Java提供一种机制叫做序列化，通过有序的格式或者字节序列持久化java对象，其中包含对象的数据，还有对象的类型，和保存在对象中的数据类型。
所以，如果我们已经序列化了一个对象，那么它可以被读取并通过对象的类型和其他信息进行反序列化，并最终获取对象的原型。
ObjectInputStream 和 ObjectOutputStream对象是高级别的流对象，包含序列化和反序列化的方法。
ObjectOutputStream 拥有很多序列化对象的方法，最常用的是：
private void writeObject(ObjectOutputStream os) throws IOException { }类似的 ObjectInputStream 提供如下方法：
private void readObject(ObjectInputStream is) throws IOException, ClassNotFoundException { }那么哪里会需要序列化呢？序列化通常在需要通过网络传输数据，或者保存对象到文件的场合使用。这里说的数据是对象而不是文本。
现在的问题是，我们的网络架构和硬盘都只能识别二进制和字节，而不能识别Java对象。
序列化就是把Java对象中的value/states翻译为字节，以便通过网络传输或者保存。另外，反序列化就是通过读取字节码，并把它翻译回java对象。
serialVersionUID概念
serialVersionUID 是用于保证同一个对象（在序列化中会被用到）可以在Deserialization过程中被载入。serialVersionUID 是用于对象的版本控制。你可以参考serialVersionUID in java serialization获取更多信息。
对于序列化：
步骤如下：
让我们看一个列子：
在 src->org.arpit.javapostsforlearning 创建Employee.java
1.Employee.java
package org.arpit.javapostsforlearning;import java.io.Serializable;public class Employee implements Serializable{ int employeeId; String employeeName; String department; public int getEmployeeId() { return employeeId; } public void setEmployeeId(int employeeId) { this.employeeId = employeeId; } public String getEmployeeName() { return employeeName; } public void setEmployeeName(String employeeName) { this.employeeName = employeeName; } public String getDepartment() { return department; } public void setDepartment(String department) { this.department = department; }}就如你所见的，如果你需要序列化任何类，那么你 必须实现 Serializable 接口 ，这个接口是标记接口（marker interface）。
Java中的标记接口（marker interface）就是一个没有任何字段或者方法的接口，简单的来说，java中把空接口叫做标记接口（marker interface）
2.SerializeMain.java
package org.arpit.javapostsforlearning;import java.io.FileOutputStream;import java.io.IOException;import java.io.ObjectOutputStream; public class SerializeMain { /** * @author Arpit Mandliya */ public static void main(String[] args) { Employee emp = new Employee(); emp.setEmployeeId(101); emp.setEmployeeName("Arpit"); emp.setDepartment("CS"); try { FileOutputStream fileOut = new FileOutputStream("employee.ser"); ObjectOutputStream outStream = new ObjectOutputStream(fileOut); outStream.writeObject(emp); outStream.close(); fileOut.close(); }catch(IOException i) { i.printStackTrace(); } }}对于反序列化:
步骤是
在包src->org.arpit.javapostsforlearning中，创建 DeserializeMain.java
3.DeserializeMain.java
package org.arpit.javapostsforlearning;import java.io.IOException;import java.io.ObjectInputStream; public class DeserializeMain { /** * @author Arpit Mandliya */ public static void main(String[] args) { Employee emp = null; try { FileInputStream fileIn =new FileInputStream("employee.ser"); ObjectInputStream in = new ObjectInputStream(fileIn); emp = (Employee) in.readObject(); in.close(); fileIn.close(); }catch(IOException i) { i.printStackTrace(); return; }catch(ClassNotFoundException c) { System.out.println("Employee class not found"); c.printStackTrace(); return; } System.out.println("Deserialized Employee..."); System.out.println("Emp id: " + emp.getEmployeeId()); System.out.println("Name: " + emp.getEmployeeName()); System.out.println("Department: " + emp.getDepartment()); }}
4.运行:
首先运行SerializeMain.java，然后运行 DeserializeMain.java，你会得到如下的结果:
Deserialized Employee...Emp id: 101Name: ArpitDepartment: CS
就这样，我们序列化了一个employee对象，并对它进行反序列化。这看起来和简单，但是如果其中包含对象引用，继承，那么情况就会变得复杂。接下来让我们一个接一个的看一下例子，看看如何在各种场合中实现序列化。
案例1 - 如果对象引用了其他对象，那该如何
我们已经看过最简单的序列化例子，现在看看，如何处理对象中引用了其他对象的场合。我们该如何序列化？引用对象也会被序列化吗？对的，你不需要显式的序列化引用对象。当你序列化任何对象，如果它包含引用对象，那么Java序列化会自动序列化该对象的整个对象图。例如，Employee现在引用了一个address对象，并且Address也引用了其他对象（例如，Home），那么当你序列化Employee对象的时候，所有其他引用对象，例如address和home将会被自动地被序列化。让我们来创建Address类，并它Address的对象作为引用，添加到employee类中。
Employee.java:
