字符串拼接方式性能比较

import java.util.ArrayList;
import java.util.List;
import org.apache.commons.lang.StringUtils;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class TestString {
private final Logger logger = LoggerFactory.getLogger(this.getClass());
@Test
public void testPlus() {
String s = "";
long ts = System.currentTimeMillis();
for (int i = 0; i < 10000; i++) {
s = s + String.valueOf(i);
}
long te = System.currentTimeMillis();
logger.info("+ cost {} ms", te - ts);
}
@Test
public void testConcat() {
String s = "";
long ts = System.currentTimeMillis();
for (int i = 0; i < 10000; i++) {
s = s.concat(String.valueOf(i));
}
long te = System.currentTimeMillis();
logger.info("concat cost {} ms", te - ts);
}
@Test
public void testJoin() {
List<String> list = new ArrayList<String>();
long ts = System.currentTimeMillis();
for (int i = 0; i < 10000; i++) {
list.add(String.valueOf(i));
}
StringUtils.join(list, "");
long te = System.currentTimeMillis();
logger.info("StringUtils.join cost {} ms", te - ts);
}
@Test
public void testStringBuffer() {
StringBuffer sb = new StringBuffer();
long ts = System.currentTimeMillis();
for (int i = 0; i < 10000; i++) {
sb.append(String.valueOf(i));
}
sb.toString();
long te = System.currentTimeMillis();
logger.info("StringBuffer cost {} ms", te - ts);
}
@Test
public void testStringBuilder() {
StringBuilder sb = new StringBuilder();
long ts = System.currentTimeMillis();
for (int i = 0; i < 100000; i++) {
sb.append(String.valueOf(i));
}
sb.toString();
long te = System.currentTimeMillis();
logger.info("StringBuilder cost {} ms", te - ts);
}
}

运行结果如下：

11:00:22,359  INFO TestString:23 - + cost 1828 ms

11:00:22,921  INFO TestString:34 - concat cost 562 ms

11:00:22,937  INFO TestString:46 - StringUtils.join cost 16 ms

11:00:22,968  INFO TestString:58 - StringBuffer cost 31 ms

11:00:23,031  INFO TestString:70 - StringBuilder cost 63 ms

总结：

用+的方式效率最差，concat由于是内部机制实现，比+的方式好了不少。

Join 和 StringBuffer，相差不大，Join方式要快些，可见这种JavaScript中快速拼接字符串的方式在Java中也非常适用。

StringBuilder 的速度最快，但其有线程安全的问题