need support for Debugging

Hi all,
           am doing my first java(GUI develoment) project . I have jsp
page for validating user login credentials as follows.

//validate.jsp
try {
            if (!up.load(userid)) {
                pp.postLoginPage("Not valid ID.");
                return;
            }

excution stops here, showing me not valid ID. I dont know why I started
debugging.
I looked the file where "up.load()" it is in the library(custom
package) .I need to find why up.load(userid) returns false.

//com.tools.UserProfile.java (package)

public boolean load(String userid)
        throws SQLException {

 if (_res == null || userid == null || userid.length() == 0) {
1.//chance of returning false ,logically this will not be
            return false;
        }
.......
.....
 Connection conn = null;
        PreparedStatement stmt = null;
        try {
            conn = _res.getConnection();

            if (conn == null) {
                return false; // 2.this can be
returning false due to no Conn
            }

       String sql = "select * from adntuser where userid=?";
            stmt = conn.prepareStatement(sql);
            stmt.setString(1, userid);
            ResultSet rs = stmt.executeQuery();

            if (!rs.next()) {
                return false; //3. or this can be
returning false.
            }
...............
...............

as I mentioned above there can be 3 situations where boolean false is
returned, can some one please help me how to find the exact one .
As it is file in Package , response is included in my calling JSP file.
I dont know how to place "println" statements in mentioned places and
debug or can I write to some messages to Log file? and see later, if so
how?

I deploy web application in Linux system.

Thanks for your time and consideration,

regards
Jaggu