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Java 22 Guide: Project Panama FFI

PolyXML provides native C/Rust XML data-binding for the modern Java Virtual Machine using Java 22+ Project Panama (Foreign Function & Memory API - JEP 454). It completely eliminates legacy JNI glue code, GC object pinning, and JNI transition overheads by leveraging native off-heap memory and downcall method handles.

📦 Build Configuration

Maven (pom.xml)

<dependencies>
    <dependency>
        <groupId>io.github.nth-bailey</groupId>
        <artifactId>polyxml</artifactId>
        <version>0.1.0</version>
    </dependency>
</dependencies>

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.13.0</version>
            <configuration>
                <release>22</release>
                <compilerArgs>
                    <arg>--enable-preview</arg>
                </compilerArgs>
            </configuration>
        </plugin>
    </plugins>
</build>

JVM Runtime Flags

Because Project Panama accesses native off-heap memory, your application requires the --enable-native-access JVM flag at runtime:

java --enable-native-access=ALL-UNNAMED -jar target/my-app.jar

1. Schema Construction & Resource Management

PolyXML schemas are native off-heap objects. PolyXML.Schema implements AutoCloseable, enabling clean deterministic cleanup with Java's standard try-with-resources:

package com.example;

import io.polyxml.PolyXML;

public class Application {
    public static void main(String[] args) {
        System.out.println("PolyXML Native Core Version: " + PolyXML.version());

        // 1. Build an off-heap native schema using try-with-resources
        try (PolyXML.Schema schema = new PolyXML.SchemaBuilder("ServerMetrics")
                .addField("serverId", "id", PolyXML.FieldKind.ATTRIBUTE, PolyXML.ScalarType.INT)
                .addField("hostname", "host", PolyXML.FieldKind.ELEMENT, PolyXML.ScalarType.STRING)
                .addField("cpuUtilization", "cpu", PolyXML.FieldKind.ELEMENT, PolyXML.ScalarType.FLOAT)
                .addField("isHealthy", "healthy", PolyXML.FieldKind.ELEMENT, PolyXML.ScalarType.BOOL)
                .build()) {

            System.out.println("Schema created successfully in off-heap memory.");
            // Native memory is automatically freed when leaving this block
        }
    }
}

2. Low-Overhead Downcalls with Project Panama

Unlike legacy JNI, which requires handwritten C wrapper functions (Java_io_polyxml_...) and context transitions that stall the JVM JIT compiler, Project Panama uses java.lang.foreign.Linker:

import java.lang.foreign.*;
import java.lang.invoke.MethodHandle;

public class NativeBridgeExample {
    private static final Linker LINKER = Linker.nativeLinker();
    private static final SymbolLookup LOOKUP = SymbolLookup.loaderLookup();

    public static void executeNativeCall() throws Throwable {
        // Direct downcall handle to native symbol
        MethodHandle versionHandle = LINKER.downcallHandle(
            LOOKUP.find("polyxml_version").orElseThrow(),
            FunctionDescriptor.of(ValueLayout.ADDRESS)
        );

        MemorySegment versionStrSeg = (MemorySegment) versionHandle.invokeExact();
        System.out.println("Native Version: " + versionStrSeg.getString(0));
    }
}

3. Off-Heap Confined Arenas & Zero-GC Pressure

When passing large XML strings or byte streams from Java into PolyXML, Java 22's Arena.ofConfined() allocates off-heap memory segments that bypass the JVM garbage collector entirely:

import java.lang.foreign.Arena;
import java.lang.foreign.MemorySegment;
import java.nio.charset.StandardCharsets;

public class OffHeapBufferExample {
    public static void allocateAndPassXml(String xmlData) {
        // Arena confines allocation to current thread and frees immediately upon exit
        try (Arena arena = Arena.ofConfined()) {
            byte[] xmlBytes = xmlData.getBytes(StandardCharsets.UTF_8);
            MemorySegment nativeBuffer = arena.allocate(xmlBytes.length);
            nativeBuffer.copyFrom(MemorySegment.ofArray(xmlBytes));

            System.out.printf("Allocated %d bytes off-heap with zero GC pressure%n", nativeBuffer.byteSize());
            // Pass nativeBuffer.address() to PolyXML native routines...
        } // Instant off-heap deallocation occurs here
    }
}

4. Enterprise Architecture: ISO 20022 Batch Processing

In high-throughput enterprise architectures (e.g. processing millions of ISO 20022 XML financial payment messages or HL7 clinical records):

  1. Singleton Native Schemas: Store PolyXML.Schema instances in static final fields or Spring Singleton beans so they are created once at application startup.
  2. Eliminate Garbage Collection Pauses: By streaming raw socket or file bytes into off-heap MemorySegment buffers, you prevent millions of short-lived XML DOM strings from exhausting the JVM Young Generation heap.
  3. Thread Safety: PolyXML's native schema handles are immutable and read-only after construction, making them safe to share concurrently across all JVM virtual threads (Project Loom).