文章目錄

入門

Kryo(github地址)是一個快速，高效的對象圖序列化Java框架。該項目的目標是速度，效率和易於使用的API。無論何時需要將對象持久化到文件，數據庫還是通過網絡，該項目都非常有用。
Kryo還可以執行自動的深層和淺層複製/克隆。這是直接從對象複製到對象，而不是對象->字節->對象

依賴

compile group: 'com.esotericsoftware', name: 'kryo', version: '4.0.1'

由於其底層依賴於 ASM 技術，與 Spring 等框架可能會發生 ASM 依賴的版本衝突,所以提供了另外一個依賴以供解決此問題
```
compile group: 'com.esotericsoftware', name: 'kryo-shaded', version: '4.0.1'
```

簡單操作


public class Person {
    private String username = "jannal";
    private String password = "123";
    ...省略getter setter...
}  

@Test
public void case1() throws FileNotFoundException {
    Kryo kryo = new Kryo();
    Output output = new Output(new FileOutputStream("person.db"));
    Person person = new Person();
    kryo.writeObject(output, person);
    output.close();
    Input input = new Input(new FileInputStream("person.db"));
    person = kryo.readObject(input, Person.class);
    input.close();
    assert "jannal".equals(person.getUsername());
}

讀寫方式

Kryo 共支持三種讀寫方式

如果類是已知的，並且對象不爲null

kryo.writeObject(output, someObject);
// ...
SomeClass someObject = kryo.readObject(input, SomeClass.class);

如果類是已知的，並且對象可能爲null

kryo.writeObjectOrNull(output, someObject);
// ...
SomeClass someObject = kryo.readObjectOrNull(input, SomeClass.class);

如果類的字節碼未知，並且對象可能爲 null

kryo.writeClassAndObject(output, object);
// ...
Object object = kryo.readClassAndObject(input);
if (object instanceof SomeClass) {
   // ...
}

API介紹

某些類無法由Kryo序列化時可以使用

//類實現了Serializable
kryo.register(SomeClass.class, new JavaSerializer());

//類實現了Externalizable
kryo.register(SomeClass.class, new ExternalizableSerializer());

自定義序列化處理器


@Test
public void case3() throws FileNotFoundException {
    Kryo kryo = new Kryo();
    kryo.register(Student.class, new StudentSerializer());
    Output output = new Output(new FileOutputStream("student.db"));
    Student student = new Student("jannal");
    kryo.writeObject(output, student);
    output.close();
    Input input = new Input(new FileInputStream("student.db"));
    student = kryo.readObject(input, Student.class);
    input.close();
    Assert.assertEquals("jannal", student.getName());
    Assert.assertEquals("jannal", student.getPerson().getUsername());
}


public class StudentSerializer extends Serializer<Student> {
    /**
     * 對象寫入字節
     */
    @Override
    public void write(Kryo kryo, Output output, Student student) {
        output.writeString(student.getName());
        output.writeString(student.getPerson().getUsername());
        output.writeString(student.getPerson().getPassword());
    }

    /**
     * 從字節中讀取轉換爲對象
     */
    @Override
    public Student read(Kryo kryo, Input input, Class<Student> clazz) {
        String name = input.readString();
        String username = input.readString();
        String password = input.readString();
        Student student = new Student(name);
        Person person = new Person();
        person.setUsername(username);
        person.setPassword(password);
        student.setPerson(person);
        return student;
    }
}

Kryo 支持對註冊行爲,當Kryo寫出對象的實例時，需要寫出一些東西來識別標識對象類，默認情況下使用類的權限定名稱和寫入對象的字節，使用類名效率不高，可以提前註冊類的標識，使用可變長度int保存。反序列化期間，註冊的類必須具有與序列化期間完全相同的ID

當ID爲較小的正整數時，它們的寫入效率最高。負ID無法有效地序列化。默認情況下原生類型、包裝類型、字符串、void使用0-9.可以將Kryo#setRegistrationRequired設置爲true,在遇到任何未註冊的類時引發異常,這樣可以防止應用程序意外使用類名字符串。


