AgentAttacher

Main.java

package net.superblaubeere27.agentattacher;

import com.sun.tools.attach.*;
import joptsimple.*;

import java.io.File;
import java.io.IOException;
import java.util.Optional;

public class Main {

    public static void main(String[] args) throws IOException, AttachNotSupportedException {
        OptionParser optionParser = new OptionParser();

        ArgumentAcceptingOptionSpec<File> agentPath = optionParser.accepts("agentPath").withRequiredArg().ofType(File.class).required();
        ArgumentAcceptingOptionSpec<String> username = optionParser.accepts("username", "The username of the minecraft session").withOptionalArg();
        AbstractOptionSpec<Void> help = optionParser.accepts("help").forHelp();

        OptionSet optionSet;

        try {
            optionSet = optionParser.parse(args);
        } catch (OptionException e) {
            System.err.println("Failed to parse options: " + e.getMessage() + " (try --help)");
            return;
        }

        if (optionSet.has(help)) {
            optionParser.printHelpOn(System.err);
            return;
        }

        File agent = optionSet.valueOf(agentPath);

        if (!agent.exists()) {
            System.err.println("Agent doesn't exist");
            return;
        }

        OptionSet finalOptionSet = optionSet;

        Optional<VirtualMachineDescriptor> first = VirtualMachine.list()
                .stream()
                .filter(vm_desc -> vm_desc.displayName().startsWith("net.minecraft.client.main.Main") && (!finalOptionSet.has(username) || vm_desc.displayName().contains(finalOptionSet.valueOf(username))))
                .findFirst();

        if (!first.isPresent()) {
            System.err.println("Minecraft session wasn't found");
            return;
        }

        VirtualMachine attach = VirtualMachine.attach(first.get());

        try {
            attach.loadAgent(agent.getAbsolutePath());
            System.out.println("Agent was loaded.");
        } catch (AgentLoadException e) {
            System.err.println("Agent failed to load: ");
            e.printStackTrace();
        } catch (AgentInitializationException e) {
            System.err.println("Agent loaded, but failed to initialize: ");
            e.printStackTrace();
        }

    }

}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>net.superblaubeere27</groupId>
    <artifactId>AgentAttacher</artifactId>
    <version>1.0-SNAPSHOT</version>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>10</source>
                    <target>10</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>3.2.1</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer
                                        implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <manifestEntries>
                                        <Main-Class>net.superblaubeere27.agentattacher.Main</Main-Class>
                                    </manifestEntries>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

    <dependencies>
        <dependency>
            <groupId>net.sf.jopt-simple</groupId>
            <artifactId>jopt-simple</artifactId>
            <version>5.0.4</version>
        </dependency>
    </dependencies>

</project>