org.springframework.instrument.InstrumentationSavingAgent.java Source code

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Here is the source code for org.springframework.instrument.InstrumentationSavingAgent.java

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/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.instrument;

import java.lang.instrument.Instrumentation;

/**
 * Java agent that saves the {@link Instrumentation} interface from the JVM
 * for later use.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @since 2.0
 * @see org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver
 */
public final class InstrumentationSavingAgent {

    private static volatile Instrumentation instrumentation;

    private InstrumentationSavingAgent() {
    }

    /**
     * Save the {@link Instrumentation} interface exposed by the JVM.
     */
    public static void premain(String agentArgs, Instrumentation inst) {
        instrumentation = inst;
    }

    /**
     * Save the {@link Instrumentation} interface exposed by the JVM.
     * This method is required to dynamically load this Agent with the Attach API.
     */
    public static void agentmain(String agentArgs, Instrumentation inst) {
        instrumentation = inst;
    }

    /**
     * Return the {@link Instrumentation} interface exposed by the JVM.
     * <p>Note that this agent class will typically not be available in the classpath
     * unless the agent is actually specified on JVM startup. If you intend to do
     * conditional checking with respect to agent availability, consider using
     * {@link org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver#getInstrumentation()}
     * instead - which will work without the agent class in the classpath as well.
     * @return the {@code Instrumentation} instance previously saved when
     * the {@link #premain} or {@link #agentmain} methods was called by the JVM;
     * will be {@code null} if this class was not used as Java agent when this
     * JVM was started or it wasn't installed as agent using the Attach API.
     * @see org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver#getInstrumentation()
     */
    public static Instrumentation getInstrumentation() {
        return instrumentation;
    }

}