单例设计模式的简单应用

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dao包

package com.bdqn.dao;import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import com.bdqn.utils.Constants;public class BaseDao {    //获取连接    static Connection conn=null;    public static Connection getConnection(){        String driver=Constants.getInstance().getValue("driver");        String url=Constants.getInstance().getValue("url");        String user=Constants.getInstance().getValue("user");        String pwd=Constants.getInstance().getValue("pwd");        try {            Class.forName(driver);            conn=DriverManager.getConnection(url, user, pwd);        } catch (ClassNotFoundException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (SQLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        return conn;    }    //关闭资源    public static void close(Connection conn){        try {            if (conn!=null) {                conn.close();            }        } catch (SQLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }    }    //增删改    public static int update(String sql,Object [] objects){        int num = 0;        PreparedStatement ps=null;        try {            conn=getConnection();            ps=conn.prepareStatement(sql);            if (objects!=null && objects.length>0) {                for (int i = 0; i < objects.length; i++) {                    ps.setObject((i+1), objects[i]);                }            }            num=ps.executeUpdate();        } catch (SQLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        return num;    }    //模糊查询    public static ResultSet getResultSet(String sql,Object [] objects){        PreparedStatement ps=null;        ResultSet rs=null;        try {            conn=getConnection();            ps=conn.prepareStatement(sql);            if (objects!=null && objects.length>0) {                for (int i = 0; i < objects.length; i++) {                    ps.setObject((i+1), objects[i]);                }            }            rs=ps.executeQuery();        } catch (SQLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        return rs;    }}

package com.bdqn.dao;import java.util.List;import com.bdqn.entity.Student;public interface StudentDao {    public int insert(Student stu);//增加    public int delete(int sid);//删除    public int update(Student stu);//修改    public List<Student> selectAllStudents();//分页查询    public List<Student> selectStudents(String sname);//模糊查询（根据名字查询）    public List<Student> selectStudents(int gid);//根据班级编号查询}

package com.bdqn.dao;import java.util.List;import com.bdqn.entity.Grade;public interface GradeDao {    public int insert(Grade grade);//增    public int delete(int gid);//删    public int update(Grade grade);//改    public List<Grade> selectAllGrade();}

bean包

package com.bdqn.entity;import java.io.Serializable;public class Grade implements Serializable{    private int gid;    private String gname;    public Grade() {    }    public Grade(int gid, String gname) {        this.gid = gid;        this.gname = gname;    }    public int getGid() {        return gid;    }    public void setGid(int gid) {        this.gid = gid;    }    public String getGname() {        return gname;    }    public void setGname(String gname) {        this.gname = gname;    }    @Override    public String toString() {        return "Grade [gid=" + gid + ", gname=" + gname + "]";    }}

package com.bdqn.entity;import java.io.Serializable;public class Student implements Serializable{    private int sid;    private String sname;    private int sage;    private String shobby;    private int gid;    public Student() {    }    public Student(int sid, String sname, int sage, String shobby, int gid) {        this.sid = sid;        this.sname = sname;        this.sage = sage;        this.shobby = shobby;        this.gid = gid;    }    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 getSage() {        return sage;    }    public void setSage(int sage) {        this.sage = sage;    }    public String getShobby() {        return shobby;    }    public void setShobby(String shobby) {        this.shobby = shobby;    }    public int getGid() {        return gid;    }    public void setGid(int gid) {        this.gid = gid;    }    @Override    public String toString() {        return "Student [sid=" + sid + ", sname=" + sname + ", sage=" + sage                + ", shobby=" + shobby + ", gid=" + gid + "]";    }}

