docs/object-serialization/java/index.md

---
title: Java Object Serialization
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Apache Fory Java provides high-performance binary object serialization. Use xlang mode for payloads
shared across Fory implementation families and native mode for JVM-family object graphs.

This Java guide is scoped to Binary Object Serialization. For other Java capabilities, use
[Row Format](../../row-format/java.md), [Fory JSON](../../json/index.md),
[Fory IDL and compiler](../../compiler/index.md), or [Fory gRPC](../../grpc/java.md).

## Binary Object Serialization

### Features

- **Generated Codecs**: JIT-generated serializers reduce virtual dispatch,
  branching, and metadata lookups on hot paths.
- **Native and Xlang Modes**: Choose Java-native object semantics or a portable
  wire format shared with other Fory implementations.
- **Compact Encoding**: Variable-length integers, metadata sharing, string
  compression, and optional numeric-array compression reduce payload size.
- **Object Graph Semantics**: Preserve shared and circular references,
  polymorphism, schema evolution, and deep-copy identity.

### Native Mode Features

- **Framework Replacement**: Replace JDK serialization, Kryo, FST, Hessian, or
  Java-only Protocol Buffers payloads in Java-only systems.
- **JDK Semantics**: Supports JDK custom serialization behavior and
  `Externalizable` in native mode.
- **Security Controls**: Class registration, type checking, depth limits, and
  configurable deserialization policies protect decoding boundaries.

### Installation

Add `fory-core` for binary object serialization. Keep all Fory modules in one
application on the same version.

Fory core supports Java 8 and later. Java Record serialization requires Java 17
or later.

#### Maven

```xml
<!-- Binary object serialization -->
<dependency>
  <groupId>org.apache.fory</groupId>
  <artifactId>fory-core</artifactId>
  <version>1.6.1</version>
</dependency>
```

#### Gradle

```kotlin
// Binary object serialization
implementation("org.apache.fory:fory-core:1.6.1")
```

#### JDK 25 and Later

On JDK 25 and later, opening `java.lang.invoke` to Fory core is also recommended. It avoids
the current-JDK Unsafe fallback and is required when Unsafe access is disabled or unavailable,
including with `--sun-misc-unsafe-memory-access=deny`. Use `ALL-UNNAMED` when Fory is on the
classpath:

```bash
--add-opens=java.base/java.lang.invoke=ALL-UNNAMED
```

Use the Fory core module name when Fory is on the module path:

```bash
--add-opens=java.base/java.lang.invoke=org.apache.fory.core
```

### Quick Start

Note that Fory creation is not cheap, the **Fory instances should be reused between serializations** instead of creating it every time. You should keep Fory as a static global variable, or instance variable of some singleton object or limited objects.

#### Single-Thread Usage

```java
import java.util.List;
import java.util.Arrays;

import org.apache.fory.*;
import org.apache.fory.config.*;

public class Example {
  public static void main(String[] args) {
    SomeClass object = new SomeClass();
    // Note that Fory instances should be reused between
    // multiple serializations of different objects.
    Fory fory = Fory.builder()
      .withXlang(true)
      .requireClassRegistration(true)
      .build();
    // Registering types can reduce class name serialization overhead, but not mandatory.
    // If class registration enabled, all custom types must be registered.
    // Registration order must be consistent if id is not specified
    fory.register(SomeClass.class);
    byte[] bytes = fory.serialize(object);
    System.out.println(fory.deserialize(bytes));
  }
}
```

#### Multi-Thread Usage

```java
import org.apache.fory.*;
import org.apache.fory.config.*;

public class Example {
  public static void main(String[] args) {
    SomeClass object = new SomeClass();
    ThreadSafeFory fory = Fory.builder()
      .withXlang(true)
      .buildThreadSafeFory();
    fory.register(SomeClass.class, 1);
    byte[] bytes = fory.serialize(object);
    System.out.println(fory.deserialize(bytes));
  }
}
```

#### Fory Instance Reuse Pattern

```java
import org.apache.fory.*;
import org.apache.fory.config.*;

public class Example {
  private static final ThreadSafeFory fory = Fory.builder()
    .withXlang(true)
    .buildThreadSafeFory();

  static {
    fory.register(SomeClass.class, 1);
  }

  public static void main(String[] args) {
    SomeClass object = new SomeClass();
    byte[] bytes = fory.serialize(object);
    System.out.println(fory.deserialize(bytes));
  }
}
```

### Xlang Mode And Native Mode

Use xlang mode for cross-language payloads and schemas shared with non-Java implementations. It is the default Java wire mode, and Java examples that use it set `.withXlang(true)` explicitly so the mode choice is visible.