package org.arpit.javapostsforlearning;import java.io.Serializable; public class Employee implements Serializable{ int employeeId; String employeeName; String department; Address address; public int getEmployeeId() { return employeeId; } public void setEmployeeId(int employeeId) { this.employeeId = employeeId; } public String getEmployeeName() { return employeeName; } public void setEmployeeName(String employeeName) { this.employeeName = employeeName; } public String getDepartment() { return department; } public void setDepartment(String department) { this.department = department; } public Address getAddress() { return address; } public void setAddress(Address address) { this.address = address; }}在 org.arpit.javapostsforlearning 包中，创建Address.java
Address.java:
package org.arpit.javapostsforlearning;public class Address { int homeNo; String street; String city; public Address(int homeNo, String street, String city) { super(); this.homeNo = homeNo; this.street = street; this.city = city; } public int getHomeNo() { return homeNo; } public void setHomeNo(int homeNo) { this.homeNo = homeNo; } public String getStreet() { return street; } public void setStreet(String street) { this.street = street; } public String getCity() { return city; } public void setCity(String city) { this.city = city; }}在包 org.arpit.javapostsforlearning中，创建SerializeDeserializeMain.java
SerializeDeserializeMain.java:
package org.arpit.javapostsforlearning;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.io.ObjectInputStream;import java.io.ObjectOutputStream; public class SerializeDeserializeMain { /** * @author Arpit Mandliya */ public static void main(String[] args) { Employee emp = new Employee(); emp.setEmployeeId(101); emp.setEmployeeName("Arpit"); emp.setDepartment("CS"); Address address=new Address(88,"MG road","Pune"); emp.setAddress(address); //Serialize try { FileOutputStream fileOut = new FileOutputStream("employee.ser"); ObjectOutputStream outStream = new ObjectOutputStream(fileOut); outStream.writeObject(emp); outStream.close(); fileOut.close(); }catch(IOException i) { i.printStackTrace(); } //Deserialize emp = null; try { FileInputStream fileIn =new FileInputStream("employee.ser"); ObjectInputStream in = new ObjectInputStream(fileIn); emp = (Employee) in.readObject(); in.close(); fileIn.close(); }catch(IOException i) { i.printStackTrace(); return; }catch(ClassNotFoundException c) { System.out.println("Employee class not found"); c.printStackTrace(); return; } System.out.println("Deserialized Employee..."); System.out.println("Emp id: " + emp.getEmployeeId()); System.out.println("Name: " + emp.getEmployeeName()); System.out.println("Department: " + emp.getDepartment()); address=emp.getAddress(); System.out.println("City :"+address.getCity()); }}运行它:
当你运行SerializeDeserializeMain.java。你会得到这样的结果：
java.io.NotSerializableException: org.arpit.javapostsforlearning.Address at java.io.ObjectOutputStream.writeObject0(Unknown Source) at java.io.ObjectOutputStream.defaultWriteFields(Unknown Source) at java.io.ObjectOutputStream.writeSerialData(Unknown Source) at java.io.ObjectOutputStream.writeOrdinaryObject(Unknown Source) at java.io.ObjectOutputStream.writeObject0(Unknown Source) at java.io.ObjectOutputStream.writeObject(Unknown Source)
我们将解释哪里出错了。我忘记了说，Address 类也必须是serializable。那么Address类必须继承serialzable接口。
Address.java:
import java.io.Serializable; public class Address implements Serializable{ int homeNo; String street; String city; public Address(int homeNo, String street, String city) { super(); this.homeNo = homeNo; this.street = street; this.city = city; } public int getHomeNo() { return homeNo; } public void setHomeNo(int homeNo) { this.homeNo = homeNo; } public String getStreet() { return street; } public void setStreet(String street) { this.street = street; } public String getCity() { return city; } public void setCity(String city) { this.city = city; }}再次运行:
当你再次运行SerializeDeserializeMain.java。你可以得到如下的结果
Deserialized Employee...Emp id: 101Name: ArpitDepartment: CSCity :Pune
案例2：如果我们不能访问引用对象的源代码（例如，你不能访问上面的Address类的源码）
如果我们不能访问到address类，那么我们该如何在Address类中实现serializable 接口？是否有另外的途径来实现呢？对的，你可以创建另外一个类，并继承Address，然后让它继承serializable 接口，但是对于下面的情况，这个方案会失败：
