简易留言板 JSP+MySQL

package db; import java.sql.*; import java.util.ArrayList; import model.LyTable; import model.User; public class DB { private String driverStr="com.mysql.jdbc.Driver"; private String connStr="jdbc:mysql://localhost:3306/sa?characterEncoding=gb2312"; private String dbusername="root"; private String dbpassword="222"; private Connection conn=null; private PreparedStatement pstmt=null; // 在构造函数中建立与数据库的连接，这样在建立DB对象的时候就连接了数据库 public DB(){ try { Class.forName(driverStr); conn = DriverManager.getConnection(connStr, dbusername, dbpassword); } catch (Exception e) { System.out.println("无法同数据库建立连接！" + e.toString()); } } // 根据username和password查询用户，查到就返回该对象，没有就返回null public User checkUser(String username,String password){ try{ pstmt=conn.prepareStatement("select * from userTable where username=? and password=?"); pstmt.setString(1, username); pstmt.setString(2, password); ResultSet rs=pstmt.executeQuery(); User user=new User(); while(rs.next()){ user.setId(rs.getInt(1)); user.setUsername(rs.getString(2)); user.setPassword(rs.getString(3)); return user; } return null; }catch(Exception e){ e.printStackTrace(); return null; } } // 查询留言信息，返回一个ArrayList public ArrayList findLyInfo(){ try{ ArrayList al=new ArrayList(); pstmt=conn.prepareStatement("select * from lyTable"); ResultSet rs=pstmt.executeQuery(); // while(rs.next()){ // System.out.println(rs.getInt(1)); // System.out.println(rs.getInt(2)); // System.out.println(rs.getDate(3)); // System.out.println(rs.getString(4)); // System.out.println(rs.getString(5)); // } while(rs.next()){ LyTable ly=new LyTable(); ly.setId(rs.getInt(1)); ly.setUserId(rs.getInt(2)); ly.setDate(rs.getDate(3)); ly.setTitle(rs.getString(4)); ly.setContent(rs.getString(5)); al.add(ly); } return al; }catch(Exception e){ e.printStackTrace(); return null; } } public String getUserName(int id){ String username = null; try{ pstmt = conn.prepareStatement("select username from userTable where id = ?"); pstmt.setInt(1, id); ResultSet rs = pstmt.executeQuery(); while(rs.next()){ username=rs.getString(1); } return username; }catch(Exception e){ e.printStackTrace(); return null; } } public boolean insertUser(String username,String pwd){ try{ pstmt=conn.prepareStatement("insert into userTable(username,password) values(?,?)"); pstmt.setString(1, username); pstmt.setString(2, pwd); pstmt.executeUpdate(); return true; }catch(Exception e){ e.printStackTrace(); return false; } } public boolean addInfo(LyTable ly){ try{ pstmt=conn.prepareStatement("insert into lyTable(userId,date,title,content) values(?,?,?,?)"); pstmt.setInt(1, ly.getUserId()); pstmt.setDate(2, ly.getDate()); pstmt.setString(3, ly.getTitle()); pstmt.setString(4, ly.getContent()); pstmt.executeUpdate(); return true; }catch(Exception e){ e.printStackTrace(); return false; } } }