEditor {
    ...

    // 获取状态:
    public String getState() {
        return buffer.toString();
    }

    // 恢复状态:
    public void setState(String state) {
        this.buffer.delete(0, this.buffer.length());
        this.buffer.append(state);
    }
}

public class Store {
    Customer customer;
    Admin admin;

    private Map<String, Product> products = new HashMap<>();

    public void addNewProduct(String name, double price) {
        Product p = new Product(name, price);
        products.put(p.getName(), p);
        // 通知用户:
        customer.onPublished(p);
        // 通知管理员:
        admin.onPublished(p);
    }

    public void setProductPrice(String name, double price) {
        Product p = products.get(name);
        p.setPrice(price);
        // 通知用户:
        customer.onPriceChanged(p);
        // 通知管理员:
        admin.onPriceChanged(p);
    }
}

public class Store {
    private List<ProductObserver> observers = new ArrayList<>();
    private Map<String, Product> products = new HashMap<>();

    // 注册观察者:
    public void addObserver(ProductObserver observer) {
        this.observers.add(observer);
    }

    // 取消注册:
    public void removeObserver(ProductObserver observer) {
        this.observers.remove(observer);
    }

    public void addNewProduct(String name, double price) {
        Product p = new Product(name, price);
        products.put(p.getName(), p);
        // 通知观察者:
        observers.forEach(o -> o.onPublished(p));
    }

    public void setProductPrice(String name, double price) {
        Product p = products.get(name);
        p.setPrice(price);
        // 通知观察者:
        observers.forEach(o -> o.onPriceChanged(p));
    }
}

// observer:
Admin a = new Admin();
Customer c = new Customer();
// store:
Store store = new Store();
// 注册观察者:
store.addObserver(a);
store.addObserver(c);

store.addObserver(new ProductObserver() {
    public void onPublished(Product product) {
        System.out.println("[Log] on product published: " + product);
    }

    public void onPriceChanged(Product product) {
        System.out.println("[Log] on product price changed: " + product);
    }
});

public interface ProductObservable { // 注意此处拼写是Observable不是Observer!
    void addObserver(ProductObserver observer);
    void removeObserver(ProductObserver observer);
}

public class Store implements ProductObservable {
    ...
}

public interface ProductObserver {
    void onEvent(ProductEvent event);
}

observers.forEach(o -> o.onPublished(p));

if (state == ONLINE) {
    // 闪烁图标
} else if (state == BUSY) {
    reply("现在忙，稍后回复");
} else if ...

public class DisconnectedState implements State {
    public String init() {
        return "Bye!";
    }

    public String reply(String input) {
        return "";
    }
}

public class ConnectedState implements State {
    public String init() {
        return "Hello, I'm Bob.";
    }

    public String reply(String input) {
        if (input.endsWith("?")) {
            return "Yes. " + input.substring(0, input.length() - 1) + "!";
        }
        if (input.endsWith(".")) {
            return input.substring(0, input.length() - 1) + "!";
        }
        return input.substring(0, input.length() - 1) + "?";
    }
}

public class BotContext {
	private State state = new DisconnectedState();

	public String chat(String input) {
		if ("hello".equalsIgnoreCase(input)) {
            // 收到hello切换到在线状态:
			state = new ConnectedState();
			return state.init();
		} else if ("bye".equalsIgnoreCase(input)) {
            /  收到bye切换到离线状态:
			state = new DisconnectedState();
			return state.init();
		}
		return state.reply(input);
	}
}

Scanner scanner = new Scanner(System.in);
BotContext bot = new BotContext();
for (;;) {
    System.out.print("> ");
    String input = scanner.nextLine();
    String output = bot.chat(input);
    System.out.println(output.isEmpty() ? "(no reply)" : "< " + output);
}

import java.util.Arrays;

public class Main {
    public static void main(String[] args) throws InterruptedException {
        String[] array = { "apple", "Pear", "Banana", "orange" };
        Arrays.sort(array, String::compareToIgnoreCase);
        System.out.println(Arrays.toString(array));
    }
}

import java.util.*;

public class Main {
    public static void main(String[] args) throws InterruptedException {
        String[] array = { "apple", "Pear", "Banana", "orange" };
        sort(array, String::compareToIgnoreCase);
        System.out.println(Arrays.toString(array));
    }

    static <T> void sort(T[] a, Comparator<? super T> c) {
        for (int i = 0; i < a.length - 1; i++) {
            for (int j = 0; j < a.length - 1 - i; j++) {
                if (c.compare(a[j], a[j + 1]) > 0) { // 注意这里比较两个元素的大小依赖传入的策略
                    T temp = a[j];
                    a[j] = a[j + 1];
                    a[j + 1] = temp;
                }
            }
        }
    }
}

public interface DiscountStrategy {
    // 计算折扣额度:
    BigDecimal getDiscount(BigDecimal total);
}

public class UserDiscountStrategy implements DiscountStrategy {
    public BigDecimal getDiscount(BigDecimal total) {
        // 普通会员打九折:
        return total.multiply(new BigDecimal("0.1")).setScale(2, RoundingMode.DOWN);
    }
}

public class OverDiscountStrategy implements DiscountStrategy {
    public BigDecimal getDiscount(BigDecimal total) {
        // 满100减20优惠:
        return total.compareTo(BigDecimal.valueOf(100)) >= 0 ? BigDecimal.valueOf(20) : BigDecimal.ZERO;
    }
}

public class DiscountContext {
    // 持有某个策略:
    private DiscountStrategy strategy = new UserDiscountStrategy();

