浅拷贝： 不额外创建子对象，只是把子对象的引用拷贝过去
深拷贝： 创建新的子对象并拷贝属性
如果把java bean划分为 DTO、DO、VO 的话就避免不了对象的copy了。一般选择的spring的工具类都是浅拷贝。当对象内部还有对象 时只能copy内部对象的引用，这样的话不利于灵活修改。
浅拷贝模式，分两步：
- 先创建一个新的同类型对象
- 把原对象的各个属性值拷贝到对应字段
spring 的BeanUtils.copyProperties(sourceBean, destBean)只针对Person对象，所以只会把左边Person对象的属性值拷贝到右边，至于子对象department，也只是拷贝了引用。具体看下面的BeanUtils.copyProperties例子。
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.beans.BeanUtils;
public class MyBeanUtilsTest {
private static List<Person> list;
@Data
@AllArgsConstructor
@NoArgsConstructor
public static class Person implements Serializable {
private String name;
private Integer age;
private Department department;
}
@Data
@AllArgsConstructor
@NoArgsConstructor
public static class Department implements Serializable{
private String name;
}
static {
list = new ArrayList<>();
list.add(new Person("小明", 18, new Department("行政部")));
}
public static void main(String[] args) {
Person bean = list.get(0);
Person copyBean = new Person();
BeanUtils.copyProperties(bean, copyBean);
System.out.println(bean == copyBean);
System.out.println("==== copyBean的属性 ====");
System.out.println(copyBean.getName());
System.out.println(copyBean.getDepartment().getName());
bean.setName("小亮");
bean.getDepartment().setName("研发部");
System.out.println("==== sourceBean修改后，copyBean的属性 ====");
System.out.println(copyBean.getName());
System.out.println(copyBean.getDepartment().getName());
}
}
false
==== copyBean的属性 ====
小明
行政部
==== sourceBean修改后，copyBean的属性 ====
小明
研发部
修改bean的department 同时也把copyBean 的department 修改了。
使用Spring提供的BeanUtils进行数据拷贝，但它有两个问题：
- 没有提供额外的映射关系，所以两个实体类字段名必须完全一致
- 不支持深拷贝
深拷贝如何实现
1、ObjectOutputStream.writeObject()
public static <T> T deepCopyObj(T object) throws IOException, ClassNotFoundException {
ByteArrayOutputStream byteOut = new ByteArrayOutputStream();
ObjectOutputStream out = new ObjectOutputStream(byteOut);
out.writeObject(object);
ByteArrayInputStream byteIn = new ByteArrayInputStream(byteOut.toByteArray());
ObjectInputStream in = new ObjectInputStream(byteIn);
T dest = (T) in.readObject();
return dest;
}
这次修改为调用深拷贝实现：
public static void main(String[] args) throws IOException, ClassNotFoundException {
Person bean = list.get(0);
Person copyBean = MyBeanUtils.deepCopyObj(bean);
System.out.println(bean == copyBean);
System.out.println("==== copyBean的属性 ====");
System.out.println(copyBean.getName());
System.out.println(copyBean.getDepartment().getName());
bean.setName("小亮");
bean.getDepartment().setName("研发部");
System.out.println("==== sourceBean修改后，copyBean的属性 ====");
System.out.println(copyBean.getName());
System.out.println(copyBean.getDepartment().getName());
}
false
==== copyBean的属性 ====
小明
行政部
==== sourceBean修改后，copyBean的属性 ====
小明
行政部
修改bean的department 也没有影响到copyBean 的department，达到了深拷贝的目的！
2、JSON序列化、反序列化也是可以的。使用ObjectMapper
先引入jackson
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-core</artifactId>
<version>2.9.6</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-annotations</artifactId>
<version>2.9.6</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.9.6</version>
</dependency>
</dependencies>
使用
public static void main(String[] args) throws IOException {
Person bean = list.get(0);
ObjectMapper objectMapper = new ObjectMapper();
String copyBeanStr = objectMapper.writeValueAsString(bean);
Person copyBean = objectMapper.readValue(copyBeanStr, new TypeReference<Person>() {});
System.out.println(bean == copyBean);
System.out.println("==== copyBean的属性 ====");
System.out.println(copyBean.getName());
System.out.println(copyBean.getDepartment().getName());
bean.setName("小亮");
bean.getDepartment().setName("研发部");
System.out.println("==== sourceBean修改后，copyBean的属性 ====");
System.out.println(copyBean.getName());
System.out.println(copyBean.getDepartment().getName());
}
false
==== copyBean的属性 ====
小明
行政部
==== sourceBean修改后，copyBean的属性 ====
小明
行政部
3、使用二方库 MapStruct
import java.util.List;
import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import org.mapstruct.Mappings;
import org.mapstruct.factory.Mappers;
@Mapper
public interface PersonConverter {
PersonConverter INSTANCE = Mappers.getMapper(PersonConverter.class);
@Mappings({
@Mapping(source = "name", target = "name"),
@Mapping(source = "age", target = "age"),
@Mapping(source = "department.name", target = "department.name"),
})
Person domain2dto(Person person);
List<Person> domain2dto(List<Person> people);
}
public static void main(String[] args) throws IOException {
Person bean = list.get(0);
Person copyBean = PersonConverter.INSTANCE.domain2dto(bean);
System.out.println(bean == copyBean);
System.out.println("==== copyBean的属性 ====");
System.out.println(copyBean.getName());
System.out.println(copyBean.getDepartment().getName());
bean.setName("小亮");
bean.getDepartment().setName("研发部");
System.out.println("==== sourceBean修改后，copyBean的属性 ====");
System.out.println(copyBean.getName());
System.out.println(copyBean.getDepartment().getName());
}
}
false
==== copyBean的属性 ====
小明
行政部
==== sourceBean修改后，copyBean的属性 ====
小明
行政部
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