JDBC工具类和JDBC连接数据库

JDBC工具类

package com.utils;

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

/**
 * @author Dell
 * JDBC工具类
 */
public class JdbcUtils {
 static String url="jdbc:mysql://localhost:3306/jdbc";
 static String user="root";
 static String password="1";
// 单例模式
 private JdbcUtils(){
  
 }
 static JdbcUtils ju=null;
// 双重判断是提高效率，加上同步是解决线程安全问题
 public static JdbcUtils getInstance(){
  if (ju==null) {
   synchronized (JdbcUtils.class) {
    if (ju == null) {
     ju = new JdbcUtils();
    }
   }
  }
  return ju;
 }
// 静态代码块加载驱动
 static{
  try {
   Class.forName("com.mysql.jdbc.Driver");
  } catch (ClassNotFoundException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
 }
// 获取连接
 public static Connection getConnection() throws SQLException{
  return DriverManager.getConnection(url, user, password);
  
 }
// 关闭资源的方法
 public static void free(ResultSet r,Statement s,Connection c){
  try {
   if (r != null) {
    r.close();
   }
  } catch (Exception e) {
   // TODO: handle exception
  }finally{
   try {
    if (s != null) {
     s.close();
    }
   } catch (Exception e2) {
    // TODO: handle exception
   }finally{
    if (c!=null) {
     try {
      c.close();
     } catch (SQLException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
    }
   }
  }
 }
}

JDBC连接数据库

package com.jdbc;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;

public class JdbcExam {
 public static void main(String[] args) {

 }

 public void connDb() {
  Connection c = null;
  Statement s = null;
  ResultSet r = null;
  try {
   c = JdbcUtils.getConnection();
   s = c.createStatement();
   r = s.executeQuery("select * from user");
   while (r.next()) {
    System.out.println(r.getObject(1) + "\t" + r.getObject(2)
      + "\t" + r.getObject(3) + "\t" + r.getObject(4) + "\t");
   }
  } catch (Exception e) {
   // TODO: handle exception
  }
  JdbcUtils.free(r, s, c);
 }
}