JDBC Connection Oralce operation

Package Com.dgh.dao;
Import java.sql.Connection;
Import Java.sql.DriverManager;
Import java.sql.PreparedStatement;
Import Java.sql.ResultSet;
Import java.sql.SQLException;
Import java.sql.Statement;
Import java.util.ArrayList;

Import java.util.List;
Import Com.dgh.model.BookPO;

Import Com.dgh.model.UserPO;    public class Dbutil {Connection conn;    Database Connection object PreparedStatement pstmt;    Preprocessing Object ResultSet RS;
				Result set object//Get database Connection object Public Dbutil () {try {class.forname ("oracle.jdbc.driver.OracleDriver");
			conn = Drivermanager.getconnection ("Jdbc:oracle:thin:@127.0.0.1:1521:dbname", "UserName", "password");
			catch (ClassNotFoundException e) {e.printstacktrace ();
			}catch (SQLException e) {e.printstacktrace ();
			}///Close individual connection objects public void Closeconn () {try{if (rs!= null) {rs.close ();
			}}catch (Exception e) {} try{if (pstmt!= null) {pstmt.close (); }}catch (Exception e) {} try{if (conn!= null) {Conn.close ();
			}catch (Exception e) {}}///query user based on UserName, returns the object when found, does not return null public Userpo CheckUser (String userName) {try {
			String sql = "SELECT * from t_user where userName =?";
			pstmt = conn.preparestatement (sql);
			Pstmt.setstring (1, userName);
			rs = Pstmt.executequery ();
			Userpo user = new Userpo ();
			    while (Rs.next ()) {//userpo.setid (rs.getstring ("Id"));
				Userpo.setusername (rs.getstring ("UserName"));
				Userpo.setpassword (rs.getstring ("password"));
			return user;
		return null;
		catch (Exception e) {e.printstacktrace ();
		} finally{Closeconn ();
	return null; 
		//According to UserName, the password queries the user, returns the object when it is found, does not return null public USERPO login (string userName, string password) {Userpo = null;
		Userpo = CheckUser (userName);
		if (Userpo!= null && password.equals (Userpo.getpassword ())) {return userpo;
		}else{return null; }//Query All Books public list<bookpo> findall () {try{list<bookpo> Booklist = new ArraylIst<bookpo> ();
			pstmt = Conn.preparestatement ("SELECT * from T_book");
			ResultSet rs = Pstmt.executequery ();
				while (Rs.next ()) {Bookpo Bookpo = new Bookpo ();
				Bookpo.setid (rs.getstring ("id"));
				Bookpo.setbookname (rs.getstring ("BookName"));
			Booklist.add (book);
		return Booklist;
		}catch (Exception e) {e.printstacktrace ();
		}finally{Closeconn ();
	return null; To determine the number of books by ID public int findbooknum (String id) {try {pstmt = conn.preparestatement (' select * from T_book whe
			Re id =? ");
			Pstmt.setstring (1,id);
			ResultSet rs = Pstmt.executequery ();
			while (Rs.next ()) {return Rs.getint ("Amount");
		} catch (Exception e) {e.printstacktrace ();
		} finally{Closeconn ();
	return 0;  Check books according to ID and update the number of books public int lendbook (String id) {try{pstmt = conn.preparestatement ("update t_book Set num =
			num-1 WHERE id =? ");
			Pstmt.setstring (1, id);
			int count = Pstmt.executeupdate ();
return count;		}catch (Exception e) {e.printstacktrace ();
		}finally{Closeconn ();
	return 0; Check the book Public list<bookpo> findbyidorname (string ID, string name) {StringBuffer sql = new Stringbuf by ID or book name
		Fer ();
		list<string> paramlist = new arraylist<string> ();
		Sql.append ("select * from T_book where 1 = 1");
			Piecing together SQL statements if (ID!= null) {Sql.append ("and id like?") based on query criteria;
		Paramlist.add (ID);
        	} if (name!= null) {Sql.append ("and name Linke?");
        Paramlist.add (name);
	        } try{pstmt = Conn.preparestatement (sql.tostring ());
			for (int i = 0; i < paramlist.size (); i++) {pstmt.setstring (i+1, "%" +paramlist.get (i) + "%");
	        }//Processing result set ResultSet rs = Pstmt.executequery ();
			list<bookpo> Booklist = new arraylist<bookpo> ();
				while (Rs.next ()) {Bookpo Bookpo = new Bookpo ();
				Bookpo.setid (rs.getstring ("id")); Bookpo.setbooknaMe (rs.getstring ("BookName"));
			Booklist.add (book);
		return Booklist;
		catch (Exception e) {e.printstacktrace ();
		} finally{Closeconn ();
	return null; //////book ID based on user ID (USERID) the public int givebackbook (string bookid) {try{pstmt = conn.preparestatement ("Sele
			CT * from T_book b,t_user u,t_book_uer bu where ");
			
		Pstmt.executequery ();
	    return 0;
		return Booklist;
		}catch (Exception e) {e.printstacktrace ();
		}finally{Closeconn ();
	return 0; /////According to User ID query book lending//Public List Findbyuserid () {//try{//list<bookpo> Booklist = new Arraylist<bookpo
> ();
pstmt = Conn.preparestatement ("select * from T_book b,t_user u,t_book_uer bu where");
ResultSet rs = Pstmt.executequery (); while (Rs.next ()) {//Bookpo Bookpo = new Bookpo ();////bookpo.setid (rs.getstring ("id"));////bookpo.setbo
Okname (rs.getstring ("BookName"));
Booklist.add (book);
}//Return booklist; }catch (Exception e)
{//E.printstacktrace ();//}finally{//Closeconn ();//}//return null;
 //	}
}