Shulou(Shulou.com)06/03 Report--

Learning notes of java singleton pattern

Tool layer:

Import java.sql.Connection

Import java.sql.DriverManager

/ / tool layer

/ / DBHelper class, which embodies the idea of singleton pattern

Public class DBHelper {

Private static Connection conn; / / Database connection object

/ / driver

Private static final String DRIVER = "com.mysql.jdbc.Driver"

/ / URL address of the database

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

/ / user name

Private static final String USERNAME = "root"

/ / password

Private static final String PASSWORD = "123456"

/ / in the static code block, responsible for loading the driver

Static {

Try {

Class.forName (DRIVER)

} catch (Exception ex) {

Ex.printStackTrace ()

}

}

/ / since it is a singleton pattern, the constructor should be privatized.

Private DBHelper () {

}

/ / A unified method for external calls

Public static Connection getConnection () throws Exception {

If (conn = = null) {

Conn = DriverManager.getConnection (URL, USERNAME, PASSWORD)

}

Return conn

}

}

Business logic layer:

Import java.sql.Connection

Import java.sql.PreparedStatement

Import java.sql.ResultSet

/ / DAO layer

/ / Student business logic class

Public class StudentsDAO {

Public static Connection conn = null;// connection object

Public static PreparedStatement stmt = null

Public static ResultSet rs = null;// result set

/ / add student method

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 ()

}

}

/ / query all student information

Public static void query () {

String sql = "select * from Students;"

Try {

Conn = DBHelper.getConnection ()

Rs = stmt.executeQuery (sql)

While (rs.next ()) {

System.out.println ("student number:" + rs.getInt ("sid") + ", name:" + rs.getString ("sname") + ", age:" + rs.getInt ("age")

+ ", gender:" + rs.getString ("gender")

}

} catch (Exception ex) {

Ex.printStackTrace ()

} finally {

DestoryResource ()

}

}

/ / method of releasing resources

Public static void destoryResource () {

Try {

/ / if (rswatches null)

/ / {

/ / rs.close ()

/ / rs=null

/ /}

If (stmt! = null) {

Stmt.close ()

Stmt = null

}

/ *

* do not release Connection resource if (connexion null) {conn.close (); conn=null;} for the time being

, /

} catch (Exception ex) {

Ex.printStackTrace ()

}

}

}

Physical layer:

Public class Students {

Private int sid;// student number

Private String sname;// name

Private int age;// age

Private String gender;// gender

Private String email;// email address

Private String address;// address

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

}

/ / keep the default construction method without parameters

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

}

}

Test layer:

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 ()

/ / Test whether it is in singleton mode

System.out.println (conn1==conn2)

Students s = new Students (55, "Zhang Wuji", 3, "male", "zwj@123.com", "Wudang Mountain")

StudentsDAO sdao = new StudentsDAO ()

If (sdao.addStudents (s)

{

System.out.println ("added successfully!")

}

Else

{

System.out.println ("add failed!")

}

}

Catch (Exception ex)

{

Ex.printStackTrace ()

}

StudentsDAO.query ()

}

}

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