原型模式

原型模式（Prototype Pattern）是用于创建重复的对象，同时又能保证性能。这种类型的设计模式属于创建型模式，它提供了一种创建对象的最佳方式。

这种模式是实现了一个原型接口，该接口用于创建当前对象的克隆。当直接创建对象的代价比较大时，则采用这种模式。例如，一个对象需要在一个高代价的数据库操作之后被创建。我们可以缓存该对象，在下一个请求时返回它的克隆，在需要的时候更新数据库，以此来减少数据库调用。

首先，既然原型模式需要创建当前对象的克隆，那么我们就不得不学习克隆（或者叫 拷贝）的知识了。

拷贝分为 浅拷贝 和 深拷贝

定义一个Car类（浅拷贝）

package top.bigking.prototype;

import java.util.Date;

/**
 * @Author ABKing
 * @Date 2020/2/11 下午2:53
 * 浅拷贝
 **/
public class Car implements Cloneable {
    private String name;
    private Date date;

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

    public Car() {
    }

    public Car(String name, Date date) {
        this.name = name;
        this.date = date;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }
}

定义一个Car2类（深拷贝）

package top.bigking.prototype;

import java.util.Date;

/**
 * @Author ABKing
 * @Date 2020/2/11 下午5:39
 * 深拷贝
 **/
public class Car2 implements Cloneable {
    private String name;
    private Date date;

    @Override
    protected Object clone() throws CloneNotSupportedException {
        Object obj = super.clone();
        Car2 car = (Car2) obj;
        car.setDate((Date) this.date.clone());
        return obj;
    }

    public Car2() {
    }

    public Car2(String name, Date date) {
        this.name = name;
        this.date = date;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }
}

测试：

package top.bigking.prototype;

import org.junit.Test;

import java.util.Date;

/**
 * @Author ABKing
 * @Date 2020/2/11 下午4:40
 **/
public class TestPrototype {
    //浅拷贝
    @Test
    public void testShallowCopy() throws CloneNotSupportedException {
        Date date = new Date(11314211L);
        Car car1 = new Car("兰博基尼", date);
        Car car2 = (Car) car1.clone(); //拷贝

        System.out.println("第一辆车：" + car1 + car1.getName() + "-----" + car1.getDate());
        System.out.println("第二辆车：" + car2 + car2.getName() + "-----" + car2.getDate());

        date.setTime(4444524L);

        System.out.println("--------修改date后-------");

        System.out.println("第一辆车：" + car1 + car1.getName() + "-----" + car1.getDate());
        System.out.println("第二辆车：" + car2 + car2.getName() + "-----" + car2.getDate());
    }
    //深拷贝
    @Test
    public void testDeepCopy() throws CloneNotSupportedException {
        Date date = new Date(11314211L);
        Car2 car1 = new Car2("兰博基尼", date);
        Car2 car2 = (Car2) car1.clone(); //拷贝

        System.out.println("第一辆车：" + car1 + car1.getName() + "-----" + car1.getDate());
        System.out.println("第二辆车：" + car2 + car2.getName() + "-----" + car2.getDate());

        date.setTime(4444524L);

        System.out.println("--------修改date后-------");

        System.out.println("第一辆车：" + car1 + car1.getName() + "-----" + car1.getDate());
        System.out.println("第二辆车：" + car2 + car2.getName() + "-----" + car2.getDate());
    }
}

运行结果分别为：

/usr/local/java/jdk1.8.0_231/bin/java -ea -Didea.test.cyclic.buffer.size=1048576 -javaagent:/usr/local/bin/idea-IU-193.5662.53/lib/idea_rt.jar=37975:/usr/local/bin/idea-IU-193.5662.53/bin -Dfile.encoding=UTF-8 -classpath /usr/local/bin/idea-IU-193.5662.53/lib/idea_rt.jar:/usr/local/bin/idea-IU-193.5662.53/plugins/junit/lib/junit5-rt.jar:/usr/local/bin/idea-IU-193.5662.53/plugins/junit/lib/junit-rt.jar:/usr/local/java/jdk1.8.0_231/jre/lib/charsets.jar:/usr/local/java/jdk1.8.0_231/jre/lib/deploy.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/cldrdata.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/dnsns.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/jaccess.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/jfxrt.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/localedata.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/nashorn.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/sunec.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/sunjce_provider.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/sunpkcs11.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/zipfs.jar:/usr/local/java/jdk1.8.0_231/jre/lib/javaws.jar:/usr/local/java/jdk1.8.0_231/jre/lib/jce.jar:/usr/local/java/jdk1.8.0_231/jre/lib/jfr.jar:/usr/local/java/jdk1.8.0_231/jre/lib/jfxswt.jar:/usr/local/java/jdk1.8.0_231/jre/lib/jsse.jar:/usr/local/java/jdk1.8.0_231/jre/lib/management-agent.jar:/usr/local/java/jdk1.8.0_231/jre/lib/plugin.jar:/usr/local/java/jdk1.8.0_231/jre/lib/resources.jar:/usr/local/java/jdk1.8.0_231/jre/lib/rt.jar:/home/king/IdeaProjects/GOF_23/target/test-classes:/home/king/IdeaProjects/GOF_23/target/classes:/home/king/maven/repository/junit/junit/4.10/junit-4.10.jar:/home/king/maven/repository/org/hamcrest/hamcrest-core/1.1/hamcrest-core-1.1.jar com.intellij.rt.junit.JUnitStarter -ideVersion5 -junit4 top.bigking.prototype.TestPrototype,testShallowCopy
第一辆车：top.bigking.prototype.Car@579bb367兰博基尼-----Thu Jan 01 11:08:34 CST 1970
第二辆车：top.bigking.prototype.Car@255316f2兰博基尼-----Thu Jan 01 11:08:34 CST 1970
--------修改date后-------
第一辆车：top.bigking.prototype.Car@579bb367兰博基尼-----Thu Jan 01 09:14:04 CST 1970
第二辆车：top.bigking.prototype.Car@255316f2兰博基尼-----Thu Jan 01 09:14:04 CST 1970

