单例模式和DAO模式

一、单例模式（设计模式的一种）

####################################懒汉式#########################################
public class TestSingle {
    
    
    private static TestSingle t =null;
    public synchronized static TestSingle newInstance(){
    
    
        if(t==null){
    
    
            return t=new TestSingle();
        }
            return t;
    }
    private TestSingle(){
    
    
    }

    public static void main(String[] args) {
    
    
        TestSingle ts= newInstance();
        System.out.println(ts);
        TestSingle ts1=newInstance();
        System.out.println(ts1);
    }
############################运行结果##############################################
cn.kgc.kb11.TestSingle@74a14482
cn.kgc.kb11.TestSingle@74a14482

###############################饿汉式##############################################
public class TestSingle2 {
    
    
    private static TestSingle2 ts=null;

    private TestSingle2(){
    
    }

    static{
    
    
        ts=new TestSingle2();
    }
    public static TestSingle2 getInstance(){
    
    
        return ts;
    }

    public static void main(String[] args) {
    
    
        TestSingle2 ts1=getInstance();
        System.out.println(ts1);
        TestSingle2 ts2=getInstance();
        System.out.println(ts2);
    }
}
###############################运行结果###########################################
cn.kgc.kb11.TestSingle2@74a14482
cn.kgc.kb11.TestSingle2@74a14482

##########################代理模式##############################################
public class Pet {
    
    
    public static final String TYPE_ONE="Dog";
    public static final String TYPE_TWO="Cat";
    public static Pet getInstance(String type){
    
    
        if(null==type)
            return null;
        if(type.equals(TYPE_ONE)){
    
    
            return new Dog();
        }
        if(type.equals(TYPE_TWO)){
    
    
            return new Cat();
        }
        return null;
    }
}
class Dog extends Pet{
    
    

}
class Cat extends Pet{
    
    

}

二、DAO模式

package cn.kgc.kb11.dao;

import cn.kgc.kb11.dao.impl.BaseDAOImpl;
import cn.kgc.kb11.entity.Student;

import java.sql.ResultSet;
import java.sql.SQLException;

public class StudentDao extends BaseDAOImpl {
    
    
    private final String DRIVER="com.mysql.jdbc.Driver";
    private final String URL="jdbc:mysql://192.168.186.100:3306/test";
    //根据学生id查询所有信息
    public Student getStudentById(String id) {
    
    
        String sql = "select * from student where stu_id=?";
        getConn(DRIVER, URL, "root", "ok");
        query(sql,id);
        ResultSet rs = getRs();
        //Data Access object
        Student s = new Student();
        try {
    
    
            if (rs.next()) {
    
    
                s.setStu_id(rs.getInt("stu_id"));
                s.setStu_name(rs.getString("stu_name"));
                s.setGrade_id(rs.getInt("grade_id"));
                s.setGender(rs.getString("gender"));
                s.setAddress(rs.getString("address"));
                s.setPhone(rs.getString("phone"));
                s.setIdCard(rs.getString("idCard"));
            }
        } catch (SQLException e) {
    
    
            e.printStackTrace();
        }
        finally {
    
    
            close();
        }
        return s;
    }
    public boolean insertIntoStudent(Student s){
    
    
        String sql="insert into student values(?,?,?,?,?,?,?)";
        getConn(DRIVER,URL,"root","ok");
        boolean update = update(sql, s.getStu_id() + "", s.getStu_name(), s.getGrade_id() + "", s.getGender(),null,null,null);
        if(update) return true;
        else return false;
    }

    public static void main(String[] args) {
    
    
        StudentDao dao=new StudentDao();
        Student s =  new Student(18,"白眉鹰王",3,"男",null,null,null);
//        Student student =dao.getStudentById("7");
//        System.out.println(student);
        boolean b = dao.insertIntoStudent(s);
        System.out.println(b ? "插入成功" : "插入失败");
    }
}

三、配置文件加载数据库访问参数

如果在java代码里添加数据库的访问信息，那么每次访问的数据库放生变化时，java里都需要重启服务，很麻烦，所以才有加载数据库访问参数的配置文件出现，修改起来比较方便。

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://192.168.186.100:3306/test
user=root
pwd=ok

public class Prop {
    
    
    static Properties p = new Properties();

    static {
    
    
        try {
    
    
            p.load(new FileInputStream("resources/db.properties"));
        } catch (FileNotFoundException e) {
    
    
            e.printStackTrace();
        } catch (IOException e) {
    
    
            e.printStackTrace();
        }
    }

    public static String getValue(String key) {
    
    
        return p.getProperty(key);
    }
}