DAO開發小試

時間 2019-11-16

標籤 dao 開發小試简体版

原文原文鏈接

數據

DAO的開發徹底圍繞着數據進行，先在數據庫中準備幾個要用到的表：java

sqlcreate table emp (
    empno int(4)    PRIMARY KEY,
    ename varchar(10),
    job varchar(9),
    hiredate    date,
    sal float(7,2)
    );

VO類

根據表中的字段創建對應的VO類：mysql

javapackage temp.vo;

import java.util.Date;

/**
 * Created by mcbird on 14/11/20.
 */
public class Emp {
    private int empno;
    private String ename;
    private String job;
    private Date hiredate;
    private float sal;

    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }

    public String getJob() {
        return job;
    }

    public void setJob(String job) {
        this.job = job;
    }

    public Date getHiredate() {
        return hiredate;
    }

    public void setHiredate(Date hiredate) {
        this.hiredate = hiredate;
    }

    public float getSal() {
        return sal;
    }

    public void setSal(float sal) {
        this.sal = sal;
    }

    public int getEmpno() {
        return empno;

    }

    public void setEmpno(int empno) {
        this.empno = empno;
    }
}

能夠看到，VO類中只包含getter和setter方法。定義完VO類以後，接下來定義一個DatebaseConnection類，用來完成數據庫的打開及關閉操做。sql

DatabaseConnection類

考慮到實踐當中，有可能使用不一樣的數據庫，所用，咱們須要寫一個通用接口，以及相應的數據庫的實現類。數據庫

DatabaseConnection通用接口

javapackage temp.dbc;


import java.sql.Connection;

/**
 * Created by mcbird on 14/11/20.
 */
public interface DatebaseConnection {
    public Connection getConnection() throws Exception;  // 取得數據庫鏈接
    public void close() throws Exception;                //關閉數據庫鏈接
}

經過這樣一個接口，可以更好的鬆耦合、更抽象。設計模式

DatabaseConnection實現類

javapackage temp.dbc.impl;

import temp.dbc.DatebaseConnection;

import java.sql.Connection;
import java.sql.DriverManager;

/**
 * Created by mcbird on 14/11/20.
 */
public class MySQLDatabaseConnection implements DatebaseConnection {
    private static final String DBDRIVER = "org.gjt.mm.mysql.Driver";
    private static final String DBURL = "jdbc://localhost:3306/temp";
    private static final String DBUSER = "root";
    private static final String DBPASSWORD = "cloudSoft@Skybility";
    private Connection conn = null;


    @Override
    public Connection getConnection() throws Exception {
        try {
            Class.forName(DBDRIVER);
            this.conn = DriverManager.getConnection(DBURL, DBUSER, DBPASSWORD);
        }catch (Exception e) {
            throw e;
        }
        return this.conn;
    }

    @Override
    public void close() throws Exception {
        if(this.conn != null) {
            try {
                this.conn.close();
            } catch (Exception e) {
                throw e;
            }
        }
    }
}

這是針對MySQL的一個實現類，還能夠針對不一樣的數據庫編寫不一樣的實現類。ide

DAO類

在DAO設計模式中，最重要的就是定義DAO接口，在定義DAO接口以前必須對業務進行詳細的分析，要清楚地知道一張表在整個系統中應該具有何種功能。測試

DAO接口

javapackage temp.dao;

import temp.vo.Emp;

import java.util.List;

/**
 * Created by mcbird on 14/11/20.
 */
public interface IEmpDAO {
    /**
     * 數據的增長操做
     * @param emp 要增長的數據對象
     * @return 是否成功增長標誌
     */
    public boolean doCreate(Emp emp) throws Exception;


    /**
     * 查詢所有數據
     * @param keyWord
     * @return
     * @throws Exception
     */
    public List<Emp> findAll(String keyWord) throws Exception;

    /**
     * 根據編號查詢僱員信息
     * @param empno
     * @return
     * @throws Exception
     */
    public Emp findById(int empno) throws Exception;
}

DAO實現類

javapackage temp.dao.impl;

import temp.dao.IEmpDAO;
import temp.vo.Emp;

import java.sql.Connection;
import java.sql.Date;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

/**
 * Created by mcbird on 14/11/20.
 */
public class EmpDAOImpl implements IEmpDAO {
    private Connection conn = null;
    private PreparedStatement pstmt = null;     //數據庫操做對象

    public EmpDAOImpl(Connection conn) {
        this.conn = conn;
    }

    @Override
    public boolean doCreate(Emp emp) throws Exception {
        boolean flag = false;
        String sql = "insert int emp (empno,ename,job,hiredate,sal) values (?,?,?,?,?)";
        this.pstmt = this.conn.prepareStatement(sql);
        this.pstmt.setInt(1, emp.getEmpno());
        this.pstmt.setString(2, emp.getEname());
        this.pstmt.setString(3, emp.getJob());
        this.pstmt.setDate(4, new Date(emp.getHiredate().getTime()));
        this.pstmt.setFloat(5, emp.getSal());

        if(this.pstmt.executeUpdate() > 0) {    //更新記錄的行數大於0
            flag = true;
        }
        this.pstmt.close();
        return flag;
    }

