reflection-remapper

reflection-remapper is a library to simplify making reflective calls, with specific support for remapped environments.

Getting reflection-remapper

Releases are published to Maven Central.

Using snapshot builds

Snapshot builds are available on the Sonatype snapshots Maven repository: https://s01.oss.sonatype.org/content/repositories/snapshots/

Consult your build tool's documentation for details on adding Maven repositories to your project.

Gradle Kotlin DSL

Click to show build.gradle.kts

repositories {
  mavenCentral()
}

dependencies {
  implementation("xyz.jpenilla:reflection-remapper:0.1.1")
}

Gradle Groovy DSL

Click to show build.gradle

repositories {
  mavenCentral()
}

dependencies {
  implementation 'xyz.jpenilla:reflection-remapper:0.1.1'
}

Using reflection-remapper

Note: The following is a basic introduction; For further details, consult the reflection-remapper Javadocs.

ReflectionRemapper

ReflectionRemapper is the interface provided by reflection-remapper for remapping class, method, and field names for reflection lookups.

Click to see Java code snippet

final Path mappingsFile = /* get path to mappings ... */;
// ReflectionRemapper provides various static factory methods, in this example we use the one from a Path
// Note that the standard ReflectionRemapper implementations store their mappings in memory, which can be multiple megabytes large in some cases.
// This means it's best to use the remapper when your program starts and then dispose of any reference to it, so it can be garbage collected.
final ReflectionRemapper reflectionRemapper = ReflectionRemapper.forMappings(mappingsFile, "fromNamespace", "toNamespace");

final String runtimeName = reflectionRemapper.remapClassName("net.minecraft.server.level.ServerPlayer");
final Class<?> serverPlayerClass = Class.forName(runtimeName); // Exception handling omitted for brevity
final String runtimeFieldName = reflectionRemapper.remapFieldName(serverPlayerClass, "seenCredits");
// ...

Reflection Proxies

A reflection proxy is a runtime generated implementation of a "reflection proxy interface", which uses cached MethodHandles to invoke the targets specified by the interface definition. Reflection proxies can also make use of a ReflectionRemapper on creation in order to allow them to work in a remapped (or not) environment. The ReflectionRemapper on its own, while powerful, tends to make already verbose reflection code even more verbose. When combined with reflection proxies, we can have relatively clean reflection code while still properly remapping.

Click to see Java code snippet

Example target class

public final class ServerLevel {
  private SleepStatus sleepStatus;

  private BlockPos findLightningTargetAround(BlockPos pos) {
    // implementation
  }
}

Example reflection proxy interface

@Proxies(ServerLevel.class) // Can use Class or fully qualified class name (for inaccessible classes)
private interface ServerLevelProxy {
  BlockPos findLightningTargetAround(ServerLevel instance, BlockPos pos);

  @FieldSetter("sleepStatus")
  void setSleepStatus(ServerLevel instance, SleepStatus value);
}

Creating and using reflection proxy instance

final ReflectionRemapper reflectionRemapper = /* get ReflectionRemapper ... */;
final ClassLoader classLoader = /* get ClassLoader for loading proxy implementations, generally it needs to be able to see any reflection proxy interfaces you want to implement */;
final ReflectionProxyFactory reflectionProxyFactory = ReflectionProxyFactory.create(reflectionRemapper, classLoader); // ReflectionProxyFactory holds a ref to it's ReflectionRemapper

// Generated proxy instances do not hold a ref to the ReflectionRemapper, and are fine to keep around.
final ServerLevelProxy proxyInstance = reflectionProxyFactory.reflectionProxy(ServerLevelProxy.class);

// ...

final ServerLevel level = /* ... */;
final BlockPos blockPos = /* ... */;
final BlockPos target = proxyInstance.findLightningTargetAround(level, blockPos);
proxyInstance.setSleepStatus(level, new SleepStatus());