java設計模式精講 Debug 方式+記憶體分析 第9章 原型模式
原型模式
9-1 原型模式講解
9-2 原型模式coding
有一個Mail類:
public class Mail {
private String name;
private String emailAddress;
private String content;
public Mail() {
System.out.println("Mail Class Constructor");
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEmailAddress() {
return emailAddress;
}
public void setEmailAddress(String emailAddress) {
this.emailAddress = emailAddress;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
@Override
public String toString() {
return "Mail{" +
"name='" + name + '\'' +
", emailAddress='" + emailAddress + '\'' +
", content='" + content + '\'' +
'}';
}
}
還有一個傳送郵件的類:
注:這裡面的MessageFormat.format方法是用來拼接字串的;
public class MailUtil {
public static void sendMail(Mail mail) {
String outputContent = "向{0}同學,郵件地址:{1},郵件內容:{2}傳送郵件成功!";
System.out.println(MessageFormat.format(outputContent, mail.getName(), mail.getEmailAddress(), mail.getContent()));
}
public static void saveOriginMailRecord(Mail mail) {
System.out.println("儲存OriginMail記錄,OriginMail:"+mail.getContent());
}
}
測試:
public class Test {
public static void main(String[]args){
Mail mail = new Mail();
mail.setContent("初始化的模板");
for (int i = 0; i < 10; i++) {
mail.setName("姓名"+i);
mail.setEmailAddress("姓名" + i + "@126.com");
mail.setContent("恭喜您,此次活動中獎了!");
MailUtil.sendMail(mail);
}
MailUtil.saveOriginMailRecord(mail);
}
}
測試結果:
Mail Class Constructor
向姓名0同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
向姓名1同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
向姓名2同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
向姓名3同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
向姓名4同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
向姓名5同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
向姓名6同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
向姓名7同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
向姓名8同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
向姓名9同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
儲存OriginMail記錄,OriginMail:恭喜您,此次活動中獎了!
現在,我們來用原型模式來寫:
我們讓Mail擁有克隆的功能,實現Cloneable介面:
public class Mail implements Cloneable{
private String name;
private String emailAddress;
private String content;
public Mail() {
System.out.println("Mail Class Constructor");
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEmailAddress() {
return emailAddress;
}
public void setEmailAddress(String emailAddress) {
this.emailAddress = emailAddress;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
@Override
public String toString() {
return "Mail{" +
"name='" + name + '\'' +
", emailAddress='" + emailAddress + '\'' +
", content='" + content + '\'' +
'}';
}
@Override
protected Object clone() throws CloneNotSupportedException {
System.out.println("Clone mail object");
return super.clone();
}
}
測試:
public class Test {
public static void main(String[]args) throws CloneNotSupportedException {
Mail mail = new Mail();
mail.setContent("初始化的模板");
for (int i = 0; i < 10; i++) {
/** 使用克隆出來的Mail */
Mail mailTemp = (Mail) mail.clone();
mailTemp.setName("姓名"+i);
mailTemp.setEmailAddress("姓名" + i + "@126.com");
mailTemp.setContent("恭喜您,此次活動中獎了!");
MailUtil.sendMail(mailTemp);
}
MailUtil.saveOriginMailRecord(mail);
}
}
測試結果:
Mail Class Constructor
Clone mail object
向姓名0同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
Clone mail object
向姓名1同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
Clone mail object
向姓名2同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
Clone mail object
向姓名3同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
Clone mail object
向姓名4同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
Clone mail object
向姓名5同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
Clone mail object
向姓名6同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
Clone mail object
向姓名7同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
Clone mail object
向姓名8同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
Clone mail object
向姓名9同學,郵件地址:姓名[email protected],郵件內容:恭喜您,此次活動中獎了!傳送郵件成功!