    // 允许客户端设置新策略:
    public void setStrategy(DiscountStrategy strategy) {
        this.strategy = strategy;
    }

    public BigDecimal calculatePrice(BigDecimal total) {
        return total.subtract(this.strategy.getDiscount(total)).setScale(2);
    }
}

DiscountContext ctx = new DiscountContext();

// 默认使用普通会员折扣:
BigDecimal pay1 = ctx.calculatePrice(BigDecimal.valueOf(105));
System.out.println(pay1);

// 使用满减折扣:
ctx.setStrategy(new OverDiscountStrategy());
BigDecimal pay2 = ctx.calculatePrice(BigDecimal.valueOf(105));
System.out.println(pay2);

// 使用Prime会员折扣:
ctx.setStrategy(new PrimeDiscountStrategy());
BigDecimal pay3 = ctx.calculatePrice(BigDecimal.valueOf(105));
System.out.println(pay3);

public class Setting {
    public final String getSetting(String key) {
        String value = readFromDatabase(key);
        return value;
    }

	private String readFromDatabase(String key) {
        // TODO: 从数据库读取
    }
}

public class Setting {
    public final String getSetting(String key) {
        // 先从缓存读取:
        String value = lookupCache(key);
        if (value == null) {
            // 在缓存中未找到,从数据库读取:
            value = readFromDatabase(key);
            System.out.println("[DEBUG] load from db: " + key + " = " + value);
            // 放入缓存:
            putIntoCache(key, value);
        } else {
            System.out.println("[DEBUG] load from cache: " + key + " = " + value);
        }
        return value;
    }
}

public abstract class AbstractSetting {
    public final String getSetting(String key) {
        String value = lookupCache(key);
        if (value == null) {
            value = readFromDatabase(key);
            putIntoCache(key, value);
        }
        return value;
    }

    protected abstract String lookupCache(String key);

    protected abstract void putIntoCache(String key, String value);
}

public class LocalSetting extends AbstractSetting {
    private Map<String, String> cache = new HashMap<>();

    protected String lookupCache(String key) {
        return cache.get(key);
    }

    protected void putIntoCache(String key, String value) {
        cache.put(key, value);
    }
}

public class RedisSetting extends AbstractSetting {
    private RedisClient client = RedisClient.create("redis://localhost:6379");

    protected String lookupCache(String key) {
        try (StatefulRedisConnection<String, String> connection = client.connect()) {
            RedisCommands<String, String> commands = connection.sync();
            return commands.get(key);
        }
    }

    protected void putIntoCache(String key, String value) {
        try (StatefulRedisConnection<String, String> connection = client.connect()) {
            RedisCommands<String, String> commands = connection.sync();
            commands.set(key, value);
        }
    }
}

AbstractSetting setting1 = new LocalSetting();
System.out.println("test = " + setting1.getSetting("test"));
System.out.println("test = " + setting1.getSetting("test"));

AbstractSetting setting2 = new RedisSetting();
System.out.println("autosave = " + setting2.getSetting("autosave"));
System.out.println("autosave = " + setting2.getSetting("autosave"));

void scan(File dir, List<File> collector) {
    for (File file : dir.listFiles()) {
        if (file.isFile() && file.getName().endsWith(".java")) {
            collector.add(file);
        } else if (file.isDir()) {
            // 递归调用:
            scan(file, collector);
        }
    }
}

public interface Visitor {
    // 访问文件夹:
    void visitDir(File dir);
    // 访问文件:
    void visitFile(File file);
}

public class FileStructure {
    // 根目录:
    private File path;
    public FileStructure(File path) {
        this.path = path;
    }
}

public class FileStructure {
    ...

    public void handle(Visitor visitor) {
		scan(this.path, visitor);
	}

	private void scan(File file, Visitor visitor) {
		if (file.isDirectory()) {
            // 让访问者处理文件夹:
			visitor.visitDir(file);
			for (File sub : file.listFiles()) {
                // 递归处理子文件夹:
				scan(sub, visitor);
			}
		} else if (file.isFile()) {
            // 让访问者处理文件:
			visitor.visitFile(file);
		}
	}
}

FileStructure fs = new FileStructure(new File("."));
fs.handle(new JavaFileVisitor());

public class JavaFileVisitor implements Visitor {
    public void visitDir(File dir) {
        System.out.println("Visit dir: " + dir);
    }

    public void visitFile(File file) {
        if (file.getName().endsWith(".java")) {
            System.out.println("Found java file: " + file);
        }
    }
}

public class ClassFileCleanerVisitor implements Visitor {
	public void visitDir(File dir) {
	}

	public void visitFile(File file) {
		if (file.getName().endsWith(".class")) {
			System.out.println("Will clean class file: " + file);
		}
	}
}

import java.io.*;
import java.nio.file.*;
import java.nio.file.attribute.*;

public class Main {
    public static void main(String[] args) throws IOException {
        Files.walkFileTree(Paths.get("."), new MyFileVisitor());
    }
}

// 实现一个FileVisitor:
class MyFileVisitor extends SimpleFileVisitor<Path> {
    // 处理Directory:
    public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
        System.out.println("pre visit dir: " + dir);
        // 返回CONTINUE表示继续访问:
        return FileVisitResult.CONTINUE;
    }

    // 处理File:
    public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
        System.out.println("visit file: " + file);
        // 返回CONTINUE表示继续访问:
        return FileVisitResult.CONTINUE;
    }
}