本文梳理一下Java中的对象复制。
我们可以发现在Object类中有如下方法：
protected native Object clone() throws CloneNotSupportedException;
那么如何使用它来实现对象的复制呢？
Shallow & Deep Clone
我们先准备一下我们需要的类：
@Data
@AllArgsConstructor
public class Employee {
private int id;
private String name;
private Department department;
}
@Data
@AllArgsConstructor
public class Department {
private int id;
private String name;
}
然后，让Employee实现Cloneable接口，并重写clone()方法。
@Data
@AllArgsConstructor
public class Employee implements Cloneable{
private int id;
private String name;
private Department department;
@Override
public Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
接着，我们创建一个原始对象original和复制对象cloned，并修改cloned的部门名称：
public class Test {
public static void main(String[] args) throws CloneNotSupportedException {
Department dept = new Department(1, "Technical");
Employee original = new Employee( 24, "yyc", dept);
var cloned = (Employee) original.clone();
System.out.println("Cloned id : " + cloned.getId());
System.out.println("Cloned name : " + cloned.getName());
System.out.println("Cloned department id: " + cloned.getDepartment().getId());
System.out.println("Cloned department name: " + cloned.getDepartment().getName());
System.out.println("-------------------------------------");
cloned.getDepartment().setName("Finance");
System.out.println("Original department name: " + original.getDepartment().getName());
System.out.println("Cloned department name: " + cloned.getDepartment().getName());
}
}
/** ------------------------------------*/
// Cloned id : 24
// Cloned name : yyc
// Cloned department id: 1
// Cloned department name: Technical
// -------------------------------------
// Original department name: Finance
// Cloned department name: Finance
与我们的期望不一致，我们期望只将cloned的部门名称改成Finance，而original的部门名称仍为Technical。
这就是Shallow Copy，浅复制。
来看下示意图：
那么，如何达到我们的期望？
也就是如何做到Deep Copy？下面提供三种解决方案：
- 所有相关对象均实现
Cloneable接口 - 复制构造器
- 序列化：
common-lang3、Jackson、Gson
示意图如下：
Cloneable
注意，Employee和Department类都需要实现Cloneable接口，并重写clone()方法。
@Data
@AllArgsConstructor
public class Employee implements Cloneable{
private int id;
private String name;
private Department department;
@Override
public Object clone() throws CloneNotSupportedException {
Employee e = (Employee) super.clone();
e.setDepartment((Department) this.department.clone());
return e;
}
}
@Data
@AllArgsConstructor
public class Department implements Cloneable {
private int id;
private String name;
@Override
public Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
public class Test {
public static void main(String[] args) throws CloneNotSupportedException {
Department dept = new Department(1, "Technical");
Employee original = new Employee( 24, "yyc", dept);
var cloned = (Employee) original.clone();
System.out.println("Cloned id : " + cloned.getId());
System.out.println("Cloned name : " + cloned.getName());
System.out.println("Cloned department id: " + cloned.getDepartment().getId());
System.out.println("Cloned department name: " + cloned.getDepartment().getName());
System.out.println("-------------------------------------");
cloned.getDepartment().setName("Finance");
System.out.println("Original department name: " + original.getDepartment().getName());
System.out.println("Cloned department name: " + cloned.getDepartment().getName());
}
}
/** ------------------------------------*/
// Cloned id : 24
// Cloned name : yyc
// Cloned department id: 1
// Cloned department name: Technical
// -------------------------------------
// Original department name: Technical
// Cloned department name: Finance
Copy Constructor
关键在于将原始对象作为参数传入该类的构造器，对于基本类型和字符串直接赋值，
对于引用类型则需要创建一个新的对象。
@Data
@AllArgsConstructor
public class Employee {
private int id;
private String name;
private Department department;
public Employee(Employee e){
this(e.getId(), e.getName(), new Department(e.getDepartment()));
}
}
@Data
@AllArgsConstructor
public class Department {
private int id;
private String name;
public Department(Department d){
this(d.getId(), d.getName());
}
}
public class Test {
public static void main(String[] args) throws CloneNotSupportedException {
Department dept = new Department(1, "Technical");
Employee original = new Employee( 24, "yyc", dept);
var cloned = new Employee(original);
System.out.println("Cloned id : " + cloned.getId());
System.out.println("Cloned name : " + cloned.getName());
System.out.println("Cloned department id: " + cloned.getDepartment().getId());
System.out.println("Cloned department name: " + cloned.getDepartment().getName());
System.out.println("-------------------------------------");
cloned.getDepartment().setName("Finance");
