java单例模式学习笔记

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工具层：

import java.sql.Connection;

import java.sql.DriverManager;

//工具层

//DBHelper类，体现了单例模式的思想

public class DBHelper {

private static Connection conn; // 数据库连接对象

// 驱动

private static final String DRIVER = "com.MySQL.jdbc.Driver";

// 数据库的URL地址

private static final String URL = "jdbc:mysql://192.168.47.196:3306/school?useUnicode=true&characterEncoding=UTF-8";

// 用户名

private static final String USERNAME = "root";

// 密码

private static final String PASSWORD = "123456";

// 在静态代码块中，负责加载驱动

static {

try {

Class.forName(DRIVER);

} catch (Exception ex) {

ex.printStackTrace();

}

}

// 既然是单例模式，应该让构造方法私有化

private DBHelper() {

}

// 外部调用的统一的方法

public static Connection getConnection() throws Exception {

if (conn == null) {

conn = DriverManager.getConnection(URL, USERNAME, PASSWORD);

}

return conn;

}

}

业务逻辑层：

import java.sql.Connection;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

//DAO层

//学生业务逻辑类

public class StudentsDAO {

public static Connection conn = null;// 连接对象

public static PreparedStatement stmt = null;

public static ResultSet rs = null;// 结果集

// 添加学生方法

public boolean addStudents(Students s) {

String sql = "insert into Students values (?,?,?,?,?,?);";

try {

conn = DBHelper.getConnection();

stmt = conn.prepareStatement(sql);

stmt.setInt(1, s.getSid());

stmt.setString(2, s.getSname());

stmt.setInt(3, s.getAge());

stmt.setString(4, s.getGender());

stmt.setString(5, s.getEmail());

stmt.setString(6, s.getAddress());

int result = stmt.executeUpdate();

if (result > 0) {

return true;

} else {

return false;

}

} catch (Exception ex) {

ex.printStackTrace();

return false;

} finally {

destoryResource();

}

}

// 查询所有的学生资料

public static void query() {

String sql = "select * from Students;";

try {

conn = DBHelper.getConnection();

rs = stmt.executeQuery(sql);

while (rs.next()) {

System.out.println("学号：" + rs.getInt("sid") + ",姓名：" + rs.getString("sname") + ",年龄:" + rs.getInt("age")

+ ",性别：" + rs.getString("gender"));

}

} catch (Exception ex) {

ex.printStackTrace();

} finally {

destoryResource();

}

}

// 释放资源的方法

public static void destoryResource() {

try {

// if(rs!=null)

// {

// rs.close();

// rs=null;

// }

if (stmt != null) {

stmt.close();

stmt = null;

}

/*

* 暂时不释放Connection资源 if(conn!=null) { conn.close(); conn=null; }

*/

} catch (Exception ex) {

ex.printStackTrace();

}

}

}

实体层：

public class Students {

private int sid;//学号

private String sname;//姓名

private int age;//年龄

private String gender;//性别

private String email;//电子邮箱

private String address;//地址

public int getSid() {

return sid;

}

public void setSid(int sid) {

this.sid = sid;

}

public String getSname() {

return sname;

}

public void setSname(String sname) {

this.sname = sname;

}

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

public String getGender() {

return gender;

}

public void setGender(String gender) {

this.gender = gender;

}

public String getEmail() {

return email;

}

public void setEmail(String email) {

this.email = email;

}

public String getAddress() {

return address;

}

public void setAddress(String address) {

this.address = address;

}

//保留默认的不带参数的构造方法

public Students()

{

}

public Students(int sid,String sname,int age,String gender,String email,String address)

{

this.sid = sid;

this.sname = sname;

this.age = age;

this.gender = gender;

this.email = email;

this.address = address;

}

}

测试层：

import java.sql.Connection;

public class Test {

public static void main(String[] args) {

// TODO Auto-generated method stub

try

{

          

 Connection conn1 = DBHelper.getConnection();

          Connection conn2 = DBHelper.getConnection();

          //测试是否是单例模式

          System.out.println(conn1==conn2);

  

 Students s = new Students(55,"张无忌",3,"男","zwj@123.com","武当山");

 StudentsDAO sdao = new StudentsDAO();

 if(sdao.addStudents(s))

 {

 System.out.println("添加成功！");

 

 }

 else

 {

 System.out.println("添加失败！");

 

 }

}

catch(Exception ex)

{

ex.printStackTrace();

}

StudentsDAO.query();

}

}

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