Lets say in your jsp page yuo have 3 text boxes with the 
name as follows.
    empName
    empMailId
    empPhoneNo
This is what you can do to form the query to search from the 
database assuming you have a single table named 
tblEmpInfo with the fields fName,fMailId,fPhoenNo.

boolean flag = false;
String query = "select * from tblEmpInfo ";

if(empName != null && empName != ""){
    if(!flag)
       flag = true;
    query += "where fName = '"+ empName + "'";
}

if(empMailId != null && empMailId != ""){
    if(!flag) {
      flag = true;
      query += "where fmailId = '"+ empMailId + "'";
    } else {
      query += "and fmailId = '"+ empMailId + "'";
    }
}

if(empPhoneNo != null && empPhoneNo != ""){
    if(!flag) {
      flag = true;
      query += "where fPhoenNo = '"+ empPhoneNo + "'";
    } else {
      query += "and fPhoenNo = '"+ empPhoneNo + "'";
    }
}

Regards,

Piyush