描述

本文描述JMH的用法。

示例

引入maven依赖

<dependency>
    <groupId>org.openjdk.jmh</groupId>
    <artifactId>jmh-core</artifactId>
    <version>1.22</version>
</dependency>
<dependency>
    <groupId>org.openjdk.jmh</groupId>
    <artifactId>jmh-generator-annprocess</artifactId>
    <version>1.22</version>
    <scope>provided</scope>
</dependency>

下面代码测试了正常方法调用和反射调用平均耗时。

@BenchmarkMode(Mode.AverageTime)
@Warmup(iterations = 5, time = 1)
@Measurement(iterations = 5, time = 1)
@OutputTimeUnit(TimeUnit.MICROSECONDS)
public class ReflectBenchMark {

    @Benchmark
    public Object reflect() {
        Baby baby = new Baby();

        Class<? extends Baby> aClass = baby.getClass();

        try {
            Method sayHello = aClass.getMethod("sayHello", null);

            Object invoke = sayHello.invoke(baby, null);

            return invoke;
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }

        return null;
    }

    @Benchmark
    public String methodNormal() {
        Baby baby = new Baby();
        return baby.sayHello();
    }


    public static void main(String[] args) throws RunnerException {

        Options options = new OptionsBuilder()
                .include(ReflectBenchMark.class.getSimpleName())
                .forks(1)
                .build();

        new Runner(options).run();

    }

}

输出

...
Benchmark                      Mode  Cnt  Score    Error  Units
ReflectBenchMark.methodNormal  avgt    5  0.003 ±  0.001  us/op
ReflectBenchMark.reflect       avgt    5  0.176 ±  0.005  us/op

@BenchmarkMode
测试类型：
- Throughput：吞吐量，每个时间单位调用次数
- AverageTime：平均时间，每次调用时间
- SampleTime：
- SingleShotTime：只运行一次，测试冷启动
- all
@Warmup
预热，iterations测试次数，time每次进行的时长，timeUnit时长单位
@Measurement
实际执行，参数和Warmup一致