摘要：背景許多時候需要對比不同的框架或工具或算法，選擇使用性能更優的那一個。通常的做法是但這樣的做法非常不嚴謹，因為當獨立頻繁運行這一小塊代碼時，可能會針對性的做一些優化工作，而在實際的生產環境中是不會有此優化的。

許多時候需要對比不同的框架或工具或算法， 選擇使用性能更優的那一個。通常的做法是

long start = System.currentTimeMillis();
for(int i=0; i
但這樣的做法非常不嚴謹， 因為當獨立頻繁運行這一小塊代碼時，Jvm可能會針對性的做一些優化工作， 而在實際的生產環境中是不會有此優化的。 如一個Jvm優化的例子
原始代碼
        int a = 1;
        int b = 2;
        int sum = a + b;

        return sum;
可能直接優化為
        return 3;
所以最好使用更嚴謹的工具 來進行benchmark的工作，
Microbenchmarkings tools are intended to bring the JVM in "stable" state prior to executing tests and run your test suite for sufficient amount of time to get statistically proven evidence of the results.
摘自：http://www.buzdin.lv/2011/01/...
而jmh就是這么一個工具
JMH is short for Java Microbenchmark Harness. JMH is a toolkit that helps you implement Java microbenchmarks correctly. JMH is developed by the same people who implement the Java virtual machine, so these guys know what they are doing.
jmh使用示例
使用jmh來對比BeanUtils和BeanCopier
代碼
@State(Scope.Thread)
public class CopyPropertiesBenchmark {
  
    private UserModel model = new UserModel();
    private BeanCopier beanCopier = BeanCopier.create(UserModel.class, UserVo.class, false);

    /**
     * 人工setter復制屬性
     *
     * @return
     */
    @Benchmark
    public UserVo manuallySetter() {
        UserVo vo = new UserVo();
        vo.setAvatar(model.getAvatar());
        vo.setNick(model.getNick());
        // ...

        return vo;
    }

    @Benchmark
    public UserVo beanUitls() {
        UserVo vo = new UserVo();
        BeanUtils.copyProperties(this.model, vo);
        return vo;
    }

    @Benchmark
    public UserVo beanCopier() {
        UserVo vo = new UserVo();
        beanCopier.copy(this.model, vo, null);
        return vo;
    }
}

運行結果
# JMH 1.14.1 (released 5 days ago)
# VM version: JDK 1.8.0_91, VM 25.91-b14
# VM invoker: /Library/Java/JavaVirtualMachines/jdk1.8.0_91.jdk/Contents/Home/jre/bin/java
# VM options: -server
# Warmup: 5 iterations, 1 s each
# Measurement: 5 iterations, 1 s each
# Timeout: 10 min per iteration
# Threads: 1 thread, will synchronize iterations
# Benchmark mode: Throughput, ops/time
# Benchmark: com.zhugw.CopyPropertiesBenchmark.beanCopier

# Run progress: 0.00% complete, ETA 00:00:30
# Fork: 1 of 1
# Warmup Iteration   1: 70737107.801 ops/s
# Warmup Iteration   2: 63704495.294 ops/s
# Warmup Iteration   3: 112706026.910 ops/s
# Warmup Iteration   4: 113979995.875 ops/s
# Warmup Iteration   5: 114595368.349 ops/s
Iteration   1: 113207053.036 ops/s
Iteration   2: 111641520.705 ops/s
Iteration   3: 111258060.492 ops/s
Iteration   4: 110293317.399 ops/s
Iteration   5: 110773170.278 ops/s


Result "beanCopier":
  111434624.382 ±(99.9%) 4285987.844 ops/s [Average]
  (min, avg, max) = (110293317.399, 111434624.382, 113207053.036), stdev = 1113057.432
  CI (99.9%): [107148636.538, 115720612.226] (assumes normal distribution)

...

# Run complete. Total time: 00:00:32

Benchmark                                Mode  Cnt          Score          Error  Units
CopyPropertiesBenchmark.beanCopier      thrpt    5  111434624.382 ±  4285987.844  ops/s
CopyPropertiesBenchmark.beanUitls       thrpt    5    2451858.127 ±   525264.183  ops/s
CopyPropertiesBenchmark.manuallySetter  thrpt    5  103524264.901 ± 17644747.083  ops/s
從上面的結果可知BeanCopier的性能優于BeanUtils, 吞吐量差距約為45倍。
參考文檔
http://tutorials.jenkov.com/j...
http://nitschinger.at/Using-J...
http://hg.openjdk.java.net/co...