2.实现接口类，这个单写在一个包里，这个类实现了接口里的所有方法。包括登录，增删改查数据库的所有方法。

public class UserDaoImpl implements IUserDao {
private Connection conn = null;
DBUtil db ;
public UserDaoImpl(){
db = new DBUtil();//连接数据库
conn = db.getConnection();// 获取连接对象
}
public User Login(String username， String pwd) {
//通过客户端传进来的username  pwd查询数据库
String sql = "select * from adduser where username = ? and password = ?";
//定义预定义语句对象 state;
PreparedStatement state;
try {
//获得state对象，检索sql语句
state = conn.prepareStatement(sql);
// 通过state 检索sql语句中的问号，给问号赋值。例如，上面的语句中，有两个问号，第一个问号赋值为username，第二个问号为password
state.setString(1， username);
state.setString(2， pwd);
//执行查询方法，返回ResultSet对象r
ResultSet r = state.executeQuery();
if(r.next()){
//通过对象r.get方法获得此用户的所有数据信息，并封装数据到实体类中。返回这个实体类对象user
User user = new User();
user.setId(r.getInt("id"));
user.setName(r.getString("name"));
user.setUsername(r.getString("username"));
user.setPwd(r.getString("password"));
user.setAge(r.getInt("age"));
user.setSex(r.getString("sex"));
return user;
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
db.closeConn(conn);
}
return null;//如果登录成功返回这个对象，如果查询不成功，返回空值，提示登录 不成功。
}
//通过一个 id查询用户的详细信息
public User QueryUser(int id) {
String sql = "select * from adduser where id = ?";
//获得预定义语句
PreparedStatement state;
try {
state = conn.prepareStatement(sql);
state.setInt(1， id);
ResultSet r = state.executeQuery();
if(r.next()){
User user = new User();
user.setId(r.getInt("id"));
user.setName(r.getString("name"));
user.setUsername(r.getString("username"));
user.setPwd(r.getString("password"));
user.setAge(r.getInt("age"));
user.setSex(r.getString("sex"));
return user;
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
db.closeConn(conn);
}
return null;
}
//查询所有的用户信息
public ArrayList<User> QueryUserall() {
String sql = "select * from adduser";
//获得预定义语句
PreparedStatement state;
ArrayList<User> list = new ArrayList<User>();
try {
state = conn.prepareStatement(sql);
ResultSet r = state.executeQuery();
while(r.next()){
User user = new User();
user.setId(r.getInt("id"));
user.setName(r.getString("name"));
user.setUsername(r.getString("username"));
user.setPwd(r.getString("password"));
user.setAge(r.getInt("age"));
user.setSex(r.getString("sex"));
list.add(user);
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
db.closeConn(conn);
}
return list;
}
// 更新用户数据，传一个对象，更新成功返回1，失败返回0；
public int UpdateUser(User user) {
String sql = "update adduser set name = ?，username = ?，password = ?，sex = ?，age = ? where id = ?";
//获得预定义语句
PreparedStatement state;
int r = 0;
try {
//获得一个操作数据库的对象state，通过state检索上述sql语句的?号，通过setString方法给? 赋值。
state = conn.prepareStatement(sql);
state.setString(1， user.getName());
state.setString(2， user.getUsername());
state.setString(3， user.getPwd());
state.setString(4， user.getSex());
state.setInt(5， user.getAge());
state.setInt(6， user.getId());
r = state.executeUpdate();//执行更新方法，更新成功返回整数，失败返回0。
} catch (SQLException e) {
e.printStackTrace();
}finally{
db.closeConn(conn);
}
return r;
}
public int addUser(User user) {
String sql = "insert into adduser(name，username，password，sex，age) values(?，?，?，?，?)";
//获得预定义语句
PreparedStatement state;
boolean r = false;
try {
state = conn.prepareStatement(sql);
state.setString(1， user.getName());
state.setString(2， user.getUsername());
state.setString(3， user.getPwd());
state.setString(4， user.getSex());
state.setInt(5， user.getAge());
r = state.execute(sql);
} catch (SQLException e) {
e.printStackTrace();
}finally{
db.closeConn(conn);
}
return r?1:0;
}
public int deletUser(int id) {
String sql = "delete from adduser where id = ?";
PreparedStatement state ;
boolean b = false;
try {
state = conn.prepareStatement(sql);
state.setInt(1， id);
b = state.execute();
} catch (Exception e) {
}
return b?1:0;
}
}