JavaEE知识与数据库连接实现增删改查功能，客户端使用json格式发增删改查用户的请求

package com.mashang.servlet.dao; import com.mashang.servlet.entity.User; import com.mashang.servlet.utils.JdbcUtil; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.util.ArrayList; import java.util.List; //这个是用来对数据库进行一个数据处理的 public class UserDao { /** * 查询用户 * @return * @throws SQLException */ public List<User> getUser() throws SQLException { //获取到连接 Connection connection = JdbcUtil.getConnection(); String sql = "select * from user"; PreparedStatement stmt = connection.prepareStatement(sql); //获取结果 ResultSet resultSet = stmt.executeQuery(); List<User> userList = new ArrayList<>(); while (resultSet.next()) { User user = new User(); user.setId(resultSet.getInt("id")); user.setName(resultSet.getString("name")); user.setUsername(resultSet.getString("username")); user.setPassword(resultSet.getString("password")); userList.add(user); } //关闭数据库的连接 JdbcUtil.close(resultSet,stmt,connection); return userList; } /** * 新增用户 */ public boolean createUser(User user) { Connection connection = null; String sql = "INSERT INTO user(username,password,name ) VALUES (?,?,?);"; PreparedStatement stmt = null; int result =0; try { connection=JdbcUtil.getConnection(); stmt=connection.prepareStatement(sql); stmt.setString(1, user.getUsername()); stmt.setString(2, user.getPassword()); stmt.setString(3, user.getName()); result= stmt.executeUpdate(); } catch (SQLException e) { e.printStackTrace(); }finally { JdbcUtil.close(stmt,connection); } if (result>0){ return true; }else { return false; } } /** * 更新用户 */ public boolean updateUser(User user) { Connection connection = null; String sql = "update user set username =?,password=?,name=? where id=?"; PreparedStatement stmt = null; int result =0; try { connection=JdbcUtil.getConnection(); stmt=connection.prepareStatement(sql); stmt.setString(1, user.getUsername()); stmt.setString(2, user.getPassword()); stmt.setString(3, user.getName()); stmt.setInt(4, user.getId()); result = stmt.executeUpdate(); } catch (SQLException e) { e.printStackTrace(); }finally { JdbcUtil.close(stmt,connection); } if (result>0){ return true; }else { return false; } } /** * 删除用户 */ public boolean deleteUser(int id){ Connection connection = null; String sql = "delete from user where id=?;" + "alter table user "; PreparedStatement stmt = null; int result =0; try { connection=JdbcUtil.getConnection(); stmt=connection.prepareStatement(sql); stmt.setInt(1, id); result = stmt.executeUpdate(); } catch (SQLException e) { e.printStackTrace(); }finally { JdbcUtil.close(stmt,connection); } if (result>0){ return true; }else { return false; } } }