Java序列化Serializable和Externalizable

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紙上得來終覺淺，絕知此事要躬行  --陸遊       問渠那得清如許，為有源頭活水來  --朱熹

什麼是Java序列化？為什麼出現Java序列化？如何?Java序列化？一、什麼是Java序列化Java序列化是指把Java對象轉換為位元組序列的過程；而Java還原序列化是指把位元組序列恢複為Java對象的過程。

二、為什麼出現Java序列化兩個進程之間進行通訊時，須要傳輸各種資訊。比方文本，映像，聲音等等，這些資訊是通過二進位流的形式進行傳輸的。

那麼進程之間是不是也能夠傳遞對象資料呢？答案是能夠的。Java的序列化和還原序列化就是將Java對象轉化為位元組序列，並在網路上進行傳輸。還原序列化將獲得的位元組序列資料產生對象。
三、如何?Java序列化
1）、對象的輸入輸出：ObjectInputStream，ObjectOutputStream。2）、對象要實現Serializable或者Externalizable介面。否則會拋出異常。
注意：在Serializable中聲明為static和transient類型的成員資料不能被序列化。
實現Serializable介面的序列化和還原序列化示範範例程式：

public class Student implements Serializable{    private String name;    private char sex;    public Student()    {    }    public Student(String name,char sex)    {        this.name = name;        this.sex = sex;    }    public void setName(String name)    {        this.name = name;    }    public void setSex(char sex)    {        this.sex = sex;    }    public String getName()    {        return this.name;    }    public char getSex()    {        return this.sex;    }}public class UseStudent{    public static void main(String[] args)    {        Student st = new Student("Tom",‘M‘);        File file = new File("O:\\Java\\com\\jieke\\io\\student.txt");        try        {            file.createNewFile();        }        catch(IOException e)        {            e.printStackTrace();        }        try        {            //Student對象序列化過程              FileOutputStream fos = new FileOutputStream(file);            ObjectOutputStream oos = new ObjectOutputStream(fos);            oos.writeObject(st);            oos.flush();            oos.close();            fos.close();            //Student對象還原序列化過程              FileInputStream fis = new FileInputStream(file);            ObjectInputStream ois = new ObjectInputStream(fis);            Student st1 = (Student) ois.readObject();            System.out.println("name = " + st1.getName());            System.out.println("sex = " + st1.getSex());            ois.close();            fis.close();        }        catch(ClassNotFoundException e)        {            e.printStackTrace();        }        catch (IOException e)        {            e.printStackTrace();        }    }}  

使用Externalizable介面進行序列化。必需要重寫writeExternal（ObjectOutput output）和readExternal（ObjectInput input）方法使用該介面的序列化方法須要我們來實現。因此能夠對static和transient資料進行序列化。

public class Person implements Externalizable {    private static final long serialVersionUID = -842029427676826563L;    public static String name;    private int age;    private transient int workDay = 5;    private String fClub;    public Person() {        System.out.println("none-arg constructor");    }    public Person(int age, String fClub) {        this.age = age;        this.fClub = fClub;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public int getWorkDay() {        return workDay;    }    public void setWorkDay(int workDay) {        this.workDay = workDay;    }    public String getfClub() {        return fClub;    }    public void setfClub(String fClub) {        this.fClub = fClub;    }    private void writeObject(ObjectOutputStream out) throws IOException {        out.defaultWriteObject();//運行預設的序列化機制          out.writeInt(workDay);        System.out.println("進行中序列持久化");    }    private void readObject(ObjectInputStream in) throws IOException,            ClassNotFoundException {        in.defaultReadObject();        workDay = in.readInt();        System.out.println("讀取持久化對象");    }    @Override    public void readExternal(ObjectInput arg0) throws IOException,            ClassNotFoundException {        // TODO Auto-generated method stub      }    @Override    public void writeExternal(ObjectOutput arg0) throws IOException {        // TODO Auto-generated method stub        }}public class Hello {    public static void main(String[] args) {        Person person = new Person(26, "Juventus");        person.setWorkDay(7);        try {            FileOutputStream fs = new FileOutputStream("foo.ser");            ObjectOutputStream os = new ObjectOutputStream(fs);            os.writeObject(person);            os.close();            Person.name = "Alex";            FileInputStream in = new FileInputStream("foo.ser");            ObjectInputStream s = new ObjectInputStream(in);            Person p = (Person) s.readObject();            System.out.println("name==" + Person.name + " age==" + p.getAge()                    + " workDay==" + p.getWorkDay() + " fClub==" + p.getfClub());        } catch (Exception e) {            e.printStackTrace();        }    }}  

當然還有非常多開源的序列化和還原序列化的庫。能夠在實際的project中進行使用。

Java序列化Serializable和Externalizable