DAO模式

什么是DAO模式：

DAO(Data Access Object Pattern)用于将低层的数据操作API与上层的业务逻辑层分离，其主要涉及以下几个部分：

1.Data Access Object Interface

定义了在model object上的标准操作接口。

2.Data Access Object concrete class

实现了1中的接口，负责从database或者xml等中操作数据。

3.Model Object or Value Object

简单的POJO对象。

一.  DAO全程是Data Access Object，是J2EE核心模式之一，主要用于上层应用程序与持久化机制之间的中间层，对于底层的数据库持久化，其各部分关系答题如下：

 

1、使用JDBC的API访问数据库

连接、SQL语句执行、结果

java.sql.Driver：各个数据库厂商需要实现该接口，驱动的标记

java.sql.Connection：封装和数据库的连接

java.sql.Statement：封装需要执行的SQL语句

java.sql.ResultSet：封装查询的结果集

java.sql.PreparedStatement接口

2、JDBC编程步骤 

step1——加载驱动

step2——获取连接对象

step3——执行SQL语句

step4——处理结果集

step5——关闭资源

3.DAO的架构 

 

 

实现接口：

示例：

public class NewsDAOImpl  implements INewsDAO{
    BaseDao dao = new BaseDao();
    @Override
    public List<News> findAll() throws Exception {
          List<News> list=new ArrayList<News>();
           String sql="select * from news";
          ResultSet rs=dao.executeQuery(sql);
          if (rs!=null) {
          while (rs.next()) {
             News grade=new News();
            grade.setId(rs.getInt(1));
            grade.setName(rs.getString(2));
            grade.setAuthor(rs.getString(3));
            grade.setCreateTime(rs.getDate(4));
            grade.setContent(rs.getString(5));
            list.add(grade);
        }
        }
            return list;
    }

}

工具类：

public class BaseDao {
    private static final String driver="com.mysql.jdbc.Driver";
    private static final String url="jdbc:mysql:///news2230";
    private static final String username="cai";
    private static final String password="root";
    
    private Connection con;
    private PreparedStatement ps;
    private ResultSet rSet;
    
    public Connection getConnection() throws Exception {
        Class.forName(driver);
        if (con==null||con.isClosed()) {
            con=DriverManager.getConnection(url,username,password);
        }
        return con;
    }
    
  
    //增加 修改 删除
    public int executeUpdate(String sql,Object...objects) throws  Exception {
        getConnection();
        ps=con.prepareStatement(sql);
    for (int i = 0; i < objects.length; i++) {
        ps.setObject(i+1, objects[i]);
    }
        int count=ps.executeUpdate();
        return  count;
        
    }
    
    //查询
    public ResultSet executeQuery(String sql,Object...objects) throws Exception{
        getConnection();
        ps=con.prepareStatement(sql);
        for (int i = 0; i < objects.length; i++) {
            ps.setObject(i+1, objects[i]);
        }
        rSet = ps.executeQuery();
        return rSet;
        
    }
    
    //释放资源
    public void closeResource(){
        try {
            if (rSet!=null) {
                 rSet.close();
             }
                if (ps!=null) {
                 ps.close();
             }
                if (con!=null) {
                 con.close();
             }
     } catch (Exception e) {
         e.printStackTrace();
     }
       
    }
}

接口：

public interface INewsDAO {
    public List<News> findAll() throws Exception;
}

实现用户操作相关的类：

public class News {
     public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Date getCreateTime() {
        return createTime;
    }
    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }
    public String getContent() {
        return content;
    }
    public void setContent(String content) {
        this.content = content;
    }
    public String getAuthor() {
        return author;
    }
    public void setAuthor(String author) {
        this.author = author;
    }
    private int id; //编号
     private String name; //姓名      
     private Date createTime;//时间
     private String content;
     public String author;
}
 

连接dao层和test层的关系：

实现接口

public class NewsServiceImpl implements INewsService {   
 INewsDAO aa=new NewsDAOImpl();
    @Override
    public List<News> findAll() throws Exception {
    
        return aa.findAll();
    }

}

定义接口：

public interface INewsService {
    public List<News> findAll() throws Exception;
}

mian方法：

    public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub
    NewManager manager=new NewManager();
    manager.toHtml();
    }

}

io流：

    

    public void writeFile(String filePath,String str) throws Exception{
        OutputStreamWriter oStreamWriter = new OutputStreamWriter(new FileOutputStream(filePath), "GBK");
        oStreamWriter.write(str);
        oStreamWriter.close();
    }
 
    public  String  readerFile(String filePath) throws Exception{

        InputStreamReader isr = new InputStreamReader(new FileInputStream(filePath), "GBK");
        char[] ch = new char[1024];
        int data = 0;
        String str = null;
        StringBuffer sb = new StringBuffer();
        while ((data = isr.read(ch)) != -1) {
            str = new String(ch, 0, data);
            sb.append(str);
        }
        System.out.println(sb.toString());
        isr.close();
        return str;
    }


    
}

调用IO实现 html：

  public void toHtml() throws Exception{
          FileIo fileio= new FileIo();
          String templatestr=fileio.readerFile("F:\\JDBC_CMS\\src\\news.template");
          INewsService service=new NewsServiceImpl();
          List<News> newlist=service.findAll();
          for (int i = 0; i < newlist.size(); i++) {
            News news=newlist.get(i);
            String rep=new String();
            rep=templatestr;
            rep=rep.replace("{title}", news.getName());
            rep=rep.replace("{author}", news.getAuthor());
            rep=rep.replace("{createTime}", news.getCreateTime().toString());
            rep=rep.replace("{content}", news.getContent());
            
            String fil="F:\\哈哈哈+"+i+".html";
            fileio.writeFile(fil, rep);
        }
        }

}

 

实现结果：