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
     
       list = new ArrayList
      
       ();        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，可见这种中快速拼接字符串的方式在中也非常适用。

StringBuilder 的速度最快，但其有线程安全的问题，而且只有JDK5支持。