使用不可序列化的属性序列化Java对象

人们可能有多种原因想要使用自定义序列化而不是依赖Java的默认序列化。最常见的原因之一是为了提高性能，但是编写自定义序列化的另一个原因是不支持默认序列化机制。具体来说，如本博文所述，自定义序列化可用于允许将较大的对象序列化，即使该对象的属性本身不能直接序列化也是如此。

下一个代码清单显示了一个简单的类，该类用于将给定类序列化为提供名称的文件，并从该文件中反序列化对象。我将在本文中使用它来演示序列化。

SerializationDemonstrator.java

package dustin.examples.serialization;import static java.lang.System.out;import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;/*** Simple serialization/deserialization demonstrator.* * @author Dustin*/
public class SerializationDemonstrator
{/*** Serialize the provided object to the file of the provided name.* @param objectToSerialize Object that is to be serialized to file; it is*     best that this object have an individually overridden toString()*     implementation as that is used by this method for writing our status.* @param fileName Name of file to which object is to be serialized.* @throws IllegalArgumentException Thrown if either provided parameter is null.*/public static <T> void serialize(final T objectToSerialize, final String fileName){if (fileName == null){throw new IllegalArgumentException("Name of file to which to serialize object to cannot be null.");}if (objectToSerialize == null){throw new IllegalArgumentException("Object to be serialized cannot be null.");}try (FileOutputStream fos = new FileOutputStream(fileName);ObjectOutputStream oos = new ObjectOutputStream(fos)){oos.writeObject(objectToSerialize);out.println("Serialization of Object " + objectToSerialize + " completed.");}catch (IOException ioException){ioException.printStackTrace();}}/*** Provides an object deserialized from the file indicated by the provided* file name.* * @param <T> Type of object to be deserialized.* @param fileToDeserialize Name of file from which object is to be deserialized.* @param classBeingDeserialized Class definition of object to be deserialized*    from the file of the provided name/path; it is recommended that this*    class define its own toString() implementation as that will be used in*    this method's status output.* @return Object deserialized from provided filename as an instance of the*    provided class; may be null if something goes wrong with deserialization.* @throws IllegalArgumentException Thrown if either provided parameter is null.*/public static <T> T deserialize(final String fileToDeserialize, final Class<T> classBeingDeserialized){if (fileToDeserialize == null){throw new IllegalArgumentException("Cannot deserialize from a null filename.");}if (classBeingDeserialized == null){throw new IllegalArgumentException("Type of class to be deserialized cannot be null.");}T objectOut = null;try (FileInputStream fis = new FileInputStream(fileToDeserialize);ObjectInputStream ois = new ObjectInputStream(fis)){objectOut = (T) ois.readObject();out.println("Deserialization of Object " + objectOut + " is completed.");}catch (IOException | ClassNotFoundException exception){exception.printStackTrace();}return objectOut;}
}

下一个代码清单说明了如何使用SerializationDemonstrator类对标准Java字符串（可序列化）进行序列化和反序列化。屏幕快照显示在代码清单之后，并通过SerializationDemonstrator类的serialize和deserialize serialize方法显示了运行String的输出（在NetBeans中）。

在字符串上运行SerializationDemonstrator方法

SerializationDemonstrator.serialize("Inspired by Actual Events", "string.dat");
final String stringOut = SerializationDemonstrator.deserialize("string.dat", String.class);

接下来的两个代码清单是针对Person.java类及其作为属性类型的一个类（ CityState.java ）。尽管Person实现了Serializable ，但CityAndState类没有实现。

人.java

package dustin.examples.serialization;import java.io.Serializable;/*** Person class.* * @author Dustin*/
public class Person implements Serializable
{private String lastName;private String firstName;private CityState cityAndState;public Person(final String newLastName, final String newFirstName,final CityState newCityAndState){this.lastName = newLastName;this.firstName = newFirstName;this.cityAndState = newCityAndState;}public String getFirstName(){return this.firstName;}public String getLastName(){return this.lastName;}@Overridepublic String toString(){return this.firstName + " " + this.lastName + " of " + this.cityAndState;}
}

CityAndState.java

package dustin.examples.serialization;/*** Simple class storing city and state names that is NOT Serializable.* * @author Dustin*/
public class CityState
{private final String cityName;private final String stateName;public CityState(final String newCityName, final String newStateName){this.cityName = newCityName;this.stateName = newStateName;}public String getCityName(){return this.cityName;}public String getStateName(){return this.stateName;}@Overridepublic String toString(){return this.cityName + ", " + this.stateName;}
}

下一个代码清单演示如何在具有不可序列化的CityState的可序列化Person类上运行SerializationDemonstrator 。代码清单后是NetBeans中输出的屏幕快照。

在具有不可序列化的CityState的可序列化人员上运行SerializationDemonstrator方法

final Person personIn = new Person("Flintstone", "Fred", new CityState("Bedrock", "Cobblestone"));
SerializationDemonstrator.serialize(personIn, "person.dat");final Person personOut = SerializationDemonstrator.deserialize("person.dat", Person.class);

serializationDemonstratorOnSerializablePersonNonSerializableCityState

在这种情况下， CityState类是我自己的类，可以将其设置为Serializable。但是，假设该类是第三方框架或库的一部分，并且我无法更改该类本身，则可以将Person更改为使用自定义序列化和反序列化，并正确使用CityState 。这在适用于Person的类SerializablePerson的下一个代码清单中显示。

