jdbc的连接数据库，使用PreparedStatement实现增删改查等接口

Posted 2020-11-29 zsbenn

首先是连接，关闭资源等数据库操作

将连接数据库，关闭资源封装在JDBCUtils里

package jdbc.utils;

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

public class JDBCUtils {
    //获取数据库连接函数
    public static Connection getConnection() throws Exception {
        Class clazz=Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");           
        String url = "jdbc:sqlserver://localhost:1433;databaseName=EDUCATION";
        Connection con = DriverManager.getConnection(url,"sa","1");
        System.out.println("连接成功");
        return con;
    }
    //关闭连接和操作指针
    public static void closeResource(Connection con,PreparedStatement ps) {
        try {
            if(ps != null)
                ps.close();
        }
        catch(Exception ex) {
            ex.printStackTrace();
        }
        try {
            if(con != null)
                con.close();
        }
        catch(Exception ex) {
            ex.printStackTrace();
        }
    }
    
    //关闭连接，信使，结果集
    public static void closeResource(Connection con,PreparedStatement ps,ResultSet resultSet) {
        try {
            if(ps != null)
                ps.close();
        }
        catch(Exception ex) {
            ex.printStackTrace();
        }
        try {
            if(con != null)
                con.close();
        }
        catch(Exception ex) {
            ex.printStackTrace();
        }
        try {
            if(resultSet != null)
                resultSet.close();
        }
        catch(Exception ex) {
            ex.printStackTrace();
        }
    }
}

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使用PreparedStatement对数据库进行单条的增删改等操作以及通用的操作

package jdbc_practice.preparedstatement.crud;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import jdbc.utils.JDBCUtils;;


/*
 * PreparedStatement代替Statement， 实现对数据库增删改
 * */

public class PreparedStatementUpdateTest {
    //增加class的一条记录
    public static void testAdd() {
        Connection con=null;
        PreparedStatement ps=null;
        try {
            con=JDBCUtils.getConnection();
            
            String sql="insert into class values(?,?)";
            ps=con.prepareStatement(sql);
            ps.setObject(1,"030103");
            ps.setObject(2, "物联网");
            ps.execute();
            System.out.println("增加成功");
        }
        catch(Exception ex) {
            ex.printStackTrace();
        }
        finally {
            JDBCUtils.closeResource(con, ps);
        }
    }
    //修改class的一条记录
    public static void testUpdate(){
        Connection con=null;
        PreparedStatement ps=null;
        try {
            con = JDBCUtils.getConnection();
            
            //建立信使ps，预编译sql语句
            String sql = "update class set cName = ? where classId = ?";
            ps = con.prepareStatement(sql);
            
            //填充占位符
            ps.setObject(1, "数媒");
            ps.setObject(2, "030100");
            
            //执行
            ps.execute();
            System.out.println("修改成功");
        }
        catch(Exception e) {
            e.printStackTrace();
        }
        finally {
            JDBCUtils.closeResource(con, ps);
        }
    }
    //删除class的一条记录
    public static void testDelete() {
        Connection con=null;
        PreparedStatement ps=null;
        try {
            con=JDBCUtils.getConnection();
            
            String sql="delete class where cName=?";
            ps=con.prepareStatement(sql);
            ps.setObject(1,"计科");
            ps.execute();
            System.out.println("删除成功");
        }
        catch(Exception ex) {
            ex.printStackTrace();
        }
        finally {
            JDBCUtils.closeResource(con, ps);
        }
    }
    
    //通用增删改，参数为预编译的sql，和可变形参args用来充当占位符
    public static void update(String sql,Object ...args) {
        Connection con = null;
        PreparedStatement ps=null;
        try {
            //1.获取连接
            con=JDBCUtils.getConnection();
            //2.预编译sql，返回ps实例
            ps=con.prepareStatement(sql);
            //填充占位符，sql中的占位符个数=args数组长度
            for(int i=0;i<args.length;i++) {
                ps.setObject(i+1, args[i]);
            }
            //4.执行
            ps.execute();
            
