java需要关注的知识点---I0之对象序列化
1。对象序列化：
序列化是什么：
序列化就是将一个对象的状态（各个属性量）保存起来，然后在适当的时候再获得。
序列化分为两大部分：序列化和反序列化。序列化是这个过程的第一部分，将数据分解成字节流，以便存储在文件中或在网络上传输。反序列化就是打开字节流并重构对象。对象序列化不仅要将基本数据类型转换成字节表示，有时还要恢复数据。恢复数据要求有恢复数据的对象实例
序列化的什么特点：
如果某个类能够被序列化，其子类也可以被序列化。声明为static和transient类型的成员数据不能被序列化。因为static代表类的状态， transient代表对象的临时数据。
什么时候使用序列化：
一：对象序列化可以实现分布式对象。主要应用例如：RMI要利用对象序列化运行远程主机上的服务，就像在本地机上运行对象时一样。
二：java对象序列化不仅保留一个对象的数据，而且递归保存对象引用的每个对象的数据。可以将整个对象层次写入字节流中，可以保存在文件中 或在网络连接上传递。利用对象序列化可以进行对象的"深复制"，即复制对象本身及引用的对象本身。序列化一个对象可能得到整个对象序列
序列化我是实现轻量级持久性。
package com.io;import java.io.ByteArrayInputStream;import java.io.ByteArrayOutputStream;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.ObjectInputStream;import java.io.ObjectOutputStream;import java.io.Serializable;import java.util.Random;public class ObjectSer implements Serializable{private static Random random = new Random(47);private Data[] d = {new Data(random.nextInt(10)),new Data(random.nextInt(10)),new Data(random.nextInt(10))};private ObjectSer next;private char c;public ObjectSer(int i, char x) {super();System.out.println("ObjectSer constructor:" + i);c = x;if(--i > 0) {next = new ObjectSer(i,(char)(x+1));}}public String toString() {StringBuilder result = new StringBuilder(":");result.append(c);result.append("(");for(Data dat:d)result.append(dat);result.append(")");if(next != null)result.append(next);return result.toString();}public ObjectSer() {super();System.out.println("Default constructor");}/** * @param args * @throws IOException * @throws FileNotFoundException * @throws ClassNotFoundException */public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {ObjectSer os = new ObjectSer(6,'a');System.out.println("os =:" +os);ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("worm.out"));out.writeObject("Object storage\n");out.writeObject(os);out.close();ObjectInputStream in = new ObjectInputStream(new FileInputStream("worm.out"));String s = (String)in.readObject();ObjectSer objects = (ObjectSer)in.readObject();System.out.println(s+ " objects: " + objects);ByteArrayOutputStream bout = new ByteArrayOutputStream();ObjectOutputStream out2 = new ObjectOutputStream(bout);out2.writeObject("Objectser storage\n");out2.writeObject(os);out2.flush();ObjectInputStream in2 = new ObjectInputStream(new ByteArrayInputStream(bout.toByteArray()));s = (String)in2.readObject();ObjectSer os2 = (ObjectSer)in2.readObject();System.out.println(s + " os2 = "+os2);}}class Data implements Serializable {private int n;public Data(int n) {this.n = n;}public String toString() {return Integer.toString(n);}}ObjectSer constructor:6ObjectSer constructor:5ObjectSer constructor:4ObjectSer constructor:3ObjectSer constructor:2ObjectSer constructor:1os =::a(853):b(119):c(802):d(788):e(199):f(881)Object storage objects: :a(853):b(119):c(802):d(788):e(199):f(881)Objectser storage os2 = :a(853):b(119):c(802):d(788):e(199):f(881)
package com.io;import java.io.Externalizable;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.io.ObjectInput;import java.io.ObjectInputStream;import java.io.ObjectOutput;import java.io.ObjectOutputStream;public class BlipsExternalizable {public static void main(String[] args) throws IOException, IOException, ClassNotFoundException {Blip1 b1 = new Blip1();Blip2 b2 = new Blip2();ObjectOutputStream dos = new ObjectOutputStream(new FileOutputStream("Blp.obj"));dos.writeObject(b1);dos.writeObject(b2);ObjectInputStream ois = new ObjectInputStream(new FileInputStream("Blp.obj"));b1 = (Blip1)ois.readObject();b2 = (Blip2)ois.readObject();}}class Blip1 implements Externalizable {public Blip1(){System.out.println("Blip1 constructor");}@Overridepublic void readExternal(ObjectInput in) throws IOException,ClassNotFoundException {System.out.println("Blip1 read");}@Overridepublic void writeExternal(ObjectOutput out) throws IOException {System.out.println("Blip1 write");}}class Blip2 implements Externalizable {Blip2() {System.out.println("Blip2 constructor");}@Overridepublic void readExternal(ObjectInput in) throws IOException,ClassNotFoundException {System.out.println("Blip2 read");}@Overridepublic void writeExternal(ObjectOutput out) throws IOException {System.out.println("Blip2 write");}}结果：Blip1 constructorBlip2 constructorBlip1 writeBlip2 writeBlip1 constructorBlip1 readException in thread "main" java.io.InvalidClassException: com.io.Blip2; com.io.Blip2; no valid constructorat java.io.ObjectStreamClass.checkDeserialize(Unknown Source)at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)at java.io.ObjectInputStream.readObject0(Unknown Source)at java.io.ObjectInputStream.readObject(Unknown Source)at com.io.BlipsExternalizable.main(BlipsExternalizable.java:21)Caused by: java.io.InvalidClassException: com.io.Blip2; no valid constructorat java.io.ObjectStreamClass.<init>(Unknown Source)at java.io.ObjectStreamClass.lookup(Unknown Source)at java.io.ObjectOutputStream.writeObject0(Unknown Source)at java.io.ObjectOutputStream.writeObject(Unknown Source)at com.io.BlipsExternalizable.main(BlipsExternalizable.java:18)
public class Blip3Externalizable implements Externalizable {private String s;private int i;public Blip3Externalizable() {super();System.out.println("Blip constructor");}public Blip3Externalizable(String s, int i) {super();System.out.println("Blip constructor(s,i)");this.s = s;this.i = i;}@Overridepublic void readExternal(ObjectInput in) throws IOException,ClassNotFoundException {System.out.println("Blip read");//reset the attribute value.s = (String)in.readObject();i = in.readInt();}@Overridepublic void writeExternal(ObjectOutput out) throws IOException {System.out.println("Blip write");out.writeObject(s);out.writeInt(i);}public static void main(String[] args) throws IOException, ClassNotFoundException {Blip3Externalizable blip = new Blip3Externalizable("String", 41);ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("blip.obj"));oos.writeObject(blip);ObjectInputStream ois = new ObjectInputStream(new FileInputStream("blip.obj"));blip = (Blip3Externalizable) ois.readObject();System.out.println(blip.i);}}