System.out.println("Original department name: " + original.getDepartment().getName());
System.out.println("Cloned department name: " + cloned.getDepartment().getName());
}
}
/** ------------------------------------*/
// Cloned id : 24
// Cloned name : yyc
// Cloned department id: 1
// Cloned department name: Technical
// -------------------------------------
// Original department name: Technical
// Cloned department name: Finance
common-lang3
注意Employee和Department类都要实现Serializable接口。
@Data
@AllArgsConstructor
public class Employee implements Serializable {
private int id;
private String name;
private Department department;
}
@Data
@AllArgsConstructor
public class Department implements Serializable {
private int id;
private String name;
}
public class Test {
public static void main(String[] args) {
Department dept = new Department(1, "Technical");
Employee original = new Employee( 24, "yyc", dept);
Employee cloned = SerializationUtils.clone(original);
System.out.println("Cloned id : " + cloned.getId());
System.out.println("Cloned name : " + cloned.getName());
System.out.println("Cloned department id: " + cloned.getDepartment().getId());
System.out.println("Cloned department name: " + cloned.getDepartment().getName());
System.out.println("-------------------------------------");
cloned.getDepartment().setName("Finance");
System.out.println("Original department name: " + original.getDepartment().getName());
System.out.println("Cloned department name: " + cloned.getDepartment().getName());
}
}
/** ------------------------------------*/
// Cloned id : 24
// Cloned name : yyc
// Cloned department id: 1
// Cloned department name: Technical
// -------------------------------------
// Original department name: Technical
// Cloned department name: Finance
Jackson
注意Employee和Department类都要有一个默认构造函数。
@Data
@AllArgsConstructor
public class Employee {
private int id;
private String name;
private Department department;
public Employee(){ }
}
@Data
@AllArgsConstructor
public class Department {
private int id;
private String name;
public Department(){}
}
public class Test {
public static void main(String[] args) throws JsonProcessingException {
Department dept = new Department(1, "Technical");
Employee original = new Employee( 24, "yyc", dept);
ObjectMapper om = new ObjectMapper();
Employee cloned = om.readValue(om.writeValueAsString(original), Employee.class);
System.out.println("Cloned id : " + cloned.getId());
System.out.println("Cloned name : " + cloned.getName());
System.out.println("Cloned department id: " + cloned.getDepartment().getId());
System.out.println("Cloned department name: " + cloned.getDepartment().getName());
System.out.println("-------------------------------------");
cloned.getDepartment().setName("Finance");
System.out.println("Original department name: " + original.getDepartment().getName());
System.out.println("Cloned department name: " + cloned.getDepartment().getName());
}
}
/** ------------------------------------*/
// Cloned id : 24
// Cloned name : yyc
// Cloned department id: 1
// Cloned department name: Technical
// -------------------------------------
// Original department name: Technical
// Cloned department name: Finance
Gson
对于Model不需要做任何修改！
@Data
@AllArgsConstructor
public class Employee {
private int id;
private String name;
private Department department;
}
@Data
@AllArgsConstructor
public class Department {
private int id;
private String name;
}
public class Test {
public static void main(String[] args) {
Department dept = new Department(1, "Technical");
Employee original = new Employee( 24, "yyc", dept);
Gson gson = new Gson();
Employee cloned = gson.fromJson(gson.toJson(original), Employee.class);
System.out.println("Cloned id : " + cloned.getId());
System.out.println("Cloned name : " + cloned.getName());
System.out.println("Cloned department id: " + cloned.getDepartment().getId());
System.out.println("Cloned department name: " + cloned.getDepartment().getName());
System.out.println("-------------------------------------");
cloned.getDepartment().setName("Finance");
System.out.println("Original department name: " + original.getDepartment().getName());
System.out.println("Cloned department name: " + cloned.getDepartment().getName());
}
}
/** ------------------------------------*/
// Cloned id : 24
// Cloned name : yyc
// Cloned department id: 1
// Cloned department name: Technical
// -------------------------------------
// Original department name: Technical
// Cloned department name: Finance
// Process finished with exit code 0
Reference
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