            System.out.println("执行成功 ");
        }
        catch (Exception ex) {
            ex.printStackTrace();
        }
        finally {
            //5.关闭资源
            JDBCUtils.closeResource(con, ps);
        }
    }
    
    
    //对上述三种操作进行测试
    public static void main(String []args) {
        String sql="insert into class values(?,?)";
        String s1,s2;
        s1="030104";
        s2="计创";
        update(sql,s1,s2);
        
        sql="delete from class where cName=?";
        s1="计创";
        update(sql,s1);
    
        sql="update class set cName=? where classId=?";
        s1="计创";
        s2="030102";
        update(sql,s1,s2);
    }
}

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使用PreparedStatement对表进行通用查询操作，即查询字段args是个可变参数

package jdbc_practice.preparedstatement.crud;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;


import java.lang.reflect.Field;

import jdbc.utils.*;
import bean.Class;

public class ClassforQuery {
    //对表的通用查询操作：即查询字段是个可变参数
    public static Class queryForClass(String sql,Object...args) {
        Connection con = null;
        PreparedStatement ps=null;
        ResultSet res = null;
        try {
            con=JDBCUtils.getConnection();
            ps=con.prepareStatement(sql);
            for(int i=0;i<args.length;i++) {
                ps.setObject(i+1, args[i]);
            }
            
            res=ps.executeQuery();
            //获取结果集的元数据 ，元数据指的是每个列的列名，String name = "Tom",String 和name是修饰Tom的元数据
            ResultSetMetaData rsmd = res.getMetaData();
            //通过rsmd来获取结果集中的列数
            int col = rsmd.getColumnCount();
            if(res.next()) {
                Class clazz = new Class();    
                //处理一行数据中的每一个列
                for(int i=0;i<col;i++) {
                    //获取每个列的属性值
                    Object value = res.getObject(i+1);
                    //获取每个列的列名
                    String colName = rsmd.getColumnName(i+1);
                    //给clazz对象的colName属性，赋值为value：通过反射
                    Field field = Class.class.getDeclaredField(colName);//先拿到属性名为colName的属性
                    field.setAccessible(true);//将属性设置为可访问
                    field.set(clazz, value);//修改该对象的该属性值为value
                }
                System.out.println("执行成功");
                return clazz;
            }
        }
        catch(Exception ex) {
            ex.printStackTrace();
        }
        finally {//finally块在return执行之后，return返回之前执行
            JDBCUtils.closeResource(con, ps, res);
        }
        return null;
    }
    
    public static void main(String []args) {
        String sql = "select classId,cName from class where classId = ?";
        String arg1 = "030100",arg2 = "";
        Class clazz = queryForClass(sql,arg1);
        System.out.println(clazz);
    }
}

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对单表查询的升级，解决了数据库表的列名和java类名不同的情况

package jdbc_practice.preparedstatement.crud;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;

import bean.Student;
import jdbc.utils.JDBCUtils;
import java.lang.reflect.Field;

public class StudentForQuery {
    public static Student queryForStudent(String sql,Object...args) {
        Connection con = null;
        PreparedStatement ps = null;
        ResultSet res = null;
        try {
            con=JDBCUtils.getConnection();
            ps=con.prepareStatement(sql);
            for(int i=0;i<args.length;i++) {
                ps.setObject(i+1, args[i]);
            }
            //获得数据集和元数据集
            res = ps.executeQuery();
            ResultSetMetaData rsmd = res.getMetaData();
            int col = rsmd.getColumnCount();
            
            
            if(res.next()) {
                Student stu = new Student();
                for(int i=0;i<col;i++) {
                    Object value = res.getObject(i+1);          //要获得的数据值
                    String colLabel = rsmd.getColumnLabel(i+1);    //要获得的元数据名称
                    
                    Field field = Student.class.getDeclaredField(colLabel);//这里要用Label以解决数据库表类名称和类属性名不同的情况
                    field.setAccessible(true);
                    field.set(stu,value);
                }
                