Process finished with exit code 0

可以很明显的看到，修改date后，时间并没有发生改变

运行第二个JUnit测试：

/usr/local/java/jdk1.8.0_231/bin/java -ea -Didea.test.cyclic.buffer.size=1048576 -javaagent:/usr/local/bin/idea-IU-193.5662.53/lib/idea_rt.jar=36785:/usr/local/bin/idea-IU-193.5662.53/bin -Dfile.encoding=UTF-8 -classpath /usr/local/bin/idea-IU-193.5662.53/lib/idea_rt.jar:/usr/local/bin/idea-IU-193.5662.53/plugins/junit/lib/junit5-rt.jar:/usr/local/bin/idea-IU-193.5662.53/plugins/junit/lib/junit-rt.jar:/usr/local/java/jdk1.8.0_231/jre/lib/charsets.jar:/usr/local/java/jdk1.8.0_231/jre/lib/deploy.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/cldrdata.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/dnsns.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/jaccess.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/jfxrt.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/localedata.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/nashorn.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/sunec.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/sunjce_provider.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/sunpkcs11.jar:/usr/local/java/jdk1.8.0_231/jre/lib/ext/zipfs.jar:/usr/local/java/jdk1.8.0_231/jre/lib/javaws.jar:/usr/local/java/jdk1.8.0_231/jre/lib/jce.jar:/usr/local/java/jdk1.8.0_231/jre/lib/jfr.jar:/usr/local/java/jdk1.8.0_231/jre/lib/jfxswt.jar:/usr/local/java/jdk1.8.0_231/jre/lib/jsse.jar:/usr/local/java/jdk1.8.0_231/jre/lib/management-agent.jar:/usr/local/java/jdk1.8.0_231/jre/lib/plugin.jar:/usr/local/java/jdk1.8.0_231/jre/lib/resources.jar:/usr/local/java/jdk1.8.0_231/jre/lib/rt.jar:/home/king/IdeaProjects/GOF_23/target/test-classes:/home/king/IdeaProjects/GOF_23/target/classes:/home/king/maven/repository/junit/junit/4.10/junit-4.10.jar:/home/king/maven/repository/org/hamcrest/hamcrest-core/1.1/hamcrest-core-1.1.jar com.intellij.rt.junit.JUnitStarter -ideVersion5 -junit4 top.bigking.prototype.TestPrototype,testDeepCopy
第一辆车：top.bigking.prototype.Car2@579bb367兰博基尼-----Thu Jan 01 11:08:34 CST 1970
第二辆车：top.bigking.prototype.Car2@255316f2兰博基尼-----Thu Jan 01 11:08:34 CST 1970
--------修改date后-------
第一辆车：top.bigking.prototype.Car2@579bb367兰博基尼-----Thu Jan 01 09:14:04 CST 1970
第二辆车：top.bigking.prototype.Car2@255316f2兰博基尼-----Thu Jan 01 11:08:34 CST 1970

Process finished with exit code 0

可以看到，时间已经发生了变化。

什么时候会用到拷贝呢？

答案是 当使用new关键字创建对象太耗时时，使用拷贝的方法可以大大加快速度

package top.bigking.prototype;

import org.junit.Test;

import java.io.ObjectInputStream;

/**
 * @Author ABKing
 * @Date 2020/2/13 下午5:39
 **/
public class TestPrototype {
    //测试直接new的方式
    @Test
    public void testNew(){
        long start = System.currentTimeMillis();
        for (int i = 0; i < 1000; i++) {
            TestCar car = new TestCar();
        }
        long end = System.currentTimeMillis();
        System.out.println("使用new的方法总耗时：" + (end - start));

    }
    @Test
    public void testCopy() throws CloneNotSupportedException {
        long start = System.currentTimeMillis();
        TestCar car1 = new TestCar();
        for (int i = 0; i < 1000; i++) {
            TestCar car2 = (TestCar) car1.clone();
        }
        TestCar car2 = (TestCar) car1.clone();
        long end = System.currentTimeMillis();
        System.out.println("使用clone()的方法总耗时： " + (end - start));
    }
}
class TestCar implements Cloneable{
    public TestCar(){
        try {
            Thread.sleep(10); // 模拟创建对象的时间
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

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

运行第一个JUnit测试，执行结果如下：

使用new的方法总耗时：10121

运行第二个JUnit测试，执行结果如下：

使用clone()的方法总耗时： 11

可以看到，差距非常明显，使用clone()方法，几乎不耗时间

 当然，值得注意的是，当new非常耗时的时候，两者差距才很明显，如果把本例中的Thread.sleep(10)注释掉，两者所耗时均为0，几乎不耗时间。

开发中的应用场景：

原型模式一般很少单独出现，一般是和工厂方法模式一起出现，通过clone的方法创建一个对象，然后由工厂方法提供给调用者。

spring中bean对象的创建实际就是两种：单例模式和原型模式（当然，原型模式需要和工厂模式搭配起来）。