Java clone 浅拷贝和深拷贝

实现 Cloneable 方式

浅拷贝

@AllArgsConstructor
public class Result implements Serializable, Cloneable {
    @Getter
    @Setter
    private int code;
    @Getter
    @Setter
    private String message;
    @Getter
    @Setter
    private Data data;

    @Override
    public Result clone() throws CloneNotSupportedException {
        return (Result) super.clone();
    }
}

@AllArgsConstructor
public class Data implements Serializable {
    @Getter
    @Setter
    private String requestId;
    @Getter
    @Setter
    private String fileName;
}

public class AnswerApp {

    public static void main(String[] args) throws Exception {
        Result result = new Result(10000, "success", new Data("1_F63BF87F4B104E9E8594AC188EBA0E03", "answer.md"));
        System.out.println(JacksonUtil.toJsonString(result));

        // 浅拷贝
        Result clone = result.clone();

        // 打印对象地址
        System.out.println(result);
        System.out.println(clone);
        // 对比克隆前后对象属性
        System.out.println(clone.getData() == result.getData());
        System.out.println(clone.getMessage() == result.getMessage());

        clone.setMessage("upload success");
        clone.getData().setFileName("answer.zip");
        System.out.println(JacksonUtil.toJsonString(result));
        System.out.println(JacksonUtil.toJsonString(clone));
    }
}

程序运行结果

{"code":10000,"message":"success","data":{"requestId":"1_F63BF87F4B104E9E8594AC188EBA0E03","fileName":"answer.md"}}
com.xiwei.xn.entity.Result@5c3bd550
com.xiwei.xn.entity.Result@91161c7
true
true
{"code":10000,"message":"success","data":{"requestId":"1_F63BF87F4B104E9E8594AC188EBA0E03","fileName":"answer.zip"}}
{"code":10000,"message":"upload success","data":{"requestId":"1_F63BF87F4B104E9E8594AC188EBA0E03","fileName":"answer.zip"}}

从运行结果看： result 和 clone 两个对象的地址是不同的，也就是说 调用 clone 方法时创建了新的对象。 但是对象内的属性的地址是一样的且修改了 clone 对象的属性值， result 对象的属性值也跟着变化， 因此克隆时， 对象内的属性只是将引用赋值给新拷贝的对象的对应的属性

结论： 一个类实现了 Cloneable 接口， 如果不对 clone 方法进行重写， 只是简单的调用 Object 类的 clone 方法， 则对象的拷贝是浅拷贝(创建了新对象， 但是对象内的属性字段克隆前后都是指向同一个堆地址， 如果对克隆后的对象进行属性修改， 克隆前后的两个对象的对应属性都会被修改)

深拷贝

@AllArgsConstructor
public class Result implements Serializable, Cloneable {
    @Getter
    @Setter
    private int code;
    @Getter
    @Setter
    private String message;
    @Getter
    @Setter
    private Data data;

    @Override
    public Result clone() throws CloneNotSupportedException {
        Result result = (Result) super.clone();
        // 需要对 result 内的属性进行重新创建对象
        result.message = new String(message);
        result.data = data.clone();
        return result;
    }
}

@AllArgsConstructor
public class Data implements Serializable, Cloneable {
    @Getter
    @Setter
    private String requestId;
    @Getter
    @Setter
    private String fileName;

    @Override
    protected Data clone() throws CloneNotSupportedException {
        return (Data) super.clone();
    }
}

public class AnswerApp {

    public static void main(String[] args) throws Exception {
        Result result = new Result(10000, "success", new Data("1_F63BF87F4B104E9E8594AC188EBA0E03", "answer.md"));
        System.out.println(JacksonUtil.toJsonString(result));

        // 深拷贝, 因为 clone 方法内对对象的属性进行重新创建并赋值
        Result clone = result.clone();

        System.out.println(result);
        System.out.println(clone);
        System.out.println(clone.getData() == result.getData());
        System.out.println(clone.getMessage() == result.getMessage());

        clone.setMessage("upload success");
        clone.getData().setFileName("answer.zip");
        System.out.println(JacksonUtil.toJsonString(result));
        System.out.println(JacksonUtil.toJsonString(clone));
    }
}

程序运行结果

{"code":10000,"message":"success","data":{"requestId":"1_F63BF87F4B104E9E8594AC188EBA0E03","fileName":"answer.md"}}
com.xiwei.xn.entity.Result@5c3bd550
com.xiwei.xn.entity.Result@91161c7
false
false
{"code":10000,"message":"success","data":{"requestId":"1_F63BF87F4B104E9E8594AC188EBA0E03","fileName":"answer.md"}}
{"code":10000,"message":"upload success","data":{"requestId":"1_F63BF87F4B104E9E8594AC188EBA0E03","fileName":"answer.zip"}}

序列化方式实现深拷贝

@SuppressWarnings("unchecked")
public static <T> T clone(T obj) throws Exception {
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ObjectOutputStream oos = new ObjectOutputStream(baos);
    oos.writeObject(obj);

    ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
    ObjectInputStream ois = new ObjectInputStream(bais);
    return (T) ois.readObject();
}