                System.out.println("执行成功");
                return stu;
            }
            
        }
        catch(Exception ex) {
            ex.printStackTrace();
        }
        finally {
            JDBCUtils.closeResource(con, ps, res);
        }
        
        return null;
    }
    
    public static void main(String[]args) {
        String sql = "select stuId as studentId,stuName as studentName from student where stuName = ?";
        String arg = "李军";
        Student stu = queryForStudent(sql,arg);
        System.out.println(stu);
    }
}

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使用PreparedStatement实现对不同表的通用的返回一个对象的查询操作

以及使用ArrayList返回对不同表的通用的返回多个对象的查询操作

package jdbc_practice.preparedstatement.crud;

import java.lang.reflect.*;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.ArrayList;
import java.util.List;

import bean.Student;
import jdbc.utils.JDBCUtils;

public class PreparedStatementQueryTest {
    //使用PreparedStatement实现对不同表的通用的返回一个对象的查询操作
    //使用泛型机制，参数里先传入一个类的类型
    public static <T> T getInstance(Class<T> clazz,String sql,Object...args) {
        Connection con = null;
        PreparedStatement ps = null;
        ResultSet res = null;
        try {
            con=JDBCUtils.getConnection();
            ps=con.prepareStatement(sql);
            for(int i=0;i<args.length;i++) {
                ps.setObject(i+1, args[i]);
            }
            
            //获得数据集和元数据集
            res = ps.executeQuery();
            ResultSetMetaData rsmd = res.getMetaData();
            int col = rsmd.getColumnCount();
            
            if(res.next()) {
                T t = clazz.newInstance();
                for(int i=0;i<col;i++) {
                    Object value = res.getObject(i+1);          //要获得的数据值
                    String colLabel = rsmd.getColumnLabel(i+1);    //要获得的元数据名称
                    
                    //通过反射给t对象指定的colName属性赋值为value
                    Field field = clazz.getDeclaredField(colLabel);
                    field.setAccessible(true);
                    field.set(t,value);
                }
                
                System.out.println("执行成功");
                return t;
            }
            
        }
        catch(Exception ex) {
            ex.printStackTrace();
        }
        finally {
            JDBCUtils.closeResource(con, ps, res);
        }
        
        return null;
    }
    
    //返回对不同表的通用的返回多个对象的查询操作
    public static <T> ArrayList<T> getForList(Class<T> clazz,String sql,Object...args){
        Connection con = null;
        PreparedStatement ps = null;
        ResultSet res = null;
        try {
            con=JDBCUtils.getConnection();
            ps=con.prepareStatement(sql);
            for(int i=0;i<args.length;i++) {
                ps.setObject(i+1, args[i]);
            }
            
            //获得数据集和元数据集
            res = ps.executeQuery();
            ResultSetMetaData rsmd = res.getMetaData();
            int col = rsmd.getColumnCount();
            
            ArrayList<T> list = new ArrayList<T>();
            while(res.next()) {
                T t = clazz.newInstance();
                for(int i=0;i<col;i++) {
                    Object value = res.getObject(i+1);          //要获得的数据值
                    String colLabel = rsmd.getColumnLabel(i+1);    //要获得的元数据名称
                    
                    //通过反射给t对象指定的colName属性赋值为value
                    Field field = clazz.getDeclaredField(colLabel);
                    field.setAccessible(true);
                    field.set(t,value);
                }
                
                list.add(t);
            }
            System.out.println("执行成功");
            return list;
        }
        catch(Exception ex) {
            ex.printStackTrace();
        }
        finally {
            JDBCUtils.closeResource(con, ps, res);
        }

        return null;
    }
    
    public static void main(String []args) {
        String sql = "select stuName as studentName,stuId as studentId from student where stuId = ?";
        String arg = "101";
        
        Student stu = getInstance(Student.class,sql,arg);
        System.out.println(stu);
        
        sql = "select stuId as studentId,stuName as studentName from student where stuId > ?";
        arg = "0";
        ArrayList<Student> list = getForList(Student.class, sql, arg);
        list.forEach(System.out::println);
        
    }
}

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