DDD领域驱动poto-framework框架快照介绍
Hibernate快照
- 当执行session.getTransaction().commit()时,Hibernate同时会清理session的一级缓存(flush),也就是将堆内存中的数据与快照中的数据进行对比,如果不一致,则会执行同步(update)操作,若相同,则不执行update。
public void testGet(){
Session session = HbnUtils.getSession();
session.beginTransaction();
try {
Student student = session.get(Student.class, 1);
student.setName("王五");
System.out.println(student);
session.getTransaction().commit();
} catch (Exception e) {
session.getTransaction().rollback();
e.printStackTrace();
}
}
首先先了解Java中的深拷贝(深复制)和浅拷贝(浅复制)
- 浅拷贝是指拷贝对象时仅仅拷贝对象本身(包括对象中的基本变量),而不拷贝对象包含的引用指向的对象。深拷贝不仅拷贝对象本身,而且拷贝对象包含的引用指向的所有对象。举例来说更加清楚:对象A1中包含对B1的引用,B1中包含对C1的引用。浅拷贝A1得到A2,A2 中依然包含对B1的引用,B1中依然包含对C1的引用。深拷贝则是对浅拷贝的递归,深拷贝A1得到A2,A2中包含对B2(B1的copy)的引用,B2 中包含对C2(C1的copy)的引用。若不对clone()方法进行改写,则调用此方法得到的对象即为浅拷贝,下面我们着重谈一下深拷贝。运行下面的程序,看一看浅拷贝:
class Professor0 implements Cloneable {
String name;
int age;
Professor0(String name, int age) {
this.name = name;
this.age = age;
}
public Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
class Student0 implements Cloneable {
String name;
int age;
Professor0 p;
Student0(String name, int age, Professor0 p) {
this.name = name;
this.age = age;
this.p = p;
}
public Object clone() {
Student0 o = null;
try {
o = (Student0) super.clone();
} catch (CloneNotSupportedException e) {
System.out.println(e.toString());
}
return o;
}
}
public class ShallowCopy {
public static void main(String[] args) {
Professor0 p = new Professor0("wangwu", 50);
Student0 s1 = new Student0("zhangsan", 18, p);
Student0 s2 = (Student0) s1.clone();
s2.p.name = "lisi";
s2.p.age = 30;
s2.name = "z";
s2.age = 45;
System.out.println("学生s1的姓名:" + s1.name + "\n学生s1教授的姓名:" + s1.p.name + "," + "\n学生s1教授的年纪" + s1.p.age);
}
}
- s2变了,但s1也变了,证明s1的p和s2的p指向的是同一个对象。这在我们有的实际需求中,却不是这样,因而我们需要深拷贝:
class Professor implements Cloneable {
String name;
int age;
Professor(String name, int age) {
this.name = name;
this.age = age;
}
public Object clone() {
Object o = null;
try {
o = super.clone();
} catch (CloneNotSupportedException e) {
System.out.println(e.toString());
}
return o;
}
}
class Student implements Cloneable {
String name;
int age;
Professor p;
Student(String name, int age, Professor p) {
this.name = name;
this.age = age;
this.p = p;
}
public Object clone() {
Student o = null;
try {
o = (Student) super.clone();
} catch (CloneNotSupportedException e) {
System.out.println(e.toString());
}
o.p = (Professor) p.clone();
return o;
}
}
public class DeepCopy {
public static void main(String args[]) {
long t1 = System.currentTimeMillis();
Professor p = new Professor("wangwu", 50);
Student s1 = new Student("zhangsan", 18, p);
Student s2 = (Student) s1.clone();
s2.p.name = "lisi";
s2.p.age = 30;
System.out.println("name=" + s1.p.name + "," + "age=" + s1.p.age);
long t2 = System.currentTimeMillis();
System.out.println(t2-t1);
}
}
class Professor2 implements Serializable {
private static final long serialVersionUID = 1L;
String name;
int age;
Professor2(String name, int age) {
this.name = name;
this.age = age;
}
}
class Student2 implements Serializable {
private static final long serialVersionUID = 1L;
String name;
int age;
Professor2 p;
Student2(String name, int age, Professor2 p) {
this.name = name;
this.age = age;
this.p = p;
}
public Object deepClone() throws IOException, OptionalDataException,
ClassNotFoundException {
ByteArrayOutputStream bo = new ByteArrayOutputStream();
ObjectOutputStream oo = new ObjectOutputStream(bo);
oo.writeObject(this);
ByteArrayInputStream bi = new ByteArrayInputStream(bo.toByteArray());
ObjectInputStream oi = new ObjectInputStream(bi);
return (oi.readObject());
}
}
public class DeepCopy2 {
public static void main(String[] args) throws OptionalDataException,
IOException, ClassNotFoundException {
long t1 = System.currentTimeMillis();
Professor2 p = new Professor2("wangwu", 50);
Student2 s1 = new Student2("zhangsan", 18, p);
Student2 s2 = (Student2) s1.deepClone();
s2.p.name = "lisi";
s2.p.age = 30;
System.out.println("name=" + s1.p.name + "," + "age=" + s1.p.age);
long t2 = System.currentTimeMillis();
System.out.println(t2-t1);
}
}
poto-framework的SnapshotUtils实现
- poto-framework就是简单的使用序列化的方式实现深度拷贝,实现很简单,SnapshotUtils工具类如下:
public class SnapshotUtils {
public static <T extends AggregateRoot> T snapshot(T aggregate)
throws IOException, ClassNotFoundException {
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(bos);
oos.writeObject(aggregate);
ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
ObjectInputStream ois = new ObjectInputStream(bis);
return (T) ois.readObject();
}
}
- poto-framework使用SnapshotUtils实现对象的深度拷贝做对象的快照,主要目的是为了解决对象包含的引用指向的对象,新老二个对象做diff发现对象的变更属性,完成数据的更新,减少不必要的更新操作。