Java中避免对象隐私泄露：防御性复制与不可变对象设计

// 假设这是原始的Date类，它是一个可变对象
public class Date {
    private int month;
    private int day;
    private int year;

    public Date(int month, int day, int year) {
        // 简化校验，后续会改进
        if (day < 1 || day > 31) {
            System.out.println("invalid day: " + day);
            System.exit(0);
        } else if (month < 1 || month > 12) {
            System.out.println("invalid month: " + month);
            System.exit(0);
        } else if (year < 2014 || year > 2024) {
            System.out.println("invalid year: " + year);
            System.exit(0);
        }
        this.month = month;
        this.day = day;
        this.year = year;
    }

    public int getDay() {
        return day;
    }

    public void setDay(int day) {
        if (day >= 1 && day <= 31) { // 注意原始代码的逻辑错误，这里已修正
            this.day = day;
        }
    }
    // 省略getMonth, getYear, setMonth, setYear等方法
}

// 假设Order类像这样简单地存储Date对象
public class Order {
    private Money amount; // 假设Money也是一个对象
    private Date orderDate;
    private String company;
    private String item;

    public Order(Money amount, Date orderDate, String company, String item) {
        this.amount = amount;
        this.orderDate = orderDate; // 直接引用
        this.company = company;
        this.item = item;
    }

    public Date getOrderDate() {
        return orderDate; // 直接返回引用
    }
    // 省略其他方法
}

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;

public class OrderTest {
    @Test
    public void OrderDatePrivacyLeaks() {
        Date d = new Date(6, 12, 2017);
        Order b = new Order(new Money(2, 33), d, "ACME Company", "widget"); // Order内部持有d的引用
        d.setDay(10); // 外部修改了d对象
        Date billDate = b.getOrderDate(); // 获取Order内部的日期
        assertEquals(12, billDate.getDay()); // 预期是12，但实际得到10
    }
}

// Date类添加拷贝构造器
public class Date {
    private int month;
    private int day;
    private int year;

    // 原始构造器（后续会改进错误处理）
    public Date(int month, int day, int year) {
        // ... 参数校验 ...
        this.month = month;
        this.day = day;
        this.year = year;
    }

    // 拷贝构造器
    public Date(Date other) {
        this.month = other.month;
        this.day = other.day;
        this.year = other.year;
    }

    // ... 其他getter/setter方法 ...
}

public class Order {
    private Money amount;
    private Date orderDate;
    private String company;
    private String item;

    public Order(Money amount, Date orderDate, String company, String item) {
        // 构造器中进行防御性复制：存储传入Date对象的副本
        this.amount = new Money(amount); // 假设Money也需要防御性复制
        this.orderDate = new Date(orderDate);
        this.company = company;
        this.item = item;
    }

    public Date getOrderDate() {
        // Getter中进行防御性复制：返回内部Date对象的副本
        return new Date(orderDate);
    }
    // ... 其他方法 ...
}

public final class Date { // 声明为final
    private final int month; // 字段声明为final
    private final int day;   // 字段声明为final
    private final int year;  // 字段声明为final

    public Date(int month, int day, int year) {
        // 改进的参数校验
        if (day < 1 || day > 31) {
            throw new IllegalArgumentException("Invalid day: " + day);
        } else if (month < 1 || month > 12) {
            throw new IllegalArgumentException("Invalid month: " + month);
        } else if (year < 2014 || year > 2024) {
            throw new IllegalArgumentException("Invalid year: " + year);
        }
        this.month = month;
        this.day = day;
        this.year = year;
    }

    // 只有getter方法，没有setter方法
    public int getMonth() {
        return month;
    }

    public int getDay() {
        return day;
    }

    public int getYear() {
        return year;
    }
    // 不提供拷贝构造器，因为不可变对象无需复制即可安全共享
}

public class Order {
    private final Money amount; // 假设Money也是不可变的
    private final Date orderDate; // Date现在是不可变的
    private final String company;
    private final String item;

    public Order(Money amount, Date orderDate, String company, String item) {
        // 如果Money也是不可变的，则可以直接赋值
        this.amount = amount;
        this.orderDate = orderDate; // 直接引用是安全的
        this.company = company;
        this.item = item;
    }

    public Date getOrderDate() {
        return orderDate; // 直接返回引用是安全的
    }
    // ... 其他方法 ...
}

public Date(int month, int day, int year) {
    if (day < 1 || day > 31) {
        throw new IllegalArgumentException("Invalid day: " + day);
    } else if (month < 1 || month > 12) {
        throw new IllegalArgumentException("Invalid month: " + month);
    } else if (year < 2014 || year > 2024) {
        throw new IllegalArgumentException("Invalid year: " + year);
    }
    this.month = month;
    this.day = day;
    this.year = year;
}