    @Override
    public List<Emp> findAll(String keyWord) throws Exception {
        List<Emp> all = new ArrayList<Emp>();
        String sql = "select empno,ename,job,hiredate,sal from emp where ename like ? or job like ?";
        this.pstmt = this.conn.prepareStatement(sql);
        this.pstmt.setString(1, "%" + keyWord + "%");
        this.pstmt.setString(2, "%" + keyWord + "%");
        ResultSet rs = this.pstmt.executeQuery();
        Emp emp = null;
        while (rs.next()) {
            emp = new Emp();
            emp.setEmpno(rs.getInt(1));
            emp.setEname(rs.getString(2));
            emp.setJob(rs.getString(3));
            emp.setHiredate(rs.getDate(4));
            emp.setSal(rs.getFloat(5));
            all.add(emp);
        }
        this.pstmt.close();
        return all;
    }

    @Override
    public Emp findById(int empno) throws Exception {
        Emp emp = null;
        String sql = "select empno,ename,job,hiredate,sal from emp where empno=?";
        this.pstmt = this.conn.prepareStatement(sql);
        this.pstmt.setInt(1, empno);
        ResultSet rs = this.pstmt.executeQuery();
        if(rs.next()) {
            emp = new Emp();
            emp.setEmpno(rs.getInt(1));
            emp.setEname(rs.getString(2));
            emp.setJob(rs.getString(3));
            emp.setHiredate(rs.getDate(4));
            emp.setSal(rs.getFloat(5));
        }
        this.pstmt.close();
        return emp;
    }
}

能夠發現，在這個實現類中，根本沒有數據庫的打開和連接操做，只是經過構造方法取得了數據庫的連接，那麼真正負責打開和關閉的操做是由誰來完成的呢？答案是，代理類。this

代理類

javapackage temp.dao.proxy;

import temp.dao.IEmpDAO;
import temp.dao.impl.EmpDAOImpl;
import temp.dbc.DatebaseConnection;
import temp.dbc.impl.MySQLDatabaseConnection;
import temp.vo.Emp;

import java.util.List;

/**
 * Created by mcbird on 14/11/20.
 */
public class EmpDAOProxy implements IEmpDAO {
    private DatebaseConnection dbc = null;
    private IEmpDAO dao = null;
    public EmpDAOProxy() throws Exception {
        this.dbc = new MySQLDatabaseConnection();
        this.dao = new EmpDAOImpl(this.dbc.getConnection());
    }

    @Override
    public boolean doCreate(Emp emp) throws Exception {
        boolean flag = false;
        try {
            if (this.dao.findById(emp.getEmpno()) == null) {
                flag = this.dao.doCreate(emp);
            }
        } catch (Exception e) {
            throw e;
        } finally {
            this.dbc.close();
        }
        return flag;
    }

    @Override
    public List<Emp> findAll(String keyWord) throws Exception {
        List<Emp> all = null;
        try {
            all = this.findAll(keyWord);
        } catch (Exception e) {
            throw e;
        } finally {
            this.dbc.close();
        }
        return all;
    }

    @Override
    public Emp findById(int empno) throws Exception {
        Emp emp = null;
        try {
            emp = this.dao.findById(empno);
        } catch (Exception e) {
            throw e;
        } finally {
            this.dbc.close();
        }
        return emp;
    }
}

能夠發現，在代理類的構造方法中實例化了數據庫鏈接類的對象以及DAO的實現類，而在代理中的各個方法只是調用了真實DAO實現類的相應方法。在代理類完成之後，最後還須要編寫工廠類，以下降代碼間的耦合度。設計

工廠類

工廠類的功能就是直接返回DAO接口的實例化對象,這樣客戶端就能夠直接經過工廠類取得DAO接口的實例化對象。代理

javapackage temp.dao.factory;

import temp.dao.IEmpDAO;
import temp.dao.proxy.EmpDAOProxy;

/**
 * Created by mcbird on 14/11/20.
 */
public class DAOFactory {
    public static IEmpDAO getIEmpDAOInstance() throws Exception {
        return new EmpDAOProxy();
    }
}

測試

javapackage temp.test;

import temp.dao.factory.DAOFactory;
import temp.vo.Emp;

import java.util.Date;

/**
 * Created by mcbird on 14/11/20.
 */
public class TestDAOInsert {
    public static void main(String[] args) throws Exception {
        Emp emp = null;
        for(int x = 0; x < 5; x++) {
            emp = new Emp();
            emp.setEmpno(1000 + x);
            emp.setEname("McBird_" + x);
            emp.setJob("Singer_" + x);
            emp.setHiredate(new Date());
            emp.setSal(100 * x);

            DAOFactory.getIEmpDAOInstance().doCreate(emp);
        }
    }
}

相關標籤/搜索

每日一句

每一个你不满意的现在，都有一个你没有努力的曾经。