PreMain.java

/*******************************************************************************
 * Copyright (c) 2009, 2025 Mountainminds GmbH & Co. KG and Contributors
 * This program and the accompanying materials are made available under
 * the terms of the Eclipse Public License 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *    Marc R. Hoffmann - initial API and implementation
 *
 *******************************************************************************/
package org.jacoco.agent.rt.internal;

import java.lang.instrument.Instrumentation;

import org.jacoco.core.runtime.AgentOptions;
import org.jacoco.core.runtime.IRuntime;
import org.jacoco.core.runtime.InjectedClassRuntime;
import org.jacoco.core.runtime.ModifiedSystemClassRuntime;

/**
 * The agent which is referred as the <code>Premain-Class</code>. The agent
 * configuration is provided with the agent parameters in the command line.
 */
public final class PreMain {

    private PreMain() {
        // no instances
    }

    /**
     * This method is called by the JVM to initialize Java agents.
     *
     * @param options
     *            agent options
     * @param inst
     *            instrumentation callback provided by the JVM
     * @throws Exception
     *             in case initialization fails
     */
    public static void premain(final String options, final Instrumentation inst)
            throws Exception {

        final AgentOptions agentOptions = new AgentOptions(options);

        final Agent agent = Agent.getInstance(agentOptions);

        final IRuntime runtime = createRuntime(inst);
        runtime.startup(agent.getData());
        inst.addTransformer(new CoverageTransformer(runtime, agentOptions,
                IExceptionLogger.SYSTEM_ERR));
    }

    private static IRuntime createRuntime(final Instrumentation inst)
            throws Exception {

        if (AgentModule.isSupported()) {
            final AgentModule module = new AgentModule();
            module.openPackage(inst, Object.class);
            final Class<InjectedClassRuntime> clazz = module
                    .loadClassInModule(InjectedClassRuntime.class);
            return clazz.getConstructor(Class.class, String.class)
                    .newInstance(Object.class, "$JaCoCo");
        }

        return ModifiedSystemClassRuntime.createFor(inst,
                "java/lang/UnknownError");
    }

}