在《java 序列化》 中已经对序列化做过简单的介绍,今天继续说一下序列化
前瞻 首先对上一篇文章中的序列化进行总结
实现java.io.Serializable
接口即可对对象进行实例化
实现Serializable接口的同时,手动指定serialVersionUID
,这样即使后面对类进行的更改,在反序列化的时候不会报错
父类没有实现该接口,子类实现了,那么父类中的属性不会序列化。解决方案就是在父类实现Serializable接口
static静态属性是不支持序列化的
transient
如果某个属性不需要序列化可以使用该关键字进行修饰
虚拟机在默认的情况下回调用对象的writeObject和readObject方法进行自定义的序列化和反序列化,如果没有则调用ObjectInputStream
里面的defaultReadObject和ObjectOutputStream
里的defaultWriteObject方法进行
如果没有实现Serializable接口,父类必须含有无惨构造函数
java.io.Externalizable 正常情况下使用java.io.Serializable
基本已经足够,但是还是有必要介绍一下java.io.Externalizable
,对于自定义序列化内容,有性能极高的需求时候还是可以采用的。
下面先看一下Externalizable的基础用法
注:部分代码里面可能会掺杂一些Lombok的注解,如有需要可以自己去配置
实验一:有默认构造函数 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 public class Animal implements Externalizable { @Getter @Setter transient String name; @Getter @Setter int age; @Override public void writeExternal (ObjectOutput out) throws IOException { out.writeObject(name); out.writeObject(age); } @Override public void readExternal (ObjectInput in) throws IOException, ClassNotFoundException { name = (String) in.readObject(); age = (int ) in.readObject(); } @Override public String toString () { return "{\r\n Animal:\r\n -- name = " + name + "\r\n -- age = " + age + " \r\n}" ; } } public class AnimalSerializableDemo { public static void main (String[] args) throws Exception { String serializableFile = "./animal.ser" ; FileOutputStream fos = null ; ObjectOutputStream oos = null ; FileInputStream fis = null ; ObjectInputStream ois = null ; fos = new FileOutputStream(new File(serializableFile)); oos = new ObjectOutputStream(fos); Animal animal = new Animal(); animal.age = 1 ; animal.name = "emo" ; oos.writeObject(animal); oos.close(); fis = new FileInputStream(new File(serializableFile)); ois = new ObjectInputStream(fis); Animal animal2 = (Animal) ois.readObject(); System.out.println(animal2); fis.close(); } }
1 2 3 4 5 6 // 输出结果 { Animal: -- name = emo -- age = 1 }
实验二:无默认构造函数 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 public class Animal2 implements Externalizable { @Getter @Setter transient String name; @Getter @Setter int age; public Animal2 (String name, int age) { this .name = name; this .age = age; } @Override public void writeExternal (ObjectOutput out) throws IOException { out.writeObject(name); out.writeObject(age); } @Override public void readExternal (ObjectInput in) throws IOException, ClassNotFoundException { name = (String) in.readObject(); age = (int ) in.readObject(); } @Override public String toString () { return "{\r\n Animal:\r\n -- name = " + name + "\r\n -- age = " + age + " \r\n}" ; } } public class Animal2SerializableDemo { public static void main (String[] args) throws Exception { String serializableFile = "./animal2.ser" ; FileOutputStream fos = null ; ObjectOutputStream oos = null ; FileInputStream fis = null ; ObjectInputStream ois = null ; fos = new FileOutputStream(new File(serializableFile)); oos = new ObjectOutputStream(fos); Animal2 animal = new Animal2("emo2" , 2 ); oos.writeObject(animal); oos.close(); fis = new FileInputStream(new File(serializableFile)); ois = new ObjectInputStream(fis); Animal2 animal2 = (Animal2) ois.readObject(); System.out.println(animal2); fis.close(); } }
1 2 3 4 5 6 7 8 // 输出结果 Exception in thread "main" java.io.InvalidClassException: com.smxknife.java2.externalizable.Animal2; no valid constructor at java.io.ObjectStreamClass$ExceptionInfo.newInvalidClassException(ObjectStreamClass.java:150) at java.io.ObjectStreamClass.checkDeserialize(ObjectStreamClass.java:790) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2001) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1535) at java.io.ObjectInputStream.readObject(ObjectInputStream.java:422) at com.smxknife.java2.externalizable.Animal2SerializableDemo.main(Animal2SerializableDemo.java:27)
实验三:Externalizable默认实现 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 public class AnimalSample implements Externalizable { @Getter @Setter transient String name; @Getter @Setter int age; @Override public void writeExternal (ObjectOutput out) throws IOException { } @Override public void readExternal (ObjectInput in) throws IOException, ClassNotFoundException { } @Override public String toString () { return "{\r\n Animal:\r\n -- name = " + name + "\r\n -- age = " + age + " \r\n}" ; } } public class AnimalSimpleSerializableDemo { public static void main (String[] args) throws Exception { String serializableFile = "./animal.ser" ; FileOutputStream fos = null ; ObjectOutputStream oos = null ; FileInputStream fis = null ; ObjectInputStream ois = null ; fos = new FileOutputStream(new File(serializableFile)); oos = new ObjectOutputStream(fos); AnimalSample animal = new AnimalSample(); animal.age = 1 ; animal.name = "emo" ; oos.writeObject(animal); oos.close(); fis = new FileInputStream(new File(serializableFile)); ois = new ObjectInputStream(fis); AnimalSample animal2 = (AnimalSample) ois.readObject(); System.out.println(animal2); fis.close(); } }
1 2 3 4 5 6 // 输出结果 { Animal: -- name = null -- age = 0 }
一二三小结 从目前来看,用法基本与Serializable类似,有以下几点不同
默认情况下,Serializable不会调用构造函数,但是从实验一和实验二可以看出Externalizable必须要有构造函数,否则会报异常错误(除此之外还有一点,这个构造函数必须是public)
使用Serializable简单一点,实现接口即可序列化,但是从实验三来看,Externalizable没有默认实现,必须手动实现序列化内容
在上面的三个实验中一直存在一个特殊的的存在–关键字transiant
,仔细看会发现这个关键字在Externalizable里面不起作用,所以,如果使用transient还是和Serializable一起使用吧