StringUtils.join

java string的工具类，可以用于对数组的转换

org.apache.commons.lang.StringUtils;

StringUtils.join(null)            = null
StringUtils.join([])                 = ""
StringUtils.join([null])          = ""
StringUtils.join(["a", "b", "c"]) = "abc"
StringUtils.join([null, "", "a"]) = "a"

String[] str = { "1", "2", "a", "b" };

// 将数组变成字符串
StringUtils.join(str)

// 将数组用逗号分隔变成字符串
StringUtils.join(str, ",")

函数实现

public static String join(Object[] array, char separator) {
        if (array == null) {
            return null;
        }
        int arraySize = array.length;
        int bufSize = (arraySize == 0 ? 0 : ((array[0] == null ? 16 : array[0].toString().length()) + 1) * arraySize);
        StringBuffer buf = new StringBuffer(bufSize);

        for (int i = 0; i < arraySize; i++) {
            if (i > 0) {
                buf.append(separator);
            }
            if (array[i] != null) {
                buf.append(array[i]);
            }
        }
        return buf.toString();
    }