如果引用类被定义为final
如果引用类引用了另外一个非可序列化的对象
那么，我们该如何序列化Employee对象？解决的办法是，标记transient。如果你不需要序列化任何字段，只需把它标记为transient。
transient Address address
在Employee类中，标记了address为transient之后，运行程序。你会得到nullPointerException，因为在反序列化过程中，Address引用将会是null。
案例3 - 如果我仍然需要保存引用对象的状态呢？（例如address对象）
如果你在反序列化过程中，标记了address为transient，它将会返回null结果。但是如果你仍然需要保存它的状态，你就需要序列化address对象。 Java序列化提供一个机制，如果你有特定签名的private方法，那么它们就会在序列化和反序列化过程中被调用，所以我们将重写Employee类的writeObject和readObject方法，然后它们就会在Employee对象序列化/反序列化过程中被调用。
Employee.java:
package org.arpit.javapostsforlearning;import java.io.IOException;import java.io.ObjectInputStream;import java.io.ObjectOutputStream;import java.io.Serializable; public class Employee implements Serializable{ int employeeId; String employeeName; String department; transient Address address; public int getEmployeeId() { return employeeId; } public void setEmployeeId(int employeeId) { this.employeeId = employeeId; } public String getEmployeeName() { return employeeName; } public void setEmployeeName(String employeeName) { this.employeeName = employeeName; } public String getDepartment() { return department; } public void setDepartment(String department) { this.department = department; } public Address getAddress() { return address; } public void setAddress(Address address) { this.address = address; } private void writeObject(ObjectOutputStream os) throws IOException, ClassNotFoundException { try { os.defaultWriteObject(); os.writeInt(address.getHomeNo()); os.writeObject(address.getStreet()); os.writeObject(address.getCity()); } catch (Exception e) { e.printStackTrace(); } } private void readObject(ObjectInputStream is) throws IOException, ClassNotFoundException { try { is.defaultReadObject(); int homeNo=is.readInt(); String street=(String) is.readObject(); String city=(String) is.readObject(); address=new Address(homeNo,street,city); } catch (Exception e) { e.printStackTrace(); } }}另外有一点需要牢记的，ObjectInputStream读取数据的顺序和ObjectOutputStream写入数据的顺序是一致的.
在包org.arpit.javapostsforlearning 中创建Address.java
Address.java:
package org.arpit.javapostsforlearning;import java.io.Serializable; public class Address { int homeNo; String street; String city; public Address(int homeNo, String street, String city) { super(); this.homeNo = homeNo; this.street = street; this.city = city; } public int getHomeNo() { return homeNo; } public void setHomeNo(int homeNo) { this.homeNo = homeNo; } public String getStreet() { return street; } public void setStreet(String street) { this.street = street; } public String getCity() { return city; } public void setCity(String city) { this.city = city; }}在包org.arpit.javapostsforlearning中创建SerializeDeserializeMain.java
SerializeDeserializeMain.java:
package org.arpit.javapostsforlearning;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.io.ObjectInputStream;import java.io.ObjectOutputStream; public class SerializeDeserializeMain { /** * @author Arpit Mandliya */ public static void main(String[] args) { Employee emp = new Employee(); emp.setEmployeeId(101); emp.setEmployeeName("Arpit"); emp.setDepartment("CS"); Address address=new Address(88,"MG road","Pune"); emp.setAddress(address); //Serialize try { FileOutputStream fileOut = new FileOutputStream("employee.ser"); ObjectOutputStream outStream = new ObjectOutputStream(fileOut); outStream.writeObject(emp); outStream.close(); fileOut.close(); }catch(IOException i) { i.printStackTrace(); } //Deserialize emp = null; try { FileInputStream fileIn =new FileInputStream("employee.ser"); ObjectInputStream in = new ObjectInputStream(fileIn); emp = (Employee) in.readObject(); in.close(); fileIn.close(); }catch(IOException i) { i.printStackTrace(); return; }catch(ClassNotFoundException c) { System.out.println("Employee class not found"); c.printStackTrace(); return; } System.out.println("Deserialized Employee..."); System.out.println("Emp id: " + emp.getEmployeeId()); System.out.println("Name: " + emp.getEmployeeName()); System.out.println("Department: " + emp.getDepartment()); address=emp.getAddress(); System.out.println("City :"+address.getCity()); }}运行 :
