JDBC的運用

使用了好久ORM框架，底層的JDBC操作就不會寫了，現在回憶一下

1、註冊驅動
2、建立連接
3、創建執行SQL的語句
4、執行語句
5、處理執行結果
6、釋放資源

---

JdbcUtils.java

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public final class JdbcUtils {
    private  static String url = "jdbc:mysql://localhost:3306/test";
    private  static String root = "root";
    private  static String password = "root";
    //單例模式
    private static JdbcUtils instance =null;
    private JdbcUtils(){

    }

    public static JdbcUtils getInstance(){
    //延時加載
        if(instance == null){
            //併發
            synchronized(JdbcUtils.class){
            if(instance == null){
                instance =new JdbcUtils();
            }
        }
    }
        return instance;
 }
    //靜態代碼塊
    static{
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    public static Connection getConnection() throws Exception{
        return DriverManager.getConnection(url, root, password);
    }

    public static void free(ResultSet rs,PreparedStatement ps,Connection conn){
        if (rs != null)
            try {
                rs.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        if (ps != null)
            try {
                ps.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        if (conn != null)
            try {
                conn.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
    }
}

具體的操作數據庫代碼DbOperate .java

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import com.pojo.StudentUser;

public class DbOperate {
    //註冊功能
    public static boolean create(String number,String username,String password,String usergroud){
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JdbcUtils.getConnection();
            String sql="insert into user_info(number,username,password,usergroud,usertype) values(?,?,?,?,0)";
            ps=conn.prepareStatement(sql);
            ps.setString(1, number);//第一個問號，預處理特殊字符
            ps.setString(2, username);//第一個問號，預處理特殊字符
            ps.setString(3, password);
            ps.setString(4, usergroud);
            int i=ps.executeUpdate();
            if(i>0){
                return true; 
            }
            return false;
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtils.free(rs, ps, conn);
        }
        return true;
    }

    //註冊時候判斷學號是否已經註冊過了，學號是唯一的
    public static boolean selectByNumber(String number){
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JdbcUtils.getConnection();
            String sql="select id from user_info where number=?";
            ps=conn.prepareStatement(sql);
            ps.setString(1, number);//第一個問號，預處理特殊字符
            rs=ps.executeQuery();
            return rs.next();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtils.free(rs, ps, conn);
        }
        return true;
    }
    //獲取個人信息
    public static StudentUser selectById(int id){
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        StudentUser stu=null;
        try {
            conn = JdbcUtils.getConnection();
            String sql="select * from user_info where id=?";
            ps=conn.prepareStatement(sql);
            ps.setInt(1, id);//第一個問號，預處理特殊字符
            rs=ps.executeQuery();
            stu=new StudentUser();
            while(rs.next()){
                stu.setChinesegrade(rs.getDouble("chinesegrade"));
                stu.setEnglishgrade(rs.getDouble("englishgrade"));
                stu.setId(rs.getInt("id"));
                stu.setMathgrade(rs.getDouble("mathgrade"));
                stu.setNumber(rs.getString("number"));
                stu.setPassword(rs.getString("password"));
                stu.setUsergroud(rs.getString("usergroud"));
                stu.setUsername(rs.getString("username"));
                stu.setUsertype(rs.getInt("usertype"));
            }
            return stu;
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtils.free(rs, ps, conn);
        }
        return null;
    }

    //列表搜索,根據人名進行
    public static List<StudentUser> selectByName(String username,int usertype,String serachname){
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        List<StudentUser> data=null;
        try {
            conn = JdbcUtils.getConnection();
            String where=" where usertype=?";

            if(username.length()>0){
                where += " and username=?";
            }
            if(serachname.length()>0){
                where += " and username like ?";
            }
            String sql="select *,(mathgrade+chinesegrade+englishgrade) as amount from user_info"+where;
            ps=conn.prepareStatement(sql);
            ps.setInt(1, usertype);//第一個問號，預處理特殊字符
            if(username.length()>0){
                ps.setString(2, username);
            }
            if(serachname.length()>0){
                ps.setString(2, "%"+serachname+"%");
            }
            rs=ps.executeQuery();
            data=new ArrayList<>();
            while(rs.next()){
                StudentUser stu=new StudentUser();
                stu.setChinesegrade(rs.getDouble("chinesegrade"));
                stu.setEnglishgrade(rs.getDouble("englishgrade"));
                stu.setId(rs.getInt("id"));
                stu.setMathgrade(rs.getDouble("mathgrade"));
                stu.setNumber(rs.getString("number"));
                stu.setPassword(rs.getString("password"));
                stu.setUsergroud(rs.getString("usergroud"));
                stu.setUsername(rs.getString("username"));
                stu.setUsertype(rs.getInt("usertype"));
                stu.setAmount(rs.getDouble("amount"));
                data.add(stu);
            }
            return data;
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtils.free(rs, ps, conn);
        }
        return null;
    }

    //錄入成績
    public static boolean updateGrade(int id,double math,double chinese,double english){
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JdbcUtils.getConnection();
            String sql="update user_info set mathgrade=?,englishgrade=?,chinesegrade=? where id=?";
            ps=conn.prepareStatement(sql);
            ps.setDouble(1, math);
            ps.setDouble(2, english);
            ps.setDouble(3, chinese);
            ps.setInt(4, id);
            int i=ps.executeUpdate();
            if(i>0){
                return true; 
            }
            return false;
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtils.free(rs, ps, conn);
        }
        return true;
    }