ObjectOutputStream類的物件用於序列化物件。ObjectInputStream類的物件用於反序列化一個物件。ObjectOutputStream繼承自OutputStream。ObjectInputStream繼承自InputStream。
類必須實現Serializable或Externalizable介面以便序列化或反序列化。Serializable介面是一個標記介面。如果想要一個Person類的物件被序列化，需要宣告Person類如下：
public class Person implements Serializable {
}
Java負責處理從/向流讀取/寫入Serializable物件的細節。只需要將物件傳到流流類的write/read方法之一。實現Externalizable介面能夠更好地控制從流中讀取物件和向物件寫入物件。
它繼承Serializable介面，宣告如下：
public interface Externalizable extends Serializable {
void readExternal(ObjectInput in) throws IOException, ClassNotFoundException;
void writeExternal(ObjectOutput out) throws IOException;
}
當從流中讀取一個物件時，Java呼叫readExternal()方法。當向一個流寫一個物件時，它呼叫writeExternal()方法。
必須編寫邏輯來分別讀取和寫入readExternal()和writeExternal()方法中的物件的欄位。
實現Externalizable介面的類如下所示：
public class Person implements Externalizable {
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
// Write the logic to read the Person object fields from the stream
}
public void writeExternal(ObjectOutput out) throws IOException {
// Write the logic to write Person object fields to the stream
}
}
以下程式碼建立ObjectOutputStream類的物件，並將物件儲存到person.ser檔案。
ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("person.ser"));
要將物件儲存到ByteArrayOutputStream，構造一個物件輸出流如下：
ByteArrayOutputStream baos = new ByteArrayOutputStream();
// Creates an object output stream to write objects to the byte array output stream
ObjectOutputStream oos = new ObjectOutputStream(baos);
使用ObjectOutputStream類的writeObject()方法通過將物件參照作為引數傳遞來序列化物件，如下所示：
oos.writeObject(p1);
最後，當完成將所有物件寫入時，使用close()方法關閉物件輸出流：
oos.close();
以下程式碼顯示Person類如何序列化,它實現可序列化介面(Serializable )。
import java.io.Serializable;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
class Person implements Serializable {
private String name = "Unknown";
private String gender = "Unknown";
private double height = Double.NaN;
public Person(String name, String gender, double height) {
this.name = name;
this.gender = gender;
this.height = height;
}
@Override
public String toString() {
return "Name: " + this.name + ", Gender: " + this.gender + ", Height: "
+ this.height;
}
}
public class Main {
public static void main(String[] args) {
Person p1 = new Person("John", "Male", 1.7);
Person p2 = new Person("Wally", "Male", 1.7);
Person p3 = new Person("Katrina", "Female", 1.4);
File fileObject = new File("person.ser");
try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(
fileObject))) {
oos.writeObject(p1);
oos.writeObject(p2);
oos.writeObject(p3);
// Display the serialized objects on the standard output
System.out.println(p1);
System.out.println(p2);
System.out.println(p3);
} catch (IOException e) {
e.printStackTrace();
}
}
}
上面的程式碼生成以下結果。
Name: John, Gender: Male, Height: 1.7
Name: Wally, Gender: Male, Height: 1.7
Name: Katrina, Gender: Female, Height: 1.4
以下程式碼顯示如何建立ObjectInputStream類的物件，並從person.ser檔案讀取物件。
ObjectInputStream ois = new ObjectInputStream(new FileInputStream("person.ser"));
要從ByteArrayInputStream讀取物件，請按如下所示建立物件輸出流：
ObjectInputStream ois = new ObjectInputStream(Byte-Array-Input-Stream-Reference);
使用ObjectInputStream類的readObject()方法來反序列化物件。
Object obj = oos.readObject();
最後，關閉物件輸入流如下：
ois.close();
以下程式碼顯示如何從檔案讀取物件。
import java.io.File;
import java.io.FileInputStream;
import java.io.ObjectInputStream;
public class Main {
public static void main(String[] args) {
File fileObject = new File("person.ser");
try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(
fileObject))) {
Person p1 = (Person) ois.readObject();
Person p2 = (Person) ois.readObject();
Person p3 = (Person) ois.readObject();
System.out.println(p1);
System.out.println(p2);
System.out.println(p3);
} catch (Exception e) {
e.printStackTrace();
}
}
}
要序列化和反序列化可外部化物件，請實現Externalizable介面。
import java.io.Externalizable;
import java.io.File;
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;
class PersonExt implements Externalizable {
private String name = "Unknown";
private String gender = "Unknown";
private double height = Double.NaN;
public PersonExt() {
}
public PersonExt(String name, String gender, double height) {
this.name = name;
this.gender = gender;
this.height = height;
}
public String toString() {
return "Name: " + this.name + ", Gender: " + this.gender + ", Height: " + this.height;
}
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
this.name = in.readUTF();
this.gender = in.readUTF();
}
public void writeExternal(ObjectOutput out) throws IOException {
out.writeUTF(this.name);
out.writeUTF(this.gender);
}
}
public class Main {
public static void main(String[] args) {
PersonExt p1 = new PersonExt("John", "Male", 6.7);
PersonExt p2 = new PersonExt("Wally", "Male", 5.7);
PersonExt p3 = new PersonExt("Katrina", "Female", 5.4);
File fileObject = new File("personext.ser");
try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(fileObject))) {
oos.writeObject(p1);
oos.writeObject(p2);
oos.writeObject(p3);
System.out.println(p1);
System.out.println(p2);
System.out.println(p3);
} catch (IOException e1) {
e1.printStackTrace();
}
fileObject = new File("personext.ser");
try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(fileObject))) {
p1 = (PersonExt) ois.readObject();
p2 = (PersonExt) ois.readObject();
p3 = (PersonExt) ois.readObject();
// Let's display the objects that are read
System.out.println(p1);
System.out.println(p2);
System.out.println(p3);
// Print the input path
System.out.println("Objects were read from " + fileObject.getAbsolutePath());
} catch (Exception e) {
e.printStackTrace();
}
}
}
上面的程式碼生成以下結果。
Name: John, Gender: Male, Height: 6.7
Name: Wally, Gender: Male, Height: 5.7
Name: Katrina, Gender: Female, Height: 5.4
Name: John, Gender: Male, Height: NaN
Name: Wally, Gender: Male, Height: NaN
Name: Katrina, Gender: Female, Height: NaN
Objects were read from F:\website\yiibai\worksp\personext.ser