oracle数据库环境的字符集是GBK的，也就是每个中文占用2个字节的长度，可以通过utl_url把相应的字符进行编码解码。
   utl_url.escape可以对字符串进行URLEncode，utl_url.escape定义如下：

FUNCTION escape(url  IN VARCHAR2 CHARACTER SET ANY_CS,escape_reserved_chars IN BOOLEAN  DEFAULT FALSE,url_charset IN VARCHAR2 DEFAULT utl_http.get_body_charset)

RETURN VARCHAR2 CHARACTER SET url%CHARSET;

begin
  dbms_output.put_line(utl_url.escape('中国http://www.baidu.com/参数/=+/',true,'GB2312'));
  dbms_output.put_line(utl_url.escape('中国http://www.baidu.com/参数/=+/',false,'UTF8'));
  dbms_output.put_line(utl_url.escape('中国http://www.baidu.com/参数/=+/','UTF8'));
end;

%D6%D0%B9%FAhttp%3A%2F%2Fwww.baidu.com%2F%B2%CE%CA%FD%2F%3D%2B%2F
%D6%D0%B9%FAhttp://www.baidu.com/%B2%CE%CA%FD/=+/
%E4%B8%AD%E5%9B%BDhttp%3A%2F%2Fwww.baidu.com%2F%E5%8F%82%E6%95%B0%2F%3D%2B%2F
%E4%B8%AD%E5%9B%BDhttp://www.baidu.com/%E5%8F%82%E6%95%B0/=+/

utl_url.unescape可以对字符串进行URLDecode，utl_url.unescape定义：

FUNCTION unescape(url IN VARCHAR2 CHARACTER SET ANY_CS,url_charset IN VARCHAR2 DEFAULT utl_http.get_body_charset)
  RETURN VARCHAR2 CHARACTER SET url%CHARSET;

begin
dbms_output.put_line( utl_url.unescape('http%3A%2F%2Fwww.baidu.com%2F%E5%8F%82%E6%95%B0%2F%3D%2B%2F','UTF8'));
end;