JDBC

時間  2019-12-17
標籤 jdbc 欄目 Java 简体版
原文   原文鏈接

JDBC(Java Database Connect)

Java是一種面向對象的語言
||語言不一樣，須要交流，找個翻譯（java只出標準，數據庫實現）
Mysql是結構化查詢語言java

正式鏈接數據庫
java鏈接數據的步驟
  1. 把Mysql的jar包拿過來加入到工程下
  2. 把該jar包解壓到本工程下，build path
    上面兩步在同一個工程下執行一次就好了
  3. 加載驅動。Class.forName("com.mysql.jdbc.Driver");
  4. 獲取鏈接對象。Connection conn = DriverManager.getConnection(url,user,password); 須要導包:import.java.sql.Connection; import java.sql.DriverManager;
    String url = "jdbc:mysql://IP:3306/數據庫名";
    String user = "root";
    String password = "數據庫密碼";
  5. 獲取執行sql語句的對象
    Statement st = conn.createStatement(); 須要導包 import java.sql.Statement;
  6. 執行sql語句。增刪改
    int row = st.executeUpdate(sql語句); row返回值表示影響的行數
    jdbc：後面加mysql：
  7. 執行sql語句，查詢
    ResultSet rs = st.executeQuery(sql);
    遍歷rs對象
    while(rs.next()){
    xx 變量名 = rs.getxx("字段名"); //獲取該記錄下指定字段的內容
    };
常見的錯誤

練習：CRUD，使用方法而且關閉資源mysql

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class CRUD {
    public static void main(String[] args) {
        //add("上海");
        //delete(4);
        //update("南京",4);
        selectall();
    }
    public static void add(String cityname) {
        Connection conn = null;
        Statement st = null;
        try {
           Class.forName("com.mysql.jdbc.Driver");
           conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/emp","root","123456");
           st = conn.createStatement();
           int row = st.executeUpdate("insert into city(cityname) values ('"+cityname+"')");
           System.out.println("受影響的行數爲："+row);
        } catch (ClassNotFoundException e) {
           e.printStackTrace();
        } catch (SQLException e) {
           e.printStackTrace();
        }finally {
           if(conn != null) {
               try {
                   conn.close();
               } catch (SQLException e) {
                   e.printStackTrace();
               }
           }
           if(st != null) {
               try {
                   st.close();
               } catch (SQLException e) {
                   e.printStackTrace();
               }
           }
        }
    }
    public static void delete(int cityid) {
        Connection conn = null;
        Statement st = null;
        try {
           Class.forName("com.mysql.jdbc.Driver");
           conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/emp","root","123456");
           st = conn.createStatement();
           int row = st.executeUpdate("delete from city where cityID = "+cityid);
           System.out.println("受影響的行數爲："+row);
        } catch (ClassNotFoundException e) {
           e.printStackTrace();
        } catch (SQLException e) {
           e.printStackTrace();
        }finally {
           if(conn != null) {
               try {
                   conn.close();
               } catch (SQLException e) {
                   e.printStackTrace();
               }
           }
           if(st != null) {
               try {
                   st.close();
               } catch (SQLException e) {
                   e.printStackTrace();
               }
           }
        }
    }
    public static void update(String cityname,int cityid) {
        Connection conn = null;
        Statement st = null;
        try {
           Class.forName("com.mysql.jdbc.Driver");
           conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/emp","root","123456");
           st = conn.createStatement();
           int row = st.executeUpdate("update city set cityname = '"+cityname+"' where cityid = "+cityid);
           System.out.println("受影響的行數爲："+row);
        } catch (ClassNotFoundException e) {
           e.printStackTrace();
        } catch (SQLException e) {
           e.printStackTrace();
        }finally {
           if(conn != null) {
               try {
                   conn.close();
               } catch (SQLException e) {
                   e.printStackTrace();
               }
           }
           if(st != null) {
               try {
                   st.close();
               } catch (SQLException e) {
                   e.printStackTrace();
               }
           }
        }
    }
    public static void selectall() {
        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;
        try {
           Class.forName("com.mysql.jdbc.Driver");
           conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/emp","root","123456");
           st = conn.createStatement();
           rs = st.executeQuery("select * from city");
           while(rs.next()) {
           int cityid = rs.getInt("cityid");
           String cityname = rs.getString("cityname");
           System.out.println(cityid+"======>"+cityname);
           }
        } catch (ClassNotFoundException e) {
           e.printStackTrace();
        } catch (SQLException e) {
           e.printStackTrace();
        }finally {
           if(conn != null) {
               try {
                   conn.close();
               } catch (SQLException e) {
                   e.printStackTrace();
               }
           }
           if(st != null) {
               try {
                   st.close();
               } catch (SQLException e) {
                   e.printStackTrace();
               }
           }
           if(rs != null) {
               try {
                  rs.close();
               } catch (SQLException e) {
                  e.printStackTrace();
               }
           }
        }   
    }
}
企業級開發

一張表對應一個操做類（crud），操做類中包含的是CRUD
例如：對emp表操做，那麼java中對應的類就是EmpDao（Data Access Object） 這個類儘可能放到dao包下
包名：企業域名反向寫 www.baidu.com====>com.baidu + 開發人員名稱縮寫 ====> com.baidu.wlq.daosql