impl包

package com.bdqn.dao.impl;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;import com.bdqn.dao.BaseDao;import com.bdqn.dao.StudentDao;import com.bdqn.entity.Student;public class StudentImpl extends BaseDao implements StudentDao{//增    @Override    public int insert(Student stu) {        String insertSql="insert into student values(?,?,?,?,?)";        Object [] objects={stu.getSid(),stu.getSname(),stu.getSage(),stu.getShobby(),stu.getGid()};        int num=this.update(insertSql, objects);        return num;    }//删    @Override    public int delete(int sid) {        String deleteSql="delete from student where sid=?";        Object [] objects={sid};        int num=this.update(deleteSql, objects);        return num;    }//改    @Override    public int update(Student stu) {        String updateSql="update student set sname=?";        Object [] objects={stu.getSname()};        int num=this.update(updateSql, objects);        return num;    }//模糊查询（根据名字查询）    @Override    public List<Student> selectStudents(String sname) {        String sql = "select * from student where sname like '%?%'";         List<Student> list=null;        try {            ResultSet rs=this.getResultSet(sql, null);            list=new ArrayList<Student>();            while (rs.next()) {                Student stu=new Student();                int id=rs.getInt("sid");                String name=rs.getString("sname");                int age=rs.getInt("sage");                String hobby=rs.getString("shobby");                int gid=rs.getInt("gid");                stu.setSid(id);                stu.setSname(name);                stu.setSage(age);                stu.setShobby(hobby);                stu.setGid(gid);                list.add(stu);            }        } catch (SQLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        return list;    }//根据班级编号查询    @Override    public List<Student> selectStudents(int gid) {        String sql = "select * from student where gid=?";         List<Student> list=null;        try {            ResultSet rs=this.getResultSet(sql, null);            list=new ArrayList<Student>();            while (rs.next()) {                Student stu=new Student();                int id=rs.getInt("sid");                String name=rs.getString("sname");                int age=rs.getInt("sage");                String hobby=rs.getString("shobby");                int gid1=rs.getInt("gid");                stu.setSid(id);                stu.setSname(name);                stu.setSage(age);                stu.setShobby(hobby);                stu.setGid(gid1);                list.add(stu);            }        } catch (SQLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        return list;    }//分页 查询    @Override    public List<Student> selectAllStudents() {        String sql = "select * from student";         List<Student> list=null;        try {            ResultSet rs=this.getResultSet(sql, null);            list=new ArrayList<Student>();            while (rs.next()) {                Student stu=new Student();                int id=rs.getInt("sid");                String name=rs.getString("sname");                int age=rs.getInt("sage");                String hobby=rs.getString("shobby");                int gid=rs.getInt("gid");                stu.setSid(id);                stu.setSname(name);                stu.setSage(age);                stu.setShobby(hobby);                stu.setGid(gid);                list.add(stu);            }        } catch (SQLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        return list;    }}

package com.bdqn.dao.impl;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;import com.bdqn.dao.BaseDao;import com.bdqn.dao.GradeDao;import com.bdqn.entity.Grade;import com.bdqn.entity.Student;public class GradeImpl extends BaseDao implements GradeDao{    @Override    public int insert(Grade grade) {        String insertSql="insert into student values(?,?)";        Object [] objects={grade.getGid(),grade.getGname()};        int num=this.update(insertSql, objects);        return num;    }    @Override    public int delete(int gid) {        String deleteSql="delete from student where gid=?";        Object [] objects={gid};        int num=this.update(deleteSql, objects);        return num;    }    @Override    public int update(Grade grade) {        String updateSql="update student set gname=?";        Object [] objects={grade.getGname()};        int num=this.update(updateSql, objects);        return num;    }    @Override    public List<Grade> selectAllGrade() {        String sql = "select * from student";         List<Grade> list=null;        try {            ResultSet rs=this.getResultSet(sql, null);            list=new ArrayList<Grade>();            while (rs.next()) {                Grade grade=new Grade();                int id=rs.getInt("gid");                String name=rs.getString("gname");                grade.setGid(id);                grade.setGname(name);                list.add(grade);            }        } catch (SQLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        return list;    }}

utils包

package com.bdqn.utils;import java.io.IOException;import java.io.InputStream;import java.util.Properties;public class Constants {    private static Constants constants;    private static Properties properties;    private Constants(){        InputStream is=null;        try {            properties=new Properties();            is=Constants.class.getClassLoader().getResourceAsStream("database.properties");            properties.load(is);        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }    }    public static synchronized Constants getInstance(){        if (constants==null) {            synchronized(Constants.class){                if (constants==null) {                    constants=new Constants();                }            }        }        return constants;    }    public String getValue(String key){        return properties.getProperty(key);    }}

测试类

package com.bdqn.test;import java.util.List;import com.bdqn.dao.GradeDao;import com.bdqn.dao.StudentDao;import com.bdqn.dao.impl.GradeImpl;import com.bdqn.dao.impl.StudentImpl;import com.bdqn.entity.Grade;import com.bdqn.entity.Student;public class Test {    public static void main(String[] args) {        StudentDao sdao=new StudentImpl();        GradeDao gdao=new GradeImpl();        /**         * 学生的全查         */        List<Student> list1=sdao.selectAllStudents();        for(Student stu : list1){            System.out.println(stu.toString());        }        /**         * 模糊查询         */        /*List<Student> list2=sdao.selectStudents("a");        for(Student stu : list2){            System.out.println(stu.toString());        }*/        /*List<Grade> list3=gdao.selectAllGrade();        for(Grade grade : list3){            System.out.println(grade.toString());        }*/    }}

目录

用 [TOC]来生成目录：

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