asm-invoke-util

A small utility that provides a faster alternative to reflections for invoking methods.

Background

Undeniably, reflections have proved to be one of the most powerful APIs introduced to Java since. However, they have also been infamous for being expensive on memory and performance.

Although they have been massively improved through updates, as well as low-level APIs like MethodHandles, it is always possible (and even necessary sometimes) to squeeze out less execution time and memory.

Implementation

Click to expand

This utility's implementation is simple: It constructs bytecode using ASM to generate a class that directly invokes the method

public class Dummy {

    public void doMagic(String spell) {
        System.out.println(spell + "! Woooosh");
    }
}

/* Implementation for the caller */
public final class DummyMethodCaller0 implements MethodCaller {

    @Override public Object call(@Nullable Object instance, Object... arguments) {
        return ((Dummy) instance).doMagic((String) arguments[0]);
    }
}

This way, we can simply acquire an instance of DummyMethodCaller0 to call the doMagic method. No reflection is needed, performs just like direct method execution.

Usage

Gradle

repositories {
    maven { url 'https://jitpack.io' }
}

dependencies {
    implementation 'com.github.Revxrsal:asm-invoke-util:1.0'
}

Maven

<repository>
    <id>jitpack.io</id>
    <url>https://jitpack.io</url>
</repository>

<dependency>
    <groupId>com.github.Revxrsal</groupId>
    <artifactId>asm-invoke-util</artifactId>
    <version>1.0</version>
</dependency>

Example

public static void main(String[] args) {
    Method method = Dummy.class.getDeclaredMethod("doMagic", String.class);
    MethodCaller caller = MethodCaller.wrap(method);
    Dummy dummy = new Dummy();
    caller.call(dummy, "Magic stuff");

    /* Or */

    BoundMethodCaller caller = MethodCaller.wrap(method).bindTo(new Dummy());
    caller.call("Magic stuff");
}

Final notes

Because this library effectively generates code that calls the method directly, it is impossible to use ASM to invoke private methods. Similarly, due to some limitations in newer Java version, it is impossible to invoke package-private ones. In such cases, the utility will automatically fallback to the MethodHandles API when ASM is not a choice.