Use native mode for Java-only traffic. Native mode is selected with `.withXlang(false)` and owns Java-specific object behavior such as JDK serialization hooks, `Externalizable`, dynamic object graphs, object copy, and Java native-mode zero-copy buffers. It is optimized for the JVM type system and supports a broader Java object surface than xlang mode. Compatible mode is enabled by default. Set `.withCompatible(false)` only when every reader and writer uses the same class schema and you want faster serialization and smaller size. If you are replacing JDK serialization, Kryo, FST, Hessian, or Java-only Protocol Buffers payloads, start with native mode.

See [Native Serialization](native.md) for Java-only serialization details and [Cross-Language Interoperability](basic-serialization.md#cross-language-interoperability) for Java xlang registration and interoperability rules.

### Thread Safety

Fory provides two thread-safe Fory instance styles:

#### `buildThreadSafeFory`

This is the default choice. It uses a fixed-size shared `ThreadPoolFory` sized to
`4 * availableProcessors()` and is the preferred instance form for virtual-thread workloads:

```java
ThreadSafeFory fory = Fory.builder()
  .withXlang(true)
  .withRefTracking(false)
  .withAsyncCompilation(true)
  .buildThreadSafeFory();
```

See more details in [Virtual Threads](virtual-threads.md).

#### ThreadLocalFory

Use `buildThreadLocalFory()` only when you explicitly want one `Fory` instance per long-lived
platform thread, or when you want to pin that choice regardless of JDK version:

```java
ThreadSafeFory fory = Fory.builder()
  .withXlang(true)
  .buildThreadLocalFory();
fory.register(SomeClass.class, 1);
byte[] bytes = fory.serialize(object);
System.out.println(fory.deserialize(bytes));
```

#### `buildThreadSafeForyPool`

Use `buildThreadSafeForyPool(poolSize)` when you want to set that fixed shared pool size
explicitly. It eagerly creates `poolSize` `Fory` instances, keeps them in shared fixed slots, and
then lets any caller borrow one through a thread-agnostic fast path. Calls only block when every
pooled instance is already in use; the pool does not key cached instances by thread identity:

```java
ThreadSafeFory fory = Fory.builder()
  .withXlang(true)
  .withRefTracking(false)
  .withAsyncCompilation(true)
  .buildThreadSafeForyPool(poolSize);
```

#### Builder Methods

```java
// Single-thread Fory
Fory fory = Fory.builder()
  .withXlang(true)
  .withRefTracking(false)
  .withAsyncCompilation(true)
  .build();

// Thread-safe Fory (thread-safe Fory backed by a pool of Fory instances)
ThreadSafeFory fory = Fory.builder()
  .withXlang(true)
  .withRefTracking(false)
  .withAsyncCompilation(true)
  .buildThreadSafeFory();

// Explicit thread-local Fory instance
ThreadSafeFory threadLocalFory = Fory.builder()
  .withXlang(true)
  .buildThreadLocalFory();
```

## Platform support

- [Android](android.md) covers Fory Core, static generated serializers, Kotlin integration, R8,
  `ByteBuffer`, and Android object-model constraints.
- [GraalVM Native Image](graalvm.md) covers build-time serializer generation, registration,
  initialization, proxies, framework integration, and diagnostics.

Fory JSON has separate [Android](../../json/android.md) and
[GraalVM Native Image](../../json/graalvm.md) deployment guides because its generated-code and
model-discovery workflows differ from Fory Core.

## Documentation map

| Group                  | Pages                                                                                                                                                                                                                                                             |
| ---------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Serialization modes    | [Basic Serialization](basic-serialization.md), [Native Serialization](native.md)                                                                                                                                                                                  |
| Common                 | [Configuration](configuration.md), [Type Registration](type-registration.md), [Schema Evolution](schema-evolution.md), [Schema Metadata](schema-metadata.md), [Custom Serializers](custom-serializers.md)                                                         |
| Java-specific features | [Advanced Features](advanced-features.md), [Compression](compression.md), [Object Copy](object-copy.md), [JDK Custom Serialization](jdk-serialization.md), [Static Generated Serializers](static-generated-serializers.md), [Virtual Threads](virtual-threads.md) |
| Platform and operate   | [Android](android.md), [GraalVM Native Image](graalvm.md), [Troubleshooting](troubleshooting.md)                                                                                                                                                                  |

Before decoding externally supplied binary payloads, read
[Java Security](security.md).