“我相信有一种经过认证的、有效的方法来做到这一点(Apache Commons?)”

是的，很明显

StringUtils.join(array, separator)

http://www.java2s.com/Code/JavaAPI/org.apache.commons.lang/StringUtilsjoinObjectarrayStringseparator.htm

The approach that I've taken has evolved since Java 1.0 to provide readability and maintain reasonable options for backward-compatibility with older Java versions, while also providing method signatures that are drop-in replacements for those from apache commons-lang. For performance reasons, I can see some possible objections to the use of Arrays.asList but I prefer helper methods that have sensible defaults without duplicating the one method that performs the actual work. This approach provides appropriate entry points to a reliable method that does not require array/list conversions prior to calling.

Java版本兼容性的可能变化包括用StringBuffer (Java 1.0)代替StringBuilder (Java 1.5)，切换出Java 1.5迭代器，并从集合(Java 1.2)中删除通用通配符(Java 1.5)。如果想进一步提高向后兼容性，可以删除使用Collection的方法，并将逻辑移到基于数组的方法中。

public static String join(String[] values)
{
    return join(values, ',');
}

public static String join(String[] values, char delimiter)
{
    return join(Arrays.asList(values), String.valueOf(delimiter));
}

// To match Apache commons-lang: StringUtils.join(values, delimiter)
public static String join(String[] values, String delimiter)
{
    return join(Arrays.asList(values), delimiter);
}

public static String join(Collection<?> values)
{
    return join(values, ',');
}

public static String join(Collection<?> values, char delimiter)
{
    return join(values, String.valueOf(delimiter));
}

public static String join(Collection<?> values, String delimiter)
{
    if (values == null)
    {
        return new String();
    }

    StringBuffer strbuf = new StringBuffer();

    boolean first = true;

    for (Object value : values)
    {
        if (!first) { strbuf.append(delimiter); } else { first = false; }
        strbuf.append(value.toString());
    }

    return strbuf.toString();
}

一个快速和简单的解决方案，没有任何第三方包括。

public static String strJoin(String[] aArr, String sSep) {
    StringBuilder sbStr = new StringBuilder();
    for (int i = 0, il = aArr.length; i < il; i++) {
        if (i > 0)
            sbStr.append(sSep);
        sbStr.append(aArr[i]);
    }
    return sbStr.toString();
}

在Java 1.8中有一个新的StringJoiner类——所以不需要Guava或Apache Commons:

String str = new StringJoiner(",").add("a").add("b").add("c").toString();

或者直接使用新流api的集合:

String str = Arrays.asList("a", "b", "c").stream().collect(Collectors.joining(","));

Apache Commons Lang确实有一个StringUtils。join方法，将字符串数组与指定的分隔符连接在一起。

例如:

String[] s = new String[] {"a", "b", "c"};
String joined = StringUtils.join(s, ",");  // "a,b,c"

然而，正如您所提到的，我怀疑在上述方法的实际实现中一定存在某种条件或子字符串处理。

如果我要执行String连接，并且没有任何其他使用Commons Lang的原因，我可能会使用自己的来减少对外部库的依赖数量。

它在StringUtils中:

http://www.java2s.com/Code/JavaAPI/org.apache.commons.lang/StringUtilsjoinObjectarrayStringseparator.htm