自从Java 8发布以来，我发现我的项目中不需要超过2 MB的Google Guava，因为我可以用普通的Java替换大部分内容。但是我真的很喜欢漂亮的Splitter API，它同时非常快。最重要的是 - 拉懒惰。它似乎可以用Pattern.splitAsStream替换。所以我准备了快速测试 - 在长字符串的中间找到一个值（即拆分整个字符串没有意义）。
package splitstream;
import com.google.common.base.Splitter;
import org.junit.Assert;
import org.junit.Test;
import java.util.StringTokenizer;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
public class SplitStreamPerfTest {
private static final int TIMES = 1000;
private static final String FIND = "10000";
@Test
public void go() throws Exception {
final String longString = IntStream.rangeClosed(1,20000).boxed()
.map(Object::toString)
.collect(Collectors.joining(" ,"));
IntStream.rangeClosed(1,3).forEach((i) -> {
measureTime("Test " + i + " with regex", () -> doWithRegex(longString));
measureTime("Test " + i + " with string tokenizer", () -> doWithStringTokenizer(longString));
measureTime("Test " + i + " with guava", () -> doWithGuava(longString));
});
}
private void measureTime(String name, Runnable r) {
long s = System.currentTimeMillis();
r.run();
long elapsed = System.currentTimeMillis() - s;
System.out.println("Check " + name +" took " + elapsed + " ms");
}
private void doWithStringTokenizer(String longString) {
String f = null;
for (int i = 0; i < TIMES; i++) {
StringTokenizer st = new StringTokenizer(longString,",",false);
while (st.hasMoreTokens()) {
String t = st.nextToken().trim();
if (FIND.equals(t)) {
f = t;
break;
}
}
}
Assert.assertEquals(FIND, f);
}
private void doWithRegex(String longString) {
final Pattern pattern = Pattern.compile(",");
String f = null;
for (int i = 0; i < TIMES; i++) {
f = pattern.splitAsStream(longString)
.map(String::trim)
.filter(FIND::equals)
.findFirst().orElse("");
}
Assert.assertEquals(FIND, f);
}
private void doWithGuava(String longString) {
final Splitter splitter = Splitter.on(',').trimResults();
String f = null;
for (int i = 0; i < TIMES; i++) {
Iterable<String> iterable = splitter.split(longString);
for (String s : iterable) {
if (FIND.equals(s)) {
f = s;
break;
}
}
}
Assert.assertEquals(FIND, f);
}
}
结果是（热身后）
Check Test 3 with regex took 1359 ms
Check Test 3 with string tokenizer took 750 ms
Check Test 3 with guava took 594 ms
如何使Java实现与Guava一样快？也许我做错了？
或者你可能知道任何工具/库和Guava Splitter一样快，它不涉及为这一个提取大量未使用的类吗？
答案 0 :(得分：1)
首先，番石榴比<{1}}，Splitter和Predicate 更多 - 您可能没有使用它提供的所有东西;我们使用它硬核，只是听到让我颤抖。无论如何，你的测试都被破坏了 - 可能有很多种方式。我已经使用Function来测试这两种方法，只是为了它的乐趣：
JMH结果：
@BenchmarkMode(org.openjdk.jmh.annotations.Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@Warmup(iterations = 5, time = 2, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 5, time = 2, timeUnit = TimeUnit.SECONDS)
@State(Scope.Thread) public class GuavaTest {
public static void main(String[] args) throws RunnerException {
Options opt = new OptionsBuilder().include(GuavaTest.class.getSimpleName())
.jvmArgs("-ea", "-Xms10g", "-Xmx10g")
.shouldFailOnError(true)
.build();
new Runner(opt).run();
}
@Param(value = { "300", "1000" })
public String tokenToSearchFor;
@State(Scope.Benchmark)
public static class ThreadState {
String longString = IntStream.range(1, 20000).boxed().map(Object::toString).collect(Collectors.joining(" ,"));
StringTokenizer st = null;
Pattern pattern = null;
Splitter splitter = null;
@Setup(Level.Invocation)
public void setUp() {
st = new StringTokenizer(longString, ",", false);
pattern = Pattern.compile(",");
splitter = Splitter.on(',').trimResults();
}
}
@Benchmark
@Fork(1)
public boolean doWithStringTokenizer(ThreadState ts) {
while (ts.st.hasMoreTokens()) {
String t = ts.st.nextToken().trim();
if (t.equals(tokenToSearchFor)) {
return true;
}
}
return false;
}
@Benchmark
@Fork(1)
public boolean doWithRegex(ThreadState ts) {
return ts.pattern.splitAsStream(ts.longString)
.map(String::trim)
.anyMatch(tokenToSearchFor::equals);
}
@Benchmark
@Fork(1)
public boolean doWithGuava(ThreadState ts) {
Iterable<String> iterable = ts.splitter.split(ts.longString);
for (String s : iterable) {
if (s.equals(tokenToSearchFor)) {
return true;
}
}
return false;
}
}
这使番石榴成为最快的。
如果您将Benchmark (tokenToSearchFor) Mode Cnt Score Error Units
GuavaTest.doWithGuava 300 avgt 5 19284.192 ± 23536.321 ns/op
GuavaTest.doWithGuava 1000 avgt 5 67182.531 ± 93242.266 ns/op
GuavaTest.doWithRegex 300 avgt 5 65780.954 ± 169044.641 ns/op
GuavaTest.doWithRegex 1000 avgt 5 182530.069 ± 409571.222 ns/op
GuavaTest.doWithStringTokenizer 300 avgt 5 34111.030 ± 61014.332 ns/op
GuavaTest.doWithStringTokenizer 1000 avgt 5 118963.048 ± 165510.183 ns/op
添加到parallel，那么它就会变得有趣，必须阅读here
答案 1 :(得分：0)
这可能很有用，您可以只导入guava中需要的部分： https://github.com/google/guava/wiki/UsingProGuardWithGuava
答案 2 :(得分：0)
你能给出pattern.split（text）并在正常的for循环中迭代结果，试试看。它可能比流更快。 虽然我不确定它是否能击败番石榴。
我的意思是......
private void doWithRegexAndSplit(String longString) {
final Pattern pattern = Pattern.compile(",");
for (int i = 0; i < TIMES; i++) {
String f = "";
String[] arr = pattern.split(longString);
for (int i = 0; i < arr.length; i++){
String t= arr[i].trim();
if (FIND.equals(t)) {
f = t;
break;
}
}
}
Assert.assertEquals(FIND, f);
}
请检查此案件的完成时间。
答案 3 :(得分：0)
您正在Pattern.splitAsStream(CharSequence)而不是Splitter.split(CharSequence)上将Splitter.on(char)与Splitter.onPattern(String)进行比较。查找与char的匹配在计算上要比查找模式匹配（正则表达式）简单得多。
如果您使用WorkflowID，您将获得如下结果：
Splitter.onPattern(",").trimResults()在哪种情况下Check Test 3 with regex took 608 ms
Check Test 3 with string tokenizer took 403 ms
Check Test 3 with guava took 306 ms
Check Test 3 with guava pattern took 689 ms
实际上比Guava的实施表现更好（假设这是一个有效的基准，这总是有问题，因为我们不使用jmh）。
我不知道任何JDK Pattern.splitAsStrimg(CharSequence)分隔解决方案类似于Guava的char。您可以自己动手，但Guava的解决方案似乎非常优化。