@Test
public void testRegister() throws FileNotFoundException {
    Kryo kryo = new Kryo();
    //id不能是負數
    kryo.register(Person.class, 10);
    Output output = new Output(new FileOutputStream("person.db"));
    Person person = new Person();
    kryo.writeObject(output, person);
    output.close();
    Input input = new Input(new FileInputStream("person.db"));
    person = kryo.readObject(input, Person.class);
    input.close();
    Assert.assertEquals("jannal", person.getUsername());
}

缺點
- Kryo 不支持 Bean 中增刪字段
- 使用 Arrays.asList(); 創建的 List 對象，會引起序列化異常
- 不支持包含無參構造器類的反序列化
- Kryo 是線程不安全的，每當需要序列化和反序列化時都需要實例化一次或者通過ThreadLocal

kryo-serializers

使用第三方庫對 Kryo 進行序列化類型的擴展kryo-serializers

compile group: 'de.javakaffee', name: 'kryo-serializers', version: '0.45'

手動註冊

kryo.register( Arrays.asList( "" ).getClass(), new ArraysAsListSerializer() );
kryo.register( Collections.EMPTY_LIST.getClass(), new CollectionsEmptyListSerializer() );
kryo.register( Collections.EMPTY_MAP.getClass(), new CollectionsEmptyMapSerializer() );
kryo.register( Collections.EMPTY_SET.getClass(), new CollectionsEmptySetSerializer() );
kryo.register( Collections.singletonList( "" ).getClass(), new CollectionsSingletonListSerializer() );
kryo.register( Collections.singleton( "" ).getClass(), new CollectionsSingletonSetSerializer() );
kryo.register( Collections.singletonMap( "", "" ).getClass(), new CollectionsSingletonMapSerializer() );
kryo.register( GregorianCalendar.class, new GregorianCalendarSerializer() );
kryo.register( InvocationHandler.class, new JdkProxySerializer() );
UnmodifiableCollectionsSerializer.registerSerializers( kryo );
SynchronizedCollectionsSerializer.registerSerializers( kryo );

// custom serializers for non-jdk libs

// register CGLibProxySerializer, works in combination with the appropriate action in handleUnregisteredClass (see below)
kryo.register( CGLibProxySerializer.CGLibProxyMarker.class, new CGLibProxySerializer( kryo ) );
// dexx
ListSerializer.registerSerializers( kryo );
MapSerializer.registerSerializers( kryo );
SetSerializer.registerSerializers( kryo );
// joda DateTime, LocalDate, LocalDateTime and LocalTime
kryo.register( DateTime.class, new JodaDateTimeSerializer() );
kryo.register( LocalDate.class, new JodaLocalDateSerializer() );
kryo.register( LocalDateTime.class, new JodaLocalDateTimeSerializer() );
kryo.register( LocalDateTime.class, new JodaLocalTimeSerializer() );
// protobuf
kryo.register( SampleProtoA.class, new ProtobufSerializer() ); // or override Kryo.getDefaultSerializer as shown below
// wicket
kryo.register( MiniMap.class, new MiniMapSerializer() );
// guava ImmutableList, ImmutableSet, ImmutableMap, ImmutableMultimap, ImmutableTable, ReverseList, UnmodifiableNavigableSet
ImmutableListSerializer.registerSerializers( kryo );
ImmutableSetSerializer.registerSerializers( kryo );
ImmutableMapSerializer.registerSerializers( kryo );
ImmutableMultimapSerializer.registerSerializers( kryo );
ImmutableTableSerializer.registerSerializers( kryo );
ReverseListSerializer.registerSerializers( kryo );
UnmodifiableNavigableSetSerializer.registerSerializers( kryo );
// guava ArrayListMultimap, HashMultimap, LinkedHashMultimap, LinkedListMultimap, TreeMultimap, ArrayTable, HashBasedTable, TreeBasedTable
ArrayListMultimapSerializer.registerSerializers( kryo );
HashMultimapSerializer.registerSerializers( kryo );
LinkedHashMultimapSerializer.registerSerializers( kryo );
LinkedListMultimapSerializer.registerSerializers( kryo );
TreeMultimapSerializer.registerSerializers( kryo );
ArrayTableSerializer.registerSerializers( kryo );
HashBasedTableSerializer.registerSerializers( kryo );
TreeBasedTableSerializer.registerSerializers( kryo );

序列化之Kryo

文章目錄

入門

讀寫方式

API介紹

kryo-serializers

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