结论：urlencode 先比URLEncoder.encode多编码 “ * ” 符号，其他都保持一致
php urlencode
phpversion()>=5.3 will compliant with RFC 3986, while phpversion()<=5.2.7RC1 is not compliant with RFC 3986.
参考 RFC3896 方式编码
返回字符串，此字符串中除了 -_. 之外的所有非字母数字字符都将被替换成百分号（%）后跟两位十六进制数，空格则编码为加号（+）。
此编码与 WWW 表单 POST 数据的编码方式是一样的，同时与 application/x-www-form-urlencoded 的媒体类型编码方式一样。
由于历史原因，此编码在将空格编码为加号（+）方面与 » RFC3896 编码（参见 rawurlencode()）不同。
php并没有完全按照 rfc3896编码，符号【~】在标准中是不用编码，但是他也编码了。
所以最终的未编码的字符列表为 [-], [_], [.]，如同其文档中描述的一样
java URLEncoder.encode
参考 RFC2396 方式编码
但是由于ie浏览器编码了除 "-", "_", ".", "*" 之外的字符，java采用了和IE一样的编码列表，
所以最终的未编码的字符列表为 [-], [_], [.], [*]
The list of characters that are not encoded has been
determined as follows:
RFC 2396 states:
-----
Data characters that are allowed in a URI but do not have a
reserved purpose are called unreserved. These include upper
and lower case letters, decimal digits, and a limited set of
punctuation marks and symbols.
unreserved = alphanum | mark
mark = "-" | "_" | "." | "!" | "~" | "*" | "'" | "(" | ")"
Unreserved characters can be escaped without changing the
semantics of the URI, but this should not be done unless the
URI is being used in a context that does not allow the
unescaped character to appear.
-----
It appears that both Netscape and Internet Explorer escape
all special characters from this list with the exception
of "-", "_", ".", "*". While it is not clear why they are
escaping the other characters, perhaps it is safest to
assume that there might be contexts in which the others
are unsafe if not escaped. Therefore, we will use the same
list. It is also noteworthy that this is consistent with
O'Reilly's "HTML: The Definitive Guide" (page 164).
As a last note, Intenet Explorer does not encode the "@"
character which is clearly not unreserved according to the
RFC. We are being consistent with the RFC in this matter,
as is Netscape.
History of related RFCs:
RFC 1738 section 2.2
only alphanumerics, the special characters "$-_.+!*'(),", and
reserved characters used for their reserved purposes may be used
unencoded within a URL.
RFC 2396 section 2.3
unreserved = alphanum | mark
mark = "-" | "_" | "." | "!" | "~" | "*" | "'" | "(" | ")"
RFC 2732 section 3
(3) Add "[" and "]" to the set of 'reserved' characters:
RFC 3986 section 2.3
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
RFC 3987 section 2.2
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"