Disconnected from the target VM, address: ‘127.0.0.1:61704’, transport: ‘socket’
儲存OriginMail記錄,OriginMail:初始化的模板
在原型模式中,還有一種常見的使用方法:通過抽象類來實現原型模式
父類實現了克隆的介面:
public abstract class A implements Cloneable {
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
子類也具有克隆的方法:
public class B extends A {
public static void main(String[]args) throws CloneNotSupportedException {
B b = new B();
b.clone();
}
}
在實際的開發當中,直接讓目標類實現Cloneable介面的方式用的比較多;
我們來說說克隆:深拷貝和淺拷貝
有一個Pig類:
public class Pig implements Cloneable{
private String name;
private Date birthday;
public Pig(String name, Date birthday) {
this.name = name;
this.birthday = birthday;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
@Override
public String toString() {
return "Pig{" +
"name='" + name + '\'' +
", birthday=" + birthday +
'}'+super.toString();
}
}
測試:
public class Test {
public static void main(String[]args) throws CloneNotSupportedException {
Date birthday = new Date(0L);
Pig pig1 = new Pig("佩奇", birthday);
Pig pig2 = (Pig) pig1.clone();
System.out.println(pig1);
System.out.println(pig2);
}
}
測試結果:這是兩個不同的物件
Pig{name=‘佩奇’, birthday=Thu Jan 01 08:00:00 CST 1970}[email protected]
Pig{name=‘佩奇’, birthday=Thu Jan 01 08:00:00 CST 1970}[email protected]
現在,我們來修改pig1的生日:
我們預期是隻修改pig1的時間:
public class Test {
public static void main(String[]args) throws CloneNotSupportedException {
Date birthday = new Date(0L);
Pig pig1 = new Pig("佩奇", birthday);
Pig pig2 = (Pig) pig1.clone();
System.out.println(pig1);
System.out.println(pig2);
pig1.getBirthday().setTime(666666666L);
System.out.println(pig1);
System.out.println(pig2);
}
}
但是實際的結果是把兩個物件的時間都進行了修改,這個就是和我們的預期就是不一樣了:
Pig{name=‘佩奇’, birthday=Thu Jan 01 08:00:00 CST 1970}[email protected]
Pig{name=‘佩奇’, birthday=Thu Jan 01 08:00:00 CST 1970}[email protected]
Pig{name=‘佩奇’, birthday=Fri Jan 09 01:11:06 CST 1970}[email protected]
Pig{name=‘佩奇’, birthday=Fri Jan 09 01:11:06 CST 1970}[email protected]
這種預設的克隆方式就是一個淺克隆的方式;
現在,我們來實現一個深克隆:
在Pig的這個類裡面實現這個方法:
@Override
protected Object clone() throws CloneNotSupportedException {
Pig pig = (Pig) super.clone();
/** 深克隆 */
pig.birthday = (Date) pig.birthday.clone();
return pig;
}
Pig的這個類如下:
public class Pig implements Cloneable{
private String name;
private Date birthday;
public Pig(String name, Date birthday) {
this.name = name;
this.birthday = birthday;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
@Override
protected Object clone() throws CloneNotSupportedException {
Pig pig = (Pig) super.clone();
/** 深克隆 */
pig.birthday = (Date) pig.birthday.clone();
return pig;
}
@Override
public String toString() {
return "Pig{" +
"name='" + name + '\'' +
", birthday=" + birthday +
'}'+super.toString();
}
}
這個時候,日期物件就不是同一個物件了:
這個時候,輸出就符合了我們的預期了:只修改了Pig1
Pig{name=‘佩奇’, birthday=Thu Jan 01 08:00:00 CST 1970}[email protected]
Pig{name=‘佩奇’, birthday=Thu Jan 01 08:00:00 CST 1970}[email protected]
Pig{name=‘佩奇’, birthday=Fri Jan 09 01:11:06 CST 1970}[email protected]
Pig{name=‘佩奇’, birthday=Thu Jan 01 08:00:00 CST 1970}[email protected]
總結:對於引用型別的變數,我們一定是注意是否要深克隆它,對於引用型別,我們還是建議克隆出來為好,否則就是留了一個隱患;
9-3 原型模式coding-克隆破壞單例
讓之前寫的單例模式實現Cloneable介面:
public class HungrySingleton implements Serializable,Cloneable{
private final static HungrySingleton hungrySingleton;
static {
hungrySingleton = new HungrySingleton();
}
private HungrySingleton() {
if (hungrySingleton != null) {
throw new RuntimeException("單例構造器禁止反射呼叫");
}
}
public static HungrySingleton getInstance() {
return hungrySingleton;
}
/** 我們加上這樣的一個方法 */
private Object readResolve() {
return hungrySingleton;
}
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
測試:
public class Test {
public static void main(String[]args) throws CloneNotSupportedException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
HungrySingleton hungrySingleton = HungrySingleton.getInstance();
Method method = hungrySingleton.getClass().getDeclaredMethod("clone");
method.setAccessible(true);
HungrySingleton cloneHungrySingleton = (HungrySingleton) method.invoke(hungrySingleton);
System.out.println(hungrySingleton);
System.out.println(cloneHungrySingleton);
}
}
執行結果:
[email protected]5dca
[email protected]8049
如果我們想要克隆不破壞單例,那麼我們可以這樣做:
public class HungrySingleton implements Serializable,Cloneable{
private final static HungrySingleton hungrySingleton;
static {
hungrySingleton = new HungrySingleton();
}
private HungrySingleton() {
if (hungrySingleton != null) {
throw new RuntimeException("單例構造器禁止反射呼叫");
}
}
public static HungrySingleton getInstance() {
return hungrySingleton;
}
/** 我們加上這樣的一個方法 */
private Object readResolve() {
return hungrySingleton;
}
@Override
protected Object clone() throws CloneNotSupportedException {
return getInstance();
}
}
現在的執行結果:這個時候,是同一個物件,還是單例的
[email protected]5dca
[email protected]5dca
如何防止克隆不破壞單例模式:
1.要麼不實現Cloneable介面
2.要麼實現了Cloneable介面,但是在重寫的方法clone方法裡面獲得物件的例項
這樣的話,就不怕克隆破壞單例模式了;
9-4 原型模式原始碼解析
我們檢視一下它的實現:
那它是如何重寫的呢?