結論：urlencode 先比URLEncoder.encode多編碼 “ * ” 符號，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.

　　參考 RFC3896 方式編碼

返回字串，此字串中除了 -_. 之外的所有非字母數字字元都將被替換成百分號（%）後跟兩位十六進位制數，空格則編碼為加號（+）。
 

此編碼與 WWW 表單 POST 資料的編碼方式是一樣的，同時與 application/x-www-form-urlencoded 的媒體型別編碼方式一樣。
由於歷史原因，此編碼在將空格編碼為加號（+）方面與 » RFC3896 編碼（參見 rawurlencode()）不同。 

php並沒有完全按照 rfc3896編碼，符號【~】在標準中是不用編碼，但是他也編碼了。

所以最終的未編碼的字元列表為 [-], [_], [.]，如同其文件中描述的一樣

java URLEncoder.encode

　　參考 RFC2396 方式編碼

　　但是由於ie瀏覽器編碼了除  "-", "_", ".", "*" 之外的字元，java採用了和IE一樣的編碼列表，

　　所以最終的未編碼的字元列表為 [-], [_], [.], [*]

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 / "-" / "." / "_" / "~"