Dao模式:

1. 新建一個dao的介面， 裡面宣告資料庫訪問規則.

2. 新建一個dao的實現類，具體實現早前定義的規則.

3. 直接使用實現.

程式碼如下: 

UserDao:

package com.test.dao;


/**
 * 定義操作資料庫的方法
 * <p>Title: UserDao</p>
 * <p>Description: </p>
 * <p>Company: www.itcast.cn</p> 
 * @version 1.0
 */
public interface UserDao {
	
	//查詢
	void findAll();

}
 

UserDaoImpl:

package com.test.dao.impl;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;

import com.test.dao.UserDao;
import com.test.util.JDBCUtil;

public class UserDaoImpl implements UserDao {



	/**
	 * 查詢
	 * <p>Title: findAll</p>
	 * <p>Description: </p>
	 * @see com.test.dao.UserDao#findAll()
	 */
	
	Connection connection = null;
	Statement statement = null;
	ResultSet resultSet = null;
	@Override
	public void findAll() {
		try {
			connection = JDBCUtil.getConn();
			statement = connection.createStatement();
			String sql ="select * from user";
			resultSet = statement.executeQuery(sql);
			while(resultSet.next()){
				String username = resultSet.getString("username");
				String password = resultSet.getString("password");
				
				System.out.println("username="+username+",password="+password);
			}
		} catch (Exception e) {
			// TODO: handle exception
		}finally{
			JDBCUtil.close(connection, resultSet, statement);
		}

	}

}
 

JunitTest:

package com.test.example;

import org.junit.Test;

import com.test.dao.UserDao;
import com.test.dao.impl.UserDaoImpl;

public class JunitTest {
	
	//查詢
	@Test
	public void testFindAll(){
		UserDao dao = new UserDaoImpl();
		dao.findAll();
	}

}

JDBCUtil:

package com.test.util;

import java.io.FileInputStream;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;

public class JDBCUtil {
	
	static String driverClass = null;
	static String url = null;
	static String name = null;
	static String password = null;
	
	//讀取jdbc.properties
	static{
		try {
			//1.建立一個屬性配置物件
			Properties properties = new Properties();
			
			//1.對應檔案位於工程根目錄  
			//InputStream is = new FileInputStream("jdbc.properties");
			
			//2.使用類載入器,讀取drc下的資原始檔  對應檔案位於src目錄底下  建議使用
			InputStream is = JDBCUtil.class.getClassLoader().getResourceAsStream("jdbc.properties");
			//2.匯入輸入流,抓取異常
			properties.load(is);
			//3.讀取屬性
			driverClass = properties.getProperty("driverClass");
			url = properties.getProperty("url");
			name = properties.getProperty("name");
			password = properties.getProperty("password");
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}
		
	}
	
	/**
	 * 註冊驅動 建立引數
	 * <p>Title: close</p>
	 * <p>Description: </p>
	 * @param connection
	 * @param resultSet
	 * @param statement
	 */
	
	public static Connection getConn(){
			
		Connection connection = null;
		//2. 建立連線 引數一： 協議 + 訪問的資料庫 ， 引數二： 使用者名稱 ， 引數三： 密碼。
		 try {
			 //Class.forName(driverClass);可寫可不寫
			 //Class.forName(driverClass);
			connection = DriverManager.getConnection(url, name, password);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}	
		return connection;
		
	}
	
	/**
	 * 釋放資源
	 * <p>Title: close</p>
	 * <p>Description: </p>
	 * @param connection
	 * @param resultSet
	 * @param statement
	 */
	public static void close(Connection connection,ResultSet resultSet,Statement statement){
		closeRS(resultSet);
		closeSt(statement);
		closeConn(connection);
		
	}
	public static void close(Connection connection,Statement statement){
		closeSt(statement);
		closeConn(connection);
		
	}
	
	private static void closeRS(ResultSet resultSet){
		try {
			if(resultSet !=null){
				resultSet.close();
			}
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}finally {
			resultSet = null;
		}
	}
	
	private static void closeSt(Statement statement){
		try {
			if(statement !=null){
				statement.close();
			}
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}finally {
			statement = null;
		}
	}
	
	private static void closeConn(Connection connection){
		try {
			if(connection !=null){
				connection.close();
			}
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}finally {
			connection = null;
		}
	}
	


}
 

jdbc.properties:

driverClass=com.mysql.jdbc.Driver
url = jdbc:mysql://localhost/jdbc
name = root
password = root

資料庫:

執行結果: