今天完成的事： 

       一 、下载了  mysql-connector-java-5.1.45-bin.jar 用 java 语言连接接数据库，简单测试 Statement 类，PreparedStatement 类。

二、实现了JdbcTemplate 类

1. package com.jdbc;

   import java.sql.*;

   public class JdbcTemplate {

   private Connection conn;

   public JdbcTemplate(){

   } 

   public JdbcTemplate(Connection conn){

   this.conn = conn;

   } 

   /**

   * 

   * @param sql 数据库sql语句

   * @param callback  

   * public interface RowCallBackHandler {

      void processRow(ResultSet rs);

   }

   * 将结果集返回给调用者操作。

   * 实现回调

   * 

   */

   public void query(String sql, RowCallBackHandler callback){

   try {

   Statement st = conn.createStatement();

   ResultSet rs=st.executeQuery(sql);

   if(callback !=null){

   callback.processRow(rs);

   }

   } catch (SQLException e) {

   // TODO Auto-generated catch block

   e.printStackTrace();

   }

   }

   /**

   * 

   * @param sql

   * @param setter

   * public interface PreparedStatementSetter {

   void setValues(PreparedStatement ps);

   }

   * 给sql语句中的（“？”）--作为占位符，设置参数。

   * 由调用者去实现占位符的替换

   * @param callback

   */

   public void query(String sql,PreparedStatementSetter setter , RowCallBackHandler callback){

   try {

   PreparedStatement ps = conn.prepareStatement(sql);

   if(setter != null){

   setter.setValues(ps);

   }

   ResultSet rs =ps.executeQuery();

   if(callback != null){

   callback.processRow(rs);

   }

   } catch (SQLException e) {

   // TODO Auto-generated catch block

   e.printStackTrace();

   }

   }

   public void update(String sql,PreparedStatementSetter setter){

   try {

   PreparedStatement ps = conn.prepareStatement(sql);

   if( setter != null){

   setter.setValues(ps);

   }

   ps.execute();

   } catch (SQLException e) {

   // TODO Auto-generated catch block

   e.printStackTrace();

   }

   }

   }

三、用写好的模板实现 接口  IStudentDAO ，并做出简单的数据库数据操作

接口实现类代码

1. package com.stuDAO;

   import java.sql.Connection;

   import java.sql.ResultSet;

   import java.sql.SQLException;

   import java.util.ArrayList;

   import java.util.List;

   import com.bean.Student;

   import com.jdbc.JdbcTemplate;

   import com.jdbc.RowCallBackHandler;

   public class StudentImpl implements IStudentDAO {

   public void saveStudent(Student stu, Connection conn) {

   JdbcTemplate jt = new JdbcTemplate(conn);

   String name = stu.getName();

   int qq = stu.getQq();

   String sch = stu.getSchool();

   long create = stu.getCreate();

   long update = stu.getUpdate();

   String sql = "insert into student(name,qq,school,create_at,update_at) values ('"+name+"',"+qq+",'"+sch+"',"+create+","+update+")";

   //System.out.println(sql);

   jt.update(sql, null);

   }

   public void deleteStudent(int id, Connection conn) {

   // TODO Auto-generated method stub

   JdbcTemplate jt = new JdbcTemplate(conn);

   String sql = "delete from student where id="+id;

   jt.update(sql, null);

   }

   public void updateStudent(Student stu, Connection conn) {

   // TODO Auto-generated method stub 偷个懒

   JdbcTemplate jt = new JdbcTemplate(conn);

   deleteStudent(stu.getId(),conn);

   saveStudent(stu,conn);

   }

   public Student findStudent(int id, Connection conn) {

   // TODO Auto-generated method stub

   JdbcTemplate jt = new JdbcTemplate(conn);

   final Student s = new Student();

   String sql = "select * from student where id="+id;

   jt.query(sql, new RowCallBackHandler(){

   public void processRow(ResultSet rs) {

   try {

   while(rs.next()){

   //System.out.println(rs.getString("name"));

   s.setId((Integer) rs.getObject(1));

   s.setName((String) rs.getObject(2));

   s.setQq((Integer) rs.getObject(3));

   s.setSchool((String) rs.getObject(4));

   s.setCreate((Long) rs.getObject(5));

   s.setUpdate((Long) rs.getObject(6));

   }

   } catch (SQLException e) {

   // TODO Auto-generated catch block

   e.printStackTrace();

   }

   }

   });

   return s;

   }

   public List<Student> findStudents(Connection conn) {

   // TODO Auto-generated method stub

   JdbcTemplate jt = new JdbcTemplate(conn);

   String sql = "select * from student";

   final List<Student> list = new ArrayList<Student>();

   jt.query(sql, new RowCallBackHandler(){

   public void processRow(ResultSet rs) {

   // TODO Auto-generated method stub

   try {

   while(rs.next()){

   Student s = new Student();

   s.setId((Integer) rs.getObject(1));

   s.setName((String) rs.getObject(2));

   s.setQq((Integer) rs.getObject(3));

   s.setSchool((String) rs.getObject(4));

   s.setCreate((Long) rs.getObject(5));

   s.setUpdate((Long) rs.getObject(6));

   list.add(s);

   }

   } catch (SQLException e) {

   // TODO Auto-generated catch block

   e.printStackTrace();

   }

   }

   });

   return list;

   }

   }

   
   

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了解修饰符  final      https://www.cnblogs.com/lwbqqyumidi/p/3513047.html