練習：抽取一個BaseDao父類（7個屬性，一個方法）
寫一個員工表的操做類EmpDao 繼承Base Dao。包含數據庫

  1. 添加員工（ename,sal,job）
  2. 刪除員工（empNo）
  3. 修改（ename，sal，job 根據empNo修改）
  4. 查詢 （根據empno查）
  5. 查詢全部員工

並寫一個測試類來測試上面5個方法測試

package com.alibaba.wlq.dao;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class BaseDao {
    protected Connection conn = null;
    protected Statement st = null;
    protected ResultSet rs = null;
    protected String driver = "com.mysql.jdbc.Driver";
    protected String url = "jdbc:mysql://localhost:3306/emp";
    protected String user = "root";
    protected String password = "123456";
    public void closeAll() {
        if(conn != null) {
           try {
               conn.close();
           } catch (SQLException e) {
               e.printStackTrace();
           }
        }
        if(st != null) {
           try {
               st.close();
           } catch (SQLException e) {
               e.printStackTrace();
           }
        }
        if(rs != null) {
           try {
               rs.close();
           } catch (SQLException e) {
               e.printStackTrace();
           }
        }
    }
}
package com.alibaba.wlq.dao;
import java.sql.DriverManager;
import java.sql.SQLException;
public class EmpDao extends BaseDao{
    /**
     * 增長員工信息
     * @param ename 員工姓名
     * @param sal  員工薪水
     * @param job  員工職位
     */
    public void add(String ename,Double sal,String job) {
           try {
               Class.forName(driver);
               conn = DriverManager.getConnection(url,user,password);
               st = <u>conn</u>.createStatement();
               String sql = "insert into emp(ename,sal,job,hiredate) values ('"+ename+"',"+sal+",'"+job+"',now())";
               int row = st.executeUpdate(sql);
               System.out.println("影響了"+row+"行");
           } catch (ClassNotFoundException e) {
               e.printStackTrace();
           } catch (SQLException e) {
               e.printStackTrace();
           }
    }
    /**
     * 根據員工編號刪除員工的信息
     * @param empno    員工編號
     */     
    public void delete(int empno) {
        try {
           Class.forName(driver);
           conn = DriverManager.getConnection(url,user,password);
           st = conn.createStatement();
           String sql = "delete from emp where empno ="+empno;
           int row = st.executeUpdate(sql);
           System.out.println("影響了"+row+"行");
        } catch (ClassNotFoundException e) {
           e.printStackTrace();
        } catch (SQLException e) {
           e.printStackTrace();
        }
    }
    /**
     * 根據員工編號查詢員工信息
     * @param empno        員工編號
     */
    public void select(int empno) {
        try {
           Class.forName(driver);
           conn = DriverManager.getConnection(url,user,password);
           st = conn.createStatement();
           String sql = "select * from emp where empno = " + empno;
           rs = st.executeQuery(sql);
           while(rs.next()) {
               System.out.println("員工編號："+rs.getInt("empno"));
               System.out.println("員工姓名："+rs.getString("ename"));
               System.out.println("員工薪資："+rs.getDouble("sal"));
               System.out.println("員工入職時間："+rs.getDate("hiredate"));
           }
        } catch (ClassNotFoundException e) {
           e.printStackTrace();
        } catch (SQLException e) {
           e.printStackTrace();
        }finally {
           closeAll();
        }
    }
    /**
     * 根據員工編號修改員工姓名、薪資、職位
     * @param ename    員工姓名
     * @param sal  薪資
     * @param job  職位
     * @param empno    員工編號
     */
    public void update(String ename,Double sal,String job,int empno) {
        try {
           Class.forName(driver);
           conn = DriverManager.getConnection(url,user,password);
           st = conn.createStatement();
           String sql = "update emp set ename = '"+ename+"',sal = '"+sal+"',job='"+job+"' where empno = "+empno;
           int row = st.executeUpdate(sql);
           System.out.println("影響了"+row+"行");
        } catch (ClassNotFoundException e) {
           e.printStackTrace();
        } catch (SQLException e) {
           e.printStackTrace();
        }finally {
           closeAll();
        }
    }
    /**
     * 查詢全部員工的信息
     * @param empno員工編號
     */
    public void selectALL() {
        try {
           Class.forName(driver);
           conn = DriverManager.getConnection(url,user,password);
           st = conn.createStatement();
           String sql = "select * from emp";
           rs = st.executeQuery(sql);
           while(rs.next()) {
               System.out.print("員工編號："+rs.getInt("empno")+"\t");
               System.out.print("員工姓名："+rs.getString("ename")+"\t");
               System.out.print("員工領導編號："+rs.getInt("mgr")+"\t");
               System.out.print("員工薪資："+rs.getDouble("sal")+"\t");
               System.out.println("員工入職時間："+rs.getDate("hiredate"));
           }
        } catch (ClassNotFoundException e) {
           e.printStackTrace();
        } catch (SQLException e) {
           e.printStackTrace();
        }finally {
           closeAll();
        }
    }
}
package com.alibaba.wlq.dao;
public class Test1 {
    public static void main(String[] args) {
        EmpDao emp = new EmpDao();
        //emp.add("劉德華",20000.0,"演員");
        //emp.delete(1016);
        //emp.select(1001);
        //emp.update("劉德華", 20000.0, "演員", 1015);
        emp.selectALL();
    }
}
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