当你运行SerializeDeserializeMain.java.你会得到如下的结果：
Deserialized Employee...Emp id: 101Name: ArpitDepartment: CSCity :Pune
现在我们就得到了address对象的状态，就如它被序列化前的一样。
序列化中的继承：
现在我们看看继承是如何影响序列化的。不管父类是不是可序列化，这将引出很多个例子。如果父类是非可序列化的，我们将如何处理，并且它是如何工作的。让我们看看例子。
我们将创建一个Person.java，作为 Employee的父类。
案例4： 如果父类是可序列化的
如果父类可序列化，那么所有的继承类将是可序列化的。
案例5： 如果父类为非可序列化呢？
如果父类为非可序列化的 ，那么我们的处理办法会很不一样。
如果父类为非可序列化的，那么它必然不会有参数构造函数。
Person.java
package org.arpit.javapostsforlearning;public class Person { String name="default"; String nationality; public Person() { System.out.println("Person:Constructor"); } public Person(String name, String nationality) { super(); this.name = name; this.nationality = nationality; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getNationality() { return nationality; } public void setNationality(String nationality) { this.nationality = nationality; } }在包org.arpit.javapostsforlearning 中创建Employee.java
Employee.java:
package org.arpit.javapostsforlearning;import java.io.Serializable; public class Employee extends Person implements Serializable{ int employeeId; String department; public Employee(int employeeId,String name,String department,String nationality) { super(name,nationality); this.employeeId=employeeId; this.department=department; System.out.println("Employee:Constructor"); } public int getEmployeeId() { return employeeId; } public void setEmployeeId(int employeeId) { this.employeeId = employeeId; } public String getDepartment() { return department; } public void setDepartment(String department) { this.department = department; }}在org.arpit.javapostsforlearning包中创建SerializeDeserializeMain.java
SerializeDeserializeMain.java:
package org.arpit.javapostsforlearning;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.io.ObjectInputStream;import java.io.ObjectOutputStream; public class SerializeDeserializeMain { /** * @author Arpit Mandliya */ public static void main(String[] args) { //Serialize Employee emp = new Employee(101,"Arpit","CS","Indian"); System.out.println("Before serializing"); System.out.println("Emp id: " + emp.getEmployeeId()); System.out.println("Name: " + emp.getName()); System.out.println("Department: " + emp.getDepartment()); System.out.println("Nationality: " + emp.getNationality()); System.out.println("************"); System.out.println("Serializing"); try { FileOutputStream fileOut = new FileOutputStream("employee.ser"); ObjectOutputStream outStream = new ObjectOutputStream(fileOut); outStream.writeObject(emp); outStream.close(); fileOut.close(); }catch(IOException i) { i.printStackTrace(); } //Deserialize System.out.println("************"); System.out.println("Deserializing"); emp = null; try { FileInputStream fileIn =new FileInputStream("employee.ser"); ObjectInputStream in = new ObjectInputStream(fileIn); emp = (Employee) in.readObject(); in.close(); fileIn.close(); }catch(IOException i) { i.printStackTrace(); return; }catch(ClassNotFoundException c) { System.out.println("Employee class not found"); c.printStackTrace(); return; } System.out.println("After serializing"); System.out.println("Emp id: " + emp.getEmployeeId()); System.out.println("Name: " + emp.getName()); System.out.println("Department: " + emp.getDepartment()); System.out.println("Nationality: " + emp.getNationality()); }}运行：
当你运行SerializeDeserializeMain.java后，你会得到如下的输出，如果父类是非可序列化的，那么在反序列化过程中，所有继承于父类的实例变量值，将会通过调用非序列化构造函数来初始化。 这里 name继承于person，所以在反序列化过程中，name将会被初始化为默认值。
案例6 - 如果父类是可序列化，但你不需要继承类为可序列化
如果你不希望继承类为可序列化，那么你需要实现 writeObject() 和readObject() 方法，并且需要抛出NotSerializableException 异常。
案例7 - 可否序列化静态变量？
不能。因为静态变量是类级别的，不是对象级别的，当你序列化一个对象的时候，是不能序列化静态变量。
总结：
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