SerializablePerson.java

package dustin.examples.serialization;import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.ObjectStreamException;
import java.io.Serializable;/*** Person class.* * @author Dustin*/
public class SerializablePerson implements Serializable
{private String lastName;private String firstName;private CityState cityAndState;public SerializablePerson(final String newLastName, final String newFirstName,final CityState newCityAndState){this.lastName = newLastName;this.firstName = newFirstName;this.cityAndState = newCityAndState;}public String getFirstName(){return this.firstName;}public String getLastName(){return this.lastName;}@Overridepublic String toString(){return this.firstName + " " + this.lastName + " of " + this.cityAndState;}/*** Serialize this instance.* * @param out Target to which this instance is written.* @throws IOException Thrown if exception occurs during serialization.*/private void writeObject(final ObjectOutputStream out) throws IOException{out.writeUTF(this.lastName);out.writeUTF(this.firstName);out.writeUTF(this.cityAndState.getCityName());out.writeUTF(this.cityAndState.getStateName());}/*** Deserialize this instance from input stream.* * @param in Input Stream from which this instance is to be deserialized.* @throws IOException Thrown if error occurs in deserialization.* @throws ClassNotFoundException Thrown if expected class is not found.*/private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException{this.lastName = in.readUTF();this.firstName = in.readUTF();this.cityAndState = new CityState(in.readUTF(), in.readUTF());}private void readObjectNoData() throws ObjectStreamException{throw new InvalidObjectException("Stream data required");}
}

上面的代码清单显示SerializablePerson具有自定义的writeObject和readObject方法，以支持自定义的序列化/反序列化， CityState适当地处理其CityState序列化类型CityState属性。接下来显示用于通过SerializationDemonstrator运行该类的代码片段以及这样做的成功输出。

在SerializablePerson上运行SerializationDemonstrator

final SerializablePerson personIn = new SerializablePerson("Flintstone", "Fred", new CityState("Bedrock", "Cobblestone"));
SerializationDemonstrator.serialize(personIn, "person.dat");final SerializablePerson personOut = SerializationDemonstrator.deserialize("person.dat", SerializablePerson.class);

上面描述的方法将允许将不可序列化的类型用作可序列化类的属性，而无需使那些字段处于瞬态状态。但是，如果前面显示的CityState实例需要在多个可序列化的类中使用，则最好使用可序列化的装饰器装饰CityState类，然后在需要序列化的类中使用该序列化的装饰器类。下一个代码清单显示SerializableCityState ，它用序列化的版本装饰CityState 。

SerializableCityState

package dustin.examples.serialization;import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.ObjectStreamException;
import java.io.Serializable;/*** Simple class storing city and state names that IS Serializable. This class* decorates the non-Serializable CityState class and adds Serializability.* * @author Dustin*/
public class SerializableCityState implements Serializable
{private CityState cityState;public SerializableCityState(final String newCityName, final String newStateName){this.cityState = new CityState(newCityName, newStateName);}public String getCityName(){return this.cityState.getCityName();}public String getStateName(){return this.cityState.getStateName();}@Overridepublic String toString(){return this.cityState.toString();}/*** Serialize this instance.* * @param out Target to which this instance is written.* @throws IOException Thrown if exception occurs during serialization.*/private void writeObject(final ObjectOutputStream out) throws IOException{out.writeUTF(this.cityState.getCityName());out.writeUTF(this.cityState.getStateName());}/*** Deserialize this instance from input stream.* * @param in Input Stream from which this instance is to be deserialized.* @throws IOException Thrown if error occurs in deserialization.* @throws ClassNotFoundException Thrown if expected class is not found.*/private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException{this.cityState = new CityState(in.readUTF(), in.readUTF());}private void readObjectNoData() throws ObjectStreamException{throw new InvalidObjectException("Stream data required");}
}

可以直接在Person类中使用此可序列化的修饰器，并且封闭的Person可以使用默认序列化，因为其字段都是可序列化的。这显示在Person改编的Person2的下一个代码清单中。

Person2.java

package dustin.examples.serialization;import java.io.Serializable;/*** Person class.* * @author Dustin*/
public class Person2 implements Serializable
{private final String lastName;private final String firstName;private final SerializableCityState cityAndState;public Person2(final String newLastName, final String newFirstName,final SerializableCityState newCityAndState){this.lastName = newLastName;this.firstName = newFirstName;this.cityAndState = newCityAndState;}public String getFirstName(){return this.firstName;}public String getLastName(){return this.lastName;}@Overridepublic String toString(){return this.firstName + " " + this.lastName + " of " + this.cityAndState;}
}

可以像下面的代码清单中所示那样执行该代码，然后在NetBeans输出窗口中看到其输出。

针对Person2 / SerializableCityState运行SerializationDemonstrator

final Person2 personIn = new Person2("Flintstone", "Fred", new SerializableCityState("Bedrock", "Cobblestone"));
SerializationDemonstrator.serialize(personIn, "person.dat");final Person2 personOut = SerializationDemonstrator.deserialize("